Why engine bearings can fail in the Olds 455, and 403 as we use them.

[Bob Dunahugh]

Bad maintenance to start. We all know about that one. These engines as we use them in the GMC are subjected to very high bearing loads. This is created by a large cylinder bore that has a reciprocating mass operating a rotating shaft at a low RPM rate. Basically lugging it in comparison to the car application with 15 inch tires that it was designed for to start with. This sort of lugging ( in our case ) will run the bearing pressure up and creates ideal conditions for the very destructive ping that you've heard of. Thus these two conditions together put the bearing pressures off the chart. This is exacerbated by bearing companies that put wider oil grooves in their bearings that are wider than the stock GM units. Thus decreasing the load carrying surface of their bearings. This wider grove is great for high-revving engines. The wider grooved bearings sound great. Just not for us. This is part of the reason we can use higher oil pressures. Not higher volumes of oil. They are NOT the same. And this is part of some of the confusion and misunderstandings.. You've heard it said that our engines need special care in rebuilding. This is because of what we subject them to. Don't be proud that you keep your RPM's down. Decrease you're bearing load on hills by shifting down. And run the RPM's up. There are very few people that pull all the time, the loads I do. With any engine. Let alone a 403. And it has 154,000 miles on it. I get by. By running it at higher RPM's. The 455 from Glen, and BJ's GMC will be here tomorrow. It will be interesting on what went wrong with the bearings. Bob Dunahugh

 

[robert mueller]

Bob,

What about the negative effects of high piston speeds in a long stroke engine like the 455?

Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia

 

[johnny]

Are the piston speeds really high enough to matter at the speeds the engine turns in the GMC?

--johnny
--
'76 23' transmode Norris upfit
Braselton, Ga.

"Sometimes I wonder what tomorrow's gonna bring when I think about my dirty life and times" --Warren Zevon

 

[robert mueller]

Depends on the engine, the final drive ratio, and the speeds you drive. I drive at the speed limit plus a bit but my upper limit is
75 pretty much. Having said that Double Trouble with a 455 and a 3.21 to 1 final drive will run all day at 75 and if I'm not careful
will drift up to 80. I can't remember what the rpm is at that speed.

Regards,
Rob M.

 

[carey bryan]

Rob,

I love it when I can reassure the pedantic mechanic.

At 5000 RPM, the Oldsmobile 403 with a stroke of 3.385 inches gives a mean piston speed of 2821 feet per minute.
At 4200 RPM, the Oldsmobile 455 with a stroke of 4.250 inches gives a mean piston speed of 2975 feet per minute.
At 4100 RPM, the Cadillac 500 with a stroke of 4.304 inches gives a mean piston speed of 2941 feet per minute.

I am quoting below from epi-eng.com about recommended mean piston speed:

"For purposes of rules of thumb, it is generally agreed that for an engine in aircraft service, 3000 fpm is a comfortable maximum MPS and experience
has shown that engines having an MPS substantially exceeding that value have experienced reliability issues."

Aircraft service, a high reliability application. High enough for a former Hamilton Standard employee, I think.

I recall a limit of 4000 feet per minute limit for design of motorcycles, so three thousand is pretty conservative. My 1970 Honda CB350 of hallowed
memory with a stroke of 1.99 inches had a redline of 10,500 rpm, for a MPS of 3483. It never broke.

I was interested to see the MPS of the 455. Just for general principles, I would keep the RPM below 4200 if I had an Oldsmobile 455. No great trick
to do so, I think. That would be extremely conservative, I think. And, as friction in an engine varies as the square of the rpm, I do like to keep
the revs down.

Best,

Carey
--
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.

 

[john r. lebetski]

I got a rod knock after a kick down passing move on my new to me coach. I had changed oil twice to try to clean out the engine, but on tear down found
a good quart of sludge in the pan. Assuming dirt got bypassed to oil passàge or strainer restricted. I don't think it's the piston speed issues as
much as the crank throws slinging oil away at RPM and trying to keep the bearings under enough pressure and volume to maintain the oil film thickness
on the throws. That is why they say you need X PSI per 1000 RPM to overcome the incresaed bleed off at the throws as RPM increases. When these were
new I used to wind them out to the programmed shift point with no issues, but now try to keep the 455 in a midrange sweet spot not lugging or revving
to the limit. So far no problems.
--
John Lebetski
Woodstock, IL
77 Eleganza II
Source America First

