Main Bearing Clearance Check

[porschedude996]

I have been looking at various YouTube videos (parts klassik) and others and I have been unable to see someone check the clearances with "Plasicgage." Any thoughts as to why?

[dannobee]

It's generally not considered to be as accurate as micrometers and bore gauges. And it needs to be cleaned off of the bearing and journal after checking.

Many people use it as a final sanity check though, just in case.

[PeteKz]

I did my first engine builds 45+ years ago using plastigage (American V-8's and 6's), and have continued since. Supposedly the mikes are more accurate, but I think I've proven to myself that plastigage is close enough.

On my last rebuild of my current engine (see below), 2 -1/2 years and 12,000 miles ago, I used plastigage to check the mains and rods. They all measured right at .002". Now, if the plastigage showed significant variation, THEN I would measure using mikes and bore gauges to find out why that is.

[Dpmulvan]

Originally Posted by dannobee

It's generally not considered to be as accurate as micrometers and bore gauges. And it needs to be cleaned off of the bearing and journal after checking.

Many people use it as a final sanity check though, just in case.

It’s probably more accurate than all the $50 Chinese micrometers and $100 dial bore gauges out there which will give you false readings and scratch up your expensive parts.

[porschedude996]

Pete, I too have used plasticgage since the early ’70s. V-8’s, inline 4’s, flat six in 1986 (911T 2.4L). The flat 6’s I can only recall doing the rods. Spillover from the past in High School Auto Shop. I checked the crankshaft myself (Mitutoyo), had the line bore checked, and he checked and polished the crankshaft. I checked the Big end of the rods, checked the wrist pin to rod fit. So given there is almost only one brand of bearing insert, I’ll move forward without checking with said Plasticgage.

Thanks for everyone’s input.

I whipped up a crankshaft assembly fixture. It’s going to be a one time usage I think, but I’m retired and enjoy the process.

[phunt]

I am starting my engine build now and I plan on using instruments to measure. mic dial-a-bore. I have used plastigage a lot but that was on v8s that have 2 sometimes 4 bolts to torque on the mains and 2 for the rods so really easy. having to torque all of the case bolts on this porsche engine I decided to measure.

[porschedude996]

Originally Posted by phunt

I am starting my engine build now and I plan on using instruments to measure. mic dial-a-bore. I have used plastigage a lot but that was on v8s that have 2 sometimes 4 bolts to torque on the mains and 2 for the rods so really easy. having to torque all of the case bolts on this porsche engine I decided to measure.

No disagreement there!

[Cloggie]

I have a brand new case, bearings, crankshaft all from Porsche.

...and yes, I am checking with plastigage just to make sure there is not a factory screw up.

I have seen several places where it is done Youtube M539 restorations, a good channel about lousy BMW's, does it on their many engine builds.

D.

[dannobee]

Yup, the final sanity check that I alluded to above. Because, you know, 5 out of 3 people have problems with fractions.

[JoeMag]

The bore gauges and mic'ing the crank, do not check if the bearing thickness is correct.

Did plasti-gauge check on mains on next version of my motor that I'm building now. I feel like I've assembled this thing many times due to the amount of dry assembling and checking I've done (everything non-factory/custom from crank to the rockers). ...however, it's worth it, caught several incorrectly made parts and issues.