cowroy
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Can you bolt a 390 top end on a 290 bottom end, or do you need a 390 crank, bearing cup, etc.? I searched for a while but never found this exact question. TIA!
Stihl MS290 to MS390 Conversion questions?
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nmurph
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Yes.
That clears it up!
Yeah, the 1127 stuff is basically interchangeable. 390 is the same saw as a 290 with a different bore. That's why the Bailey's 390 AM top end got so much run a while back. Ya can find blown up 029's and 290's all day long for peanuts and bolt the AM 390 top end right on. They even offer the complete short block assembly for around 100 bucks "unassembled". That seems to be code for bad packaging or seals not quite right, etc. I bought an "unassembled" version and the only thing I found wrong with it was the crank was poked through a pretty ragged box. The assembly was indeed assembled and fine otherwise. I have read about guys who bought the unassembled short block who had to pull the pan and re-seat bearings, seals, etc., but they're still a decent alternative and economical fix/upgrade for a blown up 029/290......if that's really what ya wanna do with one!
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cowroy
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Thanks fells! I was just wanted to make sure before I told a family member wrong.
Is it pretty noticeable power? Would you do it again?
Is it pretty noticeable power? Would you do it again?
You're adding almost 7 cc's and .5 hp to what was a 56.7cc saw. There's a difference...especially with the muffler opened up a bit. An easy mod with a 3/8" drill bit. The carb has enough adjustment to handle it adequately. It'll be a whole different saw and pull a 24" bar, but be happier with a 20 as you might expect.
Best upgrade bang for the buck out there IMHO.
Stihlofadeal64
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Yeah what he said...
Bottom line is, now that there are decent 49mm AM kits available for the 1127 series saws? Ain't no reason to put a smaller top end back on a toasted one unless it's already sitting in your inventory and free.
cowroy
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I recently put new bearing, seals, and rings in one and I thought that just the Caber rings were an upgrade over stock.
I was worried about having to get that bar stud out of the block, so i'm glad that's not necessary.
Another thought, it seems like everyone of these things that I have looked at have been lean, including the ones that weren't burned up(yet). Is this just me or do ya'll have the same experience?
I was worried about having to get that bar stud out of the block, so i'm glad that's not necessary.
Another thought, it seems like everyone of these things that I have looked at have been lean, including the ones that weren't burned up(yet). Is this just me or do ya'll have the same experience?
machinisttx
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I pulled one out of the pile at the scrapyard last weekend. Figured it was toasted, but since it was all there except the AF cover, might as well, right? When I pulled the muffler I was surprised to find a perfect P/C. Evidently they tossed it because of the broken rope on the starter.
Depending on age, cracked intake boots seem to be a typical reason for lean 1127's. My first ever "new" saw was a MS310 that was dialed in a little on the fat side from the dealer and I kept it that way until passing it along to my son last Spring. Coincidentally, the first "used" saw I ever bought was a very nice 039, also a little on the fat side. Still had the bill of sale with it and came from the same dealer years before I bought my 310, so there may be a connection there regarding the fat tuning.
As far as that bar stud goes? If ya ever need to remove one, the easiest way is to just clamp it into a vise and unscrew the saw from the stud. Plan on replacing the stud with a new one, tho.
mad_mat222
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I just purchased a cheap copy ms390 to stick in a burnt up ms290. I didn’t want to spend a lot in case it was totally junk. Anyway, it arrived and everything is ok except the pan bolts. OEM bolt is a course thread bolt and the supplied a fine thread bolt and nearly an inch shortly. I’m trying to get the supplier to sort it out but thought I would ask if there were any variants in the models that swapped to a short bolt? I doubt it because those pan bolt the engine onto the frame. Without that there would only be the one bar bolt holding it in.
If this was a complete pre-assembled short block vs. just a cylinder kit, the short bolts were just to hold it together for shipping. Regardless, you'll still need to use the long bolts to put everything together. They're self-tapping and should re-thread into the cylinder without issue. The cylinder kits themselves are rarely threaded and typically require threading by the original bolts. The self-threading bolts are normally what are used in all the Stihl clamshell saws.
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The 290s do run lean. Mine did for 10 years. In solving a sluggish reving that had developed, I removed the limiters and got it running better then new. You can leave it running lean like I did and do no harm to the saw. Then wait til you have to address a problem and fix it. I was glad I finally got around to it. A much better tool once tuned correctly.
This is an 8 year old thread.
mad_mat222
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Does age really matter. Itake relevant to a conversion so why re invent the wheel.
I get the self tapping screw but did you look at the picture. Two completely different threads. I would imagine that if you were just supposed to use the bolt on the right, it wouldn’t be tapped with a fine thread
I get the self tapping screw but did you look at the picture. Two completely different threads. I would imagine that if you were just supposed to use the bolt on the right, it wouldn’t be tapped with a fine thread
Just go to the hardware store and get socket head MACHINE screws the same length as the OE ones. Add a flat washer under each.
The replacement cylinder is tapped properly for the machine screws. Running in the OE self tappers is tempting fate.
I’ve seen where the OE shake loose and fall out.
The replacement cylinder is tapped properly for the machine screws. Running in the OE self tappers is tempting fate.
I’ve seen where the OE shake loose and fall out.
I was commenting on the other response to the 8 year old quote, not your post.
Regardless of what came with your kit, machine screws are not the correct fastener for the application..., especially ones that are too short. But they'll strip right out anyway.
I clearly noticed the difference between the two types of screws and threads. I've also used a ton of these kits in both short block and cylinder only form.
Take my advice, or leave it..., including not to expect much response from the vendor who sold you the kit.
I'll spare you the part about sealant and pressure/vac testing.
Good luck with it.
Stuff one of these in it. https://www.hlsproparts.com/Stihl-039-MS390-Pop-Up-Piston-Kit-p/cp31039.htm
I've done several of these conversions, in fact when I rebuild a 290 I always put a 390 piston/cylinder in it along with new crank seals. I have one I kept for myself but seldom get a chance to use it...
