Mondello- Thrust Bearing install

[gene]

Here is what Mondello has to say about this:

"After the clearances are checked on all the rods, install the center
thrust bearing and torque to 25 lbs.; tap on each end of the crank with a
heavy brass or hard rubber hammer. Use a small piece of wood and a metal
hammer , if this is all you have , to center the thrust bearing. Increase
the torque in 25 lb. increments until you reach the recommended torque
values, tapping the crank back and forth with each torque increase.

Using a pry bar, pry the crankshaft forward in the engine and measure the
clearance (with a feeler gauge) between the crankshaft and the bearing and
record the clearance. The clearance should be between .004 and .010. When
you do your final assembly, repeat this procedure torquing all the caps in
25 lb. increments, until recommended torque values are achieved. If you do
not center the thrust bearing in an engine, premature crankshaft failure
may occur."

This seems very straight forward so the secret must be in the $300 to $700
crank preps.

gene
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/ http://www.california.com/~eagle/

 

[blank]

Gene,

I don't get it - what's your point? Admittedly, it's Friday afternoon and
my brain's fried, so I'm probalby more than a little "humor impaired". Sure
it's a simple procedure, but Joe warns "If you do not center the thrust
bearing in an engine, premature crankshaft failure may occur". Now, is this
the root cause of the crankshaft failure problem? I don't know, but it
sounds more likely a cause than coverter "ballooning".

my $.02,
Patrick


> Here is what Mondello has to say about this:

 

[gene]

I am still looking for the final answer as to why GMC cranks break. I have
no ego in this and since I have only rebuilt 5 motors in my entire life, I
was just saying this procedure is no big deal

This is what you always do when you put the engine together. Steve must
have done this hundreds of times. This is not making the live or die
decision for the crank !!! It has to be something else, bad crank
machining, bad crank, etc. This little tap it back and forth is not going
to do it. If you take this to your engine rebuilder he will laugh at you
because this is what everyone does...... so we still do not have the answer
here, What can I go tell Statkus that will guarantee I will not have a
broken crank?????

Buy a $300 crank like Lamey does, or buy a $700 crank from Mondello, is
this the answer?

gene

>Gene,
>
>I don't get it - what's your point? Admittedly, it's Friday afternoon and
>my brain's fried, so I'm

Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/ http://www.california.com/~eagle/

 

[bill tyrrell]

Jasper Engines is a fairly large engine rebuilder - advertised in car
mags etc. I'm guessing they must have had some experience here. Has
anybody checked in with them and their warranty policies or are they
part of the controversy?

Somebody else mentioned the converter seal not being able to hold back
the oil dike over some standard limit. Is this a player?

Bill Tyrrell

>
> I am still looking for the final answer as to why GMC cranks break.

 

[lorry clavelli]

> I am still looking for the final answer as to why GMC cranks break.

When installing the torque converter, the GM assembly manual says that a
properly installed converter will be 1" inside the front face of the
transmission. The engine and trans are then solidly bolted together. Then the
instructions call for sliding the converter forward and bolting it to the
flexplate. From this it appears that that there is plenty of clearance so that
even if the converter "balloons" it won't put pressure on the back of the
crank. After all, how big could the converter get and still return to normal
size. If it was under enough pressure to balloon enough to take up all the
clearance available it wouldn't return to normal size and might even come
apart.

Looking at the pictures, I don't see any abnormal burn marks on the crank,
bearings, or bearing caps which would occur if the crank assembly was under
tremendous pressure from the converter. The back of the converter that goes
into the trans doesn't show any evidence of galling or having been in a bind.
The thrust bearing, while scarred, is pretty much intact. There are dings and
bruises on several of the parts but I think that those are the results of the
failure and not the cause.

IMO the cause is strictly a tired crank. Tired cranks break. The solution is
probably to magnaflux the crank and replace it if defective. An early model
forged crank rather than a cast crank would also be an improvement.

It would be interesting to hear the opinion of a metalurgist after he/she
inspected the crank in the picture.

Lorry

 

[gene]

I am wondering about the quality of cranks, this one had only 20,000 miles
on it since a complete rebuild.

gene

>IMO the cause is strictly a tired crank. Tired cranks break. The solution is
>probably to magnaflux the crank and replace it if defective. An early model
>forged crank rather than a cast crank would also be an improvement

Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/ http://www.california.com/~eagle/

 

[patrick flowers]

Gene,

Was the crank new or just refinished as part of the rebuild?

Patrick

>
> I am wondering about the quality of cranks, this one had only 20,000 miles
> on it since a complete rebuild.
>
> gene
>

> >IMO the cause is strictly a tired crank. Tired cranks break. The solution is
> >probably to magnaflux the crank and replace it if defective. An early model
> >forged crank rather than a cast crank would also be an improvement
--
Patrick Flowers
Mailtoatrick

The GMC Motorhome Page
http://www.gmcmotorhome.com

 

[gene]

I will have to ask Mr.C but my guess it that it was a reground crank. I am
not sure if anyone is buying new cranks, Mondello is offering to buy old
cranks on his web site.

gene

>Gene,
>
>Was the crank new or just refinished as part of the rebuild?
>
>Patrick
>

> >
> > I am wondering about the quality of cranks, this one had only 20,000 miles
> > on it since a complete rebuild.
> >
> > gene
> >

> > >IMO the cause is strictly a tired crank. Tired cranks break. The
> solution is
> > >probably to magnaflux the crank and replace it if defective. An early
> model
> > >forged crank rather than a cast crank would also be an improvement
>--
>Patrick Flowers
>Mailtoatrick
>
>The GMC Motorhome Page
>http://www.gmcmotorhome.com
>
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Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/ http://www.california.com/~eagle/