Will Plastigage show mains misaligned?

[dave w]

I'm putting together a budget SBC 350. The crank has been turned 10 / 10. I was wondering if the plastigage will show if one of the mains is misaligned? I was thinking if I put a piece of plastigage on both the bottom and top main bearings, I might be able to see a misalignment? My thinking is; if all the mains were straight, then it really would not matter if the plastigage was on the top or bottom of the main bearing. My thinking is; if plastigage is on the top and bottom of the main bearing and there is a misalignment, I would see noticeable difference in the plastigage measurement bottom / top?

Any advice is appreciated!

dave w

 

[4X4HIGH]

The only way you could have an issue with the mains not being "inline" is if it spun a main bearing and then that would be noticeable and would need to be align honed to correct the issue before the engine is even able to be assembled. Plastigage is only for checking clearances and you must only use a single piece under the main cap bearing and DO NOT turn the crank once you have plastigage in there.

 

[63chevyll]

The only way you could have an issue with the mains not being "inline" is if it spun a main bearing and then that would be noticeable and would need to be align honed to correct the issue before the engine is even able to be assembled. Plastigage is only for checking clearances and you must only use a single piece under the main cap bearing and DO NOT turn the crank once you have plastigage in there.

As much as I appreciate your good advice, but ONLY is not true.

An overheated block can also cause, a main bore not true/ straight. Had it happen,

And Dave, I wouldn't trust plasticgauge as a reference for checking main bore.
If a reputable grinder did the cranked you can almost assume the crank is straight.

Take your plasticgauge measurements, clean up and install the crank with some 5w30 oil and see how it spins.

 

[dave w]

I purchased the bare block from a company that sells core engines, Engine Rebuilder Supply (ERS). I don't know the history of the block. I don't know if the block has been overheated, or if the block spun a main bearing.

What I do know, the main caps were stamped with numbers, by ERS when they removed the crank. I measured the main cap bores, 2.6395 ~ 2.6405 both 0 degree (vertical) and 90 degree (horizontal) The block had lots of oil residue buildup, maybe even an excessive amount of oil residue buildup. The block did not smell of burnt oil, and the external OEM paint on the block had an even coloration. Most times if a block is severely overheated the paint will discolor and the oil will smell burnt. All the freeze plugs were in, and a slight amount of antifreeze drained from the block when I turned the block upside down.

I'm sure the crank grind is good and the crank is straight. I'm still thinking if the block mains are misaligned the plastigage will show either a top or bottom measurement with less or more clearances. Well that's what I think this morning. In a few hours, I'll know more after I make the plastigage measurements.

dave w

 

[dave w]

Here are some pic's of the plastigage measurements. Overall, the clearances look to be about 0.0015". I have one lower that is about 0.0010" Looks OK to me.

dave w

 

[dave w]

Here are some pic's of the plastigage measurements. Overall, the clearances look to be about 0.0015". I have one lower that is about 0.0010" Looks OK to me.

dave w

More pic's.

dave w

 

[4X4HIGH]

Is that with plastigage on both the upper and lower bearing?

The proper clearance is as follows...

#1 journal = .0008" - .002"
#2 journal = .0011" - .0023"
#3 journal = .0011" - .0023"
#4 journal = .0011" - .0023"
#5 journal = .0017 - .0032"

 

[dave w]

Is that with plastigage on both the upper and lower bearing?

Yes, I put plastigage on both upper and lower bearings. This is the first time I've used plastigage on both upper and lower bearings. Until now, I've only used plastigage on just the upper bearings.

I did not post all the pictures I took of the plastigage measurements. It looks to me all clearances are in spec.

dave w

 

[4X4HIGH]

I would now do your check again with the plastigage ONLY on the cap side and i'll bet your clearances change.

 

[blazinzuk]

I would now do your check again with the plastigage ONLY on the cap side and i'll bet your clearances change.

When I have put together motors in the past I do both bearings but separate. Uppers and then lowers.

 

[63chevyll]

I have only done uppers myself.

You should be fine tho, but worth the check.

NOTE: make sure your using new plastic gauge, not some stuff thats been sitting in a tool box for 10 years.

I have used some old PG that was giving me way big numbers and tried new stuff, mic'd it and it was all good

 

[blazinzuk]

I have only done uppers myself.

You should be fine tho, but worth the check.

NOTE: make sure your using new plastic gauge, not some stuff thats been sitting in a tool box for 10 years.

I have used some old PG that was giving me way big numbers and tried new stuff, mic'd it and it was all good

I used to do that. I might not have caught it but a machine shop had oblonged some the crank mains on an engine I built. Caused the motor to wipe out a bearing in very short order. Might not have caught it but it might have. That was an expensive mistake. The machinist I took the crank too (after the fact) suggested doing that.

 

[dave w]

I would now do your check again with the plastigage ONLY on the cap side and i'll bet your clearances change.

