Triumph Repair: Cam timing, sprocket holes, bolt holes

Question
Hi Howard,

You are probably very tired of this question. But I'm almost reluctant to start my rebuilt 1974 Spitfire 1500 engine. When I replaced the cam gear, crank gear, and chain. The old ones had marks on the gears but the new ones didn't. I set No1 top dead center and the marks were lined up with each other, I then very carfully removed the sprockets and chain together
matching up the cam sprocket holes then remounted the new parts. Everything looks good but can you tell me the best way to check to make sure it's right. Oh I also had the head off and rebuilt so I don't know were the value clearances are set yet.
Thanks
Bill

Answer
Hi Bill,
The Triumph Spitfire designed the cam sprocket so that you had 4 different positions to set the cam timing so you could get it accurate to 4 positions between one tooth off. As you have noticed there are four holes in the cam sprocket and only two bolt holes in the cam. This allows you to have two different settings by using either of the two sets of holes and two more different settings by flipping the sprocket over.

Set the valve clearance of #7 and #8 valve very accurately at .050", turn the crank and set # 1 piston at TDC of the compression stroke. (#1 and #2 valve closed)

Now check the valve clearance of #7 and #8 valves. If they are the same, the timing is correct. If not, the cam timing is off and needs to be reset by the above method. Don't forget to reset #7 and #8 valve clearance when finished.

This is called "Split Overlap" meaning the cam timing had the exact same degrees of intake valve open BTDC as the degrees of exhaust closing ATDC. Most street cars have that cam timing up until variable timing started on cars today. Most competition cams don't use "Split Overlap" in cam timing.

The procedure above is straight out of the factory manual. Another method is to put a degree wheel on the crankshaft and set it to "Split Overlap"

Howard