Crank Seal Issues

[redunshee]

I seem to be having more problems then I should when replacing seals on my Poulan 3400, 3700 and 4000 saws. Fairly often I replace a leaking seal only to have it continue to leak when I do a pressure test! I've even gone to the extent of spreading a little Dirko HT around seal but still a small leak( about 1 lb per minute). After my 3rd leaking seal on the same saw I decided to do a vacuum test which held much better( hardly moves after a minute or so). Now I know in a perfect world one would like zero leakage but how much or little will not cause running problems. Some manuals say no more than 2 lbs in 30 secs. but that seems excessive. Also seeing as how the cylinder creates a vacuum shouldn't my vacuum test ease my concerns a little when compared to the pressure test?

 

[wigglesworth]

What source are your seals coming from? I would like to have a set just in case if you know what I mean.

 

[wigglesworth]

Also are you running it any before testing it again? I know at work, sometimes once a machine gets hot after replacing seals, they seal up good. I have never tested a saw, so I dont know if that could be an issue.

 

[redunshee]

Also are you running it any before testing it again? I know at work, sometimes once a machine gets hot after replacing seals, they seal up good. I have never tested a saw, so I dont know if that could be an issue.

Wiggs, I'll answer both of your replys. Got seals from two sources: Calvin, also known as Lawnmowertech 37 and Mowerpartsweb.com. I believe they ran about $4-$5 apiece, so wasting 3 on one saw, is a kick in the a??. No, I didn't run saw before checking new seals. I hope it wouldn't make a difference cause then I'd have to kick myself in the a??. Bob

 

[wigglesworth]

Maybe im wrong? I hope for your sake i am LOL I will have to order a set. Are they both the same size?

 

[Erick]

I seem to be having more problems then I should when replacing seals on my Poulan 3400, 3700 and 4000 saws. Fairly often I replace a leaking seal only to have it continue to leak when I do a pressure test! I've even gone to the extent of spreading a little Dirko HT around seal but still a small leak( about 1 lb per minute). After my 3rd leaking seal on the same saw I decided to do a vacuum test which held much better( hardly moves after a minute or so). Now I know in a perfect world one would like zero leakage but how much or little will not cause running problems. Some manuals say no more than 2 lbs in 30 secs. but that seems excessive. Also seeing as how the cylinder creates a vacuum shouldn't my vacuum test ease my concerns a little when compared to the pressure test?

Consider that saw good and run it.... a lot of folks would love to have one that tight.

 

[pioneerguy600]

Consider that saw good and run it.... a lot of folks would love to have one that tight.

Yep you are more than good to go.
Pioneerguy600

 

[FATGUY]

I get inconsistent results. At one time, with vacuum. It dropped from 15" to 5" in 2 days (that's right, days) Other times it will take an hour or so to do the same thing. I really don't want to split the case again. (If I do, I'm interested in buying a new crank from someone) I really don't know what to do. I took the electronics and carb off, placed it under 8 psi pressure in a fish tank to see where the leak may be. Small leak from inside the oil tank portion. Pulled the saw out, drained the water. Did a vacuum test and it held with no drop for hours......Wonder if it's a gasket?

 

[redunshee]

I get inconsistent results. At one time, with vacuum. It dropped from 15" to 5" in 2 days (that's right, days) Other times it will take an hour or so to do the same thing. I really don't want to split the case again. (If I do, I'm interested in buying a new crank from someone) I really don't know what to do. I took the electronics and carb off, placed it under 8 psi pressure in a fish tank to see where the leak may be. Small leak from inside the oil tank portion. Pulled the saw out, drained the water. Did a vacuum test and it held with no drop for hours......Wonder if it's a gasket?

Maybe leak is coming from oil pump gasket that goes between pump and case. Is air coming out thru oil pump cover? If tank itself were leaking I'd think you would have a case leak due to a bad spotwhen you reassembled case halves. I may have a gasket if you need one.

 

[redunshee]

Maybe im wrong? I hope for your sake i am LOL I will have to order a set. Are they both the same size?

Yes they are the same size. I'm going to see if I can get some Monday from a local bearing dealer where I picked up my crank bearings. I'll bring a bad seal(heaven knows I've got many) and see if he can match it. I'm finding that they are harder to find.

 

[FATGUY]

Maybe leak is coming from oil pump gasket that goes between pump and case. Is air coming out thru oil pump cover? If tank itself were leaking I'd think you would have a case leak due to a bad spotwhen you reassembled case halves. I may have a gasket if you need one.

I doubled up on the pump gasket. (I made a gasket, and used the oem one). I'm thinking there's a miniscule leak either around the crankcase itself, or either the cylinder or intake manifold/cylinder gasket. Either way, a 10
" drop in vacuum over 2 days says I'm being rediculous. It's a saw, not Fort Knox. Did I mention the saw cuts like a super-beaver on steroids. Good luck in trying to stall the chain.

 

[wigglesworth]

super-beaver on steroids

Is that anything like a mighty muskrat on crack?

 

[redunshee]

I'm beginning to think that these older saws have too much wear to be air tight!

 

[litefoot]

Consider that saw good and run it.... a lot of folks would love to have one that tight.

Yep you are more than good to go.
Pioneerguy600

Redunshee,
Just to back up what these guys are saying, the Stihl 440 service manual says that if, after pressuring the crankcase to 8.7 lb, the pressure remains stable for 20 seconds, then the saw is acceptable. I know yours isn't a 440, but your test results appear to be good.

 

[Modifiedmark]

Yep like they said that saw is more then good and better then alot of them.

 

[redunshee]

Thanks to all who will let me sleep better tonight.

Bob

 

[propliner]

Try soaking those seals in transmission fluid first.

 

[redunshee]

Try soaking those seals in transmission fluid first.

Great idea. Will keep in mind for future installations. Thanks.

 

[AOD]

you need to pull a 28" Hg vaccum on your saw to make sure the seals are good, then you need to get a 2-stage vac pump and pull it down to 200 microns and have it hold overnight. Then, and only then will you know for sure that your crank seals are not leaking.