Help with charge pressure seepage around base gasket 357xp/359 hybrid

[quattro.pilot]

I'd like to ask for suggestions and technical diagnosis as to this problem I'm experiencing....which I don't believe should be happening.

I've put a 47mm Hyway "357xp" big bore cylinder on the 357 case and consistently now I'm finding that the base gasket doesn't appear to be sealing uniformly somehow. Charge pressure is being able to escape the crank case and get under & around the base gasket along 2 sides of the cylinder.

Can anyone suggest how things are leaking or how the charge pressure is getting under the gasket? Is it a case that I'm running just too pig rich?

Both the machined mating surfaces of the case and cylinder are perfectly true & flat.

Is using a Hyway base gasket part of the problem?

I'm wondering if the excessive width/size of the impulse channel (of the Hyway 47mm cylinder) as compared to the gasket is somehow contributing to this problem? That's one of the few notable differences I can see between the OE 357xp cylinder and the Hyway 47mm version.

This problem has me stymied thanks in advance to anyone able to help.

 

[Canadian farm boy]

Is the cylinder extension bottoming out in the cases?

 

[quattro.pilot]

Is the cylinder extension bottoming out in the cases?

I guess I don't actually know for certain.... it doesn't seem like it fits poorly on the case or isn't bottoming out...but maybe the clearances are soooooo close that it would take precise measurement to determine if the skirt is too tall.

 

[beaglebriar]

Hyway cylinder isn't flat would be my guess. Can you put it on a lathe and check the runout?

 

[quattro.pilot]

Hyway cylinder isn't flat would be my guess. Can you put it on a lathe and check the runout?

No I can't do any lathe work. It's flat though I've checked it with a razor blade there is no cupping, warping, or other deformation to the "trueness" of the bottom face of the cylinder.

 

[huskihl]

Was the wet spot there and getting worse while it was running? It wouldn’t be the beyond the scope of imagination that if you had it running really rich and then pulled the cylinder that the oil could have pooled there once you removed the jug

 

[beaglebriar]

Clean it all up good with brake cleaner, use a fresh gasket and use a thin layer of sealant like threebond,yamabond, dirko etc. on both sides of the gasket. That should stick it there like shít to a blanket.

Do you have any way to pressure test the saw? I have a mighty vac but prefer to use a small regulator set to 4-5 psi for problems like this. I'd air it up and squirt some soap around the base or dunk it in a pail of water and look for bubbles.

 

[quattro.pilot]

Was the wet spot there and getting worse while it was running? It wouldn’t be the beyond the scope of imagination that if you had it running really rich and then pulled the cylinder that the oil could have pooled there once you removed the jug

Near as I can tell it'll blow under the gasket there with very little run-time.... like less than 10min sorta thing mostly idling with a handful of revving. I had pulled the jug off a week ago to redo the metal intake clamp which is when I found what I have posted about. I cleaned it up, did my intake clamp project, and then used some tacky aviation gasket maker when I reinstalled the cylinder & gasket (in an attempt to seal it better and fix the problem which I've brought to you guys ha! ) . And that's where my 10min'ish of running comes in.

Out of pure curiosity I started tearing down the top end a couple days ago only to find the blow-by exactly as I had the week prior. Just given how extensive the penetration of the fuel mix is under the gasket and heavily around 2 sides of the cylinder I can't quite grasp that all of that fluid got in place & pooled during and after cylinder removal. To me it seems almost like it's being forced in past the gasket....some how it's escaping and it seems like it's blowing out in the vicinity of the transfer.

 

[quattro.pilot]

Clean it all up good with brake cleaner, use a fresh gasket and use a thin layer of sealant like threebond,yamabond, dirko etc. on both sides of the gasket. That should stick it there like shít to a blanket.

Yeah...I know you're right and that things could essentially be "glued" together... and it may come to that. But it doesn't really fix the problem at its core, and sometimes bandaiding one issue can instigate more problems in other places. All things being equal, even with this 47mm AM cylinder, if it is a good copy of the original I should be able to just use the base gasket, use the original cylinder head bolts, clamp it down and there's no funny business... lots of others have put the Hyway part straight onto their saw and not claimed to experience what I'm seeing. So to me it indicates a manufacturing defect in some way....

Do you have any way to pressure test the saw? I have a mighty vac but prefer to use a small regulator set to 4-5 psi for problems like this. I'd air it up and squirt some soap around the base or dunk it in a pail of water and look for bubbles.

Ya I am able to do all the pressure & vac testing... and funny you should mention that I had tested it a couple weeks ago and there was zero indication of any leaks. It held 0.8kpa (Husqvarna spec) all day long with no leakdown, as well as 15"hg without spilling. Compression too prior to that was over 170psi. So having observed those results I didn't pursue the soapy water method of chasing leaks. Absolutely you'd think if it were leaking crankcase pressure badly enough to push that much fuel mix under and through the gasket that there's no way it should have held pressure!

I've spent some time "decking" the height of the Hyway cylinder skirt, as it did seem a little tall as compared to the original 357xp jug. It feels like it sits better on the case now as prior I was able to rock the cylinder slightly side-to-side mostly at the exhaust end. I might use a oem base gasket when I put things back together and see where I'm at. Unfortunately I need a piston in order to replace the 46mm 357xp cylinder but we're definitely headed there as a means to which of eliminating problem parts... I would expect that it doesn't blow-by with the factory P&C and gasket! F*cking frustrating......this saw is definitely my red headed step child

 

[beaglebriar]

Yeah...I know you're right and that things could essentially be "glued" together... and it may come to that. But it doesn't really fix the problem at its core, and sometimes bandaiding one issue can instigate more problems in other places. All things being equal, even with this 47mm AM cylinder, if it is a good copy of the original I should be able to just use the base gasket, use the original cylinder head bolts, clamp it down and there's no funny business... lots of others have put the Hyway part straight onto their saw and not claimed to experience what I'm seeing. So to me it indicates a manufacturing defect in some way....




Ya I am able to do all the pressure & vac testing... and funny you should mention that I had tested it a couple weeks ago and there was zero indication of any leaks. It held 0.8kpa (Husqvarna spec) all day long with no leakdown, as well as 15"hg without spilling. Compression too prior to that was over 170psi. So having observed those results I didn't pursue the soapy water method of chasing leaks. Absolutely you'd think if it were leaking crankcase pressure badly enough to push that much fuel mix under and through the gasket that there's no way it should have held pressure!

I've spent some time "decking" the height of the Hyway cylinder skirt, as it did seem a little tall as compared to the original 357xp jug. It feels like it sits better on the case now as prior I was able to rock the cylinder slightly side-to-side mostly at the exhaust end. I might use a oem base gasket when I put things back together and see where I'm at. Unfortunately I need a piston in order to replace the 46mm 357xp cylinder but we're definitely headed there as a means to which of eliminating problem parts... I would expect that it doesn't blow-by with the factory P&C and gasket! F*cking frustrating......this saw is definitely my red headed step child

So basically you've already tried gluing it down. Did the cylinder extensions leave any noticable marks on the cases before your "machine" work?

This is why I rarely piss with AM parts. After all the time you've spent there really is no savings.

 

[quattro.pilot]

So basically you've already tried gluing it down. Did the cylinder extensions leave any noticable marks on the cases before your "machine" work?

No didn't really observe any scratched paint where it may had been rubbing or contacting.

I'll fiddle with it a little more, I tinker with my saws pretty much just for fun so I can afford the jerk-around. However I have ordered a replacement 357xp piston so push comes to shove I'll just put the oem top end back on; cause by June I'd like to have a working chainsaw.