MS 660 rebuild advice

[Fnkfab]

hey gang:
I've been lurking on here for a while, but decided its time to start asking some questions directly. I'm pretty new to the chainsaw world-- maybe 2-3 years in. It started as a homeowner thing and quickly escalated to doing some sawmilling with a DIY alaskan mill, drying lumber, and taking on some jobs with a buddy and his portable band mill.

I picked up an MS 650 last year. It seems to run pretty well. No issues with power, starts well. It's pretty well loved though. The fan is missing a couple blades, the handle is a little floppy, and the brake handle is cracked. I've replaced the pull cord and the chain tensioner mechanism recently since those both snapped. More importantly, the spark plug threads in but likes to unthread and fall out and the compression measured at 125, oh and the decomp valve flops around a little so i can't tell if that's with the valve open or not. It runs "automatic" where it closes when the saw starts and opens otherwise.

I'm preparing to tear into this and start replacing items (fan, brake lever, handle grommets, decomp valve). I'm also figuring it'd be a good idea to replace the jug and piston and rebuild the carb to get this back to a clean slate. I've got a copy of the service manual and I've watched through a couple youtube vids.

What do you all think? Sound like a plan? My plan was to drop a meteor 660 jug and piston since i understand the saws are otherwise the same. Anything to watch out for?

 

[BuckthornBonnie]

Yes, get into that saw and replace those parts mentioned above. I would avoid any aftermarket fuel lines, piston/cylinders, and more.
That cylinder- if the plug is loose and the threads are jeopardized, it should be fixed. Timesert insert or welding/retapping are the best options.
Meteor pistons are ok for this series- check what bore diameter you have since the original cylinder could have been replaced.

On this series, check the crank for play (wiggle it on both sides) and look carefully at all AV mounts.

 

[Fnkfab]

Thanks!

I managed to get into it pretty far early mornings this week. Waiting on my puller and a long T27 torx to arrive in the mail before i can take it down a bit further. Lots of broken plastic pieces, part of the top fan side AV mount was snapped, grime and missing paint in a lot of places. I'd say this thing was dropped out of a tree a couple times.

I pulled the muffler and peeked in the cylinder. I haven't looked at many but at first glance it looked like there's some decent scoring. I'll have to post some photos when i get it opened up to see what you guys think. You can clearly see the crossed threads on the spark port now also. I'm sorta thinking since i'm in this far, i might as well just replace the top end-- unless i find its OEM and you guys think its in good enough shape. More on that one.

Good tips. I'll get back to you on the rest of the AV mounts and the crank shaft wiggle.

On the upside, the carb is a walbro and looks brand new.

One question--- as i tear into this, there's all sorts of dust/grime. I've been cleaning it a bit and using a shop vac to remove it. Any tricks for keeping junk from getting into sensitive parts of the saw?

 

[Mad Professor]

For cleaning I scrape off thick stuff. Covers can be removed and cleaned separate in a bucket. Same with flywheel/clutch assy. I sometimes use diesel first, followed by detergent. A parts brush and old tooth brush for tools. Have a thick pair of nitrile gloves, the cheap ones aren't worth it.

When mostly stripped down the scrapers come out again for thick caked on stuff. Plug ex and intake. A piece of rag or paper towel wrapped in a piece of plastic baggie will keep out particles and solvents. Make sure not to get water inside P/C, flush it out soon if you do. Pull off coil assy. I leave oil pump on, then clean underneath to seal area later. Then I brush down with diesel, rinse, then detergent, rinse.

That should get you where the P/C will come off without stuff falling inside, and be able to change crank seals.

If you have access to a sonocator, they are great for cleaning out carbs.

 

[Fnkfab]

Meteor pistons are ok for this series- check what bore diameter you have since the original cylinder could have been replaced.

On this series, check the crank for play (wiggle it on both sides)

Good call here. So this is my first time with a saw open... so bear with me:

Turns out this is the OEM stihl ms660 cylinder. ( guess that explains why i didn't think the saw felt under powered, being an MS650 and all.)
When i look in the cylinder i see some wear but my gut feel is this is OK. No deep scoring/scuffing.
The top of the piston has some charred stuff on it but otherwise looks pretty good from my eyes.
The piston seems tight on the crank. The crank can slide side to side down in the case-- looks like .050" play.

Questions:

1. Do i keep the piston and cylinder or swap for a meteor? (leaning towards keep)
2. Can i re-use the cylinder gasket? My guy feel is no but its tempting to just put it back together.
3. Anything else jump out at you guys?

