Is there an accurate method of doing leak down test with timing belt off for ej 22 and 25 engines. Can youu have all pistons at mid stroke and rotate the cam by the 17mm cam bolt, or will the air pressure from leak down tester push the piston down. Is doing a leak down test with pistons at mid stroke and 100psi in the tester going to give accurate results. 

I would think unless the cylinder you are testing is at the bottom then unless the crank is blocked it seems like it will definitely move with 100psig on it.

SOHC engines are easy.

Set crank at the timing mark, passenger side cam at its timing mark.

Turn the drivers cam so the timing mark is straight down. Now all 16 valves are closed and you can turn the crank as much as you need, just be sure to only turn it clockwise.

 

DOHC heads are more difficult.

Same thing applies, set crank and passenger side cams at their proper timing marks. The drivers side cams you have to rotate at the same time to avoid valves possibly hitting each other. Kinda tricky. Use two wrenches or small breaker bars so the cams don't snap over.

Hi Sooberoo, That sounds too easy, but a great idea. When the valves are all closed the pistons can be rotated  to the top for each cylinder to be leak tested. Just never thought of that. Always too worried about piston and valves making contact. 

I have not rebuilt a Subaru engine, but I have rebuilt plenty of others and the maximum piston wear is at the top of the cylinder.  But in most cases, a failed leakdown test is due to a burned valve or a broken piston, not due to cylinder wear so crankshaft position doesn't really matter much.

 

100 psi may blow down a piston that is anywhere in the 120 degree arc from TDC -30 to TDC -150.  Anywhere in the top or bottom 30 degrees will not have enough mechanical advantage to move the piston.  All you need it the valve for the cylinder under test to be closed.

 

If you suspect a cracked cylinder wall, then do the test at BDC.

Edited December 22, 201510 yr by keith3267