Leak Down Test On My New 418 Need Help?

-
I've seen a few do a 400 grit stone hone after the machine shops finish hone, brake clean it and run single moly rings. It ended up taking thousands of miles to seat them. Talking light puffers for the 1st 2k out the breathers.

Not a good practice.
 
Here's something else you can do
Back off the rocker gear and do the LD test with the pistons at the bottoms of the bores,still listening for where the air is going; but now you can do it at 100psi without fear of the piston moving on you, plus you can tap on the valves to knock the carbon out, and seat the valves properly. 'Course sometimes the valves won't seat at all, and then you make a note of it, and continue testing.
Then after that, you can reduce the test-pressure (I use 30psi) and drive the pistons to the top, stopping at a couple of intervals, to check the bores for scratches, and finally reaching the top. On a fresh engine the top and bottom should be the same or very similar, using the identical test pressure, and I use no less than 80psi, at the top. In-frame this is usually pretty difficult so I'd have to suspect something amiss to do it. I have found wrist-pin damage this way, and cracked bores. But the bottom test is quick and easy.
I'm not usually looking for absolute pressure but rather the differences between cylinders. But when the numbers come up at less than 4%, then I get interested in absolutes real quick.
 
superchargeddrt said:
Hey Guys,
I have been getting what I think is excessive crankcase pressure. The dipstick is pushing out and I have been getting oil leaks (even on the dyno). I have the PCV connected and I have a breather on the other valve cover. After the installation and modification of the breather (added extra breathing holes) the dipstick isn't pushing out however I still have oil leaking on the exhaust and I notice oil leaking out of the transmission bell housing. Additionally I am seeing a oil film on the rear bumper and trunk panel. When I got the short block from the machine shop I noticed that I was able to rock the pistons slightly in the bores (is this normal for forged pistons?) All of this prompted the leak down test. This was done dry and on a cold engine but the results are troubling, what do you guys think?

1 = 12%
2 = 16%
3 = 3%
4 = 11%
5 = 7%
6 = 4%
7 = 12%
8 = 6%
Click to expand...

I had two sbc do that, that were honed by a reputable machine shops. I tore them back down and ball honed the w/320 grit (flex hone), and put gapless ring s in them, END OF PROBLEM!
 
oldkimmer said:
With it blowing oil when on the dyno theirs no way in hell I would of taken it from them. It needs to be fixed properly and right now. Is it possible the rings were installed upside down? I know **** can happen, but the builder should of never let it leave his shop.i would be so totally embarresed if it were me. Kim
Click to expand...

This.
 
Be very careful doing a leak down test trying to hold the crank from turning, I seen one guy rip the end off his finger when his buddy plugged in the air line at line pressure and the engine rotated, the breaker bar pinched his hand so hard that it ripped his little finger down to the bone.
 
Brian's right; it's true, at 80psi with the pistons at the top, it is dangerous.
but your results will be about as accurate as possible.

I use a 3ft pipe over the 20" bar. I set the piston to TDC, or a hair early. Then introduce the air very slowly, hanging onto the bar for dear life, and adjust the crank as may be necessary. If the crank flips over it will usually loosen the crank bolt.
My tester is home built with;one regulator,one gauge,a restrictor, and a ball-valve on the end . I dead head the gauge and set the pressure, then connect to the cylinder with the ball-valve closed, then slowly open the ball-valve. If the crank moves,I close the valve and reposition then repeat.
To figure the LD in percent with one gauge, you have to do the math. No big deal, and most times I don't bother, cuz I'm not looking for absolutes.

That's true, at 80psi with the pistons at the top, it is dangerous. Thanks Brian for the reminder.
 
AJ/FormS said:
Brian's right; it's true, at 80psi with the pistons at the top, it is dangerous.
but your results will be about as accurate as possible.

