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Re: [GMCnet] Reviving the Cad 500 [message #163613 is a reply to message #163606] Tue, 20 March 2012 08:54 Go to previous messageGo to previous message
Ken Henderson is currently offline  Ken Henderson   United States
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma:
Senior Member
Steve,

Thanks for the input. I'm as positive as I can be that the crank was done
correctly, that there was no interference, and that the bearings were
properly set up. I checked everything multiple times (OK, so CRS stopped
by now & then), then had John Beaver, a NASCAR "mechanic of the year" award
winner check everything. Then, his son, the instructor for the
"Competition Mechanics" course at the local technical college, stopped by
and checked it all again. We did check the journal/throw radii on all the
journals; they were still recessed below the journal diameters. I
Plastigaged every journal and found them all near the middle of the spec.
As I've said before, the thrust bearing clearance was lower than we liked,
so John increased it -- something he does very frequently on his racing
engines. Certainly we did ensure that the thrust bearing cap was proper
seated to the rear and that the bearings were modified with the parting
line bevel toward the rear.

As for the possibility of the machine work being faulty, we have to
remember that all this follows immediately after the identical failure of
the same seasoned factory-perfect crank. Something outside the engine
caused those failures. Not much out behind there except the transmission,
especially now that I've replaced the flex plate with one I KNOW runs true.

Y'All keep coming up with new ideas -- I'm desperate! No way I'm going to
put another engine, of any kind, ahead of that transmission until I'm
pretty darned sure I know what's caused the problems.

Ken H.



On Tue, Mar 20, 2012 at 8:16 AM, Steven Ferguson <botiemad11@gmail.com>wrote:

> I've seen this happen in BBC engines when the thrust was checked with the
> leading or trailing edge of the main bearings up against one or more fillet
> radius on the crank. It doesn't take much. I prefer to check thrust
> twice. Once with the crank sitting in the block without the main caps
> installed, then after the main caps are installed and torqued. During the
> torque process I rock the crank back and forth to ensure that I'm torquing
> in the center of the bearing surface on the crank. A lot of premium engine
> remanufactures will chamfer the edges of the bearings as cheap insurance
> against this. Another issue is how the fillet radius on the crank main
> thrust bearing is addressed during the grinding process. A friend of mine
> in San Diego built a device to measure thrust pressure during shift points.
> With a stage one shift kit installed it was amazing how much pressure was
> generated against the thrust bearing. Considerable more than normal.
> I'm not saying your CS was not in good hands Ken, just 2 cents worth here.
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
 
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