Seeking advice. Engine failure. Non-GMC

1976GMC

1976GMC

Active member
Dec 16, 2017
259
39
28
Washington State
With so many people on this forum having experience in engine rebuilding I thought I may be able to find some answers.

I recently experienced a severe set back with my daily driver. One cylinders had failed in a spectacular way - a piece broke off along the edge above
the top compression ring. I'm trying to figure out what may have caused the failure and I'm not having any luck so far.

The engine is a Mitsubishi V6 (6G74 version) from an SUV with 250k miles on it. I owned the vehicle since we bought it new. It was always maintained
on schedule, never overheated, never ran out of oil. All parts (except few external things) are still OEM from assembly in Japan. The failure
occurred at highway speed when I was passing another car. The engine started to shudder hard and check engine light came on. I stopped and pulled the
codes - misfire on #5 cylinder (the one that failed). After some testing I determined that there was no compression on the said cylinder and the
leak was going through the piston and into crankcase. Timing was on the spot correct, so no issue with the timing belt causing it.

I pulled the engine and found out that #5 piston had a hole in it. Pistons #1-4 have no wear marks at all, just normal discoloration from use.
Cylinder walls on #1-4 still show good crosshatch marks. The failure of the #5 resulted in some scoring of the cylinder wall and aluminum deposits on
the bottom of the head, but not much else. It seem that the failure occurred after some abnormal wear on the piston. Surprisingly to me, the #6
piston is showing what I presume an early stage of similar wear pattern to the #5. The wear pattern on #6 piston is very strange. The is no wear at
all on the piston skirt (where you'd expect it most), but instead there are score marks on four sides of the piston at about 45 degrees from the
piston pin. Rings are not stuck on pistons #1-4 and on #6. On #5 the rings are stuck due to damage. None of the pins are sticking (not even on th3
#5), the main bearings are within spec and show just normal and very even wear pattern on all four mains. Same goes for all the connecting rod
bearings - good even wear, no scoring, no binding. Connecting rods on affected cylinders are not bent.

So the question is - does anyone know what may have caused such weird wear pattern on the affected pistons and what could cause piston to fail in such
way?
Appreciate all of your input on this issue.

I'm going to try to attach links to photos. I hope it works.

Piston failure, top view, bank 1:
https://photos.app.goo.gl/FcmgXyMKJEDETsZ97

#5 failed piston, damage side view:
https://photos.app.goo.gl/kQCn1FXLwz67feYy6

#6 piston, no wear on skirt:
https://photos.app.goo.gl/k9L9pkG9JbdEdS5z7

#6 piston wear marks on 45 degree to pin:
https://photos.app.goo.gl/k9L9pkG9JbdEdS5z7

--
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
 
Sounds like preignition or lean injector partially plunged.
Look at the plug from that cylinder.
Typical issue as it sneaked by all the emission computer warning.

