372 xpw cylinder?

[idiotwithasaw]

Ok so I bought two cylinders off eBay that were listed as off of a 2171 jonsered. I got them in tonight and I was doing some measuring and one of them stamped 50zn21 measures 49.99 mm with my cheapo hf calipers. And the other one stamped 50zk6 measures 51.44. now I know that most 372 family top ends are stamped 50zk6 and the jonsereds are stamped with a zn designation.

They both appear to be in good shape, the 50zn21 had some minor transfer that I cleaned up with the MM method.

Did I luck into a XPW top end and not even know it? Where do I even get a piston for it?

I'll post pics next.

 

[idiotwithasaw]

 

[71dart]

51.4 is correct for the 75cc xpw.

 

[Mastermind]

OEM only for that piston sir.

 

[sunfish]

Did I luck into a XPW top end and not even know it?

I don't think I'd call it luck, but that's what ya got.

 

[idiotwithasaw]

OEM only for that piston sir.

I guess that is a yes. Good thing I hadn't already gotten ahold of Dave and ordered any. Guess I just need to go ahead and box it up and send it and a saw to Tennessee. Lol

 

[idiotwithasaw]

I don't think I'd call it luck, but that's what ya got.

why would you say that, are they not any better than the 50mm top end?

 

[sunfish]

why would you say that, are they not any better than the 50mm top end?

Yes, they are no better. Notice the larger lower transfers on the 50mm and I'd rather have the single ring. The xpw piston had two rings.

 

[Flip D]

A lot of debate on the "bigger is better" cylinder on this chassis. I put a new 51.4 cylinder on my 365 special, ran about 20 tanks thru it, and put the 48mm cylinder back on. I like the broad range of power of 365 special cylinder. I was cutting hardwood with a 20" bar and have only ran them stock.

 

[idiotwithasaw]

Ok well now that I'm discouraged, they came with one piston I measuredbit and it's the one for the 51.4 cylinder. However I'm not sure if it's useable, it looks like someone took sandpaper to the exhaust side, even if lightly, and the intake has some streaks that while not deep can still barely be felt with my fingernail.

Would you all reuse it or bite the bullet and order an expensive oem piston and do a little port work on the cylinder.

 

[sunfish]

I'd run that piston. The 51.4 does run good when ported, but so does the 50mm & 48mm.

 

[idiotwithasaw]

Ok, would you at least get new rings. I was concerned because the skirt measures almost a quarter mm smaller than the cylinder, I know that it needs clearance for oil and to keep from seizing, just seems like a lot of slack. I'm not sure what the clearances should be.

 

[sunfish]

Ok, would you at least get new rings. I was concerned because the skirt measures almost a quarter mm smaller than the cylinder, I know that it needs clearance for oil and to keep from seizing, just seems like a lot of slack. I'm not sure what the clearances should be.

New rings would be a good idea. I'm not to sure about the skirt clearances, but someone here will know.

 

[Onan18]

I put a (Sawking) ported XPW top end on a 365 special and advanced the timing Six degrees and that thing was a total animal. Easily outran any 70cc class saw I have ever ran and honestly felt like it would keep up with a 288.

Joe

 

[idiotwithasaw]

That's just it, ported, I'm hoping to be able to run it stock. Maybe take off a little at the transfer inlet do a spike60 special mod to it. Hate to ruin a perfectly good jug though. Maybe I should just tinker with the 50mm.

 

[SquareFile]

I'd run that piston. The 51.4 does run good when ported, but so does the 50mm & 48mm.

Makes ya wonder how many good 48mm were thrown out for bigger is better.

 

[Onan18]

Spike60 Special mod will definitely wake her up.

Joe

 

[idiotwithasaw]

Makes ya wonder how many good 48mm were thrown out for bigger is better.

that's more or less what Bob said in the saw college video over these saws.

 

[Chainsaw Jim]

You got lucky and you shouldn't be discouraged the slightest bit. They do make more power than the regular xp.

 

[idiotwithasaw]

Now I need to rewatch it. If someone would link it here for others that would be great. I don't know how though.