Killed the MS880 while milling

[Kicker_92]

Here's some pics of the nice clean cylinder.

The acid took most the aluminum off, but I had to wet sand with some 400 grit to knock down the ridges from the score marks. This wore through the coating below the exhaust port. The area above the port is still good.

I'm thinking it'll be fine to run like this,but would like a second opinion before I spend the time reassembling with a new piston.

Oh, and the squish measured in at approx 0.040", plus another 0.020" for the base gasket. I haven't measured the combustion chamber yet, but there's a lot of space there. Like mtngun pointed out, it seems to be pretty conservative.

The plug:

The clean cylinder:

The exhaust port:

 

[Coalsmoke]

Diesel engines are more my game (worked as a truck and equipment tech for a while), but I rebuild my own snowmobile 2 stroke engines and wouldn't put it back together looking like that (sorry, but it is my honest opinion). There is a place in the valley here that will redo Nikasil. Forget their name but can dig it out if you need it. For what its worth though, I have a saw builder in Abbotsford that gets any serious engine work on my saws. He knows his saws well, and I don't feel like messing up an expensive Husky because I pushed it a bit too far. He has done up a 395XPG for me that screams. If you need his name / number I can get that too. Have it on file here somewhere.

Mr Westspartan, I suspect that the damage done to your 180 was the result of a lean condition and not specifically the age of the gas. With our newer fuels today, you will find that when the gas starts to turn, the engine will lose its top end capacity. Small bore engines can be more susceptible to overly lean or rich conditions.

 

[mwrunt]

the plug looks lean there should be a darker tan atleast on one half of the plug. And in my opinion the cyl is toast. maybe try find a good used one of see if someone makes a cheaper aftermarket.
I noticed you are in bc it mite be cheaper to get mongoose machine to replate it. They are located in burnaby and do tons of motorcuce jugs. Mite be worth it to look them up and see

Here's some pics of the nice clean cylinder.

The acid took most the aluminum off, but I had to wet sand with some 400 grit to knock down the ridges from the score marks. This wore through the coating below the exhaust port. The area above the port is still good.

I'm thinking it'll be fine to run like this,but would like a second opinion before I spend the time reassembling with a new piston.

Oh, and the squish measured in at approx 0.040", plus another 0.020" for the base gasket. I haven't measured the combustion chamber yet, but there's a lot of space there. Like mtngun pointed out, it seems to be pretty conservative.

The plug:

The clean cylinder:

The exhaust port:

 

[Coalsmoke]

Thanks! Mongoose is the company I was trying to remember. You just saved my brain from at least 3 hours of painful wondering.

 

[Andrew96]

Actually..I don't think that plug looks 1/2 bad for ethanol enriched fuel...at least for mixture...but only because we can only see 1/2 of the plug. The side of the ceramic is pointing the wrong way to really see. The area to look at is down right now. However...it seems all for nothing if the bore won't clean up. Scratch in the chrome = bore is done.
I did notice one other detail from your latest round of photos. If you choose to have your cylinder replated...and use it again...make sure you confirm the edge I've circled. That's a very important part of the port...a very big port and it's right on the side radius. The picture might not tell the whole story but it looks like the chamfer is not enough in that area. You can see a corresponding mark up the bore from this area but I don't think that has anything to do with the initial failure. However....if you are going to use this bore again after it's rechromed..you should address that. Hmm lets be clear here...address that port BEFORE you get it rechromed. The funny chamfer could cause your right to flutter, not a good place to unload a ring since that is about the hottest area of the whole assembly, and the worst area for the ring. See the missing marks down the bore (for 3/16")?..it's unloaded (bounced off the radius edge) before.

If you were going to attempt any porting adjustments on this engine..don't just start opening things up, or changing the port timing (raising them). The easy one to see is to adjust your transfer ports instead. With an unbalanced burn pattern like you have..you would keep the longevity of this setup (current issue aside) and still make more power if the intake ports were balanced. Look at that burn pattern on the head...your left transfers cannot keep up with the right (that's why the burn pattern is off centered in that design head). Check your base gasket isn't/wasn't covering some of the port to make your engine lop sided (though it is really quite close...you're not looking for much...a mismatched base gasket to port could cause that).

 

[losttheplot]

This may have been said already.

Whatever killed your saw must be fixed before you run it again !

If there is any condition, such as an air leak or fuel starvation that caused the saw to break it will do the same to the new piston/cylinder.

Examine everything VERY carefully.
There is nothing worse than rebuilding a motor twice.

 

[mtngun]

Kicker, thanks for the excellent pictures. This is a painful experience but at least we are all learning something from it.

I'm of the school of thought that spark plug readings can't be relied on, but for what it is worth, your spark plug is consistent with a lean condition.