On Mon, Feb 17, 2020 at 9:29 PM Vadim Jitkov via Gmclist <

> With so many people on this forum having experience in engine rebuilding I
> thought I may be able to find some answers.
>
> I recently experienced a severe set back with my daily driver. One
> cylinders had failed in a spectacular way - a piece broke off along the
> edge above
> the top compression ring. I'm trying to figure out what may have caused
> the failure and I'm not having any luck so far.
>
> The engine is a Mitsubishi V6 (6G74 version) from an SUV with 250k miles
> on it. I owned the vehicle since we bought it new. It was always
> maintained
> on schedule, never overheated, never ran out of oil. All parts (except few
> external things) are still OEM from assembly in Japan. The failure
> occurred at highway speed when I was passing another car. The engine
> started to shudder hard and check engine light came on. I stopped and
> pulled the
> codes - misfire on #5 cylinder (the one that failed). After some testing
> I determined that there was no compression on the said cylinder and the
> leak was going through the piston and into crankcase. Timing was on the
> spot correct, so no issue with the timing belt causing it.
>
> I pulled the engine and found out that #5 piston had a hole in it.
> Pistons #1-4 have no wear marks at all, just normal discoloration from use.
> Cylinder walls on #1-4 still show good crosshatch marks. The failure of
> the #5 resulted in some scoring of the cylinder wall and aluminum deposits
> on
> the bottom of the head, but not much else. It seem that the failure
> occurred after some abnormal wear on the piston. Surprisingly to me, the #6
> piston is showing what I presume an early stage of similar wear pattern to
> the #5. The wear pattern on #6 piston is very strange. The is no wear at
> all on the piston skirt (where you'd expect it most), but instead there
> are score marks on four sides of the piston at about 45 degrees from the
> piston pin. Rings are not stuck on pistons #1-4 and on #6. On #5 the rings
> are stuck due to damage. None of the pins are sticking (not even on th3
> #5), the main bearings are within spec and show just normal and very even
> wear pattern on all four mains. Same goes for all the connecting rod
> bearings - good even wear, no scoring, no binding. Connecting rods on
> affected cylinders are not bent.
>
> So the question is - does anyone know what may have caused such weird wear
> pattern on the affected pistons and what could cause piston to fail in such
> way?
> Appreciate all of your input on this issue.
>
> I'm going to try to attach links to photos. I hope it works.
>
> Piston failure, top view, bank 1:
> https://photos.app.goo.gl/FcmgXyMKJEDETsZ97
>
> #5 failed piston, damage side view:
> https://photos.app.goo.gl/kQCn1FXLwz67feYy6
>
> #6 piston, no wear on skirt:
> https://photos.app.goo.gl/k9L9pkG9JbdEdS5z7
>
> #6 piston wear marks on 45 degree to pin:
> https://photos.app.goo.gl/k9L9pkG9JbdEdS5z7
>
> --
> Vadim Jitkov
> '76 Glenbrook 26'
> Pullman, WA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmcrvparts.com
1-800-752-7502
 
No expert here but my thinking is the same as jimmy's
--
Roy Keen
Minden,NV
76 X Glenbrook
 
Could be a very lean mixture, leading to elevated combustion temperatures,
and either preignition, which I suspect, or detonation, which would be the
least likely of these 2 events. Both create enormous combustion
irregularities, which easily can break parts like rings, ring lands,
abnormal flame fronts that burn holes in tops of pistons. Causes? Injectors
readily come to mind, as do intake manifold leaks, loose or faulty sensors,
obscure things like plug cross firing due to missrouted (crossed) secondary
wires. This wouldn't be the case in the event of coil pack secondary. You
stated that you were using heavy throttle at the moment of the failure.
This points to preignition as a likely suspect. Just my educated guess.
Like to have hands on that manifold, as well as the injectors,
filters, and fuel pump(s) and fuel pressure regulator. Broken parts are
symptoms, not cause agents. That is always what I look for. There will be
other opinions, these are mine.
Jim Hupy
Salem, Oregon

On Mon, Feb 17, 2020, 9:36 PM Jim Kanomata via Gmclist <

> Sounds like preignition or lean injector partially plunged.
> Look at the plug from that cylinder.
> Typical issue as it sneaked by all the emission computer warning.
>
> On Mon, Feb 17, 2020 at 9:29 PM Vadim Jitkov via Gmclist <

