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

quattro.pilot

quattro.pilot

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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 :mad: thanks in advance to anyone able to help.

20210403_123558.jpg 20210403_125627.jpg 20210403_131442.jpg 20210403_131636.jpg
 
grizz55chev

grizz55chev

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I agree with John... I'd fit it up without a gasket, check & remedy any interference, measure squish & then reassemble with an appropriate thickness gasket &/or sealant
Check the length of the cylinder bolts against the depth of the holes in the case, leave a little wiggle room so you know they're not bottoming out.
 
quattro.pilot

quattro.pilot

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Check the length of the cylinder bolts against the depth of the holes in the case, leave a little wiggle room so you know they're not bottoming out.

Plenty of room there... the bolts will thread down until almost the head touches the case deck.

I've spent some time decking the cylinder skirt as it did seem a little tall compared to the oem 357xp cylinder, and I was also able to rock the cylinder slightly from side-to-side most predominantly at the exhaust end.... after shaving down the skirt a bit it doesn't seem to rock any more. I'll continue to play with things and give it more thought, and I'll work my way towards a pressure-vacuum test pretty soon. It's just strange to me that others have stated they bought the exact same 47mm overbore cylinder, slapped it on, and didn't have nary a issue.. since I appear to be doing everything by the book I'm leaning towards a manufacturing defect of some sort. Isn't that how it works haha, a bad mechanic always blames his tools haha :nofunny:
 

dap

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Aftermarket parts almost always need mods or refinishing to fit and/or function as well as original parts. Take it as punishment for lack of precision which explains the lower cost.
 
quattro.pilot

quattro.pilot

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One thing Im wondering is why you needed to change the top end from a OEM to a hyway big bore?

Haha I dunno that's a good question maybe cause I'm foolish :rare2: . Had the bright idea that maybe the slight extra CC's might give me a bit more oomph, and online opinion indicated the saw responded well to the overbore cylinder. I was having to replace the original piston and ring anyways due to wear & low compression. So I thought I'd give it a whirl.

Perhaps its modding & changing sh*t just for the sake of modding & changing? I dunno, I definitely like modding stuff :cool:... but I'm starting to reconsider the Hyway cylinder and just go back to straight 357xp........I don't think that'd be a bad plan......
 
Bob Hedgecutter

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Perhaps its modding & changing sh*t just for the sake of modding & changing? I dunno, I definitely like modding stuff :cool:... but I'm starting to reconsider the Hyway cylinder and just go back to straight 357xp........I don't think that'd be a bad plan......

Possibly the most sensible sentence in the entire thread!
 
quattro.pilot

quattro.pilot

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Notice any difference in this area between the original cylinder on the right as viewed and the less refined cheaper version on the left as viewed?

Yeah of course Bob! I mused about this difference in my original post and some part of me can imagine crank case pressure coming back up that wider impulse channel and getting under the gasket. I just wasn't sure if it was a viable theory. But it is definitely a glaring difference, and not one I'm too thrilled by because that would represent a proper manufacturing error.
 
Bob Hedgecutter

Bob Hedgecutter

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Yeah of course Bob! I mused about this difference in my original post and some part of me can imagine crank case pressure coming back up that wider impulse channel and getting under the gasket. I just wasn't sure if it was a viable theory. But it is definitely a glaring difference, and not one I'm too thrilled by because that would represent a proper manufacturing error.

No, nothing to do with the impulse channel- look again, or run your thumb nail down the outsides of the skirt.
 
quattro.pilot

quattro.pilot

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No, nothing to do with the impulse channel- look again, or run your thumb nail down the outsides of the skirt.

I noticed the original cylinder has a "step" along the horizontal line of the skirt about halfway down. Figured that might be another oopsies as far as the copy is concerned, just didn't think all the way through as to the purpose and/or engineering consequence.

I suppose it could be some sort of additional sealing type measure that Husqvarna devised? Wherein a straight-walled skirt somehow crankcase volume/pressure more forcibly gets behind it? I dunno....still baffling because it's documented that others have taken this hyway cylinder right out of the box and strapped it to a 357xp and nobody seems to complain/document problems :omg:
 
pioneerguy600

pioneerguy600

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Look a little closer at the bottom of the intake port on the AM cylinder, does it stick out further downward than the OEM? If so it might bottom out and could prevent the cylinder from lowering all the way down to sealing tight. Many inconsistiency`s in these AM parts.
 
quattro.pilot

quattro.pilot

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Look a little closer at the bottom of the intake port on the AM cylinder, does it stick out further downward than the OEM? If so it might bottom out and could prevent the cylinder from lowering all the way down to sealing tight. Many inconsistiency`s in these AM parts.

Ohhhh, I see it now... tricky tricky.. wow. I'm usually pretty observant but that one aspect did get by me
 
quattro.pilot

quattro.pilot

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Look a little closer at the bottom of the intake port on the AM cylinder, does it stick out further downward than the OEM? If so it might bottom out and could prevent the cylinder from lowering all the way down to sealing tight. Many inconsistiency`s in these AM parts.

Ohhhh, I see it now... tricky tricky.. wow. I'm usually pretty observant but that one aspect did get by me

Think that turned out to be a optical photographic illusion. The Hyway cylinder is machined the same as OE as far as the bottom area of the intake flange is concerned

20210404_155352.jpg
 
smokey7

smokey7

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Tighten the jug down on a piece of gasket in a area you knew leaked. Then try and pull the gasket out. If you pulled it out easy. Heck gap with feelers and find what's hitting what.
 
John Stryker

John Stryker

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On a 357xp I just replaced bearings on yesterday, I noticed while reassembling it that even the OEM cylinder was quite a snug fit into the case. The case has a tapered recess, which is most likely why the OEM cylinder flange has that stepped outer diameter on the skirt. If you're still trying to figure this out, check the outside diameter versus the taper in the case, and also the depth.
 
Steve Hatfield

Steve Hatfield

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I put the same cylinder on my 359 case and runs well. No problems with installation, simple bolt on . With a thinner base gasket and 2-3 tanks running time I’m getting 170 -175lbs compression. Piston looks fine as well.
Maybe over time it will reveal its low cost but for now it’s good.
 
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