MS290-390 replacement cylinder question

[Wood Butcher]

Just picked up a new to me MS290 that has had the cylinder replaced. Peering under the plastic I noticed it has a decompression port plugged off, so I am wondering if anyone has seen cylinders other than the 49mm/MS390 jug that had a compression relief valve?

If I were really curious I'd pull off the muffler and measure the bore, however the saw seems to run pretty good at the moment so it is more of a curiosity thing than anything else, but wondered if there might be a less intrusive way of figuring out what is on it.

Thanks!

WB

 

[Johnsobri]

Just picked up a new to me MS290 that has had the cylinder replaced. Peering under the plastic I noticed it has a decompression port plugged off, so I am wondering if anyone has seen cylinders other than the 49mm/MS390 jug that had a compression relief valve?

If I were really curious I'd pull off the muffler and measure the bore, however the saw seems to run pretty good at the moment so it is more of a curiosity thing than anything else, but wondered if there might be a less intrusive way of figuring out what is on it.

Thanks!

WB

It is an aftermarket jug and maybe piston. I know some of the aftermarket stuff came with a decomp port. Might want to measure it as it maybe a 49mm 390 kit.

Brian

Ha after reading your post again looks like I didn't answer anything!

 

[Stihlofadeal64]

Pull the muffler and check it. Some have suggested using a straw, but be careful. I'd say it is probably an aftermarket MS390 cylinder. I've worked on hundreds of MS290's, and never seen one with a decomped cylinder that was not the MS390 top end. It may be a first, I won't say never...

 

[Wood Butcher]

Instead of a straw I'll just use the depth probe on a digital caliper- put the piston up enough to cover the port, take the measurement from the exhaust flange to the piston, hit zero and move the piston down and measure to the other wall.

Works faster and more accurately than pushing a straw in there, rotating the engine while explaining something to your wife, then removing the jug to retrieve the cut piece of straw and finally measuring it...

However, at this point it is more of a curiosity than anything else, I'd like to run it for a while before taking it apart but just wondering if there were a different number of fins on the different cylinders or anything?


WB

 

[Wood Butcher]

OK I admit it I lied, I pulled the muff today and measured it, 49mm so I guess I have a 64 cc saw instead of a 56 cc one.

Anyway, as far as I know everything else is still stock 290 stuff. Should I worry about a different carburetor? Seems to run fine but I haven't gotten into any wood yet (still need to dress and sharpen the chain).

Anything else I should look into before wood cutting season? I have a dead oak to deal with in the next week or two. It has an 18" bar and 325 pitch chain, which is fine for me as both my other saws (MS250 and Husky 350) use it too so only have to have one sharpening setup.

Also, it still has the screen on the muffler, should I get rid of that or leave it? It is clean right now but since I don't really have to worry about forest fires where I'm running this saw I'm tempted to remove it.

Have to admit I'm kinda anxious to see what 64c does with an 18" bar and 325 chain!

 

[H 2 H]

OK I admit it I lied, I pulled the muff today and measured it, 49mm so I guess I have a 64 cc saw instead of a 56 cc one.

Anyway, as far as I know everything else is still stock 290 stuff. Should I worry about a different carburetor? Seems to run fine but I haven't gotten into any wood yet (still need to dress and sharpen the chain).

Anything else I should look into before wood cutting season? I have a dead oak to deal with in the next week or two. It has an 18" bar and 325 pitch chain, which is fine for me as both my other saws (MS250 and Husky 350) use it too so only have to have one sharpening setup.

Also, it still has the screen on the muffler, should I get rid of that or leave it? It is clean right now but since I don't really have to worry about forest fires where I'm running this saw I'm tempted to remove it.

Have to admit I'm kinda anxious to see what 64c does with an 18" bar and 325 chain!

The carb will work just fine

 

[griffonks]

OK I admit it I lied, I pulled the muff today and measured it, 49mm so I guess I have a 64 cc saw instead of a 56 cc one.

Anyway, as far as I know everything else is still stock 290 stuff. Should I worry about a different carburetor? Seems to run fine but I haven't gotten into any wood yet (still need to dress and sharpen the chain).

Anything else I should look into before wood cutting season? I have a dead oak to deal with in the next week or two. It has an 18" bar and 325 pitch chain, which is fine for me as both my other saws (MS250 and Husky 350) use it too so only have to have one sharpening setup.

Also, it still has the screen on the muffler, should I get rid of that or leave it? It is clean right now but since I don't really have to worry about forest fires where I'm running this saw I'm tempted to remove it.

Have to admit I'm kinda anxious to see what 64c does with an 18" bar and 325 chain!

Did you start the saw yet?

Congrats on the extra CC's.

I'd like to know what your compression is with the new cylinder and piston if you have a tester too.

