on crankshafts, bearings, micrometers & plastigage

[xirdneh]

1. I am looking at two crankshafts
i tried using a Micrometer on them but could not get consistant results
i am pretty sure it's an ARTFORM to use those things
plus the micrometer only went to .000 places and i could have used that extra (4th "0")
2. i have two sets of STD Main Bearings
one set has oil groove on all ten halves
one set has oil groove on five halves, no groove on five halves
do i assume the no groove halves go on top? (if i use them)
3. the main bearings i removed were all grooved
so the groove goes all the way around journal
the crank journal is a different color where the groove was
i know the crank journal must have some wear on it (way over 200,000 miles)
so why is it not larger in diameter in the groove area?
3. i used the plastigage (green package) to see if the clearance between bearing and journal was within tolerance
all 5 journals were .003 which is the limit according to the FSM
so i am good to go
Note: 1. do not store plastigage in un-heated shop as it absorbs moisture
it was recommended by parts guy to store in plastic bag with rice in it
2. do not rotate crankshaft while plastigage is on it
get it all off

[Lil Beast]

Personally I would use the ones with the 10 grooved halves, your bearings would get better oiling if the clearance is good of course!

And for the other Q there a 50/50 chance I could be wrong but did read something about, that my book only mentionned to not mix them up. Google it you'll get an answer try with 4age instead of 3a if I can recall. Same family engine.

[Highlander]

The reason that the crank isn't larger at the grooves is that you didn't run the engine dry. The bearings are WAY softer than the crank, so that the bearings wear, not the journals. If you run the half and half bearings, yes, put the grooved ones on the block side so the oil is fed to them. Are you sure those aren't rod bearings though? I agree, I'd use the grooved ones on both sides.
Using a mic on a round part is certainly an art, part of the trick is to keep wiggling it along the rotational axis so that you know you're not cockeyed, at the same time you have to be sure that you don't have the mic off center to where you measure the diameter as being too small. Its hard to explain in writing,much easier in person

[larry mcgrath]

I would respectaly disagre with highlanders post. think about this for a moment,during the power stroke the piston and rod assy (due to the elevated pressure in the combustion chamber) are pushing downward on the crankshaft,trying to push it through the lower main bearing caps. This is the reasion that that the main bearings caps have a full width bearing (more surface aera to distribute the load ) the upper bearings are groved to provide adiquate lubrication to the main bearing assy. Instaling all groved main bearings will cause premature bearing wear and ultimatly engine failure. no BS Larry

[Highlander]

'85 FSM, EM-44, second panel down, shows upper half grooved, lower half solid. I stand corrected.

[Petros]

I do not think I have ever seen mains that did not have a groove all the way around, but the solid one should go on the bottom I would suspect. If the engine was never run dry, there should NEVER be metal to metal contact on the mains, so the should run almost indefinitely. I have take good used bearings out of one engine and installed them in another, as long as they are within spec I have never had a problem. There are some say you should never reused them and never to mix them up between engines, but if they are within spec I see no issue.

When I worked in the race shop there were real tool snobs there who did nothing but bad mouth the Plasti-gauge as a means of measuring bearing clearance. They used the mic on the journals (not that hard to do but it does take proper technique to get accurate measurements), and a bore gauge in the journals with the caps all torqued to spec. I have used both, I see no problem with the plasti-gauge, I think it is a cleaver invention. You have to make sure there is no oil in the journal and to torque it up properly, and yes, do not turn it with it in the bearing. It will tell you something about the clearance you can not always tell by using micrometer/boar gage.

Poor or sloppy technique with either will give you bad measurements. If in doubt take the crank to a machine shop for proper measurements. I have found that unless the crank journals are really damaged, just using standard bearings always works fine. I have even polished scoured journals with 800 grit wet and dry until the grooves were almost gone and found it still acceptable. Regrinding the crank and going with oversized bearings is costly and it should be rebalanced. Might be cheaper to get another crank from a wrecking yard (or a junk engine someone had laying around).