Off idle bog. Case epoxy air leak.

kevbo

kevbo

Location
dfw
Sparkplug said:
There are 2 types of test. Pressure. And vacuum. Because engines see both. And seals have 2 sides.


Alot of people would say the crank seal only sees pressure. Why when the seal goes out it pushes oil into the cover. And never pulls leaked water into the engine. But to each their own.

30 psi is way too much. I'd be willing to bet you did the damage.

Either way. Get it fixed. 10 psi with no drop at all. Ever.

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Most seals are offset so they can flex and follow a slightly out of round shaft. This offset makes them hold more pressure in one direction. In a watercraft engine its more important to keep the air out. Plus being able to push a little oil out makes the seal last a lot longer. I have noticed the water side of pump seals wear much more than to the inside one.
 
M

mikesx

kevbo said:
Most seals are offset so they can flex and follow a slightly out of round shaft. This offset makes them hold more pressure in one direction. In a watercraft engine its more important to keep the air out. Plus being able to push a little oil out makes the seal last a lot longer. I have noticed the water side of pump seals wear much more than to the inside one.
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I pressure check at 7-10 psi and while the motor is sealed up I follow with a 20-25 hg vacuum check just for this reason.
 
A

andy300

Location
California
JC-SuperJet said:
Clean the Epoxy Patch Area with Acetone or Electrical Cleaner.

Locate the leaks around the Epoxy Patch.

Grind the immediate area around the Epoxy separation or crack.

Roughen the area to be filled with new Epoxy with sandpaper for better surface anchorage.

Clean the area one more time with Acetone.

Apply the Aluminum-based Epoxy. (you can even tape cardboard "forms" to contain and shape the Epoxy perimeter)

Tip: If repair area is at the Magneto End, stand the Crankcase in the Vertical Position so the Epoxy won't sag.

Once Epoxy cures, do another Air Leakdown Test (8psi x 10min) to confirm all Air Leaks are gone.
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Great info. Thanks.
 
A

andy300

Location
California
mthomps said:
Internet issues are the reason for the double up. I do apologize for being an ass and there's no excuse for that, seriously. I type like I talk and the words don't always match my ugly ass goofy mug.

For what its worth read groupk's article on air leaks. They want 6 to 9 psi held for 8 to 10 minutes. I've tested motors that don't lose a pound of pressure and others have lost most after 10 minutes. My biggest headache was a 1 cylinder 300sx motor that leaked more air than I thought possible.

30 psi is ridiculous, pump up a crank case to that and something is getting damaged. You want to test operating conditions not brute force torcher testing.

And just to add to what sparkplug said, you would think if something holds pressure it would hold a vacuum but thats just not true. Direction of mechanical forces make a huge difference. Not that it matters for our purpose here but I operate machines for a living that can hold pressure (15k to 25kpsi ) but the job gets stopped because it can't hold a 3 torr vacuum for 10 minutes and the reason is the mechanical and wearable seals fail when pushed the opposite way.
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No apology needed. I do the same sometimes.
I thought the vacuum would be more important as its sucking in air making it leaner. Im guessing much harder to find a vacuum leak then a pressure leak though.
 
A

andy300

Location
California
Sparkplug said:
There are 2 types of test. Pressure. And vacuum. Because engines see both. And seals have 2 sides.


Alot of people would say the crank seal only sees pressure. Why when the seal goes out it pushes oil into the cover. And never pulls leaked water into the engine. But to each their own.

30 psi is way too much. I'd be willing to bet you did the damage.

Either way. Get it fixed. 10 psi with no drop at all. Ever.

Sent from my SM-G970U using Tapatalk
Click to expand...
Not sure i follow. Do you mean a lot of people say the crank only sees vacuum?
 
kevbo

kevbo

Location
dfw
andy300 said:
How do you find the vac leak if there is one? As i said before, isnt that the important one?
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Crank seals, due to their orientation , will hold more vacuum than pressure. So just put 8-10 psi in the engine to check for a damaged seal or any other leak. The check will often reveal nothing, but its good practice. I flatten everything on a lapping plate and never have leaks, some hacks always have leaks.
 
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