ms660 blown spark plug

treesandsurf

treesandsurf

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You guys ever heard of this happening: my employee was using our 660 out in the field was getting run pretty hard bucking up tons of wood from felled trees. All of a sudden a huge POP and the spark plug shot out the hole. It looks like it stripped the threads on the chainsaw itself. Never heard of such a thing and I'm curious what could have caused it... overheating?

jp:D
 
It happens sometimes if threads are a bad.
Loose plugs or over tightened plugs is main reason.

I have seen a few from bad plugs made of wrong material and don't shange shape at same time as cylinder.
But if it is a good normal plug that is sitting with correct tensionm, the temp will not affect it.
 
We had a thread about that a while back.
I've had it happen twice, both times on MS441s.
Helicoil will fix it.
 
Helicoil is a good fix, timeserts is even better.
Any way you choose it comes down to how its put in. A good job with Helicoil or timsert is just as good.
I like the timeserts better as they make a really nice repair that last a bit longer and sit a bit tighter with its flenge. Most times better than when new...
 
The washer on plug is the most common reason for failure. It is a one time thing on most plugs.
If plug is re-used/re-installed and washer already is compressed it will not sit as it should in all temps.
 
Magnus said:
The washer on plug is the most common reason for failure. It is a one time thing on most plugs.
If plug is re-used/re-installed and washer already is compressed it will not sit as it should in all temps.
Click to expand...

very interesting. First time I've heard this.
 
Only time I've seen something like this was someone using a heavy water spray into the intake of a big block 350 at high revs, blew a good portion of the plugs out.
 
My take is that the plug had been poorly tightened or had loosened for some reason, allowing some micro movement back and forth under compression and exhaust cycles...those threads are not of much volume, and they are aluminum, which has little resistance to strike force.

Helicoil works right well to effect a repair for this...not to discount Magnus' suggestion, I just don't know of that one.
 
RajElectric said:
Only time I've seen something like this was someone using a heavy water spray into the intake of a big block 350 at high revs, blew a good portion of the plugs out.
Click to expand...

A big block 350? You been telling yer girlfriend you got a big block in that minivan again?


Interesting thought though. Like water injection on a fighter plane or a kerosene engine? Or maybe the old shock treatment for "carbon" removal.
 
SouthSoundTree- said:
very interesting. First time I've heard this.
Click to expand...

Easy to see and feel. Once plug is in seat the tension is 1/4 turn at the very most. Then washer is completely compressed and do no good.
As temps change the washer act like a spring and keep the set tension.

Jonsered and others had coned plugs once upon a time... This a experience.

Timeserts is also possible to epoxy in if all else fail. There is some fine epoxy these day's... Did this a couple times when they came in with faulty set helicoils that didn't work.
 
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