Plastigauge mains, how to?

goose2 · 02-13-2006, 02:28 PM

I'd like to do a dry run on my lower end assembly to check main bearing clearances with Plastigauge. I assume I can just bolt it up and torque it down using only the main bearing saddle bolts, with no sealant to get a reading. Is this correct?
Thanks,
Randy

chancecasey · 04:46 PM

I think your method would work fine but I also would recommend getting the case bore and crank journals mic'd if you're concerned about this. The plastigauge is good for checking consistency between journals but not so great for all-out accuracy - squished wax and a piece of paper aren't the most precise of tools. Don't bother with the through-bolt o-rings for the dry run, either. Don't scrub the bearings too hard getting off the wax, either or you might mar them. Sorry if you already know all of this - I'm just trying to help contribute what little bit I think I know instead of just sucking the info one-way.

goose2 · 02-13-2006, 04:55 PM

Thanks,all good points Casey....I've already measured everything and all is well, just being obsessive....and want to make sure everything draws up properly.

911pcars · 02-13-2006, 07:31 PM

It's good to eliminate any variables and assumptions. Good thinking. Repeat for the con rod bearings.

Sherwood

Mike Juzenas · 02-13-2006, 09:22 PM

Thats funny I was just thinking of doing that! My crank and case measure out fine so its likely no problem. When I used plastigauge on the big ends of the rods it was a pain since its very easy to move the rods and smear the material. In that case I did a few and the clearance was fine. Since I mic'ed the big ends of the rods and the crank and they are all the same then the clearances should be all the same.....

Oh, I found the brake cleaner seems to take the squished plastigauge off really well...otherwise it sticks.

Cheers,

Mike

MBruns · 02-14-2006, 11:53 AM

You need to use a dial bore guage to get an accurate reading, the plastiguage is a waste of effort and crude, any movement will alter the results.
Mike Bruns JBRacing.com

afterburn 549 · 02-15-2006, 07:55 AM

hmmm did mine..maybe crude- but eliminates a few problems in the end,,call it insurance ?? Plastigauge has saved my butt at least 3 times from problems like wrong bearings in box, crank in diff under size, etc......no not all these were P cars...just one.....but that's the pt of plastiguage its your last effort in Q. control no mater how cave man it is t.m.o.

MBruns · 02-15-2006, 09:02 AM

I admit its better than doing nothing, but for all the effort wouldnt you like to be sure, a V8 bearing cap is one thing but all the work to set up a 911 case and torque it proper leaves alot of room for movement ( ie. error) and thats my only point, I build 911 engines for a living and trust the dial guage for all critical tolerences.
Mike Bruns JBRacing.com

afterburn 549 · 02-15-2006, 09:27 AM

well a lot of us will do only one in our life...so we do what we gots to do...If I had unlimited tools I agree with ya fully-but .....

Bobboloo · Bobboloo's Garage

I'm a big believer in Plastigage. Crude but effective. Errors can be made just as easily with a dial gauge. Atleast with plastigauge you know what the clearances are with the crank and bearings installed. I'd rather take the reading with the parts in rather than out.

A ways back I had a mag case line bored and prepped for a rebuild. I checked it with plastigauge and found out the line bore was off. My readings were confirmed by a highly respected shop. In short. It works.

P.S. When I took my readings I placed the Plastigage at 1, 3, 5, 7, 9, and 11 O'clock.

Mark McClure · 02-16-2006, 05:19 PM

I agree with the plastiguage. Even with bore guages unless you use them every day you are prone to errors. My experience has been with telescopic guages and they are just a piece of crap.......maybe after a lot of practice you can get it right. Or pay for more acurate easier to use tools....which you may use only a few times.

The plastiguage, if used carefully, will give you piece of mind...however if your results are questionable use the professionals. I have found every engine builder I have been to will give you some time to help measure.

Most peopl eon here are DIY'ers and we use whatever methods are

a. Available,
b. Cost effective

plastiguage is only the sleeping pill of the DIY engine builder!

Cheers

Mark.....

Scott Wolthuis · 02-20-2006, 08:49 AM

Some top engine builders don't like to use it because they only want to crush the bearings once (where the two bearing halves touch each other).
If everything checks out you may want to forgo the plastigage process. If you suspect or know you have a problem then use it.

Scott