Saw passed leak down but not vac test (should I be concerned)?

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Okie294life

Brush Popper and Amateur Tree Butcher
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i just replaced the p&c on an 028 super did the vac test, passed at 10 psi great. Went to do the vac test, and not so much. I’ve read that crank seals are usually the culprit for this so I slathered some grease on both of them and no change. I can hear some whistling, my next culprit would seem to be the impulse line, does this sound reasonable? Or could it be something else? I’m using the mitivac with a cone fitting ran through the impulse line to test with. I dunked the saw in water earlier and no pressure leaks.
 
i just replaced the p&c on an 028 super did the vac test, passed at 10 psi great. Went to do the vac test, and not so much. I’ve read that crank seals are usually the culprit for this so I slathered some grease on both of them and no change. I can hear some whistling, my next culprit would seem to be the impulse line, does this sound reasonable? Or could it be something else? I’m using the mitivac with a cone fitting ran through the impulse line to test with. I dunked the saw in water earlier and no pressure leaks.
You just replaced a piston and cyl and not the seals and gaskets and hoses? I think it is a crank seal leaking!
 
You just replaced a piston and cyl and not the seals and gaskets and hoses? I think it is a crank seal leaking!
The seals aren’t that old, maybe a 6 months. Doesn’t mean they are any good. There’s a whistling noise but it’s more around the impulse line and it changes when I mess with the line. I took it off and checked it...it’s fine. It may have a wallowed out end or something.
 
The seals aren’t that old, maybe a 6 months. Doesn’t mean they are any good. There’s a whistling noise but it’s more around the impulse line and it changes when I mess with the line. I took it off and checked it...it’s fine. It may have a wallowed out end or something.
Well just keep fiddling with it till you find it test it 3 or 4 more times move things grease things etc. If you hear it your close.
 
i just replaced the p&c on an 028 super did the vac test, passed at 10 psi great. Went to do the vac test, and not so much. I dunked the saw in water earlier and no pressure leaks.

Confusing post at best, but the saw needs new crank seals as they’re acting like check valves.

The only concern you need to have is where to source two seals, lol.

10 psi is a lot to expect from a standard oil seal, positive or negative pressure. Standard rating is half an atmospheric bar, about 7.35 psig.

You would be better off to test at 7 psi pressure max, & then 14” Hg vacuum on your MityVac gauge. It should hold both ways, all day long.
 
I think you guys are right it seems odd, since I put the seals in just a couple of months ago, and they don’t look visually tore up like the bearings are bad. I put a new impulse line in and SOS. Maybe they weren’t installed correctly or maybe not good quality? I think they are hutzl/farmer tech. Anyone have trouble with these?
 
I think you guys are right it seems odd, since I put the seals in just a couple of months ago, and they don’t look visually tore up like the bearings are bad. I put a new impulse line in and SOS. Maybe they weren’t installed correctly or maybe not good quality? I think they are hutzl/farmer tech. Anyone have trouble with these?
Put a huge gob of grease all over the seal very heavy and retest!
 
As long as it covers the inner and outer sealing area heavy they it. I bet it is a bad seal. Why FT?
Because I’m cheap. From what you guys are saying though that’s pretty much the “only” thing that would cause a vac leak and not a pressure leak, so I think I’ll try to work on that one “only” thing. I may spring for some big bucks and go with OEM on these....not sure yet.
 
OEM rubber is no too high with the exception of the intake , DO NOT USE AFTERMARKET FUEL LINES OR IMPULSE LINES , they are a time bomb at best
Seals are most likely the problem they are sealing with pressure and leaking under vacuum JMO
David
 
Because I’m cheap. From what you guys are saying though that’s pretty much the “only” thing that would cause a vac leak and not a pressure leak, so I think I’ll try to work on that one “only” thing. I may spring for some big bucks and go with OEM on these....not sure yet.
Why dont you do what I suggested first?
 
Why do the seals and not the crank bearings? Might as well spend $100 and do the motor right. I say this because if I don’t do it right I get to do it twice.

On the two stroke dirtbikes we would spray ether around the cylinder and carb manifold looking for an air leak on the bike running.
 
Why do the seals and not the crank bearings? Might as well spend $100 and do the motor right. I say this because if I don’t do it right I get to do it twice.

On the two stroke dirtbikes we would spray ether around the cylinder and carb manifold looking for an air leak on the bike running.
It doesn’t seem to have any play in the crank and I don’t feel like splitting a case, that seems like a little overkill. Will check again for play when the seals come off.
 
The 028`s are old but I have yet to replace a set of bearings in one unless changing out a damaged crank, even the seals seemed to hold up better in the 028 than the newer 026 that does often need seals but the bearings in general have not been an issue. Every saw will could be different though depending on how it was run over its lifetime, ruined air filters with missing flocking is the biggest killer of 028`s that I have seen over the years.
 
You might try product called Snoop under pressure again but you should be able to find the leak. The grease on seals is good idea the impulse line can be removed and tested but it could also be the carburetor rubber boot.
 
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