ok i did the leak teast and my motor holds air, after 5 min the needle might have moved the thickness of the needle.
now when i do the vac test it does not hold vac, the small breather on the case will suck air in, when i did the pressure test
no air would come out of it, but on the vac test it sucks air in. is there a seal that is leaking, i need help on this.

my tester is set up on the intake, spark plug is in hole and exhaust has a rubber expansion plug in it.

Quote from: Rogue1970 on October 09, 2012, 10:14:44 pm

    Ok, so what exactly does the readings tell you?  Ring issues, crank sealing issues?

    Nice DIY tester Mitch!


On engines that have power valves, it usually tells you that you need to figure out a way to keep the power valve from leaking air into the crankcase so that you get an accurate pressure and or vacuum test.


Once you solve the power valve sealing issue, a pressure test will help indicate leaking gaskets, cracks in the cases or cylinder and if the pressure lips on the crank seals are leaking.  IT WILL NOT REVEAL IF THE CRANK SEAL SUCTION LIP IS LEAKING.  Crank seals have two lips.  One lip holds pressure and the other suction.  The suction lip is the most important lip and the lip that is most apt to leak causing a lean condition at partial throttle.  A vacuum test is also necessary to accurately test for leaking crank seals.

The only time I have ever heard anyone mentioning about doing a vac test on a motor is when jerry said it.

How much vacuum is to be administered and for how long?

I have a hand vac brake bleeder.

I just had my engine rebuilt... I havent fired it up yet

It may be leaking through the PV o rings or possibly the crank seal. I still say your good. If it held 5# for 4hrs. I would say you should not be worried.

DId you oil or grease the seals when you put it back together, and did you try spinning crank a couple times and retrying. I found most engines need to be rolled over in order to seal correctly.

I just pressure checked my rebuilt motor, it leaked out the case vent. I put my finger over it an it seemed to hold pressure.

I talked to a couple people to get clue as to what to do.

One builder says that if you have fresh o rings on the power valve it should hold pressure.

Second builder says that the power valve will leak. Not to worry about it.

First builder says block off the case vent to see if it holds pressure. 6 lbs for 6 minutes.

Where is that shrugging smilie? 

Run It!!! I would be pleased with those #'s Greek.

    We double O ring the P/V bearing, but they still seem to leak, this bearing holder also has an O ring on the outside.
    Part of the problem is that O rings need to set against outer wall and shaft to seal, I called up Dez and told him I had an extra P/V bearing holder and popped out the bearing and did some measurements, the bearing itself is a 21mm x 12mm x 5mm, then there is a step cut that just 17mm x 5mm that holds the O rings, now here is where the fun happens, the P/V O ring are 12mm ID x 2.5mm wall that should be 17mm OD, well I measured three of these O rings and every one of them were under 17mm, the wall thickness varied from 2.42mm to 2.48mm using a 5 digit micrometer, an air leak only needs a .001" and some pressure to happen.
    I told Dez, hey let me order a few O rings with 3mm wall and see what happens heck we might get lucky on some cheap coin here, also said I would call a few bearing house's and see if a mechanical seal (17mm x 12mm x 5mm) would work or not, or if such a seal does exist sure could also be a cheap cure .

Boooya!!!!!

Run the son of a ****!!!

Who cares if the power valve leaks a little. Its not an issue. You guys are all looking way to far into this. Its after the crankcase. Part of the pipe.

Hey sorry not familiar with this motor yet.... Nobody esplained it dis vey befor!

That's why I was askin da questions! Thanks!