Connecting Rod Oil Clearance

[wdlanning]

Replacing pistons in V1902 engine out of a L3350. Using plastic-gauge I find one crank journal to connecting rod bearing to be almost twice the WSM spec (.003. VS .006). I find specs for minimum clearance but not maximum limit.
The crank is still in the engine and I just pulled the oil pan to remove pistons.
I would like to use as is but what are consequences,if any?

 

[JerryMT]

Replacing pistons in V1902 engine out of a L3350. Using plastic-gauge I find one crank journal to connecting rod bearing to be almost twice the WSM spec (.003. VS .006). I find specs for minimum clearance but not maximum limit.
The crank is still in the engine and I just pulled the oil pan to remove pistons.
I would like to use as is but what are consequences,if any?

What were the other journals? Is there evidence of scoring on the journal or the bearing insert? I'd recheck it if it is greatly different from the other bearings. Can't help you with the max limit.
I wouldn't use it "as is" until I knew what the max allowable clearance was. If the journal looks good I would mic it to see how round it was, and if within limits, get an smaller bearing to get the clearance within spec.

 

[TheOldHokie]

Replacing pistons in V1902 engine out of a L3350. Using plastic-gauge I find one crank journal to connecting rod bearing to be almost twice the WSM spec (.003. VS .006). I find specs for minimum clearance but not maximum limit.
The crank is still in the engine and I just pulled the oil pan to remove pistons.
I would like to use as is but what are consequences,if any?

Replacing pistons in V1902 engine out of a L3350. Using plastic-gauge I find one crank journal to connecting rod bearing to be almost twice the WSM spec (.003. VS .006). I find specs for minimum clearance but not maximum limit.
The crank is still in the engine and I just pulled the oil pan to remove pistons.
I would like to use as is but what are consequences,if any?

A quick search says connecting rod oil clearance limits are .0014/.0037. I would expect rod knock with .006 of clearance. Personally I would not put an engine together with that much clearance. If you do expect to be back in to it in the not too distant future.

Dan

 

[kubotafreak]

Second, I don't like anything over .003. Is the journal small, or the rod end large?

 

[Pau7220]

or the rod end large?

Or is it out of round?

 

[wdlanning]

Or is it out of round?

Crank journal is smaller

 

[TheOldHokie]

Crank journal is smaller

In cases like this actual measurements are needed. All we have so far is a relative difference of .006 between crankpin diameter and old bearings. We don't know where the excessive clearance is coming from.

The crankpin diameter specification for the V1902 is 43.959-43 975 mm (1.7307-1.7313 in.). What is the actual diameter of the crankpin in your engine?

Dan

 

[wdlanning]

In cases like this actual measurements are needed. All we have so far is a relative difference of .006 between crankpin diameter and old bearings. We don't know where the excessive clearance is coming from.

The crankpin diameter specification for the V1902 is 43.959-43 975 mm (1.7307-1.7313 in.). What is the actual diameter of the crankpin in your engine?

Dan

You are looking at the wrong 1902 engine specs. The WSM spec for crank pin diameter is 1.8487-1.849 in. Also found that the max oil clearance is .008. So will use standard bearings. I am told I could mix undersized and standard to be more within spec. Any thoughts on this combination?

 

[wdlanning]

In cases like this actual measurements are needed. All we have so far is a relative difference of .006 between crankpin diameter and old bearings. We don't know where the excessive clearance is coming from.

The crankpin diameter specification for the V1902 is 43.959-43 975 mm (1.7307-1.7313 in.). What is the actual diameter of the crankpin in your engine?

Dan

You are looking at the wrong 1902 engine specs. The WSM spec for crank pin diameter is 1.8487-1.849 in. Also found the max oil clearance is .008 in.
iam told I could mix undersized and standard bearings to be more in spec. Are there thoughts regarding this practice?

 

[TheOldHokie]

In cases like this actual measurements are needed. All we have so far is a relative difference of .006 between crankpin diameter and old bearings and we don't know where that extra clearance is coming from. The crankpin diameter specification for the V1902 is 43.959-43 975 mm (1.7307-1.7313 in.). What is the actual diameter of the crankpin in your engine?

Dan

You are looking at the wrong 1902 engine specs. The WSM spec for crank pin diameter is 1.8487-1.849 in. Also found that the max oil clearance is .008. So will use standard bearings. I am told I could mix undersized and standard to be more within spec. Any thoughts on this combination?

Only specs I found online but as long as you have better info then thats fine. But you still haven't told us what that crankpin actually measures so we can evaluate where the wear is coming from.

Oil clearance wear limit of .008 is still way too wide for me. That's a full bearing size under (.2 mm)

Select fit with different top and bottom bearings of the same nominal size to close things up a thou maybe two is pretty common but .004 under on one side will put the bore way out of round. Again not something I would do but given the already loose fit who knows.

YMMV,

Dan

 

[lugbolt]

throw the plastigage in the trash where it belongs.

You will ideally need a dial bore gauge and a micrometer to properly measure. Measure for taper and egg on the journals. With the proper measuring devices, your issue then becomes a no-brainer.

The few times I tried plastigage, it was inconsistent. Once it cost me a motor, thankfully it was my own motor and I have nobody to blame buy myself for not using the correct tools. I had the tools too but decided to use the other stuff.

 

[wdlanning]

Only specs I found online but as long as you have better info then thats fine. But you still haven't told us what that crankpin actually measures so we can evaluate where the wear is coming from.

Oil clearance wear limit of .008 is still way too wide for me. That's a full bearing size under (.2 mm)

Select fit with different top and bottom bearings of the same nominal size to close things up a thou maybe two is pretty common but .004 under on one side will put the bore way out of round. Again not something I would do but given the already loose fit who knows.

YMMV,

Dan

Thanks for your response and I appreciate your comments

 

[kubotafreak]

throw the plastigage in the trash where it belongs.

You will ideally need a dial bore gauge and a micrometer to properly measure. Measure for taper and egg on the journals. With the proper measuring devices, your issue then becomes a no-brainer.

The few times I tried plastigage, it was inconsistent. Once it cost me a motor, thankfully it was my own motor and I have nobody to blame buy myself for not using the correct tools. I had the tools too but decided to use the other stuff.

I have used it on many builds. I have found that it is best to buy a new package often. You use so little of the material, so much of it goes to waste especially at the end. You can tell when the green goes bad it turns dark. Many parts stores have old stock too, so watch out. I generally only use it to do the final assembled check. It does give a good visual of taper/clearance.

I dare say most jobbers do not have the proper tools to do the job right. Bore gauges, calipers, and micrometers are not cheap. I guess the real question here is if the crank is out of the block or is this an in frame job. Out of frame its a cheap grind for undersized bearings, so risking doing it cheap is foolish. If in frame, op needs to be much more specific as to the surface roughness, and measurements for any real advice. In frame needs at minimum polish before measuring. (Shoe string/600grit)

You never want to "build" to the service limit. There should be a build spec in the range of .0018- .0045in
I highly advise staying in the tighter to middle end of spec. Service spec is an inspection clearance only. Anything near the max here needs a full rebuild.