jamesjedi

The directions for my Longacre Leak Down tester say that the cylinder to be tested should be bottom dead center. I thought it was TDC???

Thanks for help.

James

jamesjedi

I see that it is TDC everywhere else that I look, but the directions say BDC. I will use TDC.

Mike C.

The only thing critical is that the valves are closed. You could take the cam off and not turn anything....

jamesjedi

I will be taking the cam box off anyways. That is a good idea. Also, I will be testing with engine cold, I think it will only make numbers higher, perhaps I could be wrong???

Thanks

beentherebaby

TDC is where the piston rocking causes the most cylinder wear. No one checks leakdown at BDC that I know of as the cylinder pressure is highest at TDC. Valves must be closed on the compression stroke. You definitely want to check at TDC.

Reimu

What's a good/bad leakdown anyway

jamesjedi

Thanks for the help. I will be doing it tonight or tomorrow.

John_AZ

Info:
Quote "Good cylinder leakdown readings should be below 5-8%".

http://bentleypublishers.wordpress.c...t-efficiently/

http://www.dietersmotorsports.com/Co...akdowntest.htm

John

M758

I did a leak down on my 5 year race motor. I found over 10% leakdown on two cylinders. When I removed the head I found two leaking valves on those same two cylinder. I did the leakdown because I felt the motor to be getting soft. Right now that motor is waiting to be re assembled once I get the head cleaned. My leaking valves are due to carbon build-up.

Oddjob

Typically they are done at TDC because no one wants to pull cams off/out.

If you have the cam tower off, try the leakdown test at different crank positions and see if you get different leakdown rates due to out of round or hour glassed cylinder walls. I would be curious what you find - let us know.

I did just recently have a shop recommend to slowly move the cylinders slightly down from TDC and see if the leakdown increases a few degrees forward of TDC. Need a long pipe on the crank to hold it while doing this...

M758

Or a flywheel lock.

944obscene

I like the above mentioned tips. I'll be remembering all of this.

jamesjedi

Well...I tested cylinder #1 and #4 at TDC. Neither cylinder would hold any pressure. I could hear the air leaking from cylinders, perhaps at the head gasket area. It is hard to tell for sure. Also, cylinder #1 had some additional leakage from the oil fill cap. They were not holding any pressure.


Could this simply be the head gasket? I hope that is all it is, otherwise I will have to get a new engine.

John_AZ

Did you try doing this?

It could be toasted valves or like you think, a completely discentegrated HG which is very common if it is the origninal.

If you are doing this on your '86 944, ebay has had a couple of ready to go heads in the $200 price range--fully newly machined. No exchange needed. (no affiliation or knowledge of seller.)

GL
John

M758

pressure in the oil filler = leaking rings.
air out the intake our exhaust = leaking valves
Air in the cooling system = leaking head gasket