Always...Always check your bearing shells

[veggie]

Today I opened up the bottom end on an engine that I am fitting into the CHP system.
This was supposed to be a general inspection to make sure everything looked good.
The residual factory test oil in the crankcase was brand new, clean and clear.
The main bearings looked nice.
Cam gears looked clean and shiny with very little backlash.
I wondered if it would be necessary to remove the con rod cap and look at the bearings ?  Hmmmmm !

Then I rotated the crank past top-dead center and heard a little knock.
Again and and again, a little knock came from the con rod bearing each time it changed direction.
Definitely needed inspection.
I grabbed my wrenched and some plastigauge and proceeded to remove the bearing cap.
Two things were discovered:

1] regardless of how clean the crankcase seemed, there was crap in the bearing surfaces.
It's as if the fellow at the factory assembled it in the parking lot on a windy day.

2] A plastigauge check revealed a clearance of 0.010"  
This would have pounded the bearing to pieces in a matter of hours.
The culprit seems to be the ends of the bearing shells which extend past the cap faces preventing the bearing cap from fully seating against it's mating face. I have included some pictures to illustrate the problem.

My question to the forum is:
Once a new set of shells are installed, how do I fix the bearing shell protrusion?
Is this a common occurrence in varying degrees?

The moral of this story....

With a new Listeroid, ALWAYS...ALWAYS...ALWAYS check the con rod bearings no matter how nice the engine looks.

veggie

[Henry W]

Veggie,
I am glad you found it. That would of hammered it self to death in no time.
This is why it is so important to check out any Listeroid, GM-90 and Changfa type engines before firing them up.

Henry

[veggie]

So what technique is used to trim bearings that extend beyond the cap face.?

...and how much protrtion (if any) is allowed?

Veggie

[mobile_bob]

there needs to be some protrusion to provide for brg crush, which causes the shells to fit
even tighter to the rod and rod cap, this keeps down fretting and provides better heat transfer.

how much crush or rather how much protrusion (nip) is the 64k question

i would expect about .003"nip, however .010" might have been needed to allow for shimming

i would start out by removing the shells, and installing the cap on the rod, torque it to spec and check the
roundness of the rod big end.  it likely is egg shaped, being wider at the parting line than from 90 degrees to the parting line.

if it turns out the rod is .007" narrower than at the parting line, then all is as it should be with a .010" nip, but you will have to install
~.007 in shims, equally distributed,

this will then assemble the rod big end with the requisite .003" crush, (with shims) and provide for a round big end hole.

now if on the other hand you measure the big end bore and it turns out to be perfectly round without shims and without the shells
when torqued, then you have way too much crush, you will need to file down the brg shell protrusion to get to about .003 crush
and assemble without shims

most of the indian engine's come with shims, so if they are machined correctly the big end is sized with the required shims in place
and the cap torqued to spec,, this makes for a nice round hole to start with, and if the id is of the correct size for the shells they intend
to use then the nip should be correct to start with.

this is why i think you need to start at the datum point, that being a bare rod, without shims or shells, with the cap on, torqued to specs to
see if it is round or whether it require shims to make it round, and work your way back from there.

bob g

[veggie]

Thanks very much Bob.
My unit does not have any shims.??
I think the extra material created the excessive .010 clearance so hopefully the hole is the correct shape when I check it.
I plan to do a practice run using the dirty shells.
I will file them to get the right nip and then plastigauge the clearance.
I'm hoping that I don't have to remove the head (to get the piston and rod out) but I will do that if it becomes necessary.

veggie

[mobile_bob]

i think you might wanna pull the head, and start from square one

you might be luckier than i am, and filing might work, but i bet the brg shells are right
and there ought to be shims or something else is awry

bob g

[BioHazard]

Do the Indians build these things for decorations or what? I can't imagine everyone buying these in 3rd world countries has the know how or technology to rebuild them from the beginning...

[veggie]

i think you might wanna pull the head, and start from square one

you might be luckier than i am, and filing might work, but i bet the brg shells are right
and there ought to be shims or something else is awry

bob g

Grrrrrrr! 

[billswan]

Veggie

Does the gm-90 use shims?

Have you seen shims in other engines you have checked out?

