<VV> Re: tight crank

[djtcz@comcast.net]

> OK, Time for the engine builders to put the thinking caps on! 
> However, upon assembling the crankcase halves, the crankshaft has a 
> tight spot for about 90 degrees. Looking from the rear of the engine the 
> tight area is between 12 and 3 o'clock. The tight spot remains despite 
> loosening and retorqing the crank halves and careful adjusting with a 
> dead blow hammer on the crankcase halves. Defined tight spot = I can 
> turn it thought the 90 degrees with moderate hand twisting on the 
> distributor gear end, but if I stop in the middle (45 degrees) it takes 
> a bit more effort to start it to turn again. It starts with a little 
> jerk and then loosens up as it goes past 90 degrees. The other 270 
> degrees are almost frictionless like past engines I have rebuilt. This 
> is telling me the journal may be touching a bearing for about 90 
> degrees. 
> 
> 
> 
> Based on other experiences it may be telling me that one main journal 
> is a bit out of concentricity with the others. (Unlikely?). Or perhaps 
> one of the bearings is not quite seated properly. The worst scenario is 
> a bent crank shaft. (The plan is to disassemble and examine the bearings 
> to see if I can determine which journal is touching the bearing. Based 
> on this I may swap the bearing halves or the 2 and 3 bearing to see if 
> this brings a better result. I'll also check it without the cam shaft to 
> eliminate that but I doubt that is the problem as the cam turns at a 
> different ratio. 

> I will also replastigage at 6 places on each journal to see if I can 
> find a tight spot like .0005 in one place and .0015 in another on the 
> same journal. I don't have equipment to set up and run out the journals 
> to find an out of round or a concentricity problem. 
> 
You can buy a dial indicator with stand for under $40. http://www.mscdirect.com/       Mighty handy for all kinds of operations.  Make simple wooden V-blocks, or Use the crankcase and a front a rear main brg shell and indictate the center main to find a bent crankshaft.  Indicate with a shell on that journal and check for journal roundness. Set up rear ends.

If the journals check round within 0.001 inch, it Sounds like maybe possibly a bent crank combined with not great bore alignment.  Chevy allowed something like 0.005 inch TIR on Tufftrided Corvette cranks, but I don't see a runout spec in the 1965 Corvair shop manual.  One test of bore alignment is a straight crank should turn freely.  As you don;t have that, comparing measurements against tolerances may be necessary.