5 replies to this topic

[racer4]

Hi all, prepping a 1990 1.6l.  During the initial evaluation, after noticing a low speed miss, we got the following:

 

 

 

dry compression test, warm engine:

 

Cyl1=180 psi, 16% leakdown

Cyl2=190psi, 73% leakdown

Cyl3=180psi, 37% leakdown

Cyl4=205psi, 19% leakdown

 

I'm not getting the cyl2 numbers.  Doesn't make sense.  Air can be heard escaping from tailpipe during cyl2 and cyl3 tests.

Leakdown gauge is a MAC, compression tester is craftsman.  Valve cover was off to inspect timing belt, so valves were verified to be closed (or should have been unless lifter was gummed up and extended all the way).

 

What would be the next step? Pull cams and re-check?  If the same, is it time to pull the head and do a valve job? Thank for any input.

[Ron Alan]

Keep oil in it and watch the temps...then drive the crap out of it until you know for sure you are down on power...then rebuild! Might be a couple years 

[Bruce Wilson]

easy enough to pop the head and rebuild.  Compression test is just to find dead holes.  Leak down is the true test. Numbers vary from builder to builder, but anything over 12% is definitely not a racecar motor.  Here's a trick I recently learned due to budget constraints.  instead of buying all new lifters, I soaked them in solvent for a couple days.  Then with my finger, pumped each of them for a while until I was satisfied they where in good working order .  I discarded the frozen ones and pulled more used ones into the process.  When I was done, I had a set of lifters that all pumped fluid out of the small hole while submerged in a shallow pan of solvent (so I could visually confirm). I was skeptical at first, but now I'm sold.  very quiet valve train and it makes excellent power.  Learned this from the '13 Nasa national champ.

[racer4]

That's why I think I'm going to pull the cams out when we do the timing belt, to see if any of the lifters are stuck.  If the numbers tighten up, then I'll change the lifters out or soak them in solvent.  Exactly what solvent did you soak them in?  Kero? Lacquer thinner might be a bit too strong. Are these known for burnt exhaust valves?  The previous owner said the engine was from a 97 thus a 1.8, but after checking the plate on the oil pan, it was just another 1990 1.6l engine. 

[PRFGDWRNCH]

Your bad leakdown readings are on 2 & 3. Are you sure that you have the pistons exactly at TDC before applying the air. If you are off by even a small amount, the air pressure will force the piston down to BDC . The exhaust valve will begin to open before BDC if the engine rotates clockwise. Been there. For 1 & 4, the timing mark is a big help.

Dave

[racer4]

Definitely positive we were at TDC.  I use a big zip tie down the spark plug hole, always have.  I even rotated the engine a few degrees either way and the numbers didn't change at all.  In fact, even after going beyond TDC, the piston didn't go to BDC with air applied, all pressure goes out the exhaust.