MS660 scored piston advice

[jeepinmatt]

I'll get some pics tonight or tomorrow. If I remember correctly, it's scored pretty badly.

 

[Bob Hedgecutter]

I'll get some pics tonight or tomorrow. If I remember correctly, it's scored pretty badly.

Scored pretty badly- could be the ring is lodged in the groove, but it sounds like you have a huge air leak to sort out- or your buddy was a bit lean when he tuned in the new carb he fitted.

 

[Mad Professor]

Yes, if the ring is stuck they generally don't run. If you pull the muffler and see scoring you likely have something that needs addressed. If you have very minor scoring or some carbon scoring they will run. I would guess trying to repair the cylinder by sanding. Meteor or OEM. I think an OEM kit is $300 and close to $200 to have a stihl shop put it together. You will need to find out if it has an air leak.

Don't despair until you try cleaning the cyl
The saw with this piston, the cylinder cleaned up good.

 

[Deleted member 117362]

Agree with above, figure out what caused the problem to begin with or you are just wasting time and parts. Vacuum check your case before pulling it down. Putting a new cylinder and piston on, only to find out you have a seal leak is a pisser.

 

[rogue60]

046 is in the 160psi range. Friend I got the saw from also tested the 660 at 110psi with his gauge. My background is engineering, machining, and metrology, so to see two different brands of testers within a couple psi makes me feel pretty good about it.

With this background I'm very surprised one would even consider a recycled toilet paper topend

 

[jeepinmatt]

With this background I'm very surprised one would even consider a recycled toilet paper topend

I wouldn't, but they all said "BEST" on the box That's why I'm relying on the collective wisdom here to sort through what's good and what's not, and also to help ensure that I send it off to get it ported because every saw needs to be

 

[jeepinmatt]

Here's some pics of the piston and cylinder. I noticed the cylinder does not have any Stihl markings on it. It does have 54ZN12 on it. Not sure if that's good, bad, or neutral.


I tried lightly sanding it with oiled up 500 grit, and it cleaned up 60-70% of the affected area, but not the worst spots. The part to the right of the exhaust port feels pretty gouged out.

 

[tug]

If you search youtube or on here you can find a video of a guy that works on saws goes by mastermind. He did a real good video of sanding transfer. It will help you out. You will have to use coarser paper on the heavy transfer. If you have a pick or something with a fine tip, I use a dental pick you can feel if it is gouges or if it is transfer buildup. If it is gouges in the plating the cylinder is likely not salvageable. It does look like gouges from what I see. There is also a ding in the exhaust port but you can chamfer that out. The 066, 660 saws have a lot of aftermarket cylinders available. I would go new OEM, used OEM or Meteor. And Either OEM or meteor on the piston. As a reference that is the kind of scoring that would make a saw not run. Again you will want to track down why that happened before you put any money into it.

 

[huskihl]

I agree with those who say stick with oem for cylinders. Meteor and Hiway seem ok for pistons. If yours won’t clean up, I’d hunt for a used decomp 066 cylinder and run an oem or Meteor piston.
I’d have time to do all the work on it and port it in a couple weeks. Pm me if you’re interested

 

[jeepinmatt]

Another wrinkle, decided to measure the piston/cylinder. Already 56mm, so it has a big bore kit in there. But the cylinder has a 54 in the number, which I would think would indicate 54mm diameter. Who knows? I think the smart solution is to rejug it. This good deal is gonna get real expensive, haha.

 

[huskihl]

The 54zn12 number sounds like oem Mahle jargon. But not in 56mm.

 

[tug]

Another wrinkle, decided to measure the piston/cylinder. Already 56mm, so it has a big bore kit in there. But the cylinder has a 54 in the number, which I would think would indicate 54mm diameter. Who knows? I think the smart solution is to rejug it. This good deal is gonna get real expensive, haha.

The 54 usually indicate the size as you have described and you usually see them on OEM cylinders. It is the cylinders with no markings that you want to watch out for. I have an 066 and a 660, both stock. So I can not speak to porting. From what I have read the oversize cylinder or big bore kit is not the way to go on these saws. New 660 are like $1200. Not sure what you have into this one but you can probably sell it for $300 or better in the condition it is currently in and about as fast as you can post it. These saws are in high demand for guys who monkey with saws.

 

[Mad Professor]

The gouge on right side of ex port looks pretty bad, unless that is just transfer.

If it is a AM cylinder (56mm) I'd be looking for a good used OEM or bite the bullet and get new.

Would have been good if the saw had a bath and pres/vac test before you took the cylinder off. Also pulled the flywheel and clutch. Don't forget clutch is left hand thread.

 

[Bob Hedgecutter]

Looking at the photos and condition of the piston, I would say you were lucky to get a compression test reading over 100psi!

 

[jp233]

I agree.... getting that much compression is actually a good sign. You can try sanding, and/or use acid very gently if you need to get some aluminum off the plating. Are the rings locked up in the groove? (I assume so, at least for the top ring. Bottom ring looks like it has some play in it).

You might be able to get away with a piston. But at least you know what you have, there. Crank seals might be suspect though. Might be time to just send it off if a porter can look at the pics and say "yeah, I can fix that and give you back a beast of a saw"