Engine teardown poll

[trbig]

especially if it spins one during riding season...

Yeah.. BTDT. If it does spin a bearing, the only reason to re-split the cases is to be able to gather what parts you can from the ruined block.


Tod

[TADracer]

If it aint broke......but then if you are showing copper then a failure is probably coming up relatively fast. Replace the bearings while in there.

On Plastigauge, I know in principle it sounds like a good way to measure the crank and cam bearing clearances. But if you have gone that far I would suggest some micrometers instead. Plastigauge has been known to give eroneous readings from time to time whereas micro's (when used correctly) give an accurate reading every time.

[randy]

I have to disagree. Micrometers are great for measuring discreet parts. The benefit of plastiguage is that you get an accurate clearance measurement with the bearing caps torqued down, providing the proper crush load on the bearing shells. In a case like this, plastiguage wins over micrometers.

[Big Daddy Funk]

If the bearings are showing copper through, it's very close to done. I would save up and do the job properly. A hammered and spun bearing is no fun whatsoever. Rick

[tarzan]

There is nothing worse than having to go back in after being right there and wondering about it.My thought is if I have to wonder about it ,just do it.

[ccogswel]

I agree with Randy. In this case plastiguage is better to use. If I was wanting to check the crank to stock spec'c then I would use a mic.

But this is where it get's me all the time. If I'm working on someone else's engine or what ever and I come accross something like this and the owner said to go ahead and put it back together knowing the possible out come I just couldn't do it. I my self would just buy what ever part to fix it right if they couldn't afford it that is just so I wouldn't have to go back into again. Wasting my time really gets to me. Even if it's for a friend. I wouldn't do it to a friend if they were helping me. I know that may be stupid on my half but that's just the way I am. And I hate that I'm like that but o-well. Now I don't know if Randy is doing this for a friend or for business or what? And I don't mean to step on anyone's toes for my thought, but for me I just couldn't put it back knowing it had copper showing. If you and the guy is willing to wait that's what I would do. IMHO.

[DGXSER]

Why didn't you say so..That's a horse of a diff. color

Copper showing on the bearing, is an entirely different picture. To me that would be like having your entire kitchen cabinets out and then realizing the water line to the sink under the cabinet was leaking, but go ahead and reinstall without fixing including putting a tiled counter top on.

Alot of work to get that far in, and not fix something that is obviously on its way out. JMHO. There is a set on ebay for $100 if it has the sizes you need.

[Rasputin]

Replace

I would side with the replace those bearings guys. If the copper is showing the babbit is gone. No time like the present, and if you put any value on your time the new bearings are cheap. Like was said before if it breaks the rest is just salvage. Oh Yeah, I almost forgot Plastiguage is better in this case.

[petejw]

Hey Todd,
Id go with plasti-guage as well to check bearing clearances, its cheap to buy and ive always found it to be accurate as long as the shaft isnt twisted.
Did you check the crank end float before dismantling the engine?
Id also check out the starter clutches while you have the engine apart, theyre a pain in the butt when they start slipping.

[prometheus578]

Copper showing...
Replace them.
You've already got the engine out... no reason not to.

[Shappers]

Here is a chart showing the different thicknesses of bearing shells (it is in mm).

I tried to measure the differences with a micrometer but it is impossible to accurately measure the shells that way as the differences are so small.

I used plastigage, but it is academic if your bearings are worn and showing copper. I would recommended just putting in the largest ones (blue).

[79XS11F]

I would change them out while it's apart. Then you will know their good to go for a long time. IMO it just doesn't make sense to not do them while the cases are split. S**T ... I would even do the con rod bearings while I was at it. I would also go with the sizes the manual calls for. Jap steel is of the highest quality so all the wear should be only on the bearings. Going with manual size should return them to factory spec.
Rob

[randy]

Shappers, why would you suggest the larger clearance bearings across the board? IIRC, the factory set each journal individually. Besides, theoretically your bearings should be replaced with tighter clearances as the crank wears.

[79XS11F]

I disagree.. Those bearing shells are so soft that you can mark them with your finger nails. Unless there's been an oil supply issue i really don't see the journals taking any appreciable wear. Make them too tight and there will be no room for the film of oil that the crank actually rides on.
Rob

[Shappers]

Shappers, why would you suggest the larger clearance bearings across the board? IIRC, the factory set each journal individually. Besides, theoretically your bearings should be replaced with tighter clearances as the crank wears.

No. I recommend fitting the largest, i.e thickest shells which take up the wear.

Rather than me bodging the explanation, let me put a quote from Rod Gibson of Classic Motorcycle Mechanics (Pg 86, April 2007 Issue). He's replying to a reader's question about the bearing clearances on an old CB400F Honda...


"Quote
Bearing shell were marked with a lick of paint to identify the size, though all sizes were stamped "STD" on the back - quite meaningless really as no "oversize" shells were ever supplied for regrinds.

The numbers stamped on the crank webs and crankcases identify the precise measurements of the bearing housings and were used to select the correct shells on the production line. However (and this is where is all goes pear shaped) the numbers will only tell you what size the journals were when the crank was new - not after 30 years and a half a million miles - so they aren't useful now.

Truth is, the difference between graded bearing shell thicknesses is so tiny as to be academic, and standard practice when reconditioning an old engine is to fit the thickest shells to compensate for wear, these are usually coded black.

For a more accurate check, use Plastigauge. You should be getting a reading of 0.041 to 0.071 if the bearing clearance is still within factory tolerances."




When I rebuilt my engine, I first selected the shells based on the numbers on the crank and cases. I bolted it all up with Plastigage and then stripped it all down. All lovely and evenly squashed Plastigage and all out of spec at 0.060mm

I then bolted it all up again using all the thickest ones, the Blues. After measuring again with Plastigage, the middle 3 had all dropped in to a lovely 0.045mm and the outer two almost in spec at 0.050mm.

This was with a crank with 36K on it !