>
> > With so many people on this forum having experience in engine rebuilding
> I
> > thought I may be able to find some answers.
> >
> > I recently experienced a severe set back with my daily driver. One
> > cylinders had failed in a spectacular way - a piece broke off along the
> > edge above
> > the top compression ring. I'm trying to figure out what may have caused
> > the failure and I'm not having any luck so far.
> >
> > The engine is a Mitsubishi V6 (6G74 version) from an SUV with 250k miles
> > on it. I owned the vehicle since we bought it new. It was always
> > maintained
> > on schedule, never overheated, never ran out of oil. All parts (except
> few
> > external things) are still OEM from assembly in Japan. The failure
> > occurred at highway speed when I was passing another car. The engine
> > started to shudder hard and check engine light came on. I stopped and
> > pulled the
> > codes - misfire on #5 cylinder (the one that failed). After some
> testing
> > I determined that there was no compression on the said cylinder and the
> > leak was going through the piston and into crankcase. Timing was on the
> > spot correct, so no issue with the timing belt causing it.
> >
> > I pulled the engine and found out that #5 piston had a hole in it.
> > Pistons #1-4 have no wear marks at all, just normal discoloration from
> use.
> > Cylinder walls on #1-4 still show good crosshatch marks. The failure of
> > the #5 resulted in some scoring of the cylinder wall and aluminum
> deposits
> > on
> > the bottom of the head, but not much else. It seem that the failure
> > occurred after some abnormal wear on the piston. Surprisingly to me,
> the #6
> > piston is showing what I presume an early stage of similar wear pattern
> to
> > the #5. The wear pattern on #6 piston is very strange. The is no wear
> at
> > all on the piston skirt (where you'd expect it most), but instead there
> > are score marks on four sides of the piston at about 45 degrees from the
> > piston pin. Rings are not stuck on pistons #1-4 and on #6. On #5 the
> rings
> > are stuck due to damage. None of the pins are sticking (not even on th3
> > #5), the main bearings are within spec and show just normal and very even
> > wear pattern on all four mains. Same goes for all the connecting rod
> > bearings - good even wear, no scoring, no binding. Connecting rods on
> > affected cylinders are not bent.
> >
> > So the question is - does anyone know what may have caused such weird
> wear
> > pattern on the affected pistons and what could cause piston to fail in
> such
> > way?
> > Appreciate all of your input on this issue.
> >
> > I'm going to try to attach links to photos. I hope it works.
> >
> > Piston failure, top view, bank 1:
> > https://photos.app.goo.gl/FcmgXyMKJEDETsZ97
> >
> > #5 failed piston, damage side view:
> > https://photos.app.goo.gl/kQCn1FXLwz67feYy6
> >
> > #6 piston, no wear on skirt:
> > https://photos.app.goo.gl/k9L9pkG9JbdEdS5z7
> >
> > #6 piston wear marks on 45 degree to pin:
> > https://photos.app.goo.gl/k9L9pkG9JbdEdS5z7
> >
> > --
> > Vadim Jitkov
> > '76 Glenbrook 26'
> > Pullman, WA
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> --
> Jim Kanomata
> Applied/GMC, Newark,CA
> jimk
> http://www.appliedgmcrvparts.com
> 1-800-752-7502
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
I'm in agreement with Jim and James. Could be long term light/ med undetected pinging that slowly eroded the metal. Then failed during passing. An
alternative theory is a slack timing belt causing retarded events and high temps due to poor efficiency.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
I'd buy running lean on those two - the timing belt would affect either everything or everything on one bank, would it not? Although 250K ain't a bad
ride, you got your money out of it. One other possibility, I'm not aware of the ignition system, but is it possible those two cylinders fire off the
same winding of the coil pack? If so, I'd go looking for a problem with that winding or its firing mechanism. A worn or broken prong on the
distributor reluctor?

--johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
 
Great input. Thank you to all for taking time with it.

The lean condition sounds like the most plausible scenario. I'm going to take injectors and get them flow tested. If #5 and #6 show significantly
lower output than the other four, that will confirm this theory.
What does a plug look like on a very lean mixture? #5 spark plug was covered in oil due to the forced ventilation with the crankcase. But I can check
to see if #6 plug is somewhat different from first four.
Would elevated combustion temperatures cause the pistons to expand unevenly and rub on the cylinder walls in such strange way?

I'm pretty confident that we can rule out the timing belt. It is an interference engine and having timing belt off the mark would result in valve
damage first. Additionally, when I pulled the engine, timing on both banks was perfectly on the mark. No slack on the belt and tensioner was in spec
with proper preload.

The engine has three individual ignition coils that are electronically controlled. They are paired to fire as 5+2, 1+4 and 3+6 (waste spark system).
Thus, this puzzle piece does not fit ether.