 

[Bob Dunahugh]

The Old's 455 has been used in racing for a long time. And operated in the 6 to 8000 RPM range. Cams are designed to make an engine run in different RPM ranges. The SFPS ( surface feet per second ) isn't an issue in our application. GM makes crate racing engines that are over 550 cubic inches that have longer strokes then the 455. SFPS was a big issue back in the day of steel pistons. Bob Dunahugh

 

[Keith V]

Cool, 4200 RPM redline for my 455 then.
Thanks!
--
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
69 Vette
29 Dodge

 

[carey bryan]

According to a GMC Western States seminar, and extrapolating:

A 3.07:1 (stock ratio) produces a cruise speed of 83.5 mph at 3,000 rpm (Second Gear 56 mph)
A 3.21:1 ratio produces a cruise speed of 80 mph at 3,000 rpm. (Second gear 54 mph)
A 3.42:1 ratio produces a cruise speed of 75 mph at 3,000 rpm. (Second gear 51 mph)
A 3.55:1 ratio produces a cruise speed of 72 mph at 3,000 rpm. (Second gear 49 mph)
A 3.70:1 ratio produces a cruise speed of 69 mph at 3,000 rpm. (Second gear 47 mph)

Given a (very) arbitrary redline of 5000 for the 403, maximum speed for second gear assuming an accurate speedometer, good luck with that, is:

3.07 93 mph
3.21 90 mph
3.42 85 mph
3.55 82 mph
3.70 78 mph
Kanomata 105 mph

For the 455 with an arbitrary 4200 rpm redline for second gear, neglecting torque converter slip, watch tire size, speedometer accuracy:

3.07 78 mph
3.21 76 mph
3.42 71 mph
3.55 69 mph
3.70 66 mph

For the 500 Cadillac at 4100 rpm:

3.07 76 mph
3.21 74 mph
3.42 69 mph
3.55 67 mph
3.70 64 mph

Bob Dunahugh may well be right, and that the piston feet per minute concerns might be outmoded, though I am sure the talk of it didn't cease after
aluminum pistons came into being starting in automotive production about 1915 give or take (so I read, I wasn't there). Remember also that in aircraft
engines those pistons are mighty heavy, too. So looking at the above, in any case the limiting case is pretty high even in second gear, and in drive,
it's ridiculously high. Note there is torque converter slip to take into account though at high rpm, it will be at its smallest.

I enjoy these ruminations, it keeps me from doing real work on the motorhome.

Carey

--
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.

 

[robert mueller]

Carey, Thanks for the numbers! I raised the subject from a long term engine reliability viewpoint. I would assume that higher piston speeds would
equate to faster bore / piston / ring wear.
--
Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426

 

[Bob Dunahugh]

John, and Teresa brought me the complete drive train out of the GMC they got from Glen, and BJ about 7:30 tonight. Removed the final drive. Then the trans. Next the intake, heads, and oil pan. Pulled 3 mains, and 2 rod bearings. All Bearings were well into the copper base. Oil pump drive was fine. Engine was very clean inside. The pistons showed no signs of preignition. The problem seems to have come from the high volume oil pump that failed. More bearing inspection time tomorrow. As beer time arrived one hour later at 8:30. Bob Dunahugh

 

[robert mueller]

Bob,

Responses below each one of your paragraphs below.

Regards,
Rob M.
The Pedantic Mechanic

-----Original Message-----
From: Bob Dunahugh

John, and Teresa brought me the complete drive train out of the GMC they got from Glen, and BJ about 7:30 tonight.Removed the final
drive. Then the trans. Next the intake, heads, and oil pan. Pulled 3 mains, and 2 rod bearings. All Bearings were well into the
copper base. Oil pump drive was fine. Engine was vary clean inside. The piston's showed no signs of pre ignition. The problem seems
to have come from the high volume oil pump that failed. More bearing inspection time tomorrow. As beer time arrived one hour latter
at 8:30. Bob Dunahugh

WHAT FAILED IN THE HIGH VOLUME OIL PUMP?

