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Cam timing...
Posted: Sat Jan 19, 2008 6:49 pm
by Matt
What with having a "warm" cam in my car I am keen to get the timing right. How many degrees difference does a single tooth make?
Due to my inability to find an accurate TDC yet the best I have been able to work out is the cam is between 5 and 10 degrees advanced
Posted: Sat Jan 19, 2008 7:41 pm
by MoggyTech
IIRC 13.84 degrees, assuming 26 tooth cam gear.
Edit : 9 degrees 40 tooth cam pulley
Posted: Sat Jan 19, 2008 8:20 pm
by bmcecosse
But the large sprocket runs at half speed!
Advanced timing is good Matt - as the chain wears in and stretches it will fall back slightly. If it was mine - I would be leaving it as is.
Posted: Sat Jan 19, 2008 8:20 pm
by Mogwai
A simple way to find true TDC is to screw a bolt into no1 plughole (I knocked the centre out of an old sparkplug & stuck a bolt through that)then turn the crank slowly until the piston touches the bolt mark the pully inline with the pointer then turn crank the other way until it touches the bolt again mark the pully and the point halfway between the two marks will be TDC.
Posted: Sat Jan 19, 2008 8:32 pm
by Matt
Thats not a bad idea... I did something similar using an old spark plug, old push rod and made it into a very rough DTI. I will give your mehod a go
Posted: Sat Jan 19, 2008 8:33 pm
by Matt
BMC its a chain thats already been used and is thus stretched, so its not going to stretch any more ;)
Posted: Sat Jan 19, 2008 8:39 pm
by bmcecosse
They keep on stretching! And whose to say your 'advanced' timing isn't ideal for your engine/use anyway ? Unless you compare on RR or with hill climbing trials you really won't know. How do the valves look on overlap at TDC - is there much difference in the lift of the two valves ?
Posted: Sat Jan 19, 2008 8:41 pm
by Matt
Im guessing that AC Dodd knows what he's talking about when he suggested the timing I ran ;)
Posted: Sat Jan 19, 2008 8:46 pm
by bmcecosse
Maybe - but then maybe he's just quoting the standard figures. If you really feel you need to move it - then offset key is the way, as I'm sure you know. But it really is a tiny tiny amount that it gets moved - and it's a load of work to do it. And when I did this some time ago (on 1340 Mini) I certainly couldn't detect any difference in the engine whatsoever! All I can say is that - in my experience - advanced cam is a whole better than retarded cam! I urge you to compare the valve lifts at overlap - you may get a pleasant surprise.