MS661C 2015 M-Tronic V3 4702A Coil Calibration Now Grenaded Piston

[skygear]

My Stihl MS661C M-Tronic 4700D with Black Solenoid and white pickup Started showing signs of the Solenoid failing years ago when I was under warranty. I brought it to the dealers attention and nothing came of it due to the unrepeatable event. Saw had to be run and cutting with normal use. Once a tank of fuel was run through it. It wouldn't start back up.

Out of warranty and problem persisted. Eventually I knew it was reliably unreliable and could predict when to use it and its temperament.

Fast forward to a couple months ago. Would only start up in reset mode and wouldn't idle. Researched to and the dealer offered to fix it at the tune of $300+. I researched more and came across the 11440071809 kit that has the 4702A Coil, Orange Fuel pickup, and White solenoid.

Dealer ordered the part and called to tell it was backordered. I called Stihl to get an ETA since the dealer ws unable to. Stihl came through and sent out to me under "Warranty"

---- Quick background. I took Small engine repair in school and have always fixed my own equipment. Own most of the tools and always investing in more. ---

Pressure/ Vacuum tested the saw AFTER installing the parts and changing the spark plug. Let sit for 12hrs with no change. Awesome, time top start it in CALIBRATION MODE>

Start the saw in mode and let idle for 90sec
Pull trigger /full throttle for 20sec until it
Goes HIGHER RPM for ~10sec
Then Down to lower 'burp'
Release trigger/ Shut off immediately.
Start saw. Settings saved.

Saw is/ was stock before this with the exception of the V3 Kit

before the final 10sec completed, The engine ceased 5 sec into it.

Disassembled the upper end and found the grenaded piston and chunks all over the cylinder and in all the ports.

I double checked everything I had done and couldn't find a leak anywhere. Too late to check for pre existing piston/ cylinder damage.

Was suggested I call Stihl. So I did. Went to the dealer and called Stihl from the dealer. Also explained the same thing to the dealer that I had done. They too said to call.

I cleaned up the Cylinder with 400-1000 grit removing all remnants of the piston. Seems ok. No power tools, just by hand.

OEM Piston from the dealer is $111.02 + tax.
OEM Online from a Dealer is $79.98 free shipping.
Other brands for the Cylinder and Piston kit are ~$150-$200
Dealer will charge me $399.99 for the complete OEM Top end

Stihl rep wants me to bring the saw in and have the dealer look at it. ~$25 diagnostic fee for out of warranty. Then the cost of parts of it Stihl decides No assistance.

Ideas Thoughts?

 

[skygear]

More work to do on the ports. But here is before and after. Should I use this cylinder?

 

[motorhead99999]

Looks like it melted im Not to into the m Tronic stuff so I’m not sure how it works but it looks like it was run real lean

 

[motorhead99999]

I have been using cross cylinders and pop up pistons in everything iv been rebuilding and been happy with them. I haven’t had bad luck with hyway either but a lot of people have

 

[motorhead99999]

I don’t know if you can do away with the m Tronic stuff and go back to original or not maybe someone else can tell u that. If I could I would so it doesn’t happen again. But I hate computerized stuff so it’s your call.

 

[MaddBomber]

I wouldn't trust that cylinder. The big gouge above the transfer is iffy at best. The squish band gouge isn't as detrimental, but yikes!
I've never seen that other than on race engines. In my experience, they usually just lose compression and quit. Yours was catastrophic. Could have been a faulty piston.
I had a lot of tuning issues with a saw. I'd pull and pull, finally get the carb dialed in, but then couldn't restart it. It was a mystery. Finally in complete frustration I pulled the jug and found the piston had a tiny crack. Replaced it and it's been stellar ever since.
Plus, I feel that the M-Tronic and A-Tune run a little lean.
Not sure which caused what... A defective piston messing with the MTronic, or a defective MTronic messing with your piston.
Please keep us updated.

 

[stihl86]

Looks like it melted im Not to into the m Tronic stuff so I’m not sure how it works but it looks like it was run real lean

I would tend to agree. Real lean for awhile with poor quality fuel. The top of the piston on the ex side looks like severe detonation. With a lack of lube thrown in.
Usually a lean condition wont do damage that bad to the top. The dealer should be able to pull the fuel numbers. That might help a little with the diagnosis.
But you should have it checked after the work is done for sure.
We've sell a ton of Mtronics. Haven't had a solenoid that caused a lean condition. They usually run too rich and wont run in start mode.
But of course it's possible. You say you pressure tested it. Did you vacuum test it first? Pressure testing will force crank seals tighter against their mating surface, and hide a leak.