The Old's 455 has been used in racing for a long time. And operated in the 6 to 8000 RPM range. Cams are designed to make an engine
run in different RPM ranges. The SFPS (surface feet per second) isn't an issue in our application. GM makes crate racing engines
that are over 550 cubic inches that have longer strokes then the 455. SFPS was a big issue back in the day of steel pistons. Bob
Dunahugh

AS I NOTED IN AN EARLIER MESSAGE THE REASON I BROUGHT UP PISTON SPEEDS IS HOW IT RELATES TO LONG TERM ENGINE RELIABILITY AND ENGINE
WEAR.

SEEMS TO ME THAT THE FASTER THE PISTONS MOVE UP AND DOWN THE BORE THE FASTER THE PISTONS, BORE, AND RINGS WILL WEAR.

YES OR NO? IF THE ANSWER IS NO I'D LIKE TO KNOW WHY NOT TO CLEAR UP MY MISCONCEPTION.

Bad maintenance to start. We all know about that one. These engines as we use them in the GMC are subjected to vary high bearing
loads. This is created by a large cylinder bore that has a reciprocating mass operating a rotating shaft at a low RPM rate.
Basically lugging it in comparison to the car application with 15 inch tires that it was designed for to start with. This sort of
lugging ( in our case ) will run the bearing pressure up, and creates ideal conditions for the vary destructive ping that you've
heard of. Thus these two conditions together put the bearing pressures off the chart. This is acerbated by bearing companies that
put wider oil groves in their bearing that are wider then the stock GM units. Thus decreasing the load carrying surface of their
bearings. This wider grove is great for high revving engines. The wider grooved bearings sound great. Just not for us. This is part
of the reason we can use higher oil pressures. Not higher volumes of oil. They are NOT the same. And this is part of some of the
confusion, and misunderstandings.. You've heard it said that our engines need special care in rebuilding. This is because of what we
subject them too. Don't be proud that you keep you're RPM's down. Decrease you're bearing load on hills by shifting down. And run
the RPM's up. There are vary few people that pull all the time, the loads I do. With any engine. Let a loan a 403. And it has
154,000 miles on it. I get by. By running it at higher RPM's. The 455 from Glen, and BJ's GMC will be here tomorrow. It will be
interesting on what went wrong with the bearings. Bob Dunahugh

 

[Bob Dunahugh]

Rob. Good questions. The bearings that I took out, all had about the same amount of damage. ( middle ones ) And were dry between the bearings and crankshaft. The crank has some grooves starting. Roller chain that drives the cam looks good. The camshaft ramps appear OK from what I see now. Lifter bottoms also look fine. Cam, and lifters need to be checked with a microscope for imperfections. . 4 lifter plungers in the lifters were collapsed due to lack of oil. The crank is locked up at this point. The front main bearing, and front rod bearings should be the locked up ones. The oil level on the dip stick was at full. I'm thinking that the relief valve spring in the HV pump failed. The HV pump relief valve spring has to move farther then a stock spring due the the extra oil that it's dumping back into the bottom of the oil pan. Thus has more load on it. And movement then stock.As to your thought on higher piston speeds would cause more ring, piston, and bore wear. Reasonable thought. The piston assemblies travel up, and down the bore the same number of times per mile at 20 MPH or at 70 MPH. The thing is that at acceleration at 20 MPH you are running a lower manifold vacuum. Thus you are running a much higher combustion chamber pressures due to the increase of fuel in the charge that is drawn into the combustion chamber. The compression ring is designed to use the combustion chamber pressures to increase the ring pressures that the ring applies to the cylinder wall. Thus the ring pressure on the cylinder is greater. With a low manifold vacuum. Your manifold vacuum gauge is a good indicator of the load on your pistons. Back to SFPS. GM used steel pistons into the 50's. The cast aluminum pistons that went into the 403, and 455. SFPS is of no concern. If you really want to reduce the load on your engine and trans, Increase mileage, Lower your engine and trans temps, Put in a 3:70 final drive from Jim K.

 

[john r. lebetski]

Need to find who's aftermarket pump and if offshore parts. I'm not a fan of high volume pumps due to drive stress loads trying to compress a liquid
beyond designed flow (bleed off) designs. Adding 15w50 to the equation compounds it. Remember the "Keep your GM car all GM" air cleaner sticker
might apply here. I think a good Olds boat motor and MH motor are very different animals and race parts don't always apply. Do you know oil brand,
type and weight they were using as I always ask this after failures (though not the cause per se looking for trends). Thanks.
--
John Lebetski
Woodstock, IL
77 Eleganza II
Source America First

 

[robert mueller]

Bob,

Responses in CAPS for clarity interspersed in your email below, I'm not shouting.