Someone on another forum suggested a possibility of a restriction in the oil gallery and thus reduced lubrication on the last two cylinders. Does
that sound like a plausible idea? If that were the case, I would expect a heavier wear/damage on the main bearings near those two cylinders or at the
very least on the rod bearings. Alas, they all looked evenly worn and without damage.
--
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
 
Ready Vadim?
If you have been reading here much, you might remember that I am a refugee from the laboratories in Detroit that do engine testing. I have seen this
type of damage before and will try to make the possible causes clear. If I loose you somewhere along the way, please say so and I will try to correct
the issue. Great pictures - by the way.

I started writing this about three hours ago, but I had to break off. That is why there are some things answered since that I also answered. Too much
information don't hurt.

Hold on tight because here we go....
What actually caused the damage to #5 piston will be hard to determine, but suffice it to say that it probably happened in a fractional second. Even
a grocery-getter engine is running with very little margin. Yours just slipped the margin.

The picture of the piston crown is typical of a pre-ignition issue. There are so many possible causes. That (again with the hands on thing) that I
cannot get more specific with out much closer examination. With the damage to the piston as it is there are several choices:
My first would be (because it is simplest) that the ignition timing to that cylinder was wrong. If this is a distributor engine, that is easy to do
just by getting wires too close together.
It is also a rear cylinder and they often are less well cooled at the cylinder liner. (Yours are parent metal, but that makes little difference.) At
full power, cylinder cooling is critical. If it was a loss of cooling jacket capability, that would also explain what happen to #6 piston. (More
below) Part of this question could be indicated by the condition of the cylinder heads. If the individual cylinder combustion chambers show variation
in operating temperature, you may have has a cooling jacket issue that you did not suspect.
That cooling could also be a failure of the piston cooling. Pistons are cooled by both the contact with the cylinder liner and by the lubricating oil
that is delivered from below. Without having been inside this engine. (I did run one for a supplier, but it ran out the durability and went home
intact.) I do not know if this oil delivery was common to both 5 & 6.
The pre-ignition issue need not be spark induced. These engines are relatively high compression. This can cause an interesting problem where the
shock wave of the spark ignition causes a detonation somewhere removed in the combustion chamber. The edges of the piston crown seen to be the usual
first choice because that is a hot area. Once it gets started, even my engines that were "by individual cycle" monitored, could not unload and shut
down fast enough to avoid extending the damage.

If this is one of the direct injection engines, then I would start thinking in terms of a lean cylinder. (Did you know that aircraft people used to
refer to automotive engines as being "gasoline cooled". But they have their own issues.) Even port injection can have similar issues, just seldom
as bad or as fast.

Once that top land was gone, the top ring could not hold the fire load and when the fire went by it quickly took out the metal below. So that damage
is what I would expect. The heat on the cross head (thrust face) of the damaged piston is an artifact of the overheat of the piston. This is part of
why big engine pistons are actually two or three separate parts with the crown and ring carrier isolated from the skirt/crosshead.

About that #6 piston. The reason that those areas are scuffed is probably that this piston was overheated as well. If you think of the piston as
being two parts. Then the fact that the skirt/crosshead got hotter than would fit in the bore should be making some sense. The actual thrust face of
a cast piston is flexible, but the wrist pin carrier and crown cannot be. So, when the piston got too big, those areas got jammed against the
liner/bore face and broke down the lubrication and cooling there. Why didn't this happen to the crown/ring carrier? Because that is smaller
diameter. Pistons are not mathematical cylinders by any means.

Now, What to do about this?
Assuming you choose to recover this engine and not just replace it.
You say the other essential parts show no distress. Correct??
It appears that there is very little top ring travel step. A finger tip can detect about 0.001. If it is more than that, you have to measure it to
know where you are going next.

