029 Super to 390 need direction plz

[BrandoninColorado]

Hello everyone, cutting season has begun on blm and I'm looking to harvest my usual pinyon and juniper for personal use. My buddy and I work together and his saw took a sh*t last year. The Ace True Value guy said it was lacking compression so I went and purchased a cylinder assy that's 49mm. I'm mechanically inclined but this is new territory for me. It's a surprise for my cutting buddy and I'm looking for direction on how to successfully complete the upgrade. Is there anyone willing to take me through this from the first step to the last? I'll need everything to be dumbed down for me I have never had the reason to tear into a small engine before. First thing I'll need is a list of sealants, cleaners, tools, and I don't know whatever's needed for the job so I can get it all setting in front of me ready to tackle this bad boy. Thanks

 

[HarleyT]

Look and see if there is any videos of it on youtube, so you can see how it is put together. The bottom cap of the engine is a problem to remove, as one has to remove the bar stud. I have heard of folks rebuilding the saw with the bottom cap still attached to the crankcase, but it is likely a real pain in the arse.

 

[svk]

I needed a pair of vise grips to get that stud out. It’s in there very tight and even after it’s loosened several turns it still takes effort to remove.

Overall this model is kind of a pain to work on but in the big picture you’ll only hopefully be rebuilding it once.

Just get the new piston and cylinder as well as seals, disassemble the saw, and reassemble. I used Motoseal for sealing the case.

 

[Jed1124]

Does the 390 use a bigger jet in the carb as well?

 

[svk]

No jets, the carb may need tuning once it’s running.

 

[Jed1124]

No jets, the carb may need tuning once it’s running.

Perhaps a larger Venturi? Not that it’s required to run I just remember people saying in years past that the 390 used something to deliver more fuel than the 290.

 

[Freudianfloyd]

I needed a pair of vise grips to get that stud out. It’s in there very tight and even after it’s loosened several turns it still takes effort to remove.

Overall this model is kind of a pain to work on but in the big picture you’ll only hopefully be rebuilding it once.

Just get the new piston and cylinder as well as seals, disassemble the saw, and reassemble. I used Motoseal for sealing the case.

I always have trouble removing the bar stud. I have however become pretty good and assembling the saw without removing the bottom portion of the crankcase. Its a little trickier, but it can be done.

 

[svk]

Perhaps a larger Venturi? Not that it’s required to run I just remember people saying in years past that the 390 used something to deliver more fuel than the 290.

You sure could bolt on a different carb but then you are potentially looking at other modifications as well.

 

[kr5258]

HD-18 carbs used a 0.56 jet on the 290 and a 0.58 jet on the 390.
HD-19 carbs used a 0.58 jet for both.