Doing the cam timing - Single overhead cam

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Guy Croft
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Location: Lincoln, UK

Doing the cam timing - Single overhead cam

Post by Guy Croft » Thu Jul 06, 2006 8:45 am

The technique for setting up (dialling-in) the camshaft on single overhead-cam head is very simple.

Tools needed are a large diameter protractor, magnetic base DTI (dial gauge) with enough range to cope with the cam lift, sharp tipped pointer. I stick the protractor to the pulley with 'Blu Tack', an invaluable substance with many uses in engine building..

If the full lift spec for the cam is inlet 110 deg, this means that the inlet valves should be fully open at 110 crank degrees after tdc, so all we need to do with a SOHC motor is find true full lift on no1 inlet valve, mark it, set the crank at 110 deg ATDC and bolt the head on. Final check and adjust can be done if we have an adjustable cam pulley - with the belt fitted.

I am asked 'do I need adjustable camwheels?' Yes - always use them. This is a race engine website, if you're building a race engine, they are essential. Everyone who did not use them either got in a bit of a mess themselves or I inherited the problem of trying to do cam timing without them to my usual standard of accuracy. I just don't have the patience to explain any more what may happen if you don't use them!

It is not necessary to shim the head prior to this op, but I usually get shimming out of the way first.

In the case of the Fiat SOHC head - this one is a 1300 big valve item from an X19, with my new GC F1 profile, the cam carrier should really be removed after this op, the head bolted down and then the carrier fitted. This is because the head nuts (or bolts, later models) on the manifold side are rather hard to get to, even with a crowfoot wrench.
SOHC cam timing_06.jpg
Paint the mark white to white for full lift, I use ordinary car touch-up - oil will not hurt the paint. The grey lubricant is moly grease and oil.
SOHC cam timing_06.jpg (118.49 KiB) Viewed 8688 times
SOHC cam timing_05.jpg
Mark the cam relative to the housing using a needle file and thoroughly wipe away any debris. This is a cast iron cam, steel cams need a tungsten engraver - or just an accurate paint mark.
SOHC cam timing_05.jpg (114.35 KiB) Viewed 8687 times
SOHC cam timing_04.jpg
The cam is at full lift halfway between the two 8mm readings (0-44 deg), ie: at 22 deg, the dti reads the true full lift (FL) of 9.35mm.
Sorry the photo is a bit dark.
SOHC cam timing_04.jpg (111.75 KiB) Viewed 8681 times
SOHC cam timing_03.jpg
The cam is rotated clockwise to 8mm on the other cam flank - see reading on the dti, protractor now reads 44 deg.
SOHC cam timing_03.jpg (111.81 KiB) Viewed 8677 times
SOHC cam timing_01.jpg
I have found appr full lift then turned the cam anti-clockwise to lift of 8mm, fitted the protractor at zero position. I you physically bolt the protractor to the cam you have to do a bit more arithmetic here because you can't zero it as easily.
SOHC cam timing_01.jpg (110.67 KiB) Viewed 8671 times
SOHC flows 06.110.JPG
These are some of the flow development results for the head in this feature, low lift flow with the big valves is so high I chose a relatively low lift cam profile.
SOHC flows 06.110.JPG (138.19 KiB) Viewed 8672 times


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