Stihl 660 piston skirt re: “I made a mistake”

[NPKenny]

First time for everything….

Saw is a bubble top Stihl MS660 with a meteor piston.

I’m a conservative porter and have never missed on a port. Figured I would rough in the exhaust after getting the transfers where I wanted them. I got everything cleaned back up, dropped the cylinder to find that I had overground the width by a lot on my exhaust port and exposed past the skirt. It’s a scalloped skirt piston and I was careless.

1. What is the risk of running like this? Lots of discussion on freeporting the bottom? But not on the skirts.

2. Rotating the piston does not cover the port.

3. There aren’t obvious piston choices to correct this. Husqvarna 288 and 385 are discussed, but require a bit of work to match the 12mm con rod and 13mm piston.

Any recommendations?

 

[Funky sawman]

Dang, that's one big exhaust port!

 

[Canadian farm boy]

First time for everything….

Saw is a bubble top Stihl MS660 with a meteor piston.

I’m a conservative porter and have never missed on a port. Figured I would rough in the exhaust after getting the transfers where I wanted them. I got everything cleaned back up, dropped the cylinder to find that I had overground the width by a lot on my exhaust port and exposed past the skirt. It’s a scalloped skirt piston and I was careless.

1. What is the risk of running like this? Lots of discussion on freeporting the bottom? But not on the skirts.

2. Rotating the piston does not cover the port.

3. There aren’t obvious piston choices to correct this. Husqvarna 288 and 385 are discussed, but require a bit of work to match the 12mm con rod and 13mm piston.

Any recommendations?

View attachment 359765


View attachment 359764

Wiseco piston from CCC specialties.

 

[Stevetheboatguy]

Hate to say it...... But looks like a ring hanger to me. Might be wrong but @Funky sawman is probably correct. One wide port.



Steven

 

[Nutball]

As far as I know, matching the pin size isn't hard, you just use a different bearing with it as the rod hole is the same size, but the Husqy bearing is thinner to fit the bigger pin. I think the issue is machine work on the piston and cylinder for the right squish and timing.

 

[NPKenny]

I can’t believe I did this. I already cut the base and band, lots of shaping in the upper transfers, epoxy in the intake, clearancing the outside of the cylinder, etc.

Found a 288 piston. It is 3mm wider across the skirt. Barely covers the port, not enough to be an ideal option.

This was shaping up REALLY nicely. Oh well. Off to find another cylinder.

 

[NPKenny]

Wiseco from CCC are all sold out and frankly, this port is way to wide to support the rings, as stated above.

 

[Stihlalltheway]

If it’s gonna blow up anyways, might as well try it with a cheap 288 piston. Have fun for a little while instead of just tossing it

 

[Dolkitafreak]

Run it, the internet says free port is so terribly bad…run it and see. You’d be shocked.

 

[Stevetheboatguy]

Wiseco from CCC are all sold out and frankly, this port is way to wide to support the rings, as stated above.

Now I'm not 100% certain that it will be a ring hanger. But would be a good idea to check the exhaust port to bore size and see what the calculator says. You kept it with generous corners and a roof arch. So it may not be a total loss. Just a good thing to be certain about before starting up. Sending a chunk of piston skirt through the case would be a major bummer.

Just looking out for you is all.


Edit. Looking back at the pics. Is the gap on both sides? Or did you accidentally shift the exh port to the coil side a bit when grinding?

Steven

 

[Nutball]

Run it, the internet says free port is so terribly bad…run it and see. You’d be shocked.

Free porting under the piston is one thing, but beside is a whole different thing. Still, at high rpm, it probably won't have much negative effect. Kind of a waste of a port job if too much power is lost though.

Can more be welded onto the side of a piston, then turned back down to perfectly round?

 

[NPKenny]

Edit. Looking back at the pics. Is the gap on both sides? Or did you accidentally shift the exh port to the coil side a bit when grinding?

Steven

It is open on the flywheel side, and just about parallel on the clutch side.

Accidentally is a reasonable word to describe this port.

 

[NPKenny]

Looks like a newer 288xp piston may indeed have wide enough skirts to make this work. I measured the older style which has the scalloped skirts.

https://opeforum.com/threads/husky-288xp-piston.6537/

From @Frogfarmer

 

[NPKenny]

The current Meteor 660 piston vs KS piston from an 288xp.



If the updated 288xp piston is anywhere close on crown height, I think I am back in business.

I will likely need to cut the base a bit more, but I have plenty of room there.

 

[cus_deluxe]

i did the same thing to a 660 and it was a complete turd. no matter what “the internet” says, youre definitely making the right move getting a piston that works better.

 

[drf256]

I realize you’re only roughed in, but that exhaust roof is way too flat IMHO. Especially at that width.

The 066/660 have notoriously narrow exhaust skirt, like most other non-strato Stihls. I had a Wiseco CCC here for the 066 and was disappointed to find out the skirts were exactly the same width as the Stock OEM slug. Dave told me that they had to keep them narrow because of the lower transfers. Maybe @srcarr52 can shed some more light on that, Dave told me he helped in the design. Dave also told me that they were coming out with a wider one, they just weren’t sure when.

I never did the 288 thing, but if you do I still think you need to raise the center of your roof. Hopefully the piston will allow it. I’m told you have to drop the jug quite a bit for the 288 to work, so you’ll probably gain the space you need. If it’s a 13mm pin, I know a 395 pin bearing will allow it to fit. I’ve done a 395 piston in a 56mm big bore jug.

I believe part of the reason the 1122 like a physically high Ex roof is because they lack port area width.

 

[srcarr52]

I realize you’re only roughed in, but that exhaust roof is way too flat IMHO. Especially at that width.

The 066/660 have notoriously narrow exhaust skirt, like most other non-strato Stihls. I had a Wiseco CCC here for the 066 and was disappointed to find out the skirts were exactly the same width as the Stock OEM slug. Dave told me that they had to keep them narrow because of the lower transfers. Maybe @srcarr52 can shed some more light on that, Dave told me he helped in the design. Dave also told me that they were coming out with a wider one, they just weren’t sure when.

I never did the 288 thing, but if you do I still think you need to raise the center of your roof. Hopefully the piston will allow it. I’m told you have to drop the jug quite a bit for the 288 to work, so you’ll probably gain the space you need. If it’s a 13mm pin, I know a 395 pin bearing will allow it to fit. I’ve done a 395 piston in a 56mm big bore jug.

I believe part of the reason the 1122 like a physically high Ex roof is because they lack port area width.

I didn’t help with the 660 piston but maybe if they made it any wider it started to cover over some of the stock lower transfers?

 

[Dolkitafreak]

Free porting under the piston is one thing, but beside is a whole different thing. Still, at high rpm, it probably won't have much negative effect. Kind of a waste of a port job if too much power is lost though.

Can more be welded onto the side of a piston, then turned back down to perfectly round?

I would bet it doesn’t lose much power if any, also, skirts are tapered not round so that adds a challenge.

 

[drf256]

I didn’t help with the 660 piston but maybe if they made it any wider it started to cover over some of the stock lower transfers?

I believe that’s what the issue was.

 

[Nutball]

I realize you’re only roughed in, but that exhaust roof is way too flat IMHO. Especially at that width.

I still think you need to raise the center of your roof.

Or a cheater bevel in just the plating, arching the plating rather than the whole port, so that the height isn't affected any noticeable amount.