Oldtee

I gave myself a pretty bad freight yesterday that cause me a night of sleep and dreams of engine extraction techniques. I did a leak down test cold and got the following results.
#1 72/80, #2 63/80, #3 45/80, #4 40/80, #5 40/80, #6 72/80, # 7 20/80 , #8 79/80.

Then I did a compression test using the old fashioned way.

#1 150, #2 170, #3 140, #4 165, #5 180, #6 170, #7 165, #8 155.

Both test done with engine stone cold. I am not happy about # 3 cyl but have no intention of pulling then engine based on this single test.

FYI I am doing a major tune up.
Comments?
ARF

jeff jackson

You're alright...just warm it up, and then test it. Cylinder sealing varies significantly with temperature. If its "stone cold".. the ring end gaps (although small in the first place)...haven't narrowed due to piston skirt expansion. Also...the valves and guides are in the same situation. I'll bet you see close to 170# on all cylinders after a proper warmup. This doesn't mean a valve job, and new head gaskets, and clearanced guides, and new seals...wouldn't improve things dramatically. Most likely so. So...you have to decide, what is aceptable performance for your car. If you want it all...the "warmed compression test" will tell you (or your mechanic)...where to go from here. Good Luck. PS...when doing the leakdown test, after a good warmup of the engine, be sure and cap the throttle body air nlet, and the exhaust pipe outlets...avalve leaking through, will render your diagnosis of the ring sealing condition, as "unreliable".

the flyin' scotsman

Oldtee...........the important component of compression readings should be within 10-15% of each other not so much the pressure reading itself.

How cold is cold?.............if the engine hasn't been run for a while perhaps you should fire her up, take her around the block and retest after she cools.

Scott M.

John;

You know better than that! On a cold engine, tsk,tsk...

Didn't I give you the leakdown numbers I got off her when I did the T-belt job??

Oldtee

I have done hundreds of leak down tests on aircraft, stone cold. It was always a rigirous test and if the engine passed there it would do OK hot. When a weak cylinder was found it was always followed up hot. In one test I got 0/80 and that just about gave me heart failure. Then I put some oil in the cylinder, pulled it through a few times and it came up to 40/80. If you gave the numbers to me I couldn't find them. I do have a card with fuel pressure numbers, tho. We did talk about it, and, you being a good guy and all, I took your word for it. I did the test to establish a base line sine I've put 7000 miles on her since you passed her to me. Hope all is well.

the flyin' scotsman

So a significant increase when adding oil to the cylinder; an indication of poor ring seal.

Have your tried a warm (not stone cold ) comp test?..........if so whats the result

ps Canada 2 Russia 0

Scott M.

John;

Just razzin' ya.

I thought I had the numbers in the folder I gave you. I'll check my files again. Like you, I did both leakdown and comp. test once I got it. I recall they were all rather decent.

Glad to see your enjoying it. It sure did add some color to my fleet of dark colored cars.

jeff jackson

Old tee...

why "follow up hot ??? I am not familiar enough with aircraft engines to make radical assumptions, but, in the case of V8s, typically the max pressure obtained by spinning the motor over "cold"...can easily be 30# less...than a warmed engine...with all the plugs out when the test is started...and the thottle held full open while cranking the motor over. The fuel pump relay should be pulled, and coil wires removed as well. As far as "leakdown tests"...Once again...I'd suspect the rtesults would be more "indicative" of operating conditions, if the engine had been fully warmed prior to capping the intake and exhaust systems and pressurizing the cylinders one by one.

mark kibort

my part euro 5 liter was 155 per hole, and dynoed at 293hp rear wheel. my 243RWHP 4.7 was 125 to 130psi per hole, and the Holbert car (S4) 85 cams, is at 320hp and has 180psi.
this is usually luke warm and about 5 hits per cylinder.

You are just fine!

MK