Hi all,

Soon will be building a motor from scratch and did a search on here since the beginning and Plastigauge has never been mentioned.

What are you top engine builders using today to check bearing clearances of rods and crank bearings.

Is there there a new way of checking this now, as I am old school and used plastigauge years ago for this sort of thing.

Cheers, Kev

For those that don't know what I'm talking about CLICK HERE

i use a "device"known to a few here as Craig Brown,aka crankshaft engineering.

I use a micrometer much more accurate

take your pick imperial or metric

Plastigauge works well and gives a accurate resalt, I mount the bearings in the case and measure them with a inside mic, the only problem is getting a consistent resalt, I think Craig uses a internal bore gauge, I had him do my last engine as we ground the crank under .008" and renitrided it , measured the bearings and Finnish grinding the crank to size to suit the bearings, a lot of the bearings you buy now are not consistent in there size.

I use it all the time on my bike engines at work. Very quick and easy. I always double check with a mic though

Dave & vduboy,

I understand you can use a micrometer and measure the outside of the crank mains and rod journals, but this doesn't give you the gap between bearing and journal. Think is is something like .001 to .003 thousands of an inch. I guess you could go off the size the bearing (shells) says it is, but is that accurate enough to give 1-3 thou difference ?

Kev

There are many methods to measure internal bores.
You can get inside mics, as well as snap gauges, or even inside callipers.

The best thing is a bore gauge though, set off the crank diameter.

I was spoilt working at Crankshaft Engineering with Sunnen brand bore gauges.
They measured down to ten thousandths of an inch, (.0001"),
so as soon as I could afford it,
I got some of my own,
but still use my inside mics for odd jobs,
and sometimes even snap gauges and inside callipers for other odd jobs that don't allow access.

Plastigage is better than not checking at all, and is the most affordable for the novice.
but unless you can remove the rod half, or case half, without squishing the material,
then you can easily get a false reading.

The ultimate way to prepare any engine is to grind the crank, to give even and correct oil clearance,
measured off the mounted bearings.

For all my engines I begin by machining the conrod, and crank case tunnels to the minimum tolerance for maximum crush,
and then measure the mounted bearings.(torqued all bolts to spec)
From here I have the crank ground to achieve the ideal oil clearance for the application.

Most times I do as Shayne had done,
and have the crank shaft pre-ground, then nitride, and finally ground to the desired clearance.

+1 for bore gauge.

I tried plastigauge, its a good indicator but far from precise. I'd say use it for a rebuild, but not for new parts (which haven't been trialled/tested). My new crank was so out of whack, pastigauge just made it more confusing as i got inconsistent results across all journals. But if it was from a motor that had been running prior, tried and tested, it was indicate well any excess clearance.

1 tried snap gauges and a micrometer on teh big ends and mains. It gave a great reading but made a mess sliding over the surface of the bearings. Had to get a new set as even with a coat of coil it scratched the surfaces. I couldn't afford a bore gauge, so dropped it all to crankshaft engineering for clearance checking by the time i go to my third set of big ends and second set of mains.

I did however use plastigauge for the cam bearings, and the clearances checked out. was a very easy test . and teh cam is spinning nicely!

I'm another for Crankshaft Engineering, plastigauge is not precise enoudh for me, but good for a guide if necessary.

Hey Kev,

When I went looking for Plastigauge about 5 years ago, the parts guy said he hadn't had anyone ask for that for about 10 years!

He did manage to get some in for me, but it was a "special order"!

Repco had it in stock