[660] Piston badly chipped, need advice on replacement-piston

[Cerberus]

TL;DR-- What type of piston do I need to get for a kit-660, whose original piston was a flat-topped, 53.75mm 2-ring? Squish was ~0.024" I think.... Also, do I need to order specialty tools? I'm not naive to engines I ported my 590 last month and do my own work, just have never worked with a piston or bottom-end, thankfully everything else looks OK except the squish-band but I expect that'll be a simple fix w/ drill or dremel!

^think that can be buffed-out?
LOL seriously though I wanna ensure I'm not only getting the right 'size&type' piston, but don't wanna get a cheap one and need to do it again shortly... Re piston size / squish, I'm quite sure this saw's cylinder is machined, the piston-top machined, I know the cylinder base was cut, should I be worried that if I get a piston, and "size things" by setting squish via base-gasket thickness, should I be worried of throwing port-timing outta whack enough to be a problem? I mean, if I hurt its power 5% I can live w/ that, but if I should be getting a piston and cylinder I will, reallllly wanna keep this cylinder though, was done better than I could ever do!!

~~~~~~~~~~~~~

This is a kit-660, incredibly well-built w/ very high % OEM, so - when I discovered that my anomalous failure-problems were due to the piston having been chipped, it was nerve-wracking getting that top off to see just how bad things were....thankfully it seems my cylinder is nearly perfect (squish band got roughed-up, should be able to refinish that with the drill or dremel, heck I can get my long-shaft die grinder in that cylinder!) Bottom-end also looks great although wanna have you guys look at this picture because I worry about that spot on the rod, where the piston's arm connects, that spot is 'see through' to (bearings?) below, but it doesn't appear the metal was damaged it appears it should be that way, just hoping for others' eyes on it!


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Ported, dropped-deck and machined-chamber(99% on this one!) cylinder appears very salvageable, just the squish-band in the comb.chamber seems affected and A) that doesn't need to be perfect &B) it's easy to smooth-out & refinish that, especially in such a large cylinder, I have drill / dremel / die-grinder am sure I can polish a surface, am happy w/ the port-work I did on my 60cc!
Plating, not so bad: (excepting above exhaust-port!)

Combustion chamber's squish-band certainly needs refinish, but shouldn't be hard:

