How much material will crank journal polishing remove?

[ToddK]

Spent a few hours today checking the bearing clearances on the engine I recently bought. The mains came in a little on the tight side, at between 0.0019" to 0.0023". However, the rods are way too tight, at around 0.0009" to 0.0014".

Now, I know I could try a different set of rod bearings, but theses are on BBC rods that have been narrowed to FE width, and the bearings have been narrowed as well. What I'm thinking is it may be easier to have the rod journals polished to reduce the diameter down 0.001". Does that sound feasible? How much material, if any, is removed with polishing a journal?

[Falcon67]

I have the same issue on a 351C rotating assembly, where the rods are in the .001~.0015 range.  There are no + oversize anything for a crank pin that is already .010 over, and only one .0005 over for a stock crank 351C application - those are obsolete/eBay only.  I have inquired about polishing and the consensus is - good luck, not interested, can't remove that little material accurately.  It's very hard to control keeping the journal round and not tapered using a sanding belt.  You'd have to use a fairly aggressive belt to actually remove much material.  My plan - when I decide to revisit that pile of parts - is to mic the big end rod bore and probably have those honed out another .0005 or so.  The guy that used to run that machine shop put the pistons on wrong anyway, so they have to go back for rework already.  A quick check seems to indicate the rods are on the small side anyway.

I have talked with many performance people about my issue, including Cailies, SDPC RaceShop, etc.

Note, if this is a stock assembly, tight isn't such a big deal.  I plan to spin mine to 6000+, so I'd like to see at least .002 on the rods.  Mains on mine are good as-is.

[blykins]

I wouldn't.

If it were .0001-.0002", then I could see it, but if you try to polish a thou off, you'll never get it round and straight. 

You are better off to get different bearings and just biting the bullet.  A bearing narrowing fixture and a lathe will make short work of it.

[mike7570]

Todd, If you are using BBC rods you had the journal turned down or off set ground to 2.20?
Why don't you sell or trade the crank and start over and have the standard journal turned down to the size you want? (if they can)

[Barry_R]

You cannot polish that much material off.

You must grind it.
It can be done by a skilled grinder - I guarantee that because I have it done every week or two.

The geographic distance works against you...

Adney Brown at Performance Crankshaft here in Detroit regularly grinds under a thou for me and repeatedly hits the target dimension.  I have asked for as little as three tenths and he has delivered.

[ToddK]

I bought this as a finished package that was supposedly ready to run. I have thought about starting over with a new crank and rods, as I have them. But then I would have to order new pistons, as my new crank is a 4.25" stroke. The crank that came in this engine has been offset ground to 4.00" stroke with the 2.200" rod journal.

I dropped the crank, rods and bearings off to my machinist this morning. He will double check my measurements and also check the rod big end size. He thinks he will be able to remove material from either the rods or crank to get clearance in spec. If he can't, a set of new bearings in 0.009" undersize will be in order.

[blykins]

Do not remove material from the rods....you will lose bearing crush. 

[ToddK]

Okay, looks like it's either the crank or new bearings.

[Falcon67]

Do not remove material from the rods....you will lose bearing crush.

Agree - I haven't had time to really go over my rod bores with a bore gauge yet so I'm hoping there is material there within spec.  If not, then might have to ship my crank to Barry and get his guy to fix it.  I just don't need the parts for a build right now, so it's not urgent.  That and the dragster build used up about two years of "hot rod money" in 6 months.  But it's still money tied up in engine parts that can't be used so it bugs the !@#$ out of me.

[Leny Mason]

Hi, What part of the Country are you in Crouser Kinetics in Missoula  Montana Will do it to, One of the best and a Ford guy. Leny Mason

[XR7]

I think he is a long way from Missoula MT Leny! He is somewhere "down under" in Australia... that is why Barry mentioned the distance problem.

[ToddK]

Yes, I'm on the west coast of Australia. About as far away from Michigan as you get.

[Leny Mason]

OPS That is a long ways away I think, I have not got to go there yet so I am just guessing. Leny Mason

[stubbie]

17,689Km's to be exact.

[mbrunson427]

Leny, I emailed you about Montana, to avoid hijacking this thread.