Do not let anybody bore all the holes to the same size. There is no reason to do this. Find a piston supplier that can and will supply single
pistons. Get their standard sizes that they supply. If you do a fast try to clean that bore with a glaze breaking hone, and when you have gotten it
pretty clean, you can't catch a finger nail in it, just get two new standard pistons. If that fails , then get block power honed NOT BORED to the
first size that cleans the scoring. If this is less than 0.002" larger than specified, you can probably get by with a standard sized piston. But get
piston sizes before you do anything else.

A lot of production and less careful shops will just bore everything 30 over. Then that engine is done. I have one of those and it really pissed me
off to find that I had a 461 instead of a 455.

You may need to match piston weights, but this is a simple operation - unless you need to remove a lot of metal.

There is no reason that this engine can't be returned to service and be as good as it ever was. If you do it, it is all just a question of attention
to detail.

Oh, If you don't have a good engine work stand, just go buy one. You will be spending a lot of time next to it.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
Interesting analysis. Makes you wonder if the fuel rail picked up a piece of crud, too.
Aviation flat motors are gasoline cooled at take off power - the carburetors open a 'power valve' whose function is to richer the mixture
substantially and let the excess fuel evaporation cool the piston and (hopefully) preclude detonation. Actually in operation, the aviation engine is
much closer to the marine engine than to an automobile engine. Both are designed to run at pretty much a constant speed and constant load. The
aviation engine, however values low weight over specific output, so we see outputs on the order of half or three quarters HP per cubic inch
displacement. Avco Lycoming made the biggest flat motor I ever messed with, a 720 CID unit which produced 400 HP. We see auto engines which peak at
700 HP or better at what - right below 400 CID, although these and most car engines probably wouldn't sustain that output over long periods of time.

--johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
 
> Interesting analysis. Makes you wonder if the fuel rail picked up a piece of crud, too.
> Aviation flat motors are gasoline cooled at take off power - the carburetors open a 'power valve' whose function is to richer the mixture
> substantially and let the excess fuel evaporation cool the piston and (hopefully) preclude detonation. Actually in operation, the aviation engine
> is much closer to the marine engine than to an automobile engine. Both are designed to run at pretty much a constant speed and constant load. The
> aviation engine, however values low weight over specific output, so we see outputs on the order of half or three quarters HP per cubic inch
> displacement. Avco Lycoming made the biggest flat motor I ever messed with, a 720 CID unit which produced 400 HP. We see auto engines which peak
> at 700 HP or better at what - right below 400 CID, although these and most car engines probably wouldn't sustain that output over long periods of
> time.
>
> --johnny

Johnny,

While that is all very true, only aircraft fall out of the sky if the motor quits. For most others, this is just an inconvenience.

Matt - BTDT with all three

--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
True dat. If we took the time we take looking at the airplane to look at our ground based rides, we'd have less stops beside the road.And if we took
the same time teaching drivers as we do flyers, it's my contention we'd have a lot fewer road crashes as well.
 
Some say the eyes are the windows to the soul. I submit it’s also an engine discussion.
Vadim gets the benefit of the hard info, the rest of us get a great ride to labs and other places we’ll likely never get to go. Well done, gentlemen.

Douglas & Virginia Smith
dsmithy18 at gmail
Lincoln Nebraska
’73 “Canyonlands” since ‘95: “Wanabizo”, Anishinabe Indian for “He gets lost driving” Yes, really.
Quadrabag/6 wheel disks/3;70 final/Paterson QuadraJet/Thorley’s/Sundry other
P&W PT6, no wait, that's the wish list...

>
> True dat. If we took the time we take looking at the airplane to look at our ground based rides, we'd have less stops beside the road.And if we took
> the same time teaching drivers as we do flyers, it's my contention we'd have a lot fewer road crashes as well. they're grounded and nobody will fly in one. 40 some thousand offed on the roads. Yawn.
>
> Crichton was right.
>
> --johnny
> --
> Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
> Braselton, Ga.
> I forgive them all, save those who hurt the dogs. They must answer to me in hell
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
What never ceases to amaze me on this forum is how the discussion threads morph and wonder off into all sorts of interesting directions, while at the
same time seamlessly providing deep dives into the main subject of discussion. My guess it happens because as we start pulling on one memory thread,
lots of other interconnecting things come with it. I laughed as soon as I saw the thread move to discussion of airplane engines vs. ground vehicle
engines. I can't even imagine what its like to sit down for a coffee of beer with you folks. Oh the places we'll go... :)

