Won’t run, low compression

[Hummelj]

I bout a Porsche 944 a few months ago from a guy who couldn’t get it to run. I found out that for some reason there is two washers on every bolt between the engine and bell housing, I do not know why but it made since that the speed and reference sensor where not getting a reading, I spaced the sensors out and the car kept trying to run, I sprayed starter fluid and got it to run full throttle at 2000 rpm for a few seconds and then died, I fixed the fuel problem and then it wouldn’t run. I took the cam tower off and the exhaust valves where bent, I replaced all valves and set the engine at tdc and the cam at the timing mark and it won’t run, I checked compression and only getting 40psi of compression, i don’t get this, why would it run before, stoping running after bending a valve, replace them, and not run. I laped the head and replaced the valve seals.

[944 Ecology]

Do a leakdown test, which will tell you where you are losing compression.

[Hummelj]

Alright I will do that

[walfreyydo]

Hi, this is my first post, but there are a few areas I would check.

As recommended already, a leakdown test is in order. Once that is done you will have an idea of where your leak is (rings, intake valves, exhaust valves). If you are not familiar with the process of running a leakdown and diagnosing leak locations, refer to google-many guides out there for performing this test.

1) You replaced the valves, did you lap them or check valve seats for proper seal? (ie: water test, air test, dye test etc).
2) Sometimes when you get bent valves, you can also have bent/worn valve guides. This is fairly easy to test by making sure there is no side to side play with the valve almost completely seated.
3) You could still be losing compression through the rings - how do the bores look? Scratches? Out of round?

After youve run your leakdown and have determined its either your intake or exhaust valves, then check valve seat condition by taking the head with the valve springs and valves installed (no cam) and run this test: https://www.youtube.com/watch?v=DkH4cNAahZQ

If you are getting bubbles you need to deal with your valve seats and/or valve face - lapping might work, might not (need to be cut). If you are NOT getting bubbles, then you have valve guide issues.

Best

[Hummelj]

Originally Posted by 944 Ecology

Do a leakdown test, which will tell you where you are losing compression.

I believe it is leaking through the piston rings but It doesn’t make since why it won’t run now?

[944 Ecology]

Originally Posted by Hummelj

I believe it is leaking through the piston rings but It doesn’t make since why it won’t run now?

No compression, no run. Don't know why it ran before, but 40 psi is too low.

[Hummelj]

I lapped all of the valve seats when I put it back together, I put some oil on one of the valves while running air in the spark plug hole and it bubbles some, so obviously its leaking. When I put some oils into the cylinder and I get 60 psi.

Originally Posted by walfreyydo

Hi, this is my first post, but there are a few areas I would check.

As recommended already, a leakdown test is in order. Once that is done you will have an idea of where your leak is (rings, intake valves, exhaust valves). If you are not familiar with the process of running a leakdown and diagnosing leak locations, refer to google-many guides out there for performing this test.

1) You replaced the valves, did you lap them or check valve seats for proper seal? (ie: water test, air test, dye test etc).
2) Sometimes when you get bent valves, you can also have bent/worn valve guides. This is fairly easy to test by making sure there is no side to side play with the valve almost completely seated.
3) You could still be losing compression through the rings - how do the bores look? Scratches? Out of round?

After youve run your leakdown and have determined its either your intake or exhaust valves, then check valve seat condition by taking the head with the valve springs and valves installed (no cam) and run this test: https://www.youtube.com/watch?v=DkH4cNAahZQ

If you are getting bubbles you need to deal with your valve seats and/or valve face - lapping might work, might not (need to be cut). If you are NOT getting bubbles, then you have valve guide issues.

Best

[Hummelj]

Yeah, it’s to low for it to try and run, i do t get why it ran before though, is it possible the previous timing was right and the valves where already bent and I timed it wrong? I don’t think I did bc I had it at tdc and lined the cam with the timing mark, the balancer shaft was also lined up.

Originally Posted by 944 Ecology

No compression, no run. Don't know why it ran before, but 40 psi is too low.

[walfreyydo]

Originally Posted by Hummelj

I lapped all of the valve seats when I put it back together, I put some oil on one of the valves while running air in the spark plug hole and it bubbles some, so obviously its leaking. When I put some oils into the cylinder and I get 60 psi.

Its entirely possible its rings AND valves. Need to run a proper leakdown test to be sure.

Sounds like you for sure have valve seat issues. Did you recut the new valves and the seats or did you just try to lap them in to the old valve seats? Thats probably your problem. I would consider taking it to a machine shop, have them diagnose and do the grinding/recutting/lapping.

Once thats done and your head is airtight, then look at your rings and bores. Assuming your bores are ok, you may only need a hone and new rings. If your bores are out of round or scoured, youll need to get them bored over (new pistons), or go with a better condition used block.

EDIT: just looked and not sure you can hone alusil bores, might want to look into that if you do plan on re-ringing (https://www.audizine.com/forum/showthread.php/754894-How-TO-Hone-Alusil-Blocks)

[Hummelj]

I lapped the old seats my self till they where smooth

Originally Posted by walfreyydo

Its entirely possible its rings AND valves. Need to run a proper leakdown test to be sure.

Sounds like you for sure have valve seat issues. Did you recut the new valves and the seats or did you just try to lap them in to the old valve seats? Thats probably your problem. I would consider taking it to a machine shop, have them diagnose and do the grinding/recutting/lapping.

Once thats done and your head is airtight, then look at your rings and bores. Assuming your bores are ok, you may only need a hone and new rings. If your bores are out of round or scoured, youll need to get them bored over (new pistons), or go with a better condition used block.