Lotus Elan

Bent camshafts

PostPost by: vxah » Sun Sep 01, 2019 7:07 pm

I was tinkering with my cylinder head the other day looking into cams and followers etc when I noticed that with just bottom cam bearings installed I could ?rock? the cam from end to end slightly!
I was initially concerned about the head being warped but, when turning the cam 180 degrees the ?rock? had gone. Placing the cam in V blocks at each end and using a dial gauge revealed a 0.006? bend in the cam!

Researching the issue I discovered this is not an unusual issue with cast cams, they can warp over time apparently the same as cylinder blocks do, I checked the rest of the half dozen cams I have about and found 4 of them bent slightly!

It would seem that the way to ?correct? the bend is to support the cam in the V blocks, find the low point and put the cam so that the ?sag? is at the bottom then, whack it with an air chisel between the lobes along the length of the cam on the top side!
I put a blunt V chisel bit in and turned the air pressure down to 50 psi, a few ?parps? later and the thing is straight!
Did all 4, good as gold! Apparently it relaxes the structure so that springs back where it should be?
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PostPost by: StressCraxx » Mon Sep 02, 2019 3:48 am

Exactly. We did this with a cast iron crank that came out of an severely overheated Kent engine. Worked perfectly.
There is no cure for Lotus, only treatment.
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PostPost by: RichardHawkins » Mon Sep 02, 2019 7:51 pm

I similarly discovered my cams were bent. On the basis that if I couldn't straighten them I would have to buy replacements I had a go. To my amazement they straightened without breaking!

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PostPost by: vxah » Mon Sep 02, 2019 8:19 pm

The air chisel really didn?t hit it that hard, I never thought it might break the cam, just maybe not work!
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