I must have a valve seating problem, correct? Could be due to a bad rebuild or maybe I managed to bend a valve when installing the head.
I must have a valve seating problem, correct? Could be due to a bad rebuild or maybe I managed to bend a valve when installing the head.
This is on an '84 944.
Could be, the 944 is very critical of valve timing.
Check Clark's Garage for info to double check the valve timing, etc.
The timing marks line up properly. Isolated to the single cylinder I've got to believe it's a problem with the valves, etc in that cylinder.
remove the cam tower and put a strait edge across the top of the valves.
Or possibly a cracked head but this is not very common. Why the HG replacement? Over heat?, Over boost? Or just regular maintenance?
Can you get access to a leakdown tester before going any further? If you can't, it's still possible to do a quick and dirty test by connecting a shop air hose to a compression tester hose screwed into the offending cylinder's spark plug hole, then putting some air to it, you want to stay around 60-70 PSI if possible. Air hissing from crankcase (you can hear this by making sure the oil cap, PCV etc are tight and then removing the dipstick) = ring sealing problem. Air hissing from intake or exhaust = valve problem. You might have to go to the back of the car and listen at the tailpipe.
944's are hydraulic tappet, right? If the valve installed height is not correct (too high), then the internal tappet bleed holes are not in the right position and the tappet can't self adjust. I ran across that on Subarus many years ago.
Curmudgeon wrote: Can you get access to a leak down tester before going any further? If you can't, it's still possible to do a quick and dirty test by connecting a shop air hose to a compression tester hose screwed into the offending cylinder's spark plug hole, then putting some air to it, you want to stay around 60-70 PSI if possible. Air hissing from crankcase (you can hear this by making sure the oil cap, PCV etc are tight and then removing the dipstick) = ring sealing problem. Air hissing from intake or exhaust = valve problem. You might have to go to the back of the car and listen at the tailpipe. 944's are hydraulic tappet, right? If the valve installed height is not correct (too high), then the internal tappet bleed holes are not in the right position and the tappet can't self adjust. I ran across that on Subarus many years ago.
Now why did I not think of that!!! I think it was lack of coffee
When testing obviously you will want to have the offending cylinder set with both valves closed. This should be easy to do by removing the caps in the cam tower that allow access to the cam tower bolts. This should let you see the position of the cam on the problem cylinder.
Replaced head gasket (and head, with rebuilt unit) due to overheat.
Guy over on Pelican Parts thinks that the valve retainer is off in the offending cylinder. I'll tear it down today or this week and see what's up.
Curmudgeon wrote: Can you get access to a leakdown tester before going any further? If you can't, it's still possible to do a quick and dirty test by connecting a shop air hose to a compression tester hose screwed into the offending cylinder's spark plug hole, then putting some air to it, you want to stay around 60-70 PSI if possible. Air hissing from crankcase (you can hear this by making sure the oil cap, PCV etc are tight and then removing the dipstick) = ring sealing problem. Air hissing from intake or exhaust = valve problem. You might have to go to the back of the car and listen at the tailpipe.
I will do this first.
When you do, make sure the piston's at bottom dead center and both valves are closed. Otherwise when you throw the air to it, the crank is gonna spin. Fingers tools etc in the way = 
Curmudgeon wrote: When you do, make sure the piston's at bottom dead center and both valves are closed. Otherwise when you throw the air to it, the crank is gonna spin. Fingers tools etc in the way =
I doubt it's possible to have both valves closed at BDC. I use TDC, both valves closed, and limit air pressure to 30 psi. Having the (std) trans in gear helps.
Was the engine run? Is this a fresh rebuild and install or did it sit and/ or was installed on the engine for a long time after the rebuild? It's not uncommon for rust to form between valve to seat faces if left for a while and will show decreased test values if the engine hasn't been run and tested cold. Running the engine for 5 min should clean the rust off in that case and provide accurate readings.
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