<VV> turn my crank

[Tony Underwood]

At 10:01 AM 11/3/2006, corvair at mts.net wrote:
>One thing I can suggest:
>
>* get shop to look at crank and estimate how much they will need to 
>turn it - likely they will say .010 undersize.
>* get a set of .010 (or the appropriate undersize) bearings and 
>install them in your block.
>* measure the diameters inside your bearings as installed.
>* get the shop to grind the crank the appropriate size to get the 
>bearing clearance you want - maybe it'll be .009 undersize or 
>something like that.
>
>Reason being - both me and a friend are in the situation where we 
>have .010 bearings and .010 U/S cranks, yet we have excessive 
>bearing clearance when the crank is installed, because the holes in 
>the block are very slightly oversized.
>
>And I would sure like to hear how people have resolved this - and I 
>need to hear it like "I've done this six times, and it's worked" as 
>opposed to "I hear you can do this - and it works" or "I hear that 
>doing **** doesn't work"....



Shim stock, used in various situations when you need to "fine tune" 
main bearing clearances.

...IF you can still find a source for it.    It came in strips, slice 
it with sharp scissors, was available in linear or tapered thickness 
so as to configure main journal bores which were "almost" round but 
not quite.   The stuff was indeed unconventional, but it worked.   I 
knew a fellow with a Chrysler Max-Wedge engine that was too "loose" 
to suit him, bought some .001 shim stock and cut it to fit, after 
doing a little sanding on the edges of the bearing inserts to let 
them "shrink" a tad.   WOrked out nicely, plastigauged out to exactly 
what he wanted, made a difference in oil pressure of almost 15 lbs 
hot idle.    As mentioned, this engine had been machined to be a tad 
bit loose.

He'd previously experienced a damaged crank when rods got starved at 
rpm, max oil pressure with 003+ mains clearances was around 40-50 lbs 
revved, which for a 426 Max-Wedge with those beefy (heavy) rods 
simply ain't enough if you wanna buzz that big fellow to 7000 
rpm.    This, with a HV oil pump to boot.

After the bearing shimming,I think he had ~ 65-75 lbs hot and 
revving.    Then again, this was a cross-drilled crank that was 
running grooved upper bearing inserts which didn't help when combined 
with loose clearances on the mains.


You would need to break out the mics and measure the main journal 
bore to see just how oversize it may be, then secure shim stock to 
suit your purpose.   Again, the shim stock is (at least it used to 
be) available in taper so as to allow you to compensate for slightly 
out of round bores.   It could be the difference between having a 
serviceable crankcase and having to get it line bored which for a 
'Vair crankcase is a rather complicated process unless you "know somebody".

Might be worth a look.


tony..