 

[Fnkfab]

For cleaning I scrape off thick stuff. Covers can be removed and cleaned separate in a bucket. Same with flywheel/clutch assy. I sometimes use diesel first, followed by detergent. A parts brush and old tooth brush for tools. Have a thick pair of nitrile gloves, the cheap ones aren't worth it.

When mostly stripped down the scrapers come out again for thick caked on stuff. Plug ex and intake. A piece of rag or paper towel wrapped in a piece of plastic baggie will keep out particles and solvents. Make sure not to get water inside P/C, flush it out soon if you do. Pull off coil assy. I leave oil pump on, then clean underneath to seal area later. Then I brush down with diesel, rinse, then detergent, rinse.

That should get you where the P/C will come off without stuff falling inside, and be able to change crank seals.

If you have access to a sonocator, they are great for cleaning out carbs.

Ha! I wished I saw this before i tore it down...

 

[Fnkfab]

That cylinder- if the plug is loose and the threads are jeopardized, it should be fixed. Timesert insert or welding/retapping are the best options.

Woof. Timesert kits are not cheap. I guess i'll wait to hear what you guys say about the P/S. If i'm going to keep it, i'll have to explore some options there.

 

[Mad Professor]

Woof. Timesert kits are not cheap. I guess i'll wait to hear what you guys say about the P/S. If i'm going to keep it, i'll have to explore some options there.

From what I can see that P/C looks pretty good. Do a quick check of P/C clearance with feeler gauges at the skirt. ~ 0.002-0.0025 " is new > 0.004" is getting worn. If that is good I'd put a set of caber rings in it, but clean it up real good.

A Stihl gasket set comes with seals, might be worth doing those, or have dealer install them when it's torn down/clean.

For spark plug threads, go to local machine shop for a timesert. I've used helicoils but the timesert is better. The cylinder is worth fixing right. It's a $300 assy from stihl

 

[president]

From what I can see that P/C looks pretty good. Do a quick check of P/C clearance with feeler gauges at the skirt. ~ 0.002-0.0025 " is new > 0.004" is getting worn. If that is good I'd put a set of caber rings in it, but clean it up real good.

A Stihl gasket set comes with seals, might be worth doing those, or have dealer install them when it's torn down/clean.

For spark plug threads, go to local machine shop for a timesert. I've used helicoils but the timesert is better. The cylinder is worth fixing right. It's a $300 assy from stihl

From what I can see that P/C looks pretty good. Do a quick check of P/C clearance with feeler gauges at the skirt. ~ 0.002-0.0025 " is new > 0.004" is getting worn. If that is good I'd put a set of caber rings in it, but clean it up real good.

A Stihl gasket set comes with seals, might be worth doing those, or have dealer install them when it's torn down/clean.

For spark plug threads, go to local machine shop for a timesert. I've used helicoils but the timesert is better. The cylinder is worth fixing right. It's a $300 assy from stihl

are the rings installed,during the test,for cyl wear?

 

[Mad Professor]

are the rings installed,during the test,for cyl wear?

It don't matter but easier without. Rings are a PITA to compress/install. Feelers are a crude measurement but quick and easy + - .001"

Cly won't wear much if any, piston does

 

[motorhead99999]

I’d throw a cross pop up in it with some caber rings. If your thinking of changing the piston

 

[Mad Professor]

I’d throw a cross pop up in it with some caber rings. If your thinking of changing the piston

Chinesium!!!!

 

[motorhead99999]

Chinesium!!!!

I’ve had good luck.

It’s quality chinesium lol

 

[Mad Professor]

I’ve had good luck.

It’s quality chinesium lol

Yesterday's Budwieser.

I'd keep the OEM piston and re-ring it if not worn.

 

[Bobby Kirbos]

Good call here. So this is my first time with a saw open... so bear with me:

Turns out this is the OEM stihl ms660 cylinder. ( guess that explains why i didn't think the saw felt under powered, being an MS650 and all.)
When i look in the cylinder i see some wear but my gut feel is this is OK. No deep scoring/scuffing.
The top of the piston has some charred stuff on it but otherwise looks pretty good from my eyes.
The piston seems tight on the crank. The crank can slide side to side down in the case-- looks like .050" play.

Questions:

1. Do i keep the piston and cylinder or swap for a meteor? (leaning towards keep)
2. Can i re-use the cylinder gasket? My guy feel is no but its tempting to just put it back together.
3. Anything else jump out at you guys?

I ran into the same thing - a 650 with a 660 top end. Not to hijack this thread, but I'm wondering if this is standard from Stihl (much like the Poulan 42cc engine thing), or if people who are "in the know" and blow up their 650 simply turn it into a 660 when rebuilding it. What have others seen relating to this??