Regards,
Rob M.

-----Original Message-----
From: Bob Dunahugh

Rob. Good questions. The bearings that I took out, all had about the same amount of damage. (middle ones)
And were dry between the bearings and crankshaft. The crank has some grooves starting.

I ASSUME THAT (middle ones) WERE 2, 3, & 4 PLEASE CONFIRM

Roller chain that drives the cam looks good.

TIGHT?

The camshaft ramps appear OK from what I see now. Lifter bottoms also look fine. Cam, and lifters need to be checked with a
microscope for imperfections.

4 lifter plungers in the lifters were collapsed due to lack of oil.

IS IT POSSIBLE THAT THE OIL IN THE LIFTER WAS PUSHED OUT BECAUSE OF SPRING PRESSURE ON THE ROCKER ARMS?

The crank is locked up at this point. The front main bearing, and front rod bearings should be the locked up ones.

WHY DO YOU SAY IT IS THE FRONT BEARINGS?

The oil level on the dip stick was at full.

I'm thinking that the relief valve spring in the HV pump failed. The HV pump relief valve spring has to move farther then a stock
spring due the the extra oil that it's dumping back into the bottom of the oil pan. Thus has more load on it. And movement then
stock.

I WOULD SUGGEST A SIDE BY SIDE COMPARISON OF THE DIFFERENCES BETWEEN AN OEM PUMP AND A MELLING HIGH VOLUME PUMP.

As to your thought on higher piston speeds would cause more ring, piston, and bore wear. Reasonable thought.

THANKS!

The piston assemblies travel up, and down the bore the same number of times per mile at 20 MPH or at 70 MPH.

I'M SORRY BUT I DON'T UNDERSTAND THIS; WOULD NOT AN ENGINE BE RUNNING AT A HIGHER RPM AT 70 MPH THAN AT 20 MPH AND THEREFORE PISTON
SPEEDS BE HIGHER?

The thing is that at acceleration at 20 MPH you are running a lower manifold vacuum. Thus you are running a much higher combustion
chamber pressures due to the increase of fuel in the charge that is drawn into the combustion chamber. The compression ring is
designed to use the combustion chamber pressures to increase the ring pressures that the ring applies to the cylinder wall. Thus
the ring pressure on the cylinder is greater. With a low manifold vacuum.

I'M SORRY BUT I DON'T UNDERSTAND THIS EITHER. ARE YOU SAYING THAT AT 20 MPH THE CYLINDER IS FILLED WITH MORE FUEL THAN AT 70 MPH?

Your manifold vacuum gauge is a good indicator of the load on your pistons. Back to SFPS. GM used steel pistons into the 50's. The
cast aluminum pistons that went into the 403, and 455. SFPS is of no concern. If you really want to reduce the load on your engine,
and trans. Increase mileage. Lower your engine, and trans temps. Put in a 3:70 final drive from Jim K. Bob Dunahugh 78 Royale
Member GMCMI

 

[robert mueller]

John,

As noted in an earlier email Dick Paterson uses Melling High Volume oil pumps, I went to the Melling website to poke around a bit
and I found these two documents.

I have not read them but the very fact that these two documents exist shows that Melling holds vendors feet to the fire!

Here's a link to Melling's 2015 Melling Tool Company Supplier Manual:

http://www.melling.com/LinkClick.aspx?fileticket=pfdb_7Bpj8Q=&tabid=1127&portalid=0&mid=2520

Here's a link to Melling's Vendor Terms and Conditions Agreement:

http://www.melling.com/LinkClick.aspx?fileticket=xebNbzylPwY=&tabid=1127&portalid=0&mid=2520

Regards,
Rob M.
The Pedantic Mechanic

 

[robert mueller]

John,

Here's a link to Melling's Standard OEM replacement for the Olds 455 oil pump for a 1975 Toronado (P/N M-22F):

Tiny URL: http://tinyurl.com/nsl422e

Full URL:
http://omnitek.co/mellingcatalog/#a...dsmobile&model=toronado%2CToronado&year=1975%
252C1975%26engine%3D8cyl%2525207.5%252520455cid%252C8Cyl%2525207.5%252520455Cid%26product-line%3D10%252C11%252C9%252Call/1

At the bottom of the page are three links to videos that explain:

1) How to correctly prime engines and oil pumps
2) Oil pump volume and pressure explanation
3) Oil pressure vs flow

I would suggest that everyone view all three of these videos as they are most educational.

