Setting up cams

[tdafforn]

Hi Guys,
The mammoth engine build is nearing completion (711m conversion). I have got the head back on and I am about to start the cam timing.
I have placed the cams back in the head using the marks on the original sprockets to get an initial timing. I have then replaced the sprockets with some adjustable ones.
My question is, is the timing going to be close enough to correct using the original sprockets and marks to allow me to turn the engine over by hand to so that I can measure the cams with a dial gauge without any nasty collisions between valves and pistons?
(I have detetmined TDC already using the dial gauge method)
Cheers
tim

[carrierdave]

Hi Tim,
If you have set the crank to TDC; Rotated the cams so that both the 4th inlet and exhaust lobs point to each other ? With the timing marks on the sprockets aligned then it should all be OK.
The only issue you may have is clearance between the bottom of the valve and the crown of the piston; this would, however become evident when trying to hand turn the engine.

Dave

[CBUEB1771]

Tim,
Your question is a bit tough to answer without knowing what you have for piston deck height and valve lift. If you have designed your long-stroke conversion for a resonable compression ratio then the valve/piston clearance will be greater than in a standard Twin Cam, all other things being equal. With an all new engine I make a test assembly of the cylinder head with valves in cylinder#1 only. I use light springs from the hardware store rather than the standard valve springs for this test. I set up the nominal cam timing with the hash marks on the cam sprockets as close as I can get them to point to each other with #1 at TDC. Then I rotate the engine by hand through the overlap condition on #1 (firing on #4). I check valve/valve and valve piston clearance by pushing down on the cam followers with a screwdriver until I sense a hard stop. I check both inlet and exhaust every few crankshaft degrees starting at about 30 degrees BTDC and ending at about 30 degrees ATDC. This gives me a good map of how much room I have to work with before starting the process of adjusting cam timing to achieve the lobe center angles specified by the cam manufacturer.

[bill308]

Russ's methodology is very conservative/safe IMHO. In addition, make sure you have the correct valve clarance(s) for the intake and exhaust.

If the fit check works for the number one cylinder, it will work for the rest.

How much clearance do we really need between the piston and valve (0.050 inches of piston travel) and valve-to-valve (0.020 inches)?

Bill

[john.p.clegg]

Tim

You could do what I have done in the past,old cam chain?split link?,make up a cam chain just to fit the camwheels and fit on the head before fitting the head....you can then turn the cams to your hearts content and watch the valves dancing with each other...

John

[tdafforn]

The block was decked to be 1mm about pistons at TDC. This was calculated using standard bore and 711m stroke combined with measured combustion chamber volumes. The lobes on the cams on no 1 are facing the correct way.
I may adjust the adjustable sprockets to take up the little bit of slack I have and then go for it.
I like the idea of taking the head apart and trying the conservative method, but the head was recently rebuilt and I am loathed to undo the good work.
I'll see how I feel!
Cheers
Tim
(Sunburnt after a day in the welsh hills driving a brand new Morgan!)