ms 440 magnum spark plug hole threads

[alabama xl]

I was just given an stihl MS 440 Magnum that is kind of a beater, but I'm hoping to get it running on the cheap in order to use as a small chainsaw mill and as a felling saw. I cleaned up most of it, and under the grime and dents it doesn't seem to be in really terrible shape. It is missing the bar adjuster, and a few screws on the top cover. and I need a spark plug. The guy who gave it to me said that it had blown the spark plug out of the cylinder, but to be honest, I cannot quite see how that could happen... maybe they didn't seat the plug properly? the mating surface for the washer looks nice and black, which doesn't seem like a good sign. outer threads are not really salvagable as far as I can tell.

I'm looking at putting in a threaded insert, and the best looking design seems to be the keensert. Any thoughts about these or others?

I was also wondering whether I should drill out and thread for a larger spark plug thread and find one with bigger thread and similar heat range to the original. Is that something that gets done ever with success?

The saw seems to have good compression so I'm hoping after spark plug fix that it will fire up and run without trouble.

If the spark plug repair doesn't work out, I was thinking about putting on oversized cylinder kit. What's the biggest that I can put on this saw? and if I put on the big bore cylinder do I need different carb/muffler to match?

 

[alexcagle]

Big bore is 52mm.
Time sert is the best, but pricey for the kit.

 

[blsnelling]

Timesert is best. However, a properly installed helicoil will work just fine.

 

[alabama xl]

my neighbor turns out to have a couple different kits. with any luck it will be the good kind. I'm gonna pull the cylinder tonight and hopefully there are no other demons lurking in there, but to be fair I got what I paid for, a free saw...

 

[alabama xl]

I've seen folks put the 460 top end on the 440. and they sell a big bore kit for the 460... And i sort of think I saw something in the last few days about someone doing that, but didn't see what all else needed doing. I'm hoping for the quick and easy fix with this cylinder for now, and use it until it croaks. This is my first stihl that I've had apart, and I've gotta say it's much better designed than the cheapies that I learned to work on as a kid. so much easier to take things apart to clean and fix. I bought a little husqvarna 435 a while back after seeing good reviews from folks. it's been relatively nice to me once I had it tuned properly, but if you have to take the carb off for anything, it's much more of a pain than it should be. and the way they stuck the oil fill hole under than handle is less than stellar design. overall I've been a lot happier with the top handle stihl that my neighbor has than I have been with the orange saw, and wish I had gone with the stihl back then too. I'm hoping this 440 is just as nice as that little arborist's saw is, but bigger and more powerful once it's got a spark again.

 

[alabama xl]

so I ended up doing this the wrong way. I had the insert type thread repair kit from my neighbor and tried to do it with the cylinder in place. As someone else noted in another thread, there aren't enough threads in a chainsaw spark plug hole to keep the tap straight. so the threads got in there slightly cocked. My buddy says to ignore this and just put the insert in, put in the spark plug and run the thing, but I don't like things to be half-arsed when I'm doing the work.

I'm wondering if anyone has ever tried something like cutting tapered pipe threads in the hole and putting a piece of aluminum in there with tapered threads to match and then boring a new spark plug hole? I have a bridgeport mill that I can pretty easily set up to get things right. I'm kicking myself a bit for not having used it to line things up for this steel insert and tap from my neighbor... This is a nice OEM stihl cylinder with little wear, and I hate for it to be trashed because of crappy spark plug thread repair. Overall the saw looked like a mess when I got it, but it has cleaned up pretty nice for what it is (free). It's almost like someone barely used it, but had a dull chain and/or left it in the mud or something.