~~~~~~~~~~~~~
Though I guess, from the right angle, the plating isn't looking so shiny at all spots (this seems limited to exhaust-side, above-outlet plating only, unsure how much of a problem this presents, I do have virtually every dremel/drill/grinder attachments possible!)


~~~~~~~~~~~~~
NOTES/Thoughts/Disregard
Reallllly worried about fitment of a modded cylinder, w/ a "stock size" piston, hate the idea of losing the custom ported cylinder BUT if it's the quickest and most reliable way back to this guy being in working-order, that is first&foremost for me (I can probably pay&ship to recreate any cylinder/piston, and simply replace after...I'm OK "buying into" this platform and having extra parts, do not plan to leave it anytime soon!!)
I made a video to show things as well, will link here:

Am new to this platform but just totally in-love with it, before I had the top off I was ready to order a blue thunder g660 if I found the bottom-end all destroyed, would just swap-over all my superior parts and go from there, I just can't see any reason to leave it / can see why it's such an iconic saw (will have a 661cm someday!!!)

 

[Ronie]

Sorry that happened, my guess is that it's a regular piston but @Mastermind would know for sure.

 

[Mastermind]

Sorry that happened, my guess is that it's a regular piston but @Mastermind would know for sure.

Yep. Just a regular piston. No way that jug is salvageable though.

 

[Cerberus]

Sorry that happened, my guess is that it's a regular piston but @Mastermind would know for sure.

It's all good I honestly am not upset I HATED that I couldn't replicate the "hyper-resistance during startup", even though this'll be a lil project it's something I'd have ended-up at anyways if staying w/ the 66* platform (and there's NO moving me from this platform, rofl, am totally in love w/ it)

Yep. Just a regular piston. No way that jug is salvageable though.

Re the jug, is it because I'd have to remove too-much material when refinishing that squish-band in the combustion chamber? Or because the plating can't be brought-back?

I've got the SKU for the OEM piston rings ($30 online, gonna go to the dealer as well), am I correct in thinking I can basically order:
- farmertec piston,
- farmertec cylinder, and
- OEM stihl rings,
and simply re-assemble? The bottom-end looked OK to me but I obviously don't have an eye for such things!!

Thanks a ton for replying, I didn't want to message you direct, and hope you don't think I was careless (actually I'm pretty sure you saw footage of me using it, I don't believe I erred I think it was just bad luck/circumstance, are you in-agreement that it was most likely a simple wood-chip entering the cylinder via the muff?)

 

[Cerberus]

If necessary I'd order a blue g660 today, if it's a better pathway than rebuild....I don't believe it is though! But will get one and swap-over everything, and "have a parts saw" at the end, if it's the best course of action. Very crappy to lose that perfect top-end, but I'll still have a 660 ('660'!) again shortly enough, and be that much better at working on them as I'm planning on spending a lotta time using it!!

 

[Ronie]

If after cleaning out the crankcase and if the bearings ran smooth I would try and find an OEM cylinder. If you can't find one, people have good things to say about the Cross cylinder. I've never tried one but I'm pretty sure @MustangMike tried them and he can tell you about them if you want to know more.


https://www.hlsproparts.com/Stihl-066-MS660-cylinder-kit-54mm-p/cp30066.htm

 

[Mastermind]

are you in-agreement that it was most likely a simple wood-chip

Absolutely not. A wood chip wouldn't cause any damage at all.

 

[Stump Shot]

Here's a couple of good pistons for a ported saw, have good rings and can be used as is.

https://www.hlsproparts.com/Meteor-Stihl-066-MS660-piston-assembly-p/pc1756.htm

https://www.sawsalvage.co/products/...hl-066-ms660-54mm?_pos=9&_sid=9d1aafcdf&_ss=r

 

[Stump Shot]

No way that jug is salvageable though.

I agree with your assessment, not much machining and you'd have a spark gap closer.

Absolutely not. A wood chip wouldn't cause any damage at all.

I'll say it, the ring hung in the exhaust port. Which most likely put it into paper weight status.

 

[Ronie]

Be careful if you use the Duke's piston, the skirts aren't as wide as the Meteor and it might not cover the exhaust. I have one I'll send you for the cost of shipping if you want to try it.

 

[Stump Shot]

Be careful if you use the Duke's piston, the skirts aren't as wide as the Meteor and it might not cover the exhaust. I have one I'll send you for the cost of shipping if you want to try it.

If(and a bigger if every day) my memory serves the Meteor is wider than OEM. I would hazard to say that the Duke's is the same as OEM but have not proven so in this specific instance, but have in all others I have used.

 

[Mastermind]

I'll say it, the ring hung in the exhaust port. Which most likely put it into paper weight status.

Very well could have. I'm normally conservative on port width, but knowing this saw was for a one cut race, I may have went too far. I searched out a New West top end for it because I'd had good luck with those in the past. But....you never know.

 

[Stump Shot]

Very well could have. I'm normally conservative on port width, but knowing this saw was for a one cut race, I may have went too far. I searched out a New West top end for it because I'd had good luck with those in the past. But....you never know.