I use a 3ft pipe over the 20" bar. I set the piston to TDC, or a hair early. Then introduce the air very slowly, hanging onto the bar for dear life, and adjust the crank as may be necessary. If the crank flips over it will usually loosen the crank bolt.
My tester is home built with;one regulator,one gauge,a restrictor, and a ball-valve on the end . I dead head the gauge and set the pressure, then connect to the cylinder with the ball-valve closed, then slowly open the ball-valve. If the crank moves,I close the valve and reposition then repeat.
To figure the LD in percent with one gauge, you have to do the math. No big deal, and most times I don't bother, cuz I'm not looking for absolutes.

That's true, at 80psi with the pistons at the top, it is dangerous. Thanks Brian for the reminder.
Click to expand...
Never thought about that, good point. I have been putting the Piston at TDC and introducing 100 PSI but I haven't had the engine move even with all of the plugs removed. I am getting ready to call my engine builder to discuss this with him.
 
Alright so I talked to my engine builder and he said that I might need to take it out and romp on it a bit. Cruise it down the interstate with short full throttle bursts. He said that if it doesn't seat the rings that he will do a leak down in my car to see what's happening, stay tuned.
 
superchargeddrt said:
Alright so I talked to my engine builder and he said that I might need to take it out and romp on it a bit. Cruise it down the interstate with short full throttle bursts. He said that if it doesn't seat the rings that he will do a leak down in my car to see what's happening, stay tuned.
Click to expand...
It never should have left his shop like it is, but good luck with driving it, keep us posted, it can be quite educational for all of us!
 
superchargeddrt said:
Alright so I talked to my engine builder and he said that I might need to take it out and romp on it a bit. Cruise it down the interstate with short full throttle bursts. He said that if it doesn't seat the rings that he will do a leak down in my car to see what's happening, stay tuned.
Click to expand...
In my humble opinion I would only do that if he is willing to stand behind any damage that may result from doing so. I suggest pulling and bringing to him now for inspection. I know it is painful to pull a new engine but you have big money into it already, don't risk more. That engine won't come close to working as hard in the car as it did on dyno, I'm surprised the guy even suggested it. Imho, if rings didn't seal on dyno then they never will. I'm sorry your project has been difficult so far Glenn, hopefully it gets sorted out soon.
 
You gotta problem OP.... Pull it down... It takes alot of blowby to knock a dipstick out of the tube...

JW
 
cpearce said:
In my humble opinion I would only do that if he is willing to stand behind any damage that may result from doing so. I suggest pulling and bringing to him now for inspection. I know it is painful to pull a new engine but you have big money into it already, don't risk more. That engine won't come close to working as hard in the car as it did on dyno, I'm surprised the guy even suggested it. Imho, if rings didn't seal on dyno then they never will. I'm sorry your project has been difficult so far Glenn, hopefully it gets sorted out soon.
Click to expand...
I will try short full throttle blasts at 60 MPH along with gearing down when I come to a stop. I will NOT beat the dog snot out of it. If I don't see any improvement it will be going back to him for sure.
 
superchargeddrt said:
I will try short full throttle blasts at 60 MPH along with gearing down when I come to a stop. I will NOT beat the dog snot out of it. If I don't see any improvement it will be going back to him for sure.
Click to expand...
It won't/shouldn't hurt anything to do that. Sounds like a probable long shot at this point but it is no real effort.
 
brian6pac said:
Try to hold at 90* off TDC and at 100 psi and then tell me that.
Click to expand...

I'll ask my 4 spd..



4 spd said no problem.

Tips.
Dont pull all the plugs.

depending on issue only pull others if necessary "head gasket blown between cylinders" remove necessary plugs only in that case.Once crank position is attained, pull the rocker shafts loose to help keep the crank from turning or air locked.

Keep your hands and finish her away from all moving parts. Haha I just had to...
 
Last edited:
I pulled one out with about 100000 miles on it /keep leaking oil pushing the dipstick out when pulling the intake I found the intake gasket around the intake to head center exhaust port crossover blew out dumping the exhaust backpressure into the crankcase so I put a timing chain in it and drove it for another 100,000miles
 
You must log in or register to reply here.
-

Back
Top