Convert stihl ms290 to ms390 or not

[Big-Cigar]

I blew up my ms290 and need a rebuild kit. People are saying make it a 390 with a slightly bigger kit that will fit. Are there any drawbacks of getting the 49mm kit as opposed to the 46mm kit. Do I need any additional parts? Ps. My mechanic is doing it.
Thanks

 

[Wood Doctor]

I have done it several times with with no additional parts, assuming you do not need a decomp valve for the big bore. Most guys can get along without it and just plug the decomp cylinder port. One time I drilled a 1" da. hole in the 290 shroud for access to the decomp valve.

 

[Big-Cigar]

Thanks, my mechanic will do what ever I want. Just doing a little research first.

 

[Jasonrkba]

I have done it several times with with no additional parts, assuming you do not need a decomp valve for the big bore. Most guys can get along without it and just plug the decomp cylinder port. One time I drilled a 1" da. hole in the 290 shroud for access to the decomp valve.

What he said.

 

[sean donato]

Do it. No point in not doing it. Either top end costs about the same as the other, and both use the same bottom end/case.

 

[Fatherwheels]

Do it. No point in not doing it. Either top end costs about the same as the other, and both use the same bottom end/case.

Will the 290 muffler bolt on to the 390 cylinder.

 

[sean donato]

As far as I can remember I reused everything save the top end from the 290 on the 390.

 

[Binthewoods]

Everything is the same, the only extra part you need is a plug for the decomp on the 390 cylinder.

 

[ironman_gq]

The 290,310,390 are all the exact same saw with different cylinders. Everything should bolt on without modification, you will need to adjust the carburetor afterward though.

 

[a. palmer jr.]

Will the 290 muffler bolt on to the 390 cylinder.

Yes.

 

[a. palmer jr.]

I have found absolutely no disadvantages of converting the 290 to a 390. I've done it several times and if I owned the 290 I wouldn't hesitate to convert it when it needed a top end. One thing I would recommend is the heat shield that the 390 saw uses between the muffler and the cylinder and the 290 does not. I always put them in my conversions...

 

[Chevboy0167]

Any thoughts on these palmer?

https://www.ebay.com/itm/202222625925?hash=item2f15686485:g:IZ4AAOSwptNasoKR

 

[a. palmer jr.]

Any thoughts on these palmer?

https://www.ebay.com/itm/202222625925?hash=item2f15686485:g:IZ4AAOSwptNasoKR

I've never used them but would probably be okay. I always bought the ones on ebay that were made of gasket material and they worked fine too at a smaller price. I have one on my current 390 and if I do any more I'll use the ones I've been using, but to each his own...

 

[Chevboy0167]

I was just curious if anybody has used them with any real world use and if they actually drop temps. Like taken cylinder and muffler temps before and after install.

I just finished a MS290 rebuild to stock. No deflector there of course although I could tear the loud box off and slip one on there.

Thank you.

 

[Ando81]

I stripped the spark plug thread on my 290 so I put the 390 too end on it. It is still running in but is going well so far. I just plugged the decomp hole and it’s easy enough to start. I probably should have looked around for a genuine top end but didn’t have a lot of time so I threw a Chinese one on and I’m reasonably happy with it. I did make sure that I used the original piston pin circlips in it though, hoping that it stays together.

 

[a. palmer jr.]

I stripped the spark plug thread on my 290 so I put the 390 too end on it. It is still running in but is going well so far. I just plugged the decomp hole and it’s easy enough to start. I probably should have looked around for a genuine top end but didn’t have a lot of time so I threw a Chinese one on and I’m reasonably happy with it. I did make sure that I used the original piston pin circlips in it though, hoping that it stays together.

I never put the Stihl circlips in a aftermarket piston, tried it once and it didn't seem like it fit too well so I stuck to the aftermarket clips. Seemed that the groove was made a little different than the Stihl one was. Maybe if I'd used a different vendor it might be okay.