 

[Wood Butcher]

I haven't run it much yet, just to verify that it started and ran. I need to mix up a separate batch of slightly rich break in fuel first, may not be necessary but makes me feel better. I'll take a compression reading in the next day or two

GM

 

[MasterMech]

If it has a stock 290/310/390 muffler on it then I'd open it up for sure. Guarantee it's gasping for air as the stock mufflers on these are very restrictive. I'd up the sizing on the rim sprocket too. Your leaving a lot of speed on the table running a stock 7/8 pin spur sprocket. I'd go at least 8 pin if not 9 with a rim sprocket conversion. IIrc the 290 has a different oil pump than the 390 but unless you want to go bigger than 18" of bar you should be fine.

 

[Stihlofadeal64]

I haven't run it much yet, just to verify that it started and ran. I need to mix up a separate batch of slightly rich break in fuel first, may not be necessary but makes me feel better. I'll take a compression reading in the next day or two

GM

You should be fine on the break in. You can actually tune the saw to run rich as well during the break in in you desire. I set the saws up for 12000 rpm on top (with a wireless tach). Then as you become more comfortable you can lean it out to the Stihl spec 12,500 on the top end (no load). Having the extra cc's in the saw is a blessing. Enjoy! :msp_thumbup:

 

[sefh3]

There was a craze about 6 months ago for 290s when Bailey's put their kits on sale for $99. I know a ton of 290's were upgraded to 390's. It's a great improvement to these saws when you mod the muffler and tune the H after opening it up. Run 50:1 and richen the H up some. Great saw for sure!!!

 

[H 2 H]

There was a craze about 6 months ago for 290s when Bailey's put their kits on sale for $99. I know a ton of 290's were upgraded to 390's. It's a great improvement to these saws when you mod the muffler and tune the H after opening it up. Run 50:1 and richen the H up some. Great saw for sure!!!

View attachment 311708

View attachment 311709

View attachment 311710

:msp_tongue:

 

[Ymountainman]

This is my ms390

IMG 6008 - YouTube

 

[Wood Butcher]

Did you start the saw yet?

Congrats on the extra CC's.

I'd like to know what your compression is with the new cylinder and piston if you have a tester too.

I just managed to find one of my testers, I have 3 or 4 of them but of course I can't seem to find the nice one when I really need it..

Anyway, compression is 143 PSI but it was measured with an old gauge so it may be a few PSI's off, I'll check it again when I find another one but the way my shop looks that might be around Christmas.

 

[Wood Butcher]

If it has a stock 290/310/390 muffler on it then I'd open it up for sure. Guarantee it's gasping for air as the stock mufflers on these are very restrictive. I'd up the sizing on the rim sprocket too. Your leaving a lot of speed on the table running a stock 7/8 pin spur sprocket. I'd go at least 8 pin if not 9 with a rim sprocket conversion. IIrc the 290 has a different oil pump than the 390 but unless you want to go bigger than 18" of bar you should be fine.

I'm planning on getting a rim sprocket eventually, I have a 30" bar made for 3/8" chain and it would be convenient to bolt on for the occasional large tree. Regarding the rim sprockets, I haven't really looked yet but where are some places to get them? I pretty much buy all my chainsaw stuff from Baileys if I buy it online, however I'm open to other suggestions. Thanks for suggesting going up a tooth or two!

I've removed the screen from the muffler, I plan on drilling it but I'd like to run it for a bit first so I can better judge if I get any performance boost, right now I have nothing to base what that would be.

 

[jd2007]

IIrc the 290 has a different oil pump than the 390 but unless you want to go bigger than 18" of bar you should be fine.

I've recently done the 290 to 390 swap & had read about updated 390 oil pumps but everything I found stated the 290 & 390 oil pumps were the same?

 

[MasterMech]

I'm planning on getting a rim sprocket eventually, I have a 30" bar made for 3/8" chain and it would be convenient to bolt on for the occasional large tree. Regarding the rim sprockets, I haven't really looked yet but where are some places to get them? I pretty much buy all my chainsaw stuff from Baileys if I buy it online, however I'm open to other suggestions. Thanks for suggesting going up a tooth or two!

I've removed the screen from the muffler, I plan on drilling it but I'd like to run it for a bit first so I can better judge if I get any performance boost, right now I have nothing to base what that would be.

My notes on the sprocket assumed you were running .325 chain (common on the 290). If you're running 3/8" I would suggest staying with 7 pin rims but e perils ting with an 8 pin is cheap and easy!

 

[MasterMech]

I've recently done the 290 to 390 swap & had read about updated 390 oil pumps but everything I found stated the 290 & 390 oil pumps were the same?

Iirc the IPL for these lists a different oil pump for the 290 vs the 310 and the 390. I would have to double check when I get home however.

 

[AKDoug]

My IPL does not show a different one. However, the original part has been superseded a couple times.

 

[Terry Syd]

Here's a thread with pictures of the various pumps and the Stihl numbers - http://www.arboristsite.com/chainsaw/242389.htm

I just popped in the upgraded piston rod on my old pump. It changed the stroke distance from .4mm to .88mm.

The newer pumps have what appears to be a piston on top of the rod. It is not a 'bearing', it is a piston to keep the volume of the cam chamber the same as the piston rod moves. You can pack the cam chamber with grease and not have to worry about it getting pumped out.