044 big bore kit question

Sparky_NY · Dec 9, 2006

Those big bore kits for the 044 have tempted me....
What I have never seen mentioned is how many cc's is the finished product?

Too bad they don't make these in the small wrist pin version, I have one 044 that is somewhat low on compression anyhow.

What if I made a couple aluminum bushings on the lathe, to reduce the piston pin bore? The wall thickness would only be 1mm so the clip would still hold the pin. Could either make them a press fit or even TIG a tiny spot weld to make sure nothing moves then run a reamer through to ensure a nice round 10mm bore.

I'm somewhat new here, and just painted a bullseye on myself, so let the flaming begin.

ciscoguy01 · Dec 9, 2006

hmmm

Sparky_NY said:
Those big bore kits for the 044 have tempted me....
What I have never seen mentioned is how many cc's is the finished product?

Too bad they don't make these in the small wrist pin version, I have one 044 that is somewhat low on compression anyhow.

What if I made a couple aluminum bushings on the lathe, to reduce the piston pin bore? The wall thickness would only be 1mm so the clip would still hold the pin. Could either make them a press fit or even TIG a tiny spot weld to make sure nothing moves then run a reamer through to ensure a nice round 10mm bore.

I'm somewhat new here, and just painted a bullseye on myself, so let the flaming begin.

I wondered that also dude. If your 44 has the small wrist pin, maybe you could pick up a seriously junked 44 for like $50 and convert that part over so you could put the BB kit on it... Lemme know whatcha find out eh?

opcorn:

Lakeside53 · Dec 9, 2006

It wasn't just the piston bore they increased - the big end bearing is larger also..

I wouldn't put any more stress on those older saw cranks. They were changed for good reason.

As for sleeving the bore - technically possible, but the fitting would be interesting. The finished bore spec on a Stihl piston is +0.00 to +0.002mm... figure that in 10,000ths inch..

The original clip won't hold - you'd need to duplicate the same grooving in the new insert, which would also need a flange on each end to allow the same.

Sparky_NY · Dec 9, 2006

Lakeside53 said:
It wasn't just the piston bore they increased - the big end bearing is larger also..

I wouldn't put any more stress on those older saw cranks. They were changed for good reason.

As for sleeving the bore - technically possible, but the fitting would be interesting. The finished bore spec on a Stihl piston is +0.00 to +0.002mm... figure that in 10,000ths inch..

The original clip won't hold - you'd need to duplicate the same grooving in the new insert, which would also need a flange on each end to allow the same.

I realize the wrist pin bearing is 12mm also, and the rod end larger for the bigger bearing. That is the heart of the problem.

Holding the bore spec wouldn't be that hard on a piece made special, mass production would be another matter. I've made cylinder liners for radio control engines and kept them within a couple tenths without much trouble.
(a 5 cylinder radial engine I made from scratch, 2.0 cu in, 1/8" wrist pins with no clips, teflon end buttons instead)

I had the same exact thought.... they changed it to 12mm for a reason....
and that was with stock displacement! Guess thats the end reason they don't make big bore kits in 10mm wrist pin size. A snapped rod is not a good thing.

Still want to know how many cc's the 044 big bore kits work out to. I was hoping someone knew offhand so I wouldn't have to calculate the new displacement!

Sparky_NY · Dec 9, 2006

ciscoguy01 said:
I wondered that also dude. If your 44 has the small wrist pin, maybe you could pick up a seriously junked 44 for like $50 and convert that part over so you could put the BB kit on it... Lemme know whatcha find out eh?opcorn:

Yea, that is another alternative. It would take some investigating to see if the crank/rod combo's are a direct sub in the small/large pin versions or other parts are different also. (other than the piston/pin)