It happens, some even on un-futzed with cylinders.

The only used one I could find on eBay was only $10 less than a whole new P&C kit.
https://www.ebay.com/itm/194421376252?epid=1700548623&hash=item2d446ac4fc:g:bykAAOSw80phXonz
https://www.ebay.com/itm/233710704065?hash=item366a3e55c1:g:3v0AAOSwl-de9nIY

Maybe take a second look at the possibility of cleaning up the used cylinder??? Slim chance, but....you never know.

 

[Cerberus]

I'm gonna make a new thread because I'm going to do 2 frankenbuilds, I don't just want this saw "when it works" I want to depend on it so I bought a G660 should land by Fri they say, and am going to trade-over all my superior parts and then continue with rebuilding this current one (though it will have a lotta blue once the G660 lands!)

The goal/intention is that I'll immediately have all the good stuff (walbro carb, stihl recoil/starter/tensioner/etc, MM put so much OEM into this thing) swapped-over to the G660 bottom-end (and probably handle), that unit will be the "reliable work-saw" and I'll continue the repair of the current unit (which will be all aftermarket, riding on the white bottom-end) but not just "to make it work" I will be porting/etc it, so I can learn/push the platform a bit, I expect that little time will be required before I've got a pair of good, reliable 660's and, when something goes wrong on my "main" unit I'll know how to fix it & have an aftermarket part on-hand to use til an OEM lands!!

So psyched!!!!

If after cleaning out the crankcase and if the bearings ran smooth I would try and find an OEM cylinder. If you can't find one, people have good things to say about the Cross cylinder. I've never tried one but I'm pretty sure @MustangMike tried them and he can tell you about them if you want to know more.


https://www.hlsproparts.com/Stihl-066-MS660-cylinder-kit-54mm-p/cp30066.htm

MM also endorses the Cross kit but, seeing your generous offer Re the piston I'm going to take you up on that IF I think I remedied things enough in that cylinder's squish-ring! (will address that below!)

Here's a couple of good pistons for a ported saw, have good rings and can be used as is.

https://www.hlsproparts.com/Meteor-Stihl-066-MS660-piston-assembly-p/pc1756.htm

https://www.sawsalvage.co/products/...hl-066-ms660-54mm?_pos=9&_sid=9d1aafcdf&_ss=r

Be careful if you use the Duke's piston, the skirts aren't as wide as the Meteor and it might not cover the exhaust. I have one I'll send you for the cost of shipping if you want to try it.

Tangential, but any "FAQ'S/wiki's/etc", or even just good threads someone knows of, on big-bore setups? Will be perusing threads here but thought to ask at least (again, 1 of my units will be one that I intentionally push, that I aim to make "as hot a woods-port as possible" for on-job use, midday here in the semi-tropical FL sun!!)

I have little doubt I'll be getting the Cross kit within the month(Nov, I mean) but really wanting to try just piston-replacement here (once I verify I'm not hurting it by doing this attempt, will be conferring w/ a competent real-life guy shortly to get good eyes on it, he's actually a Stihl authorized tech am gonna be trying to lure him to work on-the-side for me instead of through his store due to the nature of clone/kit 660's, how you cannot warrant a thing, but am happy to pay for talent's time as necessary!)

Absolutely not. A wood chip wouldn't cause any damage at all.

You've no idea how fearful I was that this was the cause, and you'd be upset at me!! Great hearing this, am still blown away at them using an open-can design on such a huge muffler, when you have that size my understanding was you can "have your cake and eat it, too" IE you can have a high-flow baffle so you get some scavenging, get some back-pressure, without sacrificing any exit-area / flow!

I agree with your assessment, not much machining and you'd have a spark gap closer.



I'll say it, the ring hung in the exhaust port. Which most likely put it into paper weight status.

Very well could have. I'm normally conservative on port width, but knowing this saw was for a one cut race, I may have went too far. I searched out a New West top end for it because I'd had good luck with those in the past. But....you never know.

It happens, some even on un-futzed with cylinders.

The only used one I could find on eBay was only $10 less than a whole new P&C kit.
https://www.ebay.com/itm/194421376252?epid=1700548623&hash=item2d446ac4fc:g:bykAAOSw80phXonz
https://www.ebay.com/itm/233710704065?hash=item366a3e55c1:g:3v0AAOSwl-de9nIY

Maybe take a second look at the possibility of cleaning up the used cylinder??? Slim chance, but....you never know.

The funny thing is that, in inspecting the cyilnder, I'd initially mistook that part of the exhaust as un-touched!!
Stump-- in a video on a heat-burnt 440 I was watching, he had nearly identical destruction of the piston and it was OEM/not ported just overheating (no clear / sure cause was even known, just 'ran hot on the mill')

Re that cylinder, if it's paperweight it's paperweight, of course, but why can't I try for a re-finish? If I'm not going to do it, I'd just like to know why yknow?? So far as I can see I'd basically just sand & buff that combustion-chamber's squish-band, and buff the cylinder walls, so far as I can see that remedies *everything*, honestly I was very surprised to hear such firm No's (though you do say, at the end, 'slim chance / never know' ;D )

