mikegarrison

I have a leakdown detector, and it is showing cyls #1,2,3 are doing fine. But cyl #4 is only holding about 20 psi of 100 psi input.

I'm not positive, but judging by the sound and some air motion, I think the extra air may be going out the inlet. But it's hard to tell.

I tried opening and closing the inlet valves to see if that helped, but it didn't. (Of course the pressure drops to zero with a valve open, then the valve sort of sucks back up and the pressure comes back up to about 20 again.)

Any suggestions? Cyl #4 is also the one that seems to get the most oil starvation problems, so that's also a possibility (the engine has been heavily tracked).

I'm definitely reaching the limits of my capability in my garage. I'm really close to buttoning it all back up again and driving (if I can!) to a shop. But it would be good to have an idea of what I may be looking at.

xviper

If you've eliminated the valves in that cylinder, then rings, head gasket or a crack in the piston are what's left.

Ek9

I'd probably try loosening the valve adjusters so, there's no possibility one of them's keeping a valve slightly open. Then, if that didn't change anything I'd toss a couple ounces of motor oil into the spark plug hole and see if the loss is less. If it's significantly better when you oil down the piston, it points to rings/bore. If it makes no difference, I'd think burned or bent valve.

Pull the cap on the radiator when you pressurize the cylinder and see if you're pushing air into the coolant, which would mean blown HG.

At this point, it can't really hurt to yank the head off and see what's going on.

mikegarrison

Cams and rockers are off the car right now, so there is definitely nothing holding the valve slightly open unless it is a damaged valve or valve seat.

Ek9

How was it running before you messed with the valves. It sounded like, from another post, that you were replacing valve retainers? I mean, if it was working well before, doesn't that suggest it might just be something stuck on the valve seat?

mikegarrison

I don't know how to "eliminate the valves in that cylinder" for sure. I guess I would have to take the head off and inspect them?

It's looking like it's time to find a shop to do this for me.

mikegarrison

Yeah, it was running fine before I started messing with it. But even before I started taking the cams off and messing with the retainers, I ran the engine and then did a hot leakdown test. 1, 2, and 3 were 97%+, but 4 wouldn't seal right. I thought maybe it was something I was doing wrong, but I still keep getting the same result.

If it is something stuck on the valve seat, how would I diagnose that and clean it off?

RED MX5

Sorry to hear you're having problems.

If there is a clear leak back through the intake then I'd be looking for a problem with the valve. More so because you just changed out the retianers. Is there a reason you can't pull the head yourself?

mikegarrison

Guess not. It's more work and more chance of screwing things up than I had budgeted for. And I've never done anything quite like this before.

And to be clear, the only retainers I have changed so far are on #1. #2, #3, and #4 are yet untouched.

Ek9

With What sounds like 80% leakdown, if it was happening while the engine was running, I'd have expected a dead miss on cylinder #4. Basically running on 3 cylinders. That it was running fine before makes me question whether there's really a problem or if this isn't just some artifact of the testing.

I'd be tempted to button it up, toss in a can of BK44K for a couple tanks and see if that cleans any goo off the valves. Can't hurt.