Foolish. spent to much time trying to find TDC on the compression stroke prepairing to install a new cam and lifters. I was just using my thumb to feel for air coming out....I couldn't tell if I was at tdc on the compression stroke or the exhaust stroke 🤔....I think/hope its true but I want to verify......is the piston just at top or bottom untill the cam and pushrods create the exhaust stroke?

 

Unless I'm mis-reading things...
The cam dictates the timing of the compression and exhaust stroke. If there is no cam in the engine, then the valves will remain closed and the cylinder will build pressure every time the piston comes up in the bore.

Am I misunderstanding the question?

 

The cam turns at half the speed of the crank, so every other revolution is compresion stroke. Watch the lifters and pushrods as they go up and down to know if you are on compresion stroke (both valves closed) or exhause stroke (exhaust valve opening or open).

Or think of it rhis way. When the intake valve or lifter starts to open (rise) the exhaust is closed unbtil the next revolution, so the exhaust pushrod on that cylinder can be adjusted. Same with the exhaust. But be sure you are turning the engine the correct direction.

Paul

 

You don't have to worry about that till it's time to adjust your pushrods. Use the timing marks on the gears. a shop manual is a must.

 

It's not a compression or exhaust stroke until the cam is installed.

 

 

My question was confusing. Over thinking it. In the end im going to put the rear cylinder at top. Align the cam and crank sprocket dots at 6 and 12 o'clock. Install rear pushrods. Then turn the wheel till the cam dots are both at 12 o'clock and Install the front. I believe that is correct . Can anyone confirm?

 

Close enough. Technically you are at 22.5 deg before TDC compression on the rear and 22.5 deg before TDC compression on the front..

 

I did notice i have to go a tad bit past the dots lining up to get the pistton all the way up when feeling with a straw. That confused me for a bit but I realized the lifters are in the same spot so figured the adjustment would be the same . Good to know its normal

 

As long as whatever push rod you want to adjust with the lifter is sitting on the base circle of the camshaft, you can adjust at that point, or if you are installing the oem push rods, rotate the engine until both lifters for that cylinder are both sitting on the base of the cam.
The straw in the cylinder thing is not precise, and just for push rod installation ,not imperative to get the piston at at perfect TDC. The crank can be moved, depending on the stroke, back an forth a few degrees while the piston stays stationary at TDC, so even if you have the piston up top, that it why you see the timing marks off a bit in relation to where the piston is.