394XP Main Bearing Case Wear?

[TravfromNZ]

There is a reason that 394 ended up in the "too hard basket" at the dealers eh? That missing bit might be it.
Did you happen to ask if anyone there remembered why the saw in question was retired? If it was burned out because of an unexplained air leak........

I didn't bother asking but the other half was worse. It looks like someone had tried to pry the main bearings out with a screwdriver and caused decent damage in the process. This one is fixable though and I'm fairly confident that things can be reassembled without an air leak. The piston and cylinder were still on the cases and it looks like it had run slightly hot/lean at some point - with some light scoring on the exhaust side of the piston and ally residue on the cylinder.

 

[TravfromNZ]

Righto. Saw is back together and everything seemed to work out in the end. On the tuning though, the manual is a little odd from a base setting perspective. My logic tells me that both Hi and Lo should be 1 turn out from seated. However, the service manual says that standard is 1.5 turns H and 1.25 turns L. Then it goes on to say that 1 turn out from seated is 'apparently' 1.5 turns out on H and 1.25 turns out on L. Here is a pic from the manual. Saw runs like crap at 1.5 turns out on H so I assume it should be both needles set to 1 turn and fine tune from there.

 

[Bob Hedgecutter]

For a brand spanking new off the showroom shelf type saw- the above applies.
Pig rich for the first 5 hours used to be our rule of thumb, then back to the shop to let them set it to what they think it should be, then to work and tune it in the wood yourself by "ear".
Worked fine back in the 1990's

Instruction book will relay what should happen from brand new, not for old, rebuilt and worn in.

 

[TravfromNZ]

Yea ok - I figured that might be the case. That manual is so strange. I would understand the rich settings (bloody rich may I add) but to then say that 1 turn out from seated somehow equals 1.5 turns is just odd. Perhaps they are looking at it from a fuel flow perspective - e.g. the sum of all the jets (including the semi-fixed one in this carb) equals 1.5 turns. Either way, Walbro themselves have a pretty consistent rule across all pre-EPA carburetors that 1 turn for both H and L is standard.

 

[9050lx]

On the slop in the bearings,used to see people place shims(feeler gauge) to take up bearing slack on wheel hubs back in motorcycle days. Kind of cringeworthy to do to a crank bearing though.

 

[TravfromNZ]

On the slop in the bearings,used to see people place shims(feeler gauge) to take up bearing slack on wheel hubs back in motorcycle days. Kind of cringeworthy to do to a crank bearing though.

Yep that would work I suppose. I don't know if I would be game enough on an engine of this type though. Upon stripping it down, I have a feeling that the clutch was out of balance quite badly - probably caused some bad harmonics as well. Ended up finding another case half.

 

[9050lx]

I wonder if an out of balance crank would hasten it, then again it was pto side and not flywheel side. so,tightish chain perhaps?

 

[TravfromNZ]

I wonder if an out of balance crank would hasten it, then again it was pto side and not flywheel side. so,tightish chain perhaps?

Yea I imagine it would. There was absolutely no wear on the flywheel side bearings and case. So probably was mainly caused by tight chains on big bars for many years.