zero crank end play on 8ba

[Dirtslinger]

Well I had way too much end play with original crank and I purchased a NOS Merc 4" crank and bought standard King bearings and now I have zero end play. Ive read that one must carefully wet sand the bearing surfaces and re measure to get an acceptable clearance, am I on the right path?

[Bored&Stroked]

I've not had this problem before, but if you have a good surface plate, I imagine you could do this? If it was mine, I'd try another set of bearings first. Also, I'd probably make a 'Mandrel Fixture' for my lathe (.003 or so over the main size), and I'd put the bearings on the mandrel, put hose clamps around them (with tape underneath) and use my lathe to take off whatever thousands I'd need. I'm a bit of a perfectionist.

[cadillac512]

I've done it many times on several different engines. Works just fine-no problem. Hold the bearing firmly and sand in a figure 8 pattern, checking often and cleaning well.

[Brian]

The problem with sanding the soft bearing material is that abrasive can and does embed itself into the surface, after all, that is why it is soft, one of the characteristics that babbit and similar white metals possess is embed-ability...B&S's method is the way to go....

[Dirtslinger]

Thanks for the replies.

[alchemy]

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There are still NOS Merc cranks out in the wild??!!

[FlatheadTed]

tape the bearings together and sand the non thrust side ,eg likely the front ,a sheet of float glass/mirror or a drill press table ,

[Kurt in NJ]

some of the NOS parts stayed on the shelf because they didn’t fit correctly, one of the tolerances was off.
A friend of mine worked a a car dealership, got a clutch that didn’t work, took it back out we’d given another one that worked, couple weeks later the non working clutch was giving to another mechanic, didn’t work, was removed and returned to parts department, it went back on the shelf,
a little tight is easy fix if the thrust surfaces are smooth, as has be mentioned, a little sanding.
a year later that clutch was given out to my friend again, he cut it in 1/2 with the torch and gave it back to the parts department

[Dirtslinger]

Originally Posted by Kurt in NJ

some of the NOS parts stayed on the shelf because they didn’t fit correctly, one of the tolerances was off.
A friend of mine worked a a car dealership, got a clutch that didn’t work, took it back out we’d given another one that worked, couple weeks later the non working clutch was giving to another mechanic, didn’t work, was removed and returned to parts department, it went back on the shelf,
a little tight is easy fix if the thrust surfaces are smooth, as has be mentioned, a little sanding.
a year later that clutch was given out to my friend again, he cut it in 1/2 with the torch and gave it back to the parts department

Ha, what shenanigans! I did have the machine shop check out the crank and they said it was good. I did some sanding today and managed to get .003 end play. Should I go for more?

[cadillac512]

.003" will work just fine. I'd leave it there.

[Bored&Stroked]

Are you running an automatic or a clutch? If it is a clutch setup, then I'd go for at least .004 (minimum). The reason is that if you plan to "have some fun" with it and a manual transmission, then heat from the clutch/flywheel will transfer into the rear of the crankshaft - making your already tight clearances, even tighter.

Since you've already figured out how to get it to .003 - just go a bit more.

Also, really check your main and rod bearing clearances - and journal conformity and taper. You should be suspect that this crank may not have been in spec (and set aside) - so mic the heck out of everything and make darn sure the clearances and journal conditions are where they should be. For a performance build, I'd want .002 to .00225 on the rods and .0025 to .00275 on the mains.

[Bored&Stroked]

Also, if running a clutch (especially in a performance engine), put a very slight chamfer on the edge of the rear main bearing shell. Just break the edge a bit. This provides a bit more oil to the rear thrust surface of the bearing/crank . . . which is a good thing.

MBRear chamfer.jpg

[Dirtslinger]

This will be a stocker except a mild cam and it is a manual. How do you recommend that I break the edge?

[FlatheadTed]

My rear main is the oper st problem considering building up the white metal 30 th Worked on a Chev that had a larger chamfer and it pored oil out ,

[petehoovie]

Originally Posted by Bored&Stroked

Also, if running a clutch (especially in a performance engine), put a very slight chamfer on the edge of the rear main bearing shell. Just break the edge a bit. This provides a bit more oil to the rear thrust surface of the bearing/crank . . . which is a good thing.

Attachment 534945

[Lawrie]

I have some ford bearings that have a little slot and hole to feed oil pressure to the thrust face.
Maybe out of a truck or some thing with an 11in clutch.
Side note, the new Burtz A engines have a pressure feed direct to the centre of the thrust bearings on the rear main ,a nice touch.
Lawrie

[Bored&Stroked]

Since this is a stocker, probably no need to chamfer the edge as you're probably not flogging the clutch anyway. I'd still want my clearances on the journals to be the same as I noted above. What rods are your running? Are you using the late 8BA rods with insert bearings or full-floaters - 99A or 29A style?

[Dirtslinger]

8ba rods, 4" merc crank, 30 over block. This engine ran when I pulled it and was standard crank and cylinder walls.