Engine Building Live Webinar

Hi Andre.

I have just watched your engine building live seminar and subsequently purchased the starter package, so firstly, thanks for your service.

I just wanted to ask a question regarding bearing clearance.

When measuring bearing clearance using the plastigauge method, my head is telling me to use two wax strips, one on either side of the crank journal for example. But watching your video you used just one.

So does this mean that when the clearance specification is given as say 1.5 - 1.9 thou, this in reality is bearing clearance measured on one side with no clearance on the opposite side?

So when the engine is running with oil pressure and equal clearance around the full circumference the clearance will be approx 0.75 thou at either side of the bearing?

Kind regards,

Andy

Hi Andrew, thanks for getting involved!

Your question is actually a pretty common one. What we're interested in is the total clearance, which is the difference between the outside diameter of the crankshaft journal and the inside diameter of the bearing shells. We only need to use one strip of plastigauge to measure this as the other side of the crank journal will be resting against the bearing surface. When the engine is running, the oil film tends to equalise the clearance from side to side, although the crankshaft will still be offset in the journal due to the forces applied to it during operation.