There are a LOT of options- some great, some good and some not so good.
The so called 56mm big bore kits from Asia- while cheap- will gain you nothing over the original and quite possibly run worse than the original bore size OEM cylinder and piston.
Original bore size was 54mm.
T27 Torx is the size you need for most anything MS660.
If you intend to continue milling with the saw- OEM is your best bet, Meteor next and Hyway if you must- this is my opinion- I am sure others will jump on and tell you the exact opposite and rave on how their 56mm big bore can outstrip an 088 on a mill, in my own experience- this is not the case. You have to form your own opinion, but milling is hell on chainsaws compared to occasional bucking with short bars.
Next question is, are you entirely sure the original cylinder cannot be saved? Many can- it just takes some work to get rid of all the transfer from the piston to make them good again- they can look beyond saving, but under the muck- they are still gold.
Then you have to know why you came to the position the saw needs a new top end- why did it fail? You need to find that out and correct it before you replace the top end and have it do the exact same soon after.
Thanks.. I'll go for 54mm.
I just pulled it all apart. The cyclinder isn't too bad.. Feels baby smooth except a tiny tiny 2 spots where the rings mashed into it. What's best way of trying to get it off to try to save it? Emry cloth?
The saw is second hand from an arborist who sold his stuff off. A friend of mine. I got it for like 125$ and used it to buck wood for 4 years. I just started milling with it. I knew when I got it that it was a bit worn. But for bucking wood it worked fine, even for milling.
Why it all of a sudden blew up? Not sure.
It was a fresh jerry can of mix- 40:1. I've mixed this in this can at this ratio many many times. I used stihl 2 stroke oil as always.
I did recently poke some holes in the muffler and take out the spark arrestor. But I adjusted the carbs properly. I have a digital tach that I use. I milled a bunch of wood with it since I did the muffler work and had zero issues.
Brand new spark plug and air filter. Literally 10 mins old when the saw just died. I was able to get it going once more fairly easily since I didn't know why it died, but then it died again. Came home, had good spark, no fuel issues and so I pulled the muffled off and saw the damage. 75 psi.
The boot between the carb and head looked new.
I never use the decompression button, but maybe it had a vacum leak? I will be putting a plug in when I get it going again.
I could throw a new top end kit and have it pressure tested..