Here is the plug from my milling saw. I just took this picture a few minutes ago. Last time it ran the weather was near zero (F) and I didn't bother to retune so the saw was running leaner than normal.

Now compare that to your squeeky clean plug.

 

[huskyhank]

Kicker, thanks for the excellent pictures. This is a painful experience but at least we are all learning something from it.

I'm of the school of thought that spark plug readings can't be relied on, but for what it is worth, your spark plug is consistent with a lean condition.

Here is the plug from my milling saw. I just took this picture a few minutes ago. Last time it ran the weather was near zero (F) and I didn't bother to retune so the saw was running leaner than normal.

Now compare that to your squeeky clean plug.

I second the above.

and...

What plug does Stihl tell you to use?
What plug was in the saw when it died?

 

[Coalsmoke]

Plug looks like the right one, but I agree, definitely been running hot.

 

[excess650]

.040" squish without a base gasket seems pretty wide, and another .020" makes it really wide, IMO. You really should check with the guys on the chainsaw board to see what they recommend for an 088/880, but I set my 660 up at .025" with base gasket. There are other guys who will set them up at .020" and mod the ports as well, but they're looking to increase RPMs. I'm a bit more conservative in that regard, and would rather have my milling saw run a little slower and cooler so as to live considerably longer.

I run 91-93 octane pump premium that I'm sure is laced with 10% ethanol, but that is what is available locally. My usual mix oil is a synthetic blend (Echo Powerblend) mixed 40-1, doesn't make excessive carbon or smoke, and leaves an oily coating on the piston. Being on the paranoid side about the fuel, I generally don't keep it around more than a month, and if in doubt, dump it out.

My milling saw is also tuned rich so as to limit RPM and increase cooling during longer cuts. If you're running stock spec RPM while milling, you're asking for trouble.

Your cleaned cylinder looks pretty bad to me. Those that I've cleaned and re-used have looked almost new. With the price of 880s, I would choose to err on the side of caution and get a new P&C.

 

[Andrew96]

Kicker, thanks for the excellent pictures. This is a painful experience but at least we are all learning something from it.

I'm of the school of thought that spark plug readings can't be relied on, but for what it is worth, your spark plug is consistent with a lean condition.

Here is the plug from my milling saw. I just took this picture a few minutes ago. Last time it ran the weather was near zero (F) and I didn't bother to retune so the saw was running leaner than normal.

Now compare that to your squeeky clean plug.

OK, I better stand as corrected ...all I can do is blame it all on the colour rendition of my monitor..and the photos. We know Mtnguns saw runs very nice...and he stated it was a little on the lean side prior to pulling the plug (the photos I see look very dark...but hey...must be my monitor!). When seeing a comparison, on the same monitor...I can see the pretty lean plug. However, you can also see mtnguns doesn't have any deposits from preignition either on the ceramic..or the electrode. So...though it's pretty lean..the preignition signs are still there (on the plug, on the piston, and in the head). Did your fixed timing move? Did the box fail so it was too advanced? If you are confident that the fuel was good...something else caused the preignition...I don't feel it was just lean temps. There is still something missing to the story. Lean yes...and?

 

[mtngun]

We know Mtnguns saw runs very nice...and he stated it was a little on the lean side prior to pulling the plug (the photos I see look very dark...but hey...must be my monitor!).

I meant lean compared to how it is normally tuned. Normally tuned to 12,000 WOT, on that cold day it was pulling 12,500 WOT.

I feel Kicker's pain.

 

[isaaccarlson]

Just where do you dump it?

Being on the paranoid side about the fuel, I generally don't keep it around more than a month, and if in doubt, dump it out.

I hope you don't dump it on the ground.

 

[Kicker_92]

Did your fixed timing move? Did the box fail so it was too advanced?

How do you change the ignition timing on these? The module is mounted with two screws, I dont see how you could adjust it?

 

[Brmorgan]

I hope you don't dump it on the ground.

I dump my old gas in the car or quad. They don't seem to mind at all, and if I do suspect some water I'll throw a bit of methyl hydrate in with it to help burn it off.

How do you change the ignition timing on these? The module is mounted with two screws, I dont see how you could adjust it?

I can't speak for an 880 per se, but a lot of ignition sets have elongated mounting holes, so you can loosen the screws and rotate it a couple degrees one way or the other. This was the case on the 041s I've been working on.

 

[Andrew96]

How do you change the ignition timing on these? The module is mounted with two screws, I dont see how you could adjust it?

