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Jensen Healey
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It seems funny, but the base circle on my "real" Lotus 107 cam, marked 777777, is smaller than the base circle on my other cam which is a reground 107 profile. Weird but true!

Kurt

Jensen Healey
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The stock cams have a base circle of 1.210 and the 107's run about 1.140. Obviously the shims have to make up the .070 difference.

I was thinking of shaving the cam carriers .050 (some of the shims were rather thin) to get into the .070- .080 range. Several valve stems have already been ground during the prior rebuild.

Anyone try this? Or should I jest get a load of thick shims?

Kurt

Judson Manning
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Kurt,

The re-grinds have a smaller base-circle to get more lift (you can't really add material to the toe of the cam), no worries, it's common practice.

If you look inside the cam buckets, you'll see there is only so much material coming into contact with the valve shim.  Go too thin with the shims and the contact point for the bucket goes from the valve stem to the upper spring seat....which is not good.

Long-term solution is to pull the head and have the stems ground another .010"-.020".  Of course grinding the valve stem too much and the shim makes contact with the upper spring seat....again not good!

Another option is to use the old-style cam tower gaskets to get another .010"-.015" clearance.  Years ago I spoke with a club member who had some metal gaskets made just for this reason.  Not perfect, but less work and money than pulling the head.

Judson

Jensen Healey
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The true Lotus cam has a small base circle which makes me think they were regrinds of left over E cams. Did Fred the fearless foreman get a job with Lotus?

 



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