Husqvarna 570 Strange air leak

[Armosh]

Rebuilding a 570 with a scored piston and cylinder on it. Got the new top end on it and now pressure and vac testing. Slowly loses pressure and will lose vacuum quickly. I assume crank seals so I pulled the flywheel, clutch and oil pump off so I could see bubbles and to my surprise now I can't build pressure at all. So out of curiosity I put the 2 oil pump bolts back in and now it'll build pressure but still loses it. Still not even one bubble from either crank seal. Then I notice some bubble coming from the oil feed line from the oil tank. Sure enough that's the leak. I didn't know that could even cause a leak. I attached a pic to show what I mean. Anyone ever seen this before? View attachment 20241002_155657.jpg

 

[Patrick62]

One time, there was an old Stihl... that had developed a problem.
It would start eventually, and run... but smoke like a locomotive. Some internal leak from the oil tank to the crankcase.
I was going to try an experiment on that saw, but condemned it instead. Wanted to drain the oil and see if the smoke went away, then fill it with premix... A pressure/vac test would have been in order like your saw.

 

[Armosh]

Just tested it again. Experimented a bit with removing the oil cap and nothing happened. That confused me so I loosened one of the oil pump bolts, sure enough leaking. Tightened both up and this time confirmed the PTO side crank seal is leaking. Not sure why I couldn't get it to bubble the first time but oh well. Now as for replacing the seal I've read conflicting things, some say you have to split the case and others say that you don't. Which is it? Anyone actually done seals on one of these saws before?

 

[altatim]

Just tested it again. Experimented a bit with removing the oil cap and nothing happened. That confused me so I loosened one of the oil pump bolts, sure enough leaking. Tightened both up and this time confirmed the PTO side crank seal is leaking. Not sure why I couldn't get it to bubble the first time but oh well. Now as for replacing the seal I've read conflicting things, some say you have to split the case and others say that you don't. Which is it? Anyone actually done seals on one of these saws before?

Ditto here, I have a 576 thats been sitting waiting for me to actually buy seals but I'm also not in a rush because I have a 572 lol.

 

[Armosh]

Ditto here, I have a 576 thats been sitting waiting for me to actually buy seals but I'm also not in a rush because I have a 572 lol.

Got the seals on order should be here in a few days but the shop manual is about as clear as mud for doing the seals lol.

 

[Armosh]

This 570 is full of surprises. Apparently the 2 bolt holes for the oil pump go all the way through into the crankcase. That is my leak. Lastnight I put the 2 bolts in without the oil pump on and pressure tested again and made the discovery that the crank wouldn't move at all. I was baffled at first until I backed out the 2 oil pump bolts out a bit and it turned again. I got to looking at some pictures of the case halves and sure enough both of those bolts go right into the crankcase. I'll be damned. This is only the second saw I've done a P&C on, the other was a clamshell. Are the oil pump bolt holes normally through holes and not blind like that?

 

[Gord404]

yes, 372 and a lot of them go right through- when testing without the oil pump on to get a clearer picture i use very short bolts with a seal on them and put a sealer on your threads whe you put the pump back in.- don't know much about that model but a 390 take a sealed bearing on the chain side- bought from the dealer