Matt - thank you for the detailed write up. Everything you say makes sense and I think I get all of it. You are 100% right - the failure happened in
a microsecond. As I said earlier, I was passing the car and suddenly engine made the most awful rattle and I felt the biggest misfire I've ever
experienced in any vehicle. The abnormality was big enough that I pulled over immediately after passing the car (I'm sure to the curses from the
other driver) and just as the CEL came on at the same time.

I've never thought of pistons as being manufactured from different materials, but now that I think about it, it makes perfect sense. You need
stiffness and strength around the pin, heat resistance on thrust face and slipperiness and wear resistance on the skirt area. Why is this not a
common knowledge for anyone who is not an engineer?

The engine is port injected with individually controlled injectors. As far as I understand they fire one at a time on intake stroke for each piston.
There is one thing I don't fully understand. You said: "It is also a rear cylinder and they often are less well cooled at the cylinder liner. (Yours
are parent metal, but that makes little difference.)" What does it mean "parent metal"? I've never came across that term before.

There is no restrictions in the water jacket in the case or in the head. I've looked all around the cylinder jackets in the case and all water
passages appear to be clean and unrestricted without any rust of calcium build up. Same goes for the heads. The theory of unintentional very lean
condition seem to be most plausible. I will definitely check the injectors for flow rates.

As far as the future of the engine, my plan is to fix it and put it back in service. I'm one of those stubborn people going for the record on this
vehicle. I got 250k miles on it (all of them are mine). As far as I know it is just past the distance to the moon. My plan is to "turn around" and
make it back... Ha ha, its time for the NASA folks to join the conversation :) I've checked the ring step - there is absolutely none present on any of
the cylinders. The only thing I can feel with my fingernail is one of the two bigger vertical scratches on the #5 bore. All bearings are in amazing
condition with oil gaps safely in the middle of the "Standard value" range for this engine and far far smaller than indicated wear limit value (this
is according to the Factory Service Manual). With that I think it might be best to leave all the bearings as they are. What do you think?

I finally was able to get hold of a good reputable machine shop not far from here. I explained to the owner what I'm dealing with and he said he can
recondition cylinders and get the right pistons ordered. I'm going to take all the parts (crank case, pistons, heads, etc.) to him tomorrow, so that
we can look at them together and confirm our plan of action. I plan on printing Matts instructions, so that I don't miss something when talking to
him. I think I'll have him clean up the heads too while we at this point. Sounds like I can do the reassembly myself, which is going to be fun and
I'm looking forward to it. It is truly surprising how much more space an engine takes when it is disassembled...

BTW, I took pictures of the combustion chambers on the heads for all pistons. I don't know if that will tell you anything, but the links are posted
below. I grouped them by order for each bank. You can see where piston material from #5 got deposited on the bottom of the head. It had completely
pulverized that piston fragment.

Again thank you all for the input. I love this kind of classroom :)

Combustion chamber:
#1 https://photos.app.goo.gl/pFKathc2H9zTrR796
#3 https://photos.app.goo.gl/VbQnrqVPLGx2GQfK6
#5 https://photos.app.goo.gl/8VtDKRYerEdk4CMf8

#2 https://photos.app.goo.gl/vVnkkN4Pkph6T2ZXA
#4 https://photos.app.goo.gl/vkgcqE3RGbeyfKQ76
#6 https://photos.app.goo.gl/qRmK5aEApzgyTXQK9


--
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
 
Certainly ask your machinist about this, but it would make sense, to me anyway, to at least polish the crankshaft and install new standard size
bearing shells.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member
 
If your going to have it torn apart, I suggest it would be beneficial to
have other things done.
Valve guides are possibly worn, etc

