How to identify an MS390 vs MS310

[msbrockman]

I am looking to buy a Stihl MS390. I found a saw that has MS310 decals on it but the owner/seller says it is an MS390. How can you positively tell the difference without disassembly?

 

[Pablo26]

I would want a paper trail of receipts showing how it became a 390, unless you knew the seller personally. There is also probably some way to run the serial number to see what it was originally. Does the seller state it was converted?

 

[msbrockman]

There is no paper trail or anything other than "his word"

 

[discounthunter]

walk away,unless he gives you a good price on a used 310.

 

[mwood1986]

walk away,unless he gives you a good price on a used 310.

I agree.
I'm new to saws and yet that just sounds way too fishy, and if he did convert it to a 390 somehow by boring and replating or rigging an 039/390 cylinder in it, is he a small motor repair man or just some dude that just rigged it together

 

[tboarder2602]

310 v 390

A stock 390 will have a decompression button, while a 310 does not. A 310 can have a larger piston & cylinder put in it and it will be the same size as a 390. A stock 390 has a 49mm diameter piston while the 310 has a 47mm (i think) . My first instinct would be to look for the decomp button. If its there, the saw is a 390. If not, it could be a 390, 310, or 290 and the only way to know is tear the saw down and measure the bore. All 3 saws are built on the same chassis.

 

[msbrockman]

Tom, Thanks.
That was extremely helpful!

 

[Streblerm]

On the 390/310 the cylinder and crankcase are all together (clamshell design) so to upgrade, one would need to replace the entire engine, not just the piston and cylinder. Otherwise it could just have had the covers switched around, or, it could be the guy is lying to you.

Any way you look at it, it is probably assembled from parts. Near me a 390 goes for about $500 and a 310 is about $400 new depending on the bar. I sure wouldn't pay more than half of the new price for a used saw of questionable history, and that would only be for a super nice example.

 

[treesquirrel]

Grab your wallet and run! Sounds like a scam to me.

 

[vw_motorsports]

As Tom stated, the 390 has a decomp button on the head and the rubber boot on the top cover. I personally have just recently converted a ms310 "straight gas death" to a ms390, the reason, Meteor does not manufacture an aftermarket piston for the 310 but they do for a 390. I was able to buy a good 390 oem cylinder and aftermarket piston for about the same price as an oem piston. A win, win combo.

As Tom stated, the 290, 310, 390 are built on the same chassis...same cranks and rods, everything is the same, just swap cylinder's and piston and you have a 390. You do have to modify the top cover for the decomp valve, it hits the top cover, and reset the carb. I had to pull the caps to get enough fuel for the CC's and muffler mod. So if the buyer says it's a 390, go to stihl's website or dealer and look over a 390 really well, he may have done the same as it costs approx the same to do the conversion. I have pics of the conversion if interested.

 

[splitpost]

my 390 doesn't have a decomp,sitting side by side with the 310 they are identical except for the badge on the starter cover, you can tell without pulling the p&c,on the side of the cylinder it has 310,390 etc cast into it just need small mirror and flashlight to see

 

[vw_motorsports]

send me your email and I'll send a pic of the cylinder I have

 

[splitpost]

310 cyl

 

[Saw Dr.]

I knew this would help someone eventually.

http://www.arboristsite.com/showthread.php?t=98960&highlight=1127+cylinder

Not all 390's have the decomp. Pull the flywheel and have a look, or pull the muffler and measure the bore. If he says no, walk away. 039/390 is 49mm, 310 is 47mm.

 

[SawTroll]

I knew this would help someone eventually.

http://www.arboristsite.com/showthread.php?t=98960&highlight=1127+cylinder

Not all 390's have the decomp. Pull the flywheel and have a look, or pull the muffler and measure the bore. If he says no, walk away. 039/390 is 49mm, 310 is 47mm.

Right - the ones that doesn't have it are the older ones, as far as I know.

Anyway, if someone changed the engine, and can't prove that the new one actually was a new OEM one - run away!

 

[bitzer]

Right, the decomp valves have been on the 390s for only a few years now. You can replace the top end and nothing else on all three saws. If the top cover has a squarer design it will not have a decomp valve. If it has a more rounded design it probably will. Stihl updated the 390s around '05 I think. I don't think a full part number exists on the outside of the cylinder, but I can't remember for sure. Bore measurement might be the only way for sure.

 

[Big_Saw]

Don't be so sure.

A stock 390 will have a decompression button, while a 310 does not. A 310 can have a larger piston & cylinder put in it and it will be the same size as a 390. A stock 390 has a 49mm diameter piston while the 310 has a 47mm (i think) . My first instinct would be to look for the decomp button. If its there, the saw is a 390. If not, it could be a 390, 310, or 290 and the only way to know is tear the saw down and measure the bore. All 3 saws are built on the same chassis.

Some 310 models have decomp buttons.

 

[nmurph]

Some 310 models have decomp buttons.

i don't believe that was a factory option.

 

[nanuk]

029 => 290 => 039/390

I've got some 029/290's and a 039 topend... when I'm ready, gonna get a piston and drop it in... doesn't appear that hard.

just need to make sure I've got the H/L to adjust! I"ve not heard of them NOT having them.. but if so, I have some spares. then probably a muff mod


if I do sell it after, I'd NOT lie about it... just let them know they have the bigger engine. No big deal as it's a frankensaw anyways.

 

[indiansprings]

The 290/310/390 are all built on the same chassis, visually really can't tell the difference. You can easily make a 290 a 390 by installing the jug and piston on the 290, same thing with the 310 you can take one and install the 390 jug and piston on the 310 and have a 390. You could so the opposite if you were nuts, take a 390 and install a 290 cylinder and piston. The swap would take about 4 1/2 to 5 hours for me to do it because of the clamshell design, it's really no big deal. I would want to know why the saw fried the 310 cylinder and piston first of all, secondly he should have a trail of where he got the jug and piston.
I would pass if it were me.