bearing clearence

[hannibal2]

can any one tell me what clearence I need between the mains cap bearings and the crankshaft because I have used the red plastiguage and its widened to an inch not good should I be using the black plastiguage ?

 

[hannibal2]

the clevite bearings are 0.010 undersized does this mean i need to have the crankshaft ground?

 

[JackFish]

Got a micrometer?
Only a measurement will tell the story.

 

[rbohm]

8) as i recall bearing clearance should be between .015 and .025" which means you use the green plastigage.

if your bearings are .010 under size, that means the crank has already been ground under size.

 

[MustangSix]

.015 - .025 is a little loose!

I think he means .0015 to .0025. Darn decimal points!

If te bearings are .010 under, you have to have the crank ground to be .010 smaller, plus the clearance you want.

 

[rbohm]

.015 - .025 is a little loose!

I think he means .0015 to .0025. Darn decimal points!

you are right i did mean .0015 to .0025, darn fingers dont want to work right sometimes.

If te bearings are .010 under, you have to have the crank ground to be .010 smaller, plus the clearance you want.

that assumes he bought new bearings to use. if the bearings he pulled out are .010us, then the crank is already ground under size.

 

[hannibal2]

looks like I need the crank ground or do I just get standard bearings?

 

[rbohm]

looks like I need the crank ground or do I just get standard bearings?

8) as i said, if the bearings that came out of the engine are marked .010 us, then the crank is already under size. measure the crank journals to be sure though.

 

[hannibal2]

As i face problem after problem with this build Im learning alot but time is passing buy to quick and I need this engine in buy christmass so I ll have to take the block to the machinist to be built decked and balanced one for more reliability when its running and for another I feel like im rushing things and thats not a good thing when doing an engine build.

 

[worken2much]

As previously posted you are looking for one and one half thousandths clearance. Two thousandths is good. One is a little skinny. Two & a half is a little loose unless your racing the thing hard. Then I'd run some 20-50 oil & let it warm up good before working it too much.

EASY to check. Get some GREEN plastigauge. Make sure your bearings and crank are dry, (no oil or pre lube) & clean. Use some carb cleaner & dry them off with compressed air or soft cloth. Install & torque your main caps one at a time and compare the plastigauge to the scale on the paper package. If you have a standard crank then you need std. bearings. If you have a std. crank then .010 under bearings will not work. It would be like putting a size 10 foot into a size 9 shoe.

If you need them, there are .001 under bearings if the std. shells yield clearances that are too loose. You can also mix and match them as needed with std. shells to get where you need to be. It's a trick from the old days when money was tight to keep from having to spend the bucks turning the crank. Works fine.

If you are a LITTLE tight on the bearing clearances you can hand sand off the back off the bearing shell with some emery cloth and gain a half thousandths pretty easily. This works well except on the thrust bearing, it's a little tougher to gain clearnace with it.

Shouldn't take more than an evening or two to sort out the mains & rods. It isn't hard, give it a try.

Worken2much

 

[rbohm]

8) i agree with everything worken2much said, except this

If you are a LITTLE tight on the bearing clearances you can hand sand off the back off the bearing shell with some emery cloth and gain a half thousandths pretty easily. This works well except on the thrust bearing, it's a little tougher to gain clearnace with it.

a better choice would be to polish the journals to gain bearing clearance as needed. if you remove material from the back of the bearing shells, you lose bearing crush that holds the bearing in place, and contrary to popular opinion the bearing tangs are not enough to prevent the bearing from spinning if you lose the bearing crush.

 

[worken2much]

I don't think the very very, (a half thousandths) small amount taken off the back of the shell inhibits the crush fit to any substantial degree. When I hand sand them with emery cloth it takes little off, maybe I should have said polish, not sand. At any rate, I've not had any ill effects from it and run my motors very hard on circle tracks.

If you polish the crank with a long piece of emery cloth wrapped around the journal you need to be careful not to make a flat spot by sawing back and forth too long in one place. The other thing I don't like about this process is the grit from the cloth invariably gets into the oil passages in the journal and into the block. I'm assumming the engine is on a stand upside down. Maybe you have a trick or two when polishing the crank I haven't thought of?

Thanks
Worken2much

 

[rbohm]

8) since we never did final assembly until after all the bearings had the clearance we wanted, if we used emory cloth(extremely fine grain cloth), we would clean the crank before we final assembly, and we would lube the crank with stp(this was 1979).

 

[hannibal2]

thanks allot for the info .I am going to have the engine fully balanced for that reliability.

 

[Lazy JW]

Some folks go to the effort of measuring all of the journals and bearing shells to find the thickest/thinnest, then mix and match to get the best clearance. They will also purchase -.001" undersize shells for the mix/match and even use a standard insert with a minus insert in the same bearing.

These aren't idiot mechanics either but some pretty high-end, big names do this stuff, and they disdain the use of Plastgage. They are WAY more serious than I, and I will continue using my Plastigage.
Joe

 

[worken2much]

So if I check each bearing individually, mixing and matching shells as required, using plastigauge not a micrometer........do I then become a high end idiot?

Hey...lookee me, I finally excelled at something!

Have fun
Worken2much