What happened to my MS390?
- Thread starter a. palmer jr.
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cuinrearview
Red saw lover
Best statement in this thread.
I wouldn`t be surprised if it tossed a circlip and tore up the bore and piston, some times one can feel the damage done but others it does not seem that or feel that bad when pulling the engine over. I only had one engine brought to me that this had happened to and I could not tell exactly why the rings were hung up until I pulled it down, seen others where the ring broke upon startup. Neither saw ever got fixed as the owners refused to pay for good parts.
If 11o is the true reading you are lacking . Do you pull till it stops rising or stop at a number?
Plus 1!
Trolling is fun, I guess. I kind of knew you were trolling right off the bat but mid thread started to doubt your intelligence a bit and got scared for you.
110 is kinda low to get it to fire. It might be a PIA,but my advise is to tear down the saw, get to the engine, and take it apart to see if anythings wrong. While there you can check ring gap etc. If it had gobs of compression then 110#, my guess is something internal like a ring catching on a port happened.
You aint going to get rich working on saws, lucky if you beeak even!! Lol. People that dont want to spend the money to make the saw right dont make it with me. There are a very few AM cylinder makers that I will consider putting cylinders on the saws I fix, Hyway being one of them, but even they have different grades of cylinders,A,B,C etc. Only get the cylinders in the Hyway branded box. Meteor is another. Used to use Tecomec many years ago. As far as the $50 new p&c go, I stay away. It might be good, chances are it wont last. And, to tear apart a saw multiple times, especially a clamshell, and get paid to tear it down once really pisses me off. Thats why I really dont like Chinese parts, especially p&c.
I haven't checked the saw any further, it's in the twenties today and I have plenty of time to check this out. It's supposed to be warmer tomorrow, might check the compression (110 was a guess). I have a 390 of my own that I put together like this one and it has stayed together for several years now and cuts very well when I have some wood to use it on...One these Chinese cylinders I think it is good to find a vendor that you've had good luck with and stick with it. One of the vendors that I've never had a problem with is Vostore. Rebuilt a few saws with their kits and so far so good...
I would like to see the comp numbers.
I think the engine would have to actually run before it tosses a circlip...As stated it only started once for a second or two and ran out of prime and quit. I didn't hear any strange noises..
I'll try to check it tomorrow if everything goes well.
If it started then it ran, the only way you will know what happened to this engine is to tear it down, it won`t be fixed by members on here. We all like a guessing game from time to time but this thread is ,
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We still talking about chainsaws?
I guess...
Not too many of the 390 used cylinders available around here...I have a few of the 45mm used cylinders and maybe a piston or two but the owner didn't want that.
Another thing that kinda bugs me about rebuilding these used 290s is that the air pre-filter is always missing. I guess the owners just throw them away. This one is missing also. I know it doesn't have anything to do with this problem but....
People that break stuff keep you in business.
OK...Curiosity got the better of me and I decided to brave the 25 degree weather and check the compression. Cold compression, cranking until the gauge stopped and it was barely 90psi. Guess I was wrong, something must have broken upon startup, maybe a ring? I'll pull the muffler tomorrow and see if there's any damage in there, supposed to be a balmy 37 degrees...Maybe I can take a pic of it if I can get this ancient camera working...
