Air Leak

[ski4]

i have a thread in carnage about this but i wanted a more pointed thread to get ideas

rebuilt motor is not holding pressure, i have the cleanest motor on the planet now since i have been spraying soapy water all over the damn thing

the only thing i can think of is the head orings are not sealing properly and it's leaking our the cooling passages.

does that sound plausible?

i am at work now and will check later when i get home but i am stumped

 

[keefer]

Could be, cap em off and re test. Maybe one of the compression O-rings was pinched in the head during assembly. I use a little grease to hold em in the head while setting it on the cyl. If the leak stops, pull the head and check it out.

 

[Matt_E]

If the Orings are faulty, plugging the cooling passages won't reveal that (unless you pump it up 100 times and let it leak down each time).

The cooling passages will be at lower pressure than the rest of the motor.

 

[ski4]

i'm loosing ya matt. if i do block the outlets on the head and the ex. manifold it should stop the leaking though if that is the culprit or no?

 

[Matt_E]

Say you do have a leak at the Orings. Say you plug the cooling outlets.
Then you pump up the motor for the leak down test.
I am assuming the leak you are experiencing is a slow leak. That means the motor will be pressurized, but not the cooling passages - because they are sealed from the rest of the motor, minus the leak.
So, if there is a [slow] leak, the cooling passage will eventually equalize with the higher pressure in the rest of the motor. But your leak down gauge will still show you a drop of pressure, because the volume of air you initially pumped into the motor is good for the initial pressure only for the volume of air in the motor. Once it gets distributed into motor and cooling passages, your pressure will be lower.

If it's a fast leak, you should be able to work it out then.

 

[ski4]

i got ya now.:Banane01:
i am feeling a little slow this morning, too many 4 am days over the past wek building motors and aviary's and painting kids rooms etc
yes it is a fairly slow leak

it will hold pressure for maybe a minute then go to zero

 

[Matt_E]

That is a rather fast leak. What psi are you pumping it up to?
I would plug the cooling passages well, then pump it up a few times after it's back to zero. If it's indeed the O-Rings (and you did a good job sealing the cooling passages), then the leak rate should slow.

You know, with a leak that fast, you should be able to locate it, one would think.

 

[ski4]

i know that is what is driving me nuts
i literally emptied a whole spray bottle of soapy stuff on the motor.

i am taking it up to 6 lbs each time, from 6 to 2-3 it will leak fast then the last pound or two lows down a lot

 

[Matt_E]

Is it a ported cylinder and cases?

If it's not the O-Rings, carefully inspect the bottoms of the water jacket around the cylinder / the tops of the transfer/boost ports and check for cracks.
look at the cases if they are ported. Particularly in the flywheel area and the intake area.

 

[ski4]

cyl. is ported the cases are not ( but iv'e been there with the holey ported cases)

i will check them again tonight
thanks

 

[Matt_E]

I vote O-Rings though.

 

[ski4]

i hope so too
that is at lest a cheap easy fix ( maybe)

 

[Matt_E]

Stupid question...your spark plugs are tight, right?

 

[ski4]

yep , i had hoped it would be that easy and snugged em up a bit , :frown:
it would not be unlike me to do that though and spend 3 days chasing my tail to figure it out

 

[Matt_E]

What is on the motor? Carbs, intake, exhaust manifold, etc? Or is it just the shortblock?

 

[ski4]

just the manifolds and the motor carbs and exhaust are off

 

[Matt_E]

Two pulse fittings, I assume?
Are you just using one or both for the test?

 

[ski4]

nope, just the one pulse fitting and air tight

 

[ski4]

ok
plugged off all the cooling system lines. absolutely not a single bit of movement in the air pressure.

pulled off the old head and wow@@@:banghead: :banghead: :banghead: :bigeyes:

rear cylinder compression ring folded in 1/2 and broken in 4 places??????????

odd since it was round and intact when i dropped the head straight down on the motor. wtf could have done that:sneaky: since i have not even run this thing yet

 

[waxhead]

Are we talking about compression rings on the piston here ??

or are you talking about the 0-ring
if its the o-ring then its moved as you have put the head on there really isnt much else that can do that

Unless the dome has been turning in the head as you tighten the spark plugs but even then i wouldnt think it would fold it in half