Discussion
Andy - thanks for the posts, and the very helpful website.
Sorry if this is elementary, but a piston will be at the top of its cycle twice in the four stroke cycle - once on ingnition and once at the top of the exhaust stroke. If the cam is timed for the inlet valve to open 108 degrees after TDC, it must be 108 degrees after the piston has been at the top of the exhaust stroke (induction, compression, power, exhaust)?
p.s. Very helpful website. I didn't have the luxury of having the engine out so I could rotate the engine from the flywheel end, and did encouter the problems you mentioned setting the degree guage accurately. In the end I drilled out the disk so that it was a tight enough fit to sit on the shaft, but could be rotated independently of the crankshaft bolt.
Sorry if this is elementary, but a piston will be at the top of its cycle twice in the four stroke cycle - once on ingnition and once at the top of the exhaust stroke. If the cam is timed for the inlet valve to open 108 degrees after TDC, it must be 108 degrees after the piston has been at the top of the exhaust stroke (induction, compression, power, exhaust)?
p.s. Very helpful website. I didn't have the luxury of having the engine out so I could rotate the engine from the flywheel end, and did encouter the problems you mentioned setting the degree guage accurately. In the end I drilled out the disk so that it was a tight enough fit to sit on the shaft, but could be rotated independently of the crankshaft bolt.
rad when you put the cam in get no1 piston as close as you can to the top, the key way on the crank will be roughly between 1 and 2 o;clock turn the cam to keyway to 9 o'clock and you should have 2 dots one on the cam and one on crank sprocket which should within reason line up, then you can go ahead with your cam timing!! if you want a detailed description on cam timing i can do it but not tonight!
Thanks Rob but I timed the cam in on Saturday (being my first time and not knowing all the tricks of the trade it took me nearly all day - but I did check everything 100 times for obvious reasons!).
The reason I got slightly confused at first was that I fitted the new cam at the same position to the crank as the one I withdrew. The old cam was at TDC on the compression stroke (so I knew where to align the distributor to on re-fitting). Therefore, when I turned the engine over to time in the new cam, the inlet was not opening 180 degrees after TDC as the piston was still on the power stroke - took me a little while to work out why! Needless to say I will be turing everything over by hand and double checking again when the heads are re-fitted.
I used a dial guage to find TDC rather than the piston stop method, and found it very accurate with a bit of concentration.
The reason I got slightly confused at first was that I fitted the new cam at the same position to the crank as the one I withdrew. The old cam was at TDC on the compression stroke (so I knew where to align the distributor to on re-fitting). Therefore, when I turned the engine over to time in the new cam, the inlet was not opening 180 degrees after TDC as the piston was still on the power stroke - took me a little while to work out why! Needless to say I will be turing everything over by hand and double checking again when the heads are re-fitted.
I used a dial guage to find TDC rather than the piston stop method, and found it very accurate with a bit of concentration.
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