On Thu, Feb 20, 2020 at 7:28 AM Carl Stouffer via Gmclist <

> Certainly ask your machinist about this, but it would make sense, to me
> anyway, to at least polish the crankshaft and install new standard size
> bearing shells.
> --
> Carl Stouffer
> '75 ex Palm Beach
> Tucson, AZ.
> Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive,
> Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American
> Eagles,
> Solar battery charging. GMCSJ and GMCMI member
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.gmcrvparts.com
1-800-752-7502
 
Vadim,

The reference to parent metal is just habit. Most of the engines I have run had cylinder liners that were not the same material as the cylinder block
and crankcase. This has both advantages and disadvantages, but I will not go down that list right now.

And, Oh Yes, most pistons in modern engines have inserts in the castings to improve the structure where it is needed. This is not new and it is why
scrap pistons have a much lower value than if they were clean aluminum. Multi-part pistons actually start at a smaller bore than you might expect.
Commercial diesels at that way from only a 4" bore. But then again diesels tend to be brutal about their pistons.

What I do want to point out to you right now is that the condition of the intake valves of both #5&6 is different than the rest. This means something
was different. It may just be cooling, but I don't think so. Both of the rear cylinder's valves are different that the other four. Now, one of the
things you have to crank into the evaluation is that with virtually all V-pattern engines coolant flow is down the block and back the head. Then it
is up to the engineers to put the correct holes in the gasket so as to control the flow in that area so things get enough cooling.

You say that you did not see anything in the cooling jacket during disassembly, we what ever it was may have left by then. Carefully inspect both
gaskets. You may not be able to see the witness marks but that still is a possibility.

Since you have found a good shop, have him re-seat the valves. He can also blast those and then heads clean and you may have an engine that runs
better than new when you are done.

As to assembly, if you print the pages and check off the steps, you will be less likely to make a mistake. Do not be too proud to take something
apart because you did not check that step. If you really don't mind being kind of anal about the whole job, do a full build book. (I have always done
this because I had a good mentor.) That really will end up being two different files (spreadsheets are good for this) one of those should be the
supplier and part numbers of everything you had to buy to do the assembly. The other should contain all the measurements of the components and
thereby it can also include the clearances of related parts. (Gee, you have that all in the spreadsheet, just have it do the math.)

While you are at it all, record the combustion chamber volume, the piston relief or protrusion as the clearance volume in the bore and the gasket
thickness and bore. This way you will have a real record of the compression ratio. You may have to contact the cylinder head gasket supplier for the
design compressed thickness of the part.

With all that, if you have questions or doubts (or just want to bounce something off me) I am in the Black's list. If you ring my home phone, that is
a better bet as the cell is unreliable at home. I read that @ddress all the time as it comes to my phone and my desk.

I wish you an effective effort. I as you can guess, I have been at this a while but it never gets old. The pride you can hold when you get it beck
running will be real. (My most recent was the 455/461 in my coach. It broke a piston, and I did every that I could do my self. This was engine 23
and I don't count engines I can carry.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
Just returned from the mechanic's shop. His first words were - that crankcase doesn't look bad at all. :) After looking at the busted piston, he
confirmed your suspicion of lean condition and detonation that took out #5 piston. He said his will re-hone all bores. He is pretty sure that #6
cylinder will clean out just fine without any other work, but he'll have to check #5 after honing it to see if all scratches come out. I emphasized
that I wanted to avoid boring it out as much as possible. He will get back to me after cleaning everything and trying to machine hone it. He agreed
that the main bearings were in good condition and he did not want to replace them. Crankshaft checked out good too. He will polish the bearing
surfaces but no other work needed there. He suggested that we replace rod bearings, since, as he put it, they take more hard beating relative to main
bearings. I think I'm OK with that. He will also check the compression ring seat clearances and that will determine if we will go with all new
pistons or just two.

I agree with Matt's observation of the heads. It definitely confirms the different running conditions on 5 and 6. I'll take a close look at the head
gaskets.

