ms880 MS880 Rumbling noise

[Muddy42]

23 hours ago, KMWilliamsWoodcraft said:

hey guys, i recently put a new meteor piston kit in my ms880 as the previous piston put in by the PO was a cheap Chinese golf brand and it was scored up and actually had a crack in it...it was running ok however was low on compression hence why i put a new piston in.  While i was doing this i also put in two new crank seals, exhaust and base cylinder gasket. Saw is now at 165 PSI compression HOWEVER there's now a strange rumbling noise ive not heard before and it wasn't there before, nor is it present on my other ms880. 

The saw seems to be running lean and doesn't want to idle if the screw is set low and it cuts out sometimes and bogs out. When it cuts out it can be hard to start again but will fire up easily if the choke is on... prior to the new piston it was actually running pretty well. I didn't remove the carb. In this very poorly taken video you can hear the low rumbling noise and it seems like its coming from the flywheel side. I swapped over the entire clutch side from my other 880 to this one and the noise didn't go away so i can clarify its nothing to do with that side. There is also 0 play in the crankshaft either side, no up down no left right its all tight so im assuming that means the bearings are good? but it sounds like a bearing rumble...

Has anyone experienced this before? Im going to try and get a vacuum/pressure tester and test for air leaks as i feel its running lean and then move on to the carb and check the impulse line, does this sound like a good plan of action?

cheers everyone!

and heres the old piston i pulled out...cylinder wasnt bad at all, came up good after a little scrub up.

 

 

I've just checked your video of the GOLF piston again.  As you say, you have pretty bad damage on both the exhaust side and intake sides.  Its a good thing you replaced this.  Also where both circlips intact? Did the new meteor piston have any play or tolerance?

 

[KMWilliamsWoodcraft]

48 minutes ago, Muddy42 said:

 

I've just checked your video of the GOLF piston again.  As you say, you have pretty bad damage on both the exhaust side and intake sides.  Its a good thing you replaced this.  Also where both circlips intact? Did the new meteor piston have any play or tolerance?

 

Hey bud, yes both circlips were intact. the intake side of the cylinder was pretty much perfect, the exhaust side had some transfer which i cleaned up. new piston was a nice fit and didnt seem to have any slop.

[KMWilliamsWoodcraft]

If i am going to tackle this rebuild myself, what do i need to buy in total and replace if im splitting the crankcase and replacing the main bearings? this would be my first time undertaking such a job.

[spudulike]

The grey plug colour is where the piston has overheated and the aluminium has vaporised and spattered on to the plug. This is the stage after being white (overheated).

The piston has partially melted although the saw has continued to run. I would say that the melted aluminium has probably worked its way down to the main bearings. Typically this can cause the saws bottom end to make a "hollow" rumbling sound, I had the same on my 357.

What do you need to do the job - experience or/and a decent dollop of engineering skills.

The main difficulty is how you do the actual splitting of the cases -  I did do a tutorial on a 660 some time ago on my "whats on your bench" thread. I have pics of what I used - a BIG G clamp, a splitter - donated by ADW (Many thanks) and a homemade splitter - two pieces of angle iron.

Don't use a big hammer on it, a positive is that this machine is BIG and is therefore easier to get splitters in. Once you have all the bearings and crank in, the crank will feel tight so bash each crank end with a copper mallet to take any stress out and the crank will become much smoother to turn - like silk.