Crank polishing
 

Got a crank that needs polishing to get another .001-.0015 on the rod throws. Anyone have a method for doing this in house, or is a machine shop the ONLY way to get this done... trying to meet a deadline.

Re: Crank polishing
 

You should never try to polish crank to remove material for clearance as you will not have flat journal in the end.

Re: Crank polishing
 

Can't find +.001" bearings?

Re: Crank polishing
 

Marvin,
You could just "polish" the bearings instead. After all, aren't they made of a softer metal than the crank? I'm JUST KIDDING. Just call the crazy Ukarainian and I'm sure he will get the right parts for you before you even get back out to the garage.

Re: Crank polishing
 

Bearings are already .001 oversize and coated so I can't polish them, no .002 available. Looks like a trip to the machine shop, I don't have access to a lathe.

Re: Crank polishing
 

You can't polish what you need in the crankshaft. Get the bearings you need undersize and have your crankshaft grinder set the clearance with the crank grind. If you try to polish the journal will be swaybacked.

Re: Crank polishing
 

Open up the rod bores to max spec, if that don't put clearance to where it needs to be, grind the crank -.010".

Re: Crank polishing
 

Won't resizing the rod end change the crush on the bearing?

Re: Crank polishing
 

The range is usually only .0005", if your rod bores are slightly undersized, going to max bore spec may get your clearance closer to where you want it to be. Removing the flashing from the back of the bearing shell with Scotchbrite can help gain a tenth or two of clearance as well.

Re: Crank polishing
 

Rods could be @ low side (small side) of spec,if they are new rods maybe under spec,new rods need to checked also,most are left under specs about .0005. just don't go over high side spec of rod housing bore
Try to polish that off crank won't be good,can't remove that much evenly by polishing
BTW if make journal .001-.0015 smaller clearance will open up around .003 or more,I think you meant you want to increase your clearance .001-.0015,but thought I would mention that just in case
Mike Taylor 3601

Re: Crank polishing
 

Marvin…Do it right, the crankshaft grinder will finish it for your desired clearance. No point meeting a deadline with questionable clearances. MB.

Re: Crank polishing
 

Mike,

I'm looking for .003 - .0035 on the rods, and I'm at .0023. My simplest solution would be to have the machine shop take the throws to 2.4985. Right now they are 2.5000 - 2.4999. I don't want to go to .010 under, that would require getting all new bearings as well, and put me into a 3-4 week wait. (I also wonder if .010, or even .0015 would take out enough metal to warrant a rebalance).

Re: Crank polishing
 

No you will be fine. A good crank grinder should be able to have the crank back to you in a few hours. MB.

Re: Crank polishing
 

If your crank grinder can take .0007-.0012 off each journal he's much better than mine and I doubt that. I'd run it like it is before I'd try to polish it off. Just another opinion.
Pete

Re: Crank polishing
 

Most new racing connecting rods of good quality come in with a big end bore 0.0002" under the low limit as given in most machine shop manuals, for maximum bearing crush, which allows for the correct eccentricity with a racing bearing. Yes, you can get away with opening them up. But I prefer to avoid that. And I never use Scotchbrite on either side of a bearing, just a personal preference.

A good machinist can usually set up and take as little as 0.0005" off of the main journals. However, it will take a great machinist with a really good, tight grinder to take 0.0007" off of the rod journals. Asking a guy to do that, I'd think no less than $250 would be a fair price. Very few will even attempt it. There simply are not that many dedicated master machinists grinding crankshafts anymore, it does not pay what it is worth, given the low cost of the economy aftermarket crankshafts.

It will be next to impossible to polish a journal as much as you want and not have it out of round and tapered, possibly "hour glassed". No way I'd do that, either.

Are you measuring the bearings with the coating already applied? Because the coating is about 0.0002" per bearing half. If you are, that would put you at 0.0027" actual clearance, which, if everything is good, should be okay on a 2.5" journal. It might be on the tight side of ideal.

Re: Crank polishing
 

I'm just wondering why so much clearance is needed, I run barely over .002" on BB Chryslers. My buddy was running 3.5-4 on his blown alcohol hemi drag boat with 70 weight oil, that I understood.

Re: Crank polishing
 

I would run the .0023,like Alan said the coating takes away some clearance,your where I would set clearance on that size journal and would use around 20wt. oil.
Mike Taylor 3601
Paul,
.0035-.004is actually on the tight side for blown hemi w/70 wt. alot are set .005-.006 due to started cold and zinged wide open

Re: Crank polishing
 

I was looking for .003 - 0035, seems to work pretty well on the BB Olds motors. The measurement was with the coating. I checked the bore on the rods, and they were slightly under spec (.0002), a very light hone put me right on the money. Thanx for the suggestions and advice, guys.

Re: Crank polishing
 

Alan,

I know a machinist would have to be crazy precise to cut rod journals that close, the setup would take hours to get right... much easier to just cut to .010", but that would mean new bearings/coatings, too, and the Clevite 542HXN doesn't come in that size. Calico informed me that their coating is .0003", and I was measuring .0023 on the rods, which bothered me. A light hone on the rods and scrubbing the backside of the bearings got me in the ballpark. Thanx