Engine crankshaft wear measurement

[Welderpaul]

I need to measure the wear on my engine crankshaft shells to suss out what 'oversize' shells i need to fit due to engine wear.

A few sources lead me to use Plastigauge strips.

How many do you need to put in? A small strip at 12, 3, 6, 9 o clock?

Cheers all.

 

[AndyStobbs]

Used to use one strip per shell. Stick it to the shell with a dab of grease, torque up the caps. Dissasemble and compare to the included guide to ascertain the oil clearance (or air clearance in your case).

 

[Welderpaul]

The strips are 100mm long...1 strip wrapped round the shaft then?

 

[ajlelectronics]

Not sure if I have understood correctly, but you do realise that you can't just fit thicker shells? The crank needs grinding to the next size down if the wear warrants it. Measurement using a micrometer for journal size and ovality. You could just fit new shells of the same size, provided wear is moderate, otherwise it will knock out the new shells in double quick time.

 

[rtbcomp]

This is their website

http://plastigauge.co.uk/how-plastigauge-works/

 

[AndyStobbs]

You cut the strips down to the width of the shell. First time I encountered plastigauage it was described to me as 'jumped up, precision made plastercine' and thats basically all it is.
If your gap warrants it you won't need to regrind crank. Is this for mains or big ends, or both?

 

[Pete.]

This is how you use it, cut a strip full width of the journal, clamp up the bearing, unclamp the bearing then use the paper gauge to read the clearance. you must take care not to rotate the bearing when you're doing this.

 

[rikrobson]

the Plastiguage is a set exact size. when the cap is torques up the plasiguage is obviously squashed. since you started with a known size the volume os €stuff will be displaced laterally yo the thickness of the gap/clearence you are measuring. the resulting width is measured using the guage provided calibrated in the resulting thickness

 

[gordon stephenson]

As said, snap off a full width piece, stick to the bottom keep shell with very small amount of grease and torque up, remove keep and compare the width of the plastigauge with the sizes printed on the packet.

 

[wristpin]

A lot easier and more accurate to "mike" up the crank and compare with the engine manufacturers published wear limits, but if you don't have a micrometer or vernier it's probably a lot easier and safer to take the crank to an engine reconditioning shop and get them to do it.
The problem with using the plastigauge is that unless you have a new set of shells you are measuring the sum of two sets of wear and I have not come across an engine manufacturer that publishes that figure as opposed to reject figures for crank journal diameter and ovality.

 

[Pete.]

Ovality check first, with a micrometer. It's a comparative test so you don't even need to calibrate. If the ovality is within bounds next is oil clearance check.

Plastigauge measures the oil clearance. If it's within limits and the shells appear in good condition you need do nothing. If it's not then you have to buy two or three pairs of new shells and gauge it again. Here my way to check without wasting too much money on shells you won't use.

Suppose there are four sizes of shell available, 1 being the tightest and 4 being the loosest. Buy one pair of size 2 and a pair of size 3. Gauge the journal with size 2, if it's loose you need a 1 for that journal, if it's tight do it again with size 3. If it's still tight you need a 4. Done like this, you can map the oil clearance of all the journals with 2 new shell pairs and the odds are on that you'll use one or both so not much money wasted.