Here's a link to the high flow version P/N M-22FHV:

http://omnitek.co/mellingcatalog/#ag/part/M-22FHV

As you can see it produces 20% more flow than the OEM version, however, it is at the same pressure.

Bob believes that the reason Glen & BJ's engine failed was because:

Quote:

I'm thinking that the relief valve spring in the HV pump failed. The HV pump relief valve spring has to move farther then a stock
spring due the extra oil that it's dumping back into the bottom of the oil pan. Thus has more load on it. And movement then stock.

Unquote:

Bob may be correct, however, it depends on the diameter of the piston in the relief valve and the area of the port through which the
oil dumps. That's why I noted that we needed a side by side comparison of a standard OEM Oldsmobile 455 oil pump and a Melling high
volume pump.

Regards,
Rob M.
The Pedantic Mechanic

 

[Ken H.]

IIRC, it was Joe Mondello who reported having seen the oil pump's relief
valve stick open as Bob suspects. The pumps he sold (and perhaps the
company still does) were very slightly modified in the area of the relief
valve to eliminate that possibility. AFAIK, that's the only reason for
their premium over the price of the standard Mellig pumps. When I
installed a HV pump, I used a Dremel tool to clean up the casting as Joe
described. Sad part is, my memory's too bad to remember what exactly I
did. Careful examination should show what's needed.

Ken H.

On Sat, Jun 13, 2015 at 10:31 PM, Robert Mueller
wrote:

> ​...
>
> Bob believes that the reason Glen & BJ's engine failed was because:
>
> Quote:
>
> I'm thinking that the relief valve spring in the HV pump failed. The HV
> pump relief valve spring has to move farther then a stock
> spring due the extra oil that it's dumping back into the bottom of the oil
> pan. Thus has more load on it. And movement then stock.
>

 

[robert mueller]

Ken,

Your email caused a memory synapse to fire and I remembered these photos by Bob Drewes:

http://www.gmcmhphotos.com/photos/mechanical/p50094-oil-pump-housing.html

I then decided to do a search for "Oil Pump" and here's what came up.

Here's a photo that Gene posted:

http://www.gmcmhphotos.com/photos/misc/p37898-patterson-oil-pump.html

Here's one from Kelvin:

http://www.gmcmhphotos.com/photos/455-r-26amp-3br-engine-work/p10860.html

Here's something on the oil pump from Arch:

http://www.gmcmhphotos.com/photos/melling-22fhv-oil-pump-pressure/p18204.html

This is most interesting as it notes the Melling pump only puts out 6 to 8 psi more.

Regards,
Rob M.
The Pedantic Mechanic

 

[Bob Dunahugh]

Pistons and rods are out. Now need to find out why the HV pump wasn't able to deliver oil to the crankshaft bearings. Whenever the proper amount of oil isn't provided by the oil pump, The bearings that are the farthest from the pump Will be the first to deteriorate. And the bearings closest to the pump will survive a little longer. In this case. 1 and 2 rod bearings seized up. 3 and 4 spun And took the bearing locking tabs off. Crankshaft and rods for 3 and 4 are severely damaged. May not want to repair the crank and #3 and 4 rods. Rob, As to your questions, above should have answered 2 of them. Roller chain was a little loose. But that's how roller chains run. Yes. The 4 lifters should have stayed up As they have check valves in them. I'm taking them apart to see what happened. As to the HV oil pump, HV pumps generally have 23 to 50% longer pump gears, Thus pump 23 to 50% more oil. And take 23 to 50 % more HP to operate with the same amount of excess heat produced. Not more pressure. As to the 20 to 70 MPH comment. The distance a piston travels in its bore per mile of road traveled. Is always the same no matter the speed of the coach. Thus the SFPS will increase over a shorter period of time. As to the air/fuel charge put into the combustion chamber at 20 MPH. Generally at 20 you are increasing your speed. And your vacuum is low. Thus you have more air/fuel going into the chamber. At 70 You're generally just cruising with a high vacuum with a lower air/fuel charge. If you're pulling a hill at 70. The vacuum is low. So the air/fuel mixture is larger.. Hope this adds some clarity to my E-mail. Thanks for asking. Tomorrow I'll be working on the trans and final drive.