Ms290 Big Bore Rebuild

Keepfixin · April 15, 2024, 02:12:37 AM

Hey everybody. Just got together another ms290 big bore today. Was an unbranded big bore kit from eBay for $22! Finish was real good and seem to be better than a NWP brand kit on the outside. Didn't have to open up exhaust bolt slots or modify the ground wire pocket on cylinder.
This ms290 was almost completely wore out. Lots of river silt in the air where it came from. Both bearings were getting loose and they were made in Turkey and had polyamide cages. Starter pulley hole is way oversized from wear. Had a broken clutch spring. Compression was 118 psi. Also the kill switch wouldn't stay in the off position!
So I used the lower clam shell from another ms290 bog bore build and assembled the pieces. Used SKF 6203-C3 bearings, Hyway crank seals, and sealed it with Motoseal 29132. Using a press sure made bearing installation so easy!! Let it sit in a warm area for about 16 hrs before starting. Also I modified the exhaust to a slit instead of two holes. Several pulls later it fired up and idled after 1.5 turns up on the idle. L and H needles were bottomed out rich then I moved them to just above halfway in the limiter range. Sounds great! Still waiting for clutch springs so I'll be onto another saw tomorrow. Hope this is informative to someone!

Keepfixin · April 15, 2024, 02:52:12 AM

Pictures! Box the kit came in.
Muffler after opening it up.
Stock muffler with a grinder mark on it :-)
Carbon deposits on old piston.
Piston skirt wore smooth. Left side by wrist pin still has machine marks. Then a step down to the smooth skirt!

Keepfixin · April 15, 2024, 10:55:07 PM

Just checked compression and it was 142 psi after 20 minutes of running. Definitely feel it when cranking it over! Now waiting for clutch springs to finish putting it together!