~~~~~

Have never been so in love w/ broken hardware!! Once I have 2....oh boy this is going to be so much fun, could never have done this w/o the ginormous list of OEM's that MM put on there (oh and the high end 32" B&C setup he sent*), I was cringing ordering just the g660 this morning lol, but - with what I have via this on-hand, and how much info is on this forum for the 66* platform, I wanna "dig-in" ;D
(*have to note just how generous MM was-- not only did he slap on this great Walbro carb and a ton of expensive OEM parts, and send a 32" B&C for it - w/ a fresh tip on the bar!-- but he sent it super-expedited and refused to take my CC info even for shipment! I'd initially been thinking to just get the blue one, the combo - and the knowledge & parts - that's the ticket for me!!!

 

[Stump Shot]

I'm gonna make a new thread because I'm going to do 2 frankenbuilds, I don't just want this saw "when it works" I want to depend on it so I bought a G660 should land by Fri they say, and am going to trade-over all my superior parts and then continue with rebuilding this current one (though it will have a lotta blue once the G660 lands!)

The goal/intention is that I'll immediately have all the good stuff (walbro carb, stihl recoil/starter/tensioner/etc, MM put so much OEM into this thing) swapped-over to the G660 bottom-end (and probably handle), that unit will be the "reliable work-saw" and I'll continue the repair of the current unit (which will be all aftermarket, riding on the white bottom-end) but not just "to make it work" I will be porting/etc it, so I can learn/push the platform a bit, I expect that little time will be required before I've got a pair of good, reliable 660's and, when something goes wrong on my "main" unit I'll know how to fix it & have an aftermarket part on-hand to use til an OEM lands!!

So psyched!!!!



MM also endorses the Cross kit but, seeing your generous offer Re the piston I'm going to take you up on that IF I think I remedied things enough in that cylinder's squish-ring! (will address that below!)





Tangential, but any "FAQ'S/wiki's/etc", or even just good threads someone knows of, on big-bore setups? Will be perusing threads here but thought to ask at least (again, 1 of my units will be one that I intentionally push, that I aim to make "as hot a woods-port as possible" for on-job use, midday here in the semi-tropical FL sun!!)

I have little doubt I'll be getting the Cross kit within the month(Nov, I mean) but really wanting to try just piston-replacement here (once I verify I'm not hurting it by doing this attempt, will be conferring w/ a competent real-life guy shortly to get good eyes on it, he's actually a Stihl authorized tech am gonna be trying to lure him to work on-the-side for me instead of through his store due to the nature of clone/kit 660's, how you cannot warrant a thing, but am happy to pay for talent's time as necessary!)





You've no idea how fearful I was that this was the cause, and you'd be upset at me!! Great hearing this, am still blown away at them using an open-can design on such a huge muffler, when you have that size my understanding was you can "have your cake and eat it, too" IE you can have a high-flow baffle so you get some scavenging, get some back-pressure, without sacrificing any exit-area / flow!




The funny thing is that, in inspecting the cyilnder, I'd initially mistook that part of the exhaust as un-touched!!
Stump-- in a video on a heat-burnt 440 I was watching, he had nearly identical destruction of the piston and it was OEM/not ported just overheating (no clear / sure cause was even known, just 'ran hot on the mill')

Re that cylinder, if it's paperweight it's paperweight, of course, but why can't I try for a re-finish? If I'm not going to do it, I'd just like to know why yknow?? So far as I can see I'd basically just sand & buff that combustion-chamber's squish-band, and buff the cylinder walls, so far as I can see that remedies *everything*, honestly I was very surprised to hear such firm No's (though you do say, at the end, 'slim chance / never know' ;D )

~~~~~

Have never been so in love w/ broken hardware!! Once I have 2....oh boy this is going to be so much fun, could never have done this w/o the ginormous list of OEM's that MM put on there (oh and the high end 32" B&C setup he sent*), I was cringing ordering just the g660 this morning lol, but - with what I have via this on-hand, and how much info is on this forum for the 66* platform, I wanna "dig-in" ;D
(*have to note just how generous MM was-- not only did he slap on this great Walbro carb and a ton of expensive OEM parts, and send a 32" B&C for it - w/ a fresh tip on the bar!-- but he sent it super-expedited and refused to take my CC info even for shipment! I'd initially been thinking to just get the blue one, the combo - and the knowledge & parts - that's the ticket for me!!!

I'm not a big fanboy for BB kits so I really don't pay attention to much reading on the subject.

Yes that part of the cylinder most likely wasn't touched. Sometimes things just happen like that for no apparent reason.

As to the "why" you can see the damage to the piston, it's harder to see the damage to the cylinder at the ports edge. Cleaning it up is tough to do and if it removes plating that leaves edges exposed that's not a good thing for the rings to be going over and over which can just lead you to the next failure.

I mistakenly thought this was a genuine Stihl saw at first that needed repaired, so that said much of my advice above isn't very good as the $$$ values involved are way off.

 

[Nutball]

I want to depend on it so I bought a G660

Sorry, carry on

 

[Nutball]

I haven't seen the damaged ports, but there is a chance you can carefully remove the bad plating and smooth it with a diamond burr making sure that the edge of the plating is overall rounded so it can't catch a ring again. You don't have to grind the port changing it's timing, just change where the edge of the plating is. The rough squish band will make detonation much more likely. It looks like a lot of material will need to be removed to smooth it out.

 

[Stump Shot]

I haven't seen the damaged ports, but there is a chance you can carefully remove the bad plating and smooth it with a diamond burr making sure that the edge of the plating is overall rounded so it can't catch a ring again. You don't have to grind the port changing it's timing, just change where the edge of the plating is. The rough squish band will make detonation much more likely. It looks like a lot of material will need to be removed to smooth it out.

freeport

 

[Nutball]

I didn't say it would be perfect, but yeah.

 

[smokey7]

Wow