Cross Performance 660 top end failure

[Gunn]

What are advantages / disadvantages to having a harder of softer ring? Harder would last longer but more prone to hanging?

Soft rings wear quicker. That means they seat and wear in faster. They also wear out quicker. They supposedly don't wear out the bore plating as quickly.

Fcast- rings last longer but possibly harder on the bore plating.

 

[Keith Gandy]

The chamfer or bevel at the port only matters on the plating. Fine sandpaper by hand works well. Grinding shouldn't be necessary and will run the risk of chipping off chunks of plating.

Jim would it be possible to see a close up of the way u like the edges? Thankz

 

[Chainsaw Jim]

Jim would it be possible to see a close up of the way u like the edges? Thankz

 

[Keith Gandy]

View attachment 79776

Looks great. What grit do u use on them and what do u hone the cylinder with? Thanks

 

[Chainsaw Jim]

Looks great. What grit do u use on them and what do u hone the cylinder with? Thanks

Fresh 220 grit.

 

[Mattyo]

Jeez Jim that's Purdy. Not much bevel though. ...those run ok for ya ? I'm always worried about not having enough bevel

 

[Rob Stafari]

Jeez Jim that's Purdy. Not much bevel though. ...those run ok for ya ? I'm always worried about not having enough bevel

Have you ever seen the inside of a dokita cylinder? First time I looked at the 7910 cylinder I got from @fordf150 I thought I might have been sent a defective cylinder. The ports are barely beveled and I was so used to seeing pictures of port work and old oem Stihl cylinders bevels I thought it might have been a reject that got passed through somehow. He got out some others for me to show me I just had to look closer. A lot like what Jim just posted, hard to see. They seem to run good with few failure from it though.

 

[Adirondackstihl]

This is a stock 45mm Husqvarna 350 cylinder.

 

[Chainsaw Jim]

Jeez Jim that's Purdy. Not much bevel though. ...those run ok for ya ? I'm always worried about not having enough bevel

Don't forget the rings never touch the aluminum part of the bevel. On the exhaust pictured you should be able to zoom in close enough to see the bevel is there and it's approximately .015". The polished edge gives an illusion that the plating ends abruptly but it actually doesn't. The plating is beveled smooth so there's no defined edge to stand out.
The orange line is the edge of the plating...

 

[T.Roller]

View attachment 79776

That is beautiful work!

 

[Chainsaw Jim]

That is beautiful work!

Thanks man. That's @Heffalump's wife's 034s.

 

[Mattyo]

Very. Very nice

 

[MustangMike]

I'm running two Cross MMWS 660 cylinders w/o any issues so far. I did bevel the ports thoroughly with 220 grit paper. On the second cylinder, the bevels looked good, but when I ran my finger on the bottom of the exhaust port, I did not like the way it felt (can't see that bevel).

IMO, checking the bevels is part of what you have to do with the lower cost Chinese cylinders, but both mine run fairly strong.

That is great of Bruce to be sending you a replacement. Good luck with it.

 

[MustangMike]

Although the bevel on the top of the Exhaust port looked OK, I beveled the crap out of it because the exhaust roof was very flat. I tried to give the bevel a bit of an arch.

 

[Brewz]

@Gentleman
If you haven't sent it yet, I don't expect a replacement mate.
That wasn't my intention at all and I appreciate your generosity!

Also, @Mastermind, I in no way wanted to give you or your work to develop this product a bad name.
The timing and port shapes are great and you have no control over the final finish in every unit.
I have ported cylinders with flatter edges that this has with no issues.
I just found a photo I took of the exhaust port and believe I can see the issue on the exhaust floor.
I never noticed the burs until now.
I have circled the spot where it hung.



Check out this Hyway 660 cylinder exhaust roof if you want to see flat!
I have used a couple like these with no issue.
Shame about the 30* of blowdown



I did some measuring and checking of the cross performance piston and cylinder this arvo and it all measures perfect.
A new caber ring in the bore runs all the way down with even ring gap and is just off touching all the way. Perfect!
The piston measures fine and is round.
Ring gaps were fine .
I think it caught on the bur on the exhaust floor.

What I hope to come from this thread is for us all to pay more attention to stuff like this on aftermarket cylinders, I know I will be in future.

 

[Chainsaw Jim]

I was going to ask about that spot on the exhaust floor. It appeared to be raised there but since you didn't mention it I figured it might be from the impact of the grenade.

 

[CR888]

Its a tough gig with AM kits.....we all love the savings and potential to revive saws that may not be financially sensible to use OEM. I hope we can work out how to minimise failures with these kits from both ends...at the factory and the bench. On the subject of chamfers, Chainsaw-Jim has the right idea. Many go way overboard chamfering ports in the wrong areas and just taking too much off. Ones index finger and some fine sandpaper in the ports vulnerable area is all that's needed. I hope Brews sorts out his saw, it sucks when something like that happens. I just hope Gentleman & Randy don't get deterred from doing more projects like the Cross kits. Its a real first where that relationship is bridged between tuner and factory to make these bolt on performance parts for us to enjoy. I hope they do more of it and hope it succeeds.

 

[fordf150]

Jeez Jim that's Purdy. Not much bevel though. ...those run ok for ya ? I'm always worried about not having enough bevel

if the ports arent overly large it doesnt take much of a bevel. some of the Dolkita cylinders take a very discerning eye to even see the bevel and I've seen some husky cylinders the same way....like chainsaw jim's picture. Some people just go overboard with it...ya know, if a little is good, allot is more better

 

[MustangMike]

Its a tough gig with AM kits.....we all love the savings and potential to revive saws that may not be financially sensible to use OEM. I hope we can work out how to minimise failures with these kits from both ends...at the factory and the bench. On the subject of chamfers, Chainsaw-Jim has the right idea. Many go way overboard chamfering ports in the wrong areas and just taking too much off. Ones index finger and some fine sandpaper in the ports vulnerable area is all that's needed. I hope Brews sorts out his saw, it sucks when something like that happens. I just hope Gentleman & Randy don't get deterred from doing more projects like the Cross kits. Its a real first where that relationship is bridged between tuner and factory to make these bolt on performance parts for us to enjoy. I hope they do more of it and hope it succeeds.

Boy do I agree with this post.

Would love to see a hybrid P&C for the 440 kits next.

Tony, was your cylinder ruined, or just your piston?

 

[MustangMike]

I thought the roof on my second Cross cylinder was very flat also: