[howndog]

Hi Alfisti
I recently performed a leak down test on my 1750 spider. I was burning oil and fowling plugs very quickly. Compression is at 120 across all at wide open throttle with a warm engine. The results are confusing. According to the test I have good cylinder rings. I recently rebuilt the SPICA and added a 10.5 lift intake cam. I’m wanting to replace the valve seals but am not sure that’s the problem. Any advice would be appreciated b

ciao!

 

[otteud96]

Leak down will give insight to percentage of compression loss, not psi.... what is the state of the engine and what and when was the spica done? So many variables...need some more info. good luck

 

[howndog]

Spica was gone over the summer. I believe engine is original with 120000 miles. According to the leak test there is 10% loss. I was hoping to narrow down the possibility of either rings or valves.

 

[vintagemilano]

Hi there, leak down results are normally in relation to a reference number from a calibrated orifice, usually, when I've done it anyway, is 80psi. Then the result is something like 74/80, which is often converted to a percentage as mentioned above. Your 120, sounds like an absolute number from a compression test. If all four cylinders are close to 120 then that should be ok.
For oil consumption, valve seals are normally indicated if there is a visible blue cloud on start up. I suppose if there is also blue smoke at idle that could also be valve seals as that is when manifold vacuum is at it's highest. I don't know of a really good way to definitively test for worn oil control rings, some have said to get someone to follow you and see what the tailpipe looks like when you really tromp on it.

 

[howndog]

Thanks for the replies guys. For clarity I did a compression test as well. That was 120. The leak down test I performed doesn’t show the compression. One dial shows the amount of air pressure being applied to the piston. The other shows the percentage of loss. My loss was in the moderate range. That said the air pressure was set to about 40 psi. The car burns oil on startup and when I accelerate.
as an aside can the valve seals be changed without removing the head?

 

[vintagemilano]

Papajam had some great comments about that here,

stem seal tool

hi, i have a 1985 gtv 2.0 which burns alot of smoke out of the exhaust mostly when you go back onto the throttle after changing gears. I was advised to change the stem seals which could fix the problem but theres a possibility it may not i believe? I heard there was a special tool to do this job...

www.alfabb.com

 

[spiderserie4]

yes valve seals, springs etc can be changed w/o head removal.
stem seal tool
EDIT beaten to the post by vintagemilano

this tool has been discussed before on BB and looks like it might be a good one to use to remove the collets.
Valve spring compressor

Papajam never used rope in the cylinders, he said the piston set to TDC held the valve just fine when you popped the collets.

 

[otteud96]

The issue IMO is that the engine has alot of miles and it uses oil. Valve guide seals without valve guides is pointless. The state of the rings pistons and or cyl walls is ??? What is the shape of the bearings...It is hard to say change any one item and have that be it.... minimally removing and rebuilding the head is always good ...on an engine with alot of miles. Good luck hope all goes well.

 

[930cabman]

I agree with otteud96, rebuild the motor. Throwing time/money doing a 1/2 job may get you 1/2 of what you are looking for but why not just do it right

 

[msiert]

Is the 10% leak down test lost in one cylinder or all of them and is 10% loss in itself bad enough to justify a head job or engine rebuild, could you even notice it on a street car?

Is the lost from the rings or intake valves or exhaust valves, or should I say which valves or which cylinders rings are leaking pressure. Sometimes the rings and valves both leak in a cylinder, 5% loss at the rings and 5% loss on a valve that shows up as a 10% on a cylinder as a whole.

The beauty of the leak down test is you can look at each cylinder seperatly and narrow down (in that cylinder) if the rings or the intake valve or the exhaust valve or a combination of them is leaking.

For a 10% loss I wouldn't do a thing but keep on driving and enjoy.