Check the inserts to see if they are marked standard, would have to be as an under size should lock up the engine if the crank is standard.

Mike that crank it might be under size.

I have a metro 16/1 I am working on it definitely is not a normal roid it has NO shims and I will bet it is not meant to have any. If I remember what I have read of the gm-90 it might be of better quality and is built without shims to a more modern standard.

You may have mismatched parts a .010 undersize crankpin should not be in a new engine but these things are built in a part of the world where that just might happen.

Or Try installing a new insert you must have one?

Billswan

[vdubnut62]

Veggie

snip



You may have mismatched parts a .010 undersize crankpin should not be in a new engine but these things are built in a part of the world where that just might happen.



Billswan

I have a 79 chevy 4x4 with a 350 4 bolt main engine that I bought from the original owner, he swears nothing had ever been touched since new
but it had a .010 under crank in it from GM.
Just sayin'  stuff happens!
Ron

[mobile_bob]

Billswan makes a good point, we really don't know if the crank is standard or undersized

i remember american motors engine came factory new with all sorts of std, undersize,  mains rods
and even cam brgs

you could just as easily gotten a 258 six with std mains and .020 under rods as the other way around
iirc they even might come with oversize pistons from the factory.

this happened i believe in the later years before american motors went under, but illustrates what you have to do
to get by when things get tough.

its entirely possible you have an undersize crankpin, or some mismatch rod brg of another size that maybe isn't right
for that engine.  for all we know they make a bigger hp gm90 that uses larger id shells.

the more i think about it, i would recommend taking it down and getting out the mic's and see what is going on.

might make the difference in an engine that is right and an engine that damages the crank and rod, or worse.

bob g

[veggie]

The GM90 engine do not use shims.
I will check the dimensions and report back.
Step one (Simplest) is to correct the nip and see if that fixes the clearances.
If that doesn't work, the head comes off and things get a bit more serious.

veggie

[playdiesel]

Wow Veggie, a lot a crap went through that bearing already, good thing you checked it out. Not sure how it applies to Indian assemblies but in the originals there were shims in the rod and they were not designed to change clearances but to adjust the crush, or nip as Bob has said, on the inserts. In my experiance you need .002 or so crush and if you have more than that things just bend like the cap and rod it self. Bob has explained it well. Sounds like your inserts were designed around shms that were not used. Bob has explained the entire proceedure better than I can. It should be a sticky for working on the bottom end of these engines.

[vdubnut62]

Now wait just a minute. If Veggie's engine was designed for shims, and none were used,  and the correct bearing shells were in it to start with, and the rod cap was tightened, the darn thing would be locked up - not have .010 clearance and an audible knock when turned over by hand.
I believe that it has the wrong rod bearing, or the journal is undersized, or possibly a problem with the rod itself. I'm putting my money on either rod bearing or journal (or both). The only way to tell is get the micrometers out.
That said, I have been wrong more times than right and I always want to learn.
Now, what am I missing?
Ron

[playdiesel]

Ron, What expactly is wrong with Veggies engine is conjecture until he measures. My experinace with Indian clones is very limited but I am a little experianced with what is properly known as non-precision bearing bores. If the insert is over sized for the bore of the rod, which is Veggie's problem, and the rod is tightened three things can happen. 1.The bearing metal is pushed outward at the parting line giving the locked up condition you suggest. 2 The rod and or cap bends around the inserts to touch at the outer edges.  and 3 Assembly torque is reached before either 1 or 2 is reached. or 4. SOme combination of 1-3.  None of the above will cause low clearance where we normaly measure things with plastigauge, at the middle of the cap. Pinch, if it occurs will near the parting lines. Basicaly the weakest part gives when you have more crush or nip than you should have and believe it or not it usualy isnt the bearing insert. The rod and cap wil usualy bend to meet or never meet at all at torque.. An experiance asembler can detect these problems as it will come up to torque slowly or "spongy assembly" is often used. The original Lister manual tells you to check for crush or nip by torqueing the cap then loosen one bolt and measure how far the rod opens up on the off side. I think it says .004 is correct but dont quote me on that. If I had similar parts and ten minutes in the shop I could show it to you'all lots easier than trying to explain it here, sorry.