holds pressure but not vacuum

[dall]

hello question here working on a buddys saw and he says wont idle. its a husky 575 i did a pressure test and vacuum test passed the pressure but not vacuum . i have a mighty mite 8500 . it loses 2 pounds a second . any ideas and suggestions

 

[huskihl]

Decomp

 

[tree monkey]

crank seal

 

[dall]

i sprayed wd40 on both sides but couldnt really tell if it was being sucked in

 

[CR888]

I'm with T/monkey crank seal. You rotate crank when testing?

 

[Adirondackstihl]

Weren't they known for cylinder gasket issues?

 

[DELETED (Struggle)]

crank seal

Did you get me a set of cranks seals attached to a 461 yet?

 

[TJ the Chainsaw Mechanic]

I go with Decomp as well, And the crank seals. Pressure test it and turn the crank, and that might do the trick.

 

[dall]

i turned the crank yes

 

[DELETED (Struggle)]

how much pressure are you applying?

 

[dall]

10

 

[DELETED (Struggle)]

That should be plenty to make it leak. Like Scott said cranks seals most likely. If it were a base gasket or likes of it would leak more likely ether way. Have you ruled out decomp?

 

[Canadian farm boy]

How are the crank bearings? Any play in them?

 

[old guy]

I put lite oil on the bearing seal, it's easy to see it get sucked in, actually a few drops of colored mix oil works good.

John

 

[huskihl]

I use a heavy oil on vacuum leaks. Tip the saw on its side and dump some on the seal. When the gauge stops going down, you found it

 

[Gunn]

I had the opposite with a cutters edge 670. It would hold vac but not pressure. The clutch side crank seal was leaking.

 

[dall]

decomp seems fine but didnt check it. piston and cylinder look new .ill try a colored oil tomorrow bearings feel nice smooth and tight .

 

[heimannm]

You will need to remove the compression release and install a bolt with am o-ring, or try pulling the compression release out and holding it while testing. I always remove the compression release and block it off whether pressure or vacuum testing since they are frequently the source of a leak.

Mark