Good Day!

I am wondering what is the easiest way to find compression TDC when doing a leakdown test? I know I could prob do a trial n error with finding TDC of the cyl and doing a leak down. If I get 100% leak down then its on the exh stroke, then rotate the crank to TDC again on that cyl to get comp stroke. I was just wondering if there was an easier way?

Thanks!

BTW- getting 151, 64, 150, 145 on my 2.3L with 8.5:1. Not looking good for Cyl #2 (left to right facing front of motor)

 

Not 100% accurate, but stick a long screwdriver down the plug hole, and rotate the CS slowly until you find TDC for it.

 

That's what I do. You can also take the TB top cover off and line up the marks to the VC.

 

I know how to find TDC but to know if its on the compression stroke or the exh stroke is what Im after. or maybe it's a trial and error.

 

Are there two timing marks on Evo cams? I know on a DSM you can have them 180 out that you need to make sure that dial pin is straight up. also need to make sure you either have the screw driver in the cylinder closest to the timing belt or the furthest. not the inside pistons. I've had friends put their cars in time and that's what they did.

 

At TDC the valves are closed. The intake and exhaust stroke happens before/after that.

 

There is one timing mark per cam gear. If both cam gear's mark is lined up with the VC mark, then you are at TDC.

 

ok... so what I gather from what you guys have told me is that @ TDC on no matter what cyl, both in/ex valves are closed and I can do the test from there, correct? Which makes sense to me as well.

 

Your cams gears will show you TDC twice for one rotation of the crank. One time the valves shut and the pistons will be at TDC in cylinders 1 & 4. The next time the valves shut and the pistons will be at TDC in cylinders 2 & 3. The spark and fuel is alternated between the cylinders that are at TDC. So if you have spark on one rotation at cylinder 1 you will not have the spark on cylinder 4. the next time both 1&4 come to TDC you will have spark in cylinder 4 and no spark in cylinder one.

One cylinder will fire each time TDC is reached and it alternates between the pairs of cylinder 1 & 4 or cylinders 2 & 3. A cylinder will only be fired once during the one revolution of the crank.

Hope this helps, you probably already know, I am just throwing it out there for others who may pass through and did not know already.