 

[skygear]

I would tend to agree. Real lean for awhile with poor quality fuel. The top of the piston on the ex side looks like severe detonation. With a lack of lube thrown in.
Usually a lean condition wont do damage that bad to the top. The dealer should be able to pull the fuel numbers. That might help a little with the diagnosis.
But you should have it checked after the work is done for sure.
We've sell a ton of Mtronics. Haven't had a solenoid that caused a lean condition. They usually run too rich and wont run in start mode.
But of course it's possible. You say you pressure tested it. Did you vacuum test it first? Pressure testing will force crank seals tighter against their mating surface, and hide a leak.

Yep. Vacuum then pressure tested.

The fuel was a week old and mixed with the Premium Stihl mix.

 

[skygear]

I wouldn't trust that cylinder. The big gouge above the transfer is iffy at best. The squish band gouge isn't as detrimental, but yikes!
I've never seen that other than on race engines. In my experience, they usually just lose compression and quit. Yours was catastrophic. Could have been a faulty piston.
I had a lot of tuning issues with a saw. I'd pull and pull, finally get the carb dialed in, but then couldn't restart it. It was a mystery. Finally in complete frustration I pulled the jug and found the piston had a tiny crack. Replaced it and it's been stellar ever since.
Plus, I feel that the M-Tronic and A-Tune run a little lean.
Not sure which caused what... A defective piston messing with the MTronic, or a defective MTronic messing with your piston.
Please keep us updated.

The gouge was from where one of the rings broke and was hammered into the top.

I'd prefer Stihl replacement kit 1144 020 1200 but at ~$400 quoted from my dealer. I have to wait unless by some miracle, Stihl/dealer warranties an old saw...

 

[skygear]

The whole cylinder is smooth to the touch and the gouges on my end don't look bad under a 10x loop.

That gouge circled, I can still smooth out further. I wanted to get it as clean as possible first to see where I was at.

 

[huskihl]

The v3 mtronic calibration only applies to a 462. To reset the mtron on a 661, you start it in the choke position and let it run 60 seconds. Without touching the trigger, shut the saw off. Place in run position and start the saw. After idling for 60 seconds, make a few long cuts.

 

[trains]

The v3 mtronic calibration only applies to a 462. To reset the mtron on a 661, you start it in the choke position and let it run 60 seconds. Without touching the trigger, shut the saw off. Place in run position and start the saw. After idling for 60 seconds, make a few long cuts.

661's over here with v3 have the reset procedure that the op did, even seen it in manuals that came with them too.

 

[huskihl]

661's over here with v3 have the reset procedure that the op did, even seen it in manuals that came with them too.

Sorry for the misinfo. Thought it was only on the 462

 

[Jexy]

watch this video:

 

[frank_]

that piston looks like a classic case of detonation to me, too much spark advance ?

 

[skygear]

that piston looks like a classic case of detonation to me, too much spark advance ?

This was 100% stock before the v1 4700d to the v3 4702a upgrade. No timing advance, no muffler porting, no port work, nothing. Just ran her stock in factory config with the exception of the bar which is a 25" Stihl.

 

[skygear]

watch this video:

Yep. I'v read all the documentation and watched his videos.

 

[frank_]

This was 100% stock before the v1 4700d to the v3 4702a upgrade. No timing advance, no muffler porting, no port work, nothing. Just ran her stock in factory config with the exception of the bar which is a 25" Stihl.

i,m assuming the 4702a is the ignition coil ? and was accusing that of the spark advance
a google pic search on "detonated piston" brings up a lot of your type or piston damage

 

[skygear]

i,m assuming the 4702a is the ignition coil ? and was accusing that of the spark advance
a google pic search on "detonated piston" brings up a lot of your type or piston damage

Ah. Yes. That is the ignition coil. I'm looking now at the pics. You can also advance the timing by filing down the "key" as well and was thinking that was where you were headed.

 

[Mad Professor]

I love my old Stihls.

Carbs without limiters, caps that screw and don't flip, .............no need for a dealer, except parts.