1957 S4 Mk2 Valve timing

[BrianReynolds]

Another question for those experienced in rebuilding the Mk2 S4. I am at the stage of valve timing the engine, I have set up 2 dial indicators with the cylinder head off. I set no 1 piston 3/16” BTDC ( 0.0187”) then another dial on the No 1 Inlet valve cam follower. The closest I can get the timing after trying all 3 engine sprocket keyways is that the cam follower has lifted 0.003” when the piston is at 0.187” BTDC. This appears to be accurate according to Waller and Modern Motorcycle Mechanics. However, as you can see from the photo, the actual timing marks are way out. The 2 holes in the camshaft sprocket do not line up with the mark on the crankshaft sprocket I have read that the timing marks can be inaccurate . It is set that the inlet valve will start to open at 3/16” BTDC which I think is correct?

[klaus gerhard]

I remember that Bruce Longman modified the timing of his Mk2 engine by using a stepped woodruff key.

[nevhunter]

20 teeth with 3 keyway options get's it to 5 degree increments. I'd accept that in the retard direction (valves) as it will advance as the case heats up. Nev

[Roger Gwynn]

You need the cam instruction sheet that explains the best way to do this and how important it is to know which cam you have See 'SQ4 valve tining' here https://draganfly.co.uk/ariel-technical-articles/

[BrianReynolds]

Thanks for the helpful responses. Bruce Longman’s level of detail is above and beyond, but extremely useful in understanding the process. Thankfully I did not have to make a stepped woodruff key to get mine within spec.

[Simon.Gardiner]

I'm surprised Bruce's article isn't in the AOMCC online library (I think it might be soon... )

SG

[Roger Gwynn]

The version on the Draganfly site was written by Bruce in 2006 and subsequently edited and re-written by me in 2012, as noted in the document. The technical bit is mainly Bruce, I mainly made it more readable, hopefully.
Here is an original for the club website

1960-37 how to time.docx

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