As far as being anal during the assembly, I'd wager I'm on the far end of the Normal distribution curve right next to the OCD level :) I feel good
about it. I got the detailed book and all tightening specifications and torque sequences. I'm looking forward to get at it.

Couple questions that you might help me with - during assembly, when assembling the bearings, do you need to lubricate back side of the bearing
(against the rod), or just the bearing surface that will be in contact with the crank case? 2. What is a good break in procedure after rebuild.
There is too many different ways of doing it and many contradict the others. Manual calls for 5x30 grade of engine oil, and that is all that engine
ever had. Any special oil for break in period? How soon to change it out?

--
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
 
> Couple questions that you might help me with What is a good break in procedure after rebuild. There is too many different ways of doing it and
> many contradict the others. Manual calls for 5x30 grade of engine oil, and that is all that engine ever had. Any special oil for break in period?
> How soon to change it out?

I have a little different philosophy/opinion about break-in. IMO, if machining and cylinder preparation is done correctly with modern day equipment,
break-in occurs for the most part in the first several hundred to 1K miles. I also believe that it is not only not necessary, but a mistake to use
"Break-in oil" to break-in a new/rebuilt engine. Break-in oils are supposed to be formulated to allow parts to 'wear-in" to each other...in other
words allow some wear to take place. Why would you want to do that to new bearings? Some wear must take place on the cylinder walls for rings to seat
and seal properly. So, how does oil select the parts that it allows to wear. It can't. If you look at a freshly honed cylinder wall under a
microscope, the hone leaves scratches...peaks and valleys. Break-in is the rings just knocking the peaks off, metal that is filtered out by the oil
filter and comes out in the first oil change which I believe should take place in the first 100 miles. It does not take a special oil to allow peaks
to get knocked off, so IMO use whatever oil you plan to run in the engine be it Dino or Synthetic. Change after the first 20 minutes of lifter/cam
break-in, (oil and filter) and again at 100mi, 500mi, and 1000 miles. Then go to your normal oil change intervals. During this break-in period I think
it is important to place a "Filter Mag" on the filter to magnetically catch as much break-in metal as possible. The last engine I built was my Cad
500. I broke it in with 0W40 Mobile 1. I did NOT use any ZDDP additives. I just ran from NW Wisconsin to Jacksonville FL, about 1500 miles. The
engine consumed 1/2pint over that 3 day period. This engine with now 24K miles, has never needed additional oil added between changes. To help with
controlling oil consumption, I also did some things to rod and main bearings, valve guides, a special piston ring, and got control of the PCV system.
I can elaborate on this if you wish.

In addition, I believe that with todays oil formulations, we should be using the synthetic multigrade oils. 5W30 allows good immediate flow to the
bearing surfaces on morning starts while maintaining viscosity on hot runs. I personally use 0W40 Mobil 1 "FS" European Car Formula, ACEA A3/B3,
A3/B4, API SN synthetic, or use 5W30 Quaker State Ultimate Durability, dexos 1 Gen 2, API SN "Plus", synthetic (green bottle) because of their wear
protection capabilities. Both of these oils are available at Walmart for under $25 for a 5 qt pail. I like the "0W" weight for start-up in cold
Wisconsin weather, and the "40W" for hot running. Has worked well for me. So, this is all JMHO based on my own personal experience. Take it for what
it's worth.
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.
 
Mr. John specified breakin oil a particulaor one in fact, and said a couple or three hundred miles was plenty. One more run on the freeway when the
rain quits, and I'll change it for regular.

--johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
 
Valid point. As far as I know you have to not keep the engine at constant RPM for too long during first couple hundred miles. I like the idea of
the magnet on the oil filter. I cut open filters at oil changes and check how everything looks in there. Would be interesting to see what kind of
goop magnet will attract out of the oil during the breaking oil change.
I ran 5x30 Quaker state oil on this engine. Had served me well so far.
--
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
 
You must log in or register to reply here.
GMCMI Fall 2026 Rally
Applied GMC

Share this page

Share this page
Top Bottom
Back