Another MS290 Rebuild Thread

[94BULLITT]

I got a MS 290 that had been straight gassed. It is a pretty good looking saw. Forgot to get a pic of it before I tore it down. I got a ebay MS390 cylinder for $27. I also got a set of AM bearings and seals. The bearing will be in Monday.

Here is the tore down



New piston




Cylinder






Any thoughts on the cylinder? I think they should have chamfered around the ports better.

Cranks seals, wrist pins, rings



I don't link the clips that came with the cylinder. I may reuse the old circlips or buy new ones.

Right now I have the degree wheel on it but that is all the farther I got. Maybe tomorrow I'll find TDC and get some numbers. This is my first time porting a saw.

 

[TJ the Chainsaw Mechanic]

 

[94BULLITT]

I also have an 039 that is muffler modded so I can swap the stock muffler of this saw on the 039 for a comparison when I get done.

 

[MustangMike]

I recently converted a 029 to 390, it runs, but still waiting on some parts.

I was going to play with the ports, then decided not to, they did not look that bad, and these saws are just weird! I think it would be easier to do/learn porting on a more traditional saw. You can't delete the gasket or cut the base on these things.

Good luck with your project.

 

[huskihl]

I picked up a smoked ms310 and put my 039 motor in it. I widened both the exhaust and intake, and squared off and lowered the bottom of the intake a few degrees. After a mm, it absolutely smoked a stock 039. They like to breathe better both in and out. I never touched the ignition timing tho. That might help too

 

[fearofpavement]

You will HAVE to do some level of muff mod if you only have the two small slots in the outlet of the muffler. It just won't breathe enough to run well. Some mufflers had more openings. Probably as much as any saw out there, these are really choked down and opening them up a bit makes a significant difference in power output.

 

[MustangMike]

Finally got all my parts today, and my 029/390 conversion seems to be running well. Got it to idle smoothly, and it feels good, but the chain I threw on it is dull and needs to be sharpened, then I will know how it feels.

Just happy my parts all finally came and it runs well.

 

[94BULLITT]

Here are the timing numbers from my AM cylinder

INT- 159
TRANS-120
EXH- 166
BD-19

 

[huskihl]

Here are the timing numbers from my AM cylinder

INT- 159
TRANS-120
EXH- 166
BD-19

Ex dur is 166? Or 156? Your bd # is off a bit.

166 is really high. That's an opening of 97. 120 xfer gives 23° bd. 156 ex duration opens at 102. Which would be more normal with a bd of 18

 

[94BULLITT]

Ex dur is 166? Or 156? Your bd # is off a bit.

166 is really high. That's an opening of 97. 120 xfer gives 23° bd. 156 ex duration opens at 102. Which would be more normal with a bd of 18

I'm pretty sure it is 166 but I can check again in the morning.

 

[drf256]

Kevin is correct. Numbers are off.

23* of BD is what you want on a quad. The cylinder looks ok. You have a great guide for how wide you can go built right in, provided the piston skirts are the same width or better.

I'd only touch it if you feel comfortable doing it. You'll need to make sure you chamfer your ports correctly at the end.

I'd just leave it alone, personally.

 

[94BULLITT]

@huskihl I checked again this AM, exhaust is 166.

 

[94BULLITT]

Kevin is correct. Numbers are off.

23* of BD is what you want on a quad. The cylinder looks ok. You have a great guide for how wide you can go built right in, provided the piston skirts are the same width or better.

I'd only touch it if you feel comfortable doing it. You'll need to make sure you chamfer your ports correctly at the end.

I'd just leave it alone, personally.

I wanna do something to the cylinder. Why do you say you would leave it alone?

 

[Chainsaw Jim]

I like the exhaust port, that thing looks huge and has a good shape. The intake sucks butt. Is that a little ramp on the floor that pitches the charge upwards and away from the crank bearings? I'd definitely hog out that intake. The chamfer bevel only needs to be relieved a measurable amount for the rings when the plating is intact.
Even on oem cylinders the open ports can have very sharp edges and though the rings may not make contact, the piston skirts do and it can cut into them pretty good.

 

[czar800]

Some good popcorn!

 

[Terry Syd]

When I looked at the 390 cylinder with that 'lip' in the bottom of the intake port I had to think 'why did they do that?'. It appears they were directing the intake charge to go in horizontally in order to maximize the time/area for the timing. If the port goes in at an angle it reduces the 'area' of the port.

I suppose the factory worked out the time/area they wanted for the engine and then designed the intake port to get that time/area.

 

[drf256]

I wanna do something to the cylinder. Why do you say you would leave it alone?

Cause you're apt to make it worse than it is and it's a clam shell motor that's difficult to make changes on.

 

[94BULLITT]

I was checking BD wrong, I have 23-24*.

 

[huskihl]

If you wanna play, widen the intake and exhaust to within 2mm of the skirt and take that lip out of the bottom of the intake. And dont raise or lower the exhaust, just polish it up. Mine runs with my ported 036 just fine

 

[94BULLITT]

If you wanna play, widen the intake and exhaust to within 2mm of the skirt and take that lip out of the bottom of the intake. And dont raise or lower the exhaust, just polish it up. Mine runs with my ported 036 just fine

Should I do anything with the intake timing?

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