I've already installed the crank, and I'm in the process of final assembly.
Here is what I'm willing to bet:
Crank Grind $$
Block Bore / Hone $$$
Rod Resizing $$
Cylinder Head Service $$$
Re-Ground Roller Camshaft $$
New Roller Lifters $$$
New HV Oil Pump & New Oil Pump Shaft $$
New Rod & Main Bearing $$
New Fel Pro KS2666 Gasket Set $$
New Plain Cast Rings $$

I'm betting the clearances I measured won't change even if I were to measure just the top or bottom main bearings. I've got some serious cash I'm betting on my measurements!

Care to see my bet and raise the stakes?

dave w

 

[wasted wages]

Not to be a ass or anything....but why do you insist on outing everything Scott ( 4x4 High) mentions in his replies?

I think his answers have valid perspective that related directly to your question you posted. And if you want to bet the farm on your clearances...why did you ask the question in the first place ?

I've been on this site for about 6 years, Scott knows his stuff....there are many others on this site that will back up that statement..

He doesn't need me to defend him....his work ethic and willingness to help and knowledge stand for themselves.


If you don't like the responses from him, simply say thanks and move on....
I'm sure he has better things to do than engage in pissing contests...


Oh....and my name is Frank....and I have building engines transmissions and rears for over 30 years......just in case you want to start a pissing contest with me....better bring your A-game..

I'm sure I've forgoten more than you know...

 

[dave w]

Not to be a ass or anything....but why do you insist on outing everything Scott ( 4x4 High) mentions in his replies?

I think his answers have valid perspective that related directly to your question you posted. And if you want to bet the farm on your clearances...why did you ask the question in the first place ?

I've been on this site for about 6 years, Scott knows his stuff....there are many others on this site that will back up that statement..

He doesn't need me to defend him....his work ethic and willingness to help and knowledge stand for themselves.


If you don't like the responses from him, simply say thanks and move on....
I'm sure he has better things to do than engage in pissing contests...


Oh....and my name is Frank....and I have building engines transmissions and rears for over 30 years......just in case you want to start a pissing contest with me....better bring your A-game..

I'm sure I've forgoten more than you know...

Hi Frank,
I guess I did not use the correct Smile Icon? I don't post here to piss people off!

I was hoping to share an alternative use of plastigage to find a misalignment of main journals. I've posted a couple pics below to show what I think an aligned and misaligned main jounal looks like. I was hoping to show that the plastgage measurement would be different on the top and bottom if the main journal was misaligned. I really don't know if this "outside the box" thinking for plastigage is effective?

As for betting, I simply wanted to say I'm putting out some serious money on my measurements. If the mains are aligned, I would expect to see the plastigage measurement the same if measureing either top or bottom. I don't think the soft material of plastigage will affect the measurements if installed on the top and bottom.

dave w

 

[wasted wages]

I think the point Scott was making and I agree is,, that if the plastigauge is on both the top and the bottom of the journal you will have a small amount of interference fit at both the top and bottom of the journal as the plastigauge is now suspending the crank off of the bearing saddle in the block.....

I would think you would want the crank to lay as flat as it can in the saddle and then compress the plastigauge from the main cap side only to get a true clearance number...

I know its splitting hairs.... but it is really the proper way to get a correct reading..

think of it this way....The alignment could just as well be out of wack horizontally....are you checking it that way also ??? it would be impossible to gauge every direction using plastigauge.... and then you are still using the crank as the standard.....it could have it's own machining flaws and warps....

Plastigauge is really a last resort method of checking clearances, and not the proper tool for checking the alignment bore of the mains in a block.

You would be better to pull the crank and bearings and use a machinists straight edge and feeler gauges in the saddles....

Your crank grinder or machine shop may have "standards" ( basically a straight shaft turned to a specific tolerance) that they can lay in the block and torque up the caps and see if it will turn...If it wont turn and locks down the shaft....then I would be concerned...

These methods will give a lot more peace of mind when you spin the engine over to fire it up that first time than with plastigauge....

If you have that big of an investment in parts.....100 bucks more to have the mains checked for alignment is the way I would go....

 

[Treeman587]

I've already installed the crank, and I'm in the process of final assembly.
Here is what I'm willing to bet:
Crank Grind $$
Block Bore / Hone $$$
Rod Resizing $$
Cylinder Head Service $$$
Re-Ground Roller Camshaft $$
New Roller Lifters $$$
New HV Oil Pump & New Oil Pump Shaft $$
New Rod & Main Bearing $$
New Fel Pro KS2666 Gasket Set $$
New Plain Cast Rings $$

I'm betting the clearances I measured won't change even if I were to measure just the top or bottom main bearings. I've got some serious cash I'm betting on my measurements!

Care to see my bet and raise the stakes?

dave w

Wait. I'm confused. How much more does $$$ cost compared to $$.

BTW, if it blows up, it wont be worth even $