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Need help with leak down test results
#1
Fyi, I'm not expert here!

I have a 1992 HO 302 that I'm working on for my car.  I converted it from efi to carb.  
I didn't mess with the block or heads. Just the parts for the efi/carb swap.
I don't know much about the engine's history.
It's on an engine stand. No oil in it currently.

I ran a leak down test, figuring I could get an idea of its health.
So far I've checked 4 of the cylinders.  At TDC of course.

3 have an 80% leak and 1 is closer to 90%.  Each leak is coming out of the dipstick tube.

I assume that means the rings are worthless? 80-90% leak seems so high though. 

Anyone have an idea what I should do next or what this might mean?

Thank you
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#2
Put it in. The engine uses oil to seal. The engine is dry so it will let air pass thru the rings. I do believe you are over thinking a bit.

In the car on a compression test, cylinders need to be within 75% of each other. I am more than confident yours will be fine.
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#3
(07-10-2018, 04:27 AM)Ryunker Wrote: Put it in.  The engine uses oil to seal. The engine is dry so it will let air pass thru the rings. I do believe you are over thinking a bit.

In the car on a compression test, cylinders need to be within 75% of each other. I am more than confident yours will be fine.


I was hoping there could be a reason it was so leaky.  Thanks. I'll do that and see what happens.
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#4
Spray or pour a little bit of oil down each spark plug hole and turn motor over by hand a few times. Then try the test again. Should be better but 80% is a shit ton of leak!

Kevin

1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]




                                                                                             
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#5
Oil or no oil, 80% leak is terrible. Using a leak down tester can be tricky. It is hard to keep the engine from counter rotating when the cylinder is pressurized. When that happens, you get very big leak down percentages. Get the piston for the cylinder under test where you think it should be and install plugs in the other 7 cylinders. This should help prevent the engine from counter rotating and allow an accurate leak down measurement. Chuck
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#6
(07-10-2018, 09:22 AM)c9zx Wrote: Oil or no oil, 80% leak is terrible. Using a leak down tester can be tricky. It is hard to keep the engine from counter rotating when the cylinder is pressurized. When that happens, you get very big leak down percentages. Get the piston for the cylinder under test where you think it should be and install plugs in the other 7 cylinders. This should help prevent the engine from counter rotating and allow an accurate leak down measurement. Chuck

Brooks425,
Just to add to what c9zx is saying it would advisable to have the harmonic balancer marked (fully degreed or aftermarket that is fully degreed) so you know what cylinder is at TDC and to keep it there while doing the test.
try doing this on a v twin with 210 lbs. cranking pressure only to read less than 2% leakdown.
would never recommend a leakdown test on an engine that is not in the car and has been recently run.
Boilermaster
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#7
Hard to imagine 80 to 90% leakdown, even with bad rings. When you say it was at TDC, was that for each piston (with valves closed) or TDC on the damper? What kind of gauges did you use for the test?

Normal procedure would be to run a compression test on a warm engine, and if you have bad results use a leakdown test (on a warm engine) to pin point the problem.

Without knowing anything about the engine I would have to consider it a rebuilder and tear it down. The only time anyone should install a used engine is if it came out of a running vehicle with known mileage, and so it could be inspected while still in the vehicle (oil condition, etc.). It's way too much work to install an engine only to find out that it is bad. An alternative would be to run a used engine on a test stand.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#8
I do a leak down test on every new build while it is on the stand. Not to get the actual leak percentage but just a "go or no go" check before I put it in the car or take it to the dyno. If something is wrong it is better, easier, and cheaper to find out early on, and I am hyper-careful/paranoid when it comes to new builds. Chuck
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#9
Chuck, is correct. Top dead center becomes not top dead center when you apply air. Use a breaker bar to stay at tdc. Normal results would be 10-12% leakage on a stock engine. The other thing you could do is regulate the air pressure down to 100 psi or less to prevent the engine from going back to become where the valves open. The only way your getting that big of leakage out the dipstick is if you have holes in Pistons. Do you have normal compression results?


[Image: image.jpg]

Dennis
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#10
I always die my leakdowns with 100psi. Makes the math a whole lot easier!!! Lol.

Kevin

1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]




                                                                                             
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