Well it might be a fixed position (non adjustable) pickup (I don't have an 880). Are the screws tight? Did the box fail and it's advanced? Something changed...providing the fuel was good.
You'll have to put the ignition question on hold until it's all back together, you complete all the pressure tests, and get to fire it off. You might choose to check the timing but usually when the solid state ignitions fail..the timing is stuck, or non existant. It will make it interesting to start if it's stuck. Testing your timing is just one detail on your list of checks.

 

[timberwolf]

Looks like the pistong just got too hot over the exhaust side. Lots of things can tip the balance, plugged up cooling fins or fan cover, running lean on fuel.

To make the 880 into a milling machiene I would be inclined to get the squish down too about .030, this will help prevent preignition and heating of the exhaust side of the piston crown. Get an older 088 non rev limited coil so the saw AF mixture can be set with less guessing, open the muffler up and richen the jets. The extra HP gained by the saw not fighting the muffler restriction will allow it to work a little less to get the same work done. Same goes for some basic port clean up work. Keeping the RPM up with a little extra HP lets the fan do more cooling. Bogging the saw on a mill is real tough on it, produces a lot of heat but it slows the fan reducing cooling and then with the saw falling out of the powerband the cut takes longer (tripple whammy).

Good fuel and oil always, don't let the saw run dry in the cut. Keep the fan and cooling fins clear, let the saw warm up and cool down a little before and after big cuts and chain sharp.

The vast majority of saw ignitions are dead simple and don't have any advance curves. They may retard a bit at very low RPM for starting, but I have seen no significant timing shifts from idle upto WOT no load.

 

[Kicker_92]

To make the 880 into a milling machiene I would be inclined to get the squish down too about .030, this will help prevent preignition and heating of the exhaust side of the piston crown.

Thanks Timberwolf, I've been reading through some of your posts on your 880 buildup, thats an impressive machine!

I've decided to do a bit of work on the cylinder before I reuse it, have decked about 0.035" off to give me around 0.025" squish. It slipped when I was milling (no lathe), so I might have taken a bit too much off. I'll increase the base gasket or dome the piston a bit if it went too far.

I've already widened the exhaust and intake ports to about 2mm from the edge of the piston skirt, and and now working on smoothing up the exhuast passage. I'll clean up the flash off the piston tomorrow.

 

[Kicker_92]

BobL or Timberwolf:

Do you guys have a stock compression reading from your MS880?

 

[BobL]

To make the 880 into a milling machiene I would be inclined to get the squish down too about .030, this will help prevent preignition and heating of the exhaust side of the piston crown. Get an older 088 non rev limited coil so the saw AF mixture can be set with less guessing, open the muffler up and richen the jets. The extra HP gained by the saw not fighting the muffler restriction will allow it to work a little less to get the same work done. Same goes for some basic port clean up work. Keeping the RPM up with a little extra HP lets the fan do more cooling. Bogging the saw on a mill is real tough on it, produces a lot of heat but it slows the fan reducing cooling and then with the saw falling out of the powerband the cut takes longer (tripple whammy).

Good fuel and oil always, don't let the saw run dry in the cut. Keep the fan and cooling fins clear, let the saw warm up and cool down a little before and after big cuts and chain sharp.

All this is one reason why I installed a temp gauge. As you say, pushing the saw hard so it drops of the power curve and sits at say 6500 - 7000 rpm sees the temp rise noticeably. This is why I was slightly concerned with using an 8 pin with mildly aggressive rakers but it only dropped the operating RPM in hardwood by a couple of hundred rpm

My sensor is not ideally located (it's in a small gap above the exhaust manifold) so what the sensor measures is the temperature of the cooling air after it has passed over part of the cylinder. But it is still better than nothing.

As reported by the sensor, if the ambient air temp is 70F the saw at idle eventually reaches about 140F.

Milling sees it increase quickly but only by about 20F, then the temp rise slows down and the final operating temp depends on 101 variables. eg
How hard the saw is being pushed
Wood hardness
Amount of contact between wood and saw or width of cut
Sprocket size
Size of chain
Sharpness of chain
Depth of rakers

It's easy to see the effect or some of these factors eg the temp increases quicker if the saw is pushed hard and dropping the RPM, but I can't really see any temp difference between using 7 or 8 pin sprockets.

As I said, once the saw has reached a nominal operating temp ~160F, the temp continues to increase. All being well, the final temp at the end of the slab (~170F) is a useful indicator of how things are going. If I don't touch up the chain and cut another slab the temperature at the end of that slab can be 190F.

When ever the saw has been working (eg sensor measuring ~170F, ) and then left to idle (or stopped) the temp at the sensor rises immediately by about 30F at idle (and over 50F if stopped) because the amount of cooling has dropped off or ceased.

I then leave the saw to idle until it reaches <150F - this can take as much as 2 minutes.