Measuring bearing clearences

[tadd]

Ok, so I know of two ways to determine rod and main bearing clearance...

1. Torque up rod or case, measure with dial bore gauge. Measure bearing thickness with a cone anvil mike. Measure journal with flat anvil mike. Do math.

2. Insert bearings, torque rods or case. Measure with dial bore gauge. Measure crank. Subtract.

I've always done #1 cause I always end up digging a ditch in the bearing (never fails ) and I've been told that once a bearing is crushed it will never 'bite' as well again.

I've also been told that proper clearance isn't measured unless the bearing is under crush since they are designed slightly egg till crushed.

Thoughts anyone... No, plastigauge is not acceptable .

Tadd

[Hawkeye's-911T]

Bump!

[tom1394racing]

What's wrong with plastigage?

[tadd]

Tom:
Plastigauge can be all over the place. The manufacture of the string itself is pretty accurate, but there is a lot of noise in the 'squishing' and 'reading'.

There have been a lot of articles on this topic... one link for your viewing pleasure.

Plastigage Versus Micrometer - Accuracy Test - Car Craft Magazine

tadd

[cgarr]

Those bore gauges are good but its really an art to using them. You could have guys measure the same bore and come up with 5 different readings too.

[LUFTMAN]

i have built many a engine with plastigage no problems works for me

[Neil '67 911S]

Originally Posted by cgarr

Those bore gauges are good but its really an art to using them. You could have guys measure the same bore and come up with 5 different readings too.

I agree with Craig. I bring my cases to an engine builder. He doesn't do Porsche engines but he's been using a bore gauge for decades on the stuff he does rebuild. Well worth the few sheckles.

[Steve@Rennsport]

Originally Posted by tadd

Ok, so I know of two ways to determine rod and main bearing clearance...

1. Torque up rod or case, measure with dial bore gauge. Measure bearing thickness with a cone anvil mike. Measure journal with flat anvil mike. Do math.

2. Insert bearings, torque rods or case. Measure with dial bore gauge. Measure crank. Subtract.

I've always done #1 cause I always end up digging a ditch in the bearing (never fails ) and I've been told that once a bearing is crushed it will never 'bite' as well again.

I've also been told that proper clearance isn't measured unless the bearing is under crush since they are designed slightly egg till crushed.

Thoughts anyone... No, plastigauge is not acceptable .

Tadd

Good advice,....

[Neilk]

I will be getting my crank and newly line bored case back from Competition Engineering in the next couple of weeks. Is it everyone's consensus that I still need to, at the very least, use plastigauge to measure clearances? I know Wayne's book says it is a must, but I would like to know about real world scenarios.

Thanks,
Neil

[tadd]

No matter who did the work, YOU should always double check.

Reputation does not completetly eliminate human error.

It is your dollars in the end....

tadd