MS390 / 039 pop up piston

[94BULLITT]

Nice, it handled the big bar very well for a non pro saw. My cross piston came yesterday.

 

[D B Cooper]

Is a compression release helpful with the pop up piston?

 

[darkimpulse]

Subbed. Great work, the pop up really pulls nice.

 

[Terry Syd]

Is a compression release helpful with the pop up piston?

I not only use a compression release on a my Huztl 390 jug, but I also put on a Chinese 066 coil with the 4 degree retard on starting.

I buggered up the plastic starting mechanism when I had a kick-back out cutting. I had to use my back up saw to finish the work. I thought it was ridiculous to have to go through a starting drill like an 064 just to start a 64cc engine. With the compression release and the coil, I just pull and go. No drill - and it always starts.

Gentleman did me a deal. He saw what it costs to get a piston to Oz and he gave me the 'Deal of the Day'. If this saw was an evil 'sleeper' before the piston, I can't wait to sneak up on some unsuspecting wood cutter after I get the piston in.

Yeah, its an old 029, the bottom of the barrel homeowner saw. The giggles I get from using it is worth the expense I put in it. I must be sick...

 

[drf256]

Though I did expect a higher compression reading, I’m not disappointed at all with the performance.

@Gentleman

Very nice job Dave.

 

[Fruecrue]

Very nice job Dave.

Thanks Al.
Much easier the second time in when everything is clean.

 

[srcarr52]

Timing was 100/125/78
Squish .028”

Good deal. A little tighter than stock but plenty of room for manufacturing differences.

 

[blsnelling]

Though I did expect a higher compression reading, I’m not disappointed at all with the performance.

@Gentleman

Much stronger. Was this a piston swap ONLY? No muffler work, timing advance, etc?

 

[Fruecrue]

Much stronger. Was this a piston swap ONLY? No muffler work, timing advance, etc?

From start to finish in this thread, yes.
Saw was previously muffler modded, advanced and mildly ported (exhaust only, widened less than 1/16” overall)
New piston and pin were lighter than what was removed.
The only variable I can’t guarantee exactly is timing.
I built this saw out of a bunch of junk, including a flywheel with the cast key sheared.
I tried to replicate the same advance (1/2 key) but cannot guaranty it’s accuracy.

Edit: new piston was also slightly taller and squish was decreased about .002”.

 

[71dart]

I got my 039 pop-up!
The piston looks nice.
I'm not overly impressed with the piston pin circlips which measure .039" and seem soft while the oem circlips measure .032" and seem lighter and springier. They don't interchange obviously but that's fairly typical.
I'm waiting on new crank seals because when I originally put this saw together, I used 1194 as a sealant and I literally had to rip the rubber off the seals to get the crank out of the cylinder.

 

[Fruecrue]

I used the circlips that came with it. Didn’t even trim the ears, which I normally do.
Last time I trimmed one with side cutters, that little bastard ear shot like a bullet and buried itself in the meat of my palm.

 

[Northwet]

My piston came in the mail today. The circlips that came with mine didn't have ears.

 

[Fruecrue]

My piston came in the mail today. The circlips that came with mine didn't have ears.

Consistency is hard to come by with Chinese parts.

 

[71dart]

My piston came in the mail today. The circlips that came with mine didn't have ears.

Mine definitely had ears. Big ears that I trimmed back a bit.

 

[jk14]

Nice work, she's a sleeper for sure. Anyone running the cross performance 039 cylinder kit yet?

I don't believe it comes with the popup but for $35 I figured I couldn't go wrong. I picked one up during the black Friday sale to resurrect a toasted 029. I guess we'll see soon enough.

 

[MustangMike]

Nice work, she's a sleeper for sure. Anyone running the cross performance 039 cylinder kit yet?

I don't believe it comes with the popup but for $35 I figured I couldn't go wrong. I picked one up during the black Friday sale to resurrect a toasted 029. I guess we'll see soon enough.

Looking forward to hearing about that, cause often 390s are made from smaller cousins, so an OEM cylinder is N/A!

 

[D B Cooper]

I ordered one of those cross cylinders bearings seals also. Now i just need to locate a transplant patient.

 

[D B Cooper]

I noticed in the technical specs on the pop up piston.

• This piston will ONLY fit the OEM, Cross or Hyway brand cylinders.
  It will not fit in most of the Chinese brand cylinders.

 

[MustangMike]

I noticed in the technical specs on the pop up piston.

• This piston will ONLY fit the OEM, Cross or Hyway brand cylinders.
  It will not fit in most of the Chinese brand cylinders.

Likely, those are just the ones the know it will fit.

 

[Dub11]

I noticed in the technical specs on the pop up piston.

• This piston will ONLY fit the OEM, Cross or Hyway brand cylinders.
  It will not fit in most of the Chinese brand cylinders.

Some of the Chinese ones had a d shaped combustion chamber and stuff.