I’d throw a cross pop up in it with some caber rings. If your thinking of changing the piston

On my rebuild, I used an OEM, gently used Mahle jug, the pop-up piston, and Caber rings. I bought an after market gasket set for something like $20(US). So far it's running quite well. Having never run a 660 with a stock piston, I have no way of knowing how the pop-up effects performance beyond what others have posted on youtube, but the saw is hard to stop.

 

[motorhead99999]

Yesterday's Budwieser.

I'd keep the OEM piston and re-ring it if not worn.

I agree I try to keep oem if not in to bad of shape

 

[motorhead99999]

I ran into the same thing - a 650 with a 660 top end. Not to hijack this thread, but I'm wondering if this is standard from Stihl (much like the Poulan 42cc engine thing), or if people who are "in the know" and blow up their 650 simply turn it into a 660 when rebuilding it. What have others seen relating to this??


On my rebuild, I used an OEM, gently used Mahle jug, the pop-up piston, and Caber rings. I bought an after market gasket set for something like $20(US). So far it's running quite well. Having never run a 660 with a stock piston, I have no way of knowing how the pop-up effects performance beyond what others have posted on youtube, but the saw is hard to stop.

I have turned a couple ms 290-310 into -390s for friends and my self with the pop ups and it’s amazing how well they run. I have a 290 with a muffler mod and timing Bump and a 390 with the pop up in a factory jug with muffler mod and it’s twice the saw it was stock. Doing just a muffler mod to them makes a big difference too. I don’t really wanna tear apart a good running 660 to note differences but someday it will have one in it.

 

[Fnkfab]

I ran into the same thing - a 650 with a 660 top end. Not to hijack this thread, but I'm wondering if this is standard from Stihl (much like the Poulan 42cc engine thing), or if people who are "in the know" and blow up their 650 simply turn it into a 660 when rebuilding it. What have others seen relating to this??.

From what I've read here, they are the same saw otherwise. Stihl was just trying to offer a lower power/price point with the 650.

On my rebuild, I used an OEM, gently used Mahle jug, the pop-up piston, and Caber rings. I bought an after market gasket set for something like $20(US). So far it's running quite well. Having never run a 660 with a stock piston, I have no way of knowing how the pop-up effects performance beyond what others have posted on youtube, but the saw is hard to stop.

I have no doubt it would run and well for a while. My worries with the clone hardware would be material quality and tolerancing which should equate to wear/lifetime and failure mode. There are plenty of clones out there running and people doing work with them. This saw is my milling saw-- so its going to see some rough conditions. I also don't have a backup yet. Per my OP, the the P/C options are OEM or meteor.

From what I can see that P/C looks pretty good. Do a quick check of P/C clearance with feeler gauges at the skirt. ~ 0.002-0.0025 " is new > 0.004" is getting worn. If that is good I'd put a set of caber rings in it, but clean it up real good.

A Stihl gasket set comes with seals, might be worth doing those, or have dealer install them when it's torn down/clean.

For spark plug threads, go to local machine shop for a timesert. I've used helicoils but the timesert is better. The cylinder is worth fixing right. It's a $300 assy from stihl

I'll pick up a feeler gauge this morning-- that's a great quick and dirty check.
I'll find someone to do the timesert, have got that advice from a few folks now.

Is the thinking that while I'm down this far, i might as well replace the crank case gaskets as well? Or did you just mean the jug gaskets?

 

[Mad Professor]

From what I've read here, they are the same saw otherwise. Stihl was just trying to offer a lower power/price point with the 650.



I have no doubt it would run and well for a while. My worries with the clone hardware would be material quality and tolerancing which should equate to wear/lifetime and failure mode. There are plenty of clones out there running and people doing work with them. This saw is my milling saw-- so its going to see some rough conditions. I also don't have a backup yet. Per my OP, the the P/C options are OEM or meteor.



I'll pick up a feeler gauge this morning-- that's a great quick and dirty check.
I'll find someone to do the timesert, have got that advice from a few folks now.

Is the thinking that while I'm down this far, i might as well replace the crank case gaskets as well? Or did you just mean the jug gaskets?

Just jug gasket unless you need to do bottom end bearings or have a leak. Complete stihl gasket set costs less than just seals alone

 

[Fnkfab]

Well the feeler gauge set i picked up had the smallest one at .0015" and there was no getting that in there.
So im going to go ahead and keep the P/C here.

Regarding replacing the jug seal. It looks like the cylinder comes off OK with a couple stihl tools ("assembly drift" 1111 893 4700 and circlip "installing tool 5910 890 2212"). The first is cheap enough, but the second looks to be $120. I guess i'll meander down to the local shop/dealer and see if they can timesert the cylinder and drop a new gasket in for me.