STIHL 037 custom hybrid build pic heavy

[volks-man]

how about a little 036 with a 72cc top end?
it can be done.

the idea for this 'poor man's big bore' came from member 'russ61' in this thread: http://www.arboristsite.com/showthread.php?t=128234

i took his idea to mount a 038m p/c on a 036 and ran with it. 038 + 036 = 037

the case needs clearancing to allow the cylinder base to sit far enough toward the pto side. i used a carbide bit with a flat end and freehand milled the non-machined lump off the case. a steady hand is a must!!! i finished it off with a fine file.

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here is how much you need to open the case up or the piston skirt @ bdc.
the two faint scratched lines are roughly where i wanna be.

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case roughed out with old piston installed.

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the 038m cylinder is abit more portly than the 036. cylinder fins must be trimmed.

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[volks-man]

even with the grinding, it is still a very tight fit.

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the base of the cylinder needed to be milled just a tad. @ tdc the piston cleared the squish ring excessively. though i do not recall how much it was (doh!) it was small enough a difference to mill the base on my planer table using sand paper. basically you place the cylinder on the paper, push down, and slide forward. at the end of a stroke lift up, turn 90* and repeat.
it takes slow deliberate actions to keep everything even!!!

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the cylinder holes need to be egged toward center. even then the stock torx bolt's heads will not clear the jug itself. i used a small diameter allen head form lowes get around this.
surprise, surprise. the 036 top cover has nothing to mount to on the 038m cylinder. enter this little contraption. all it is is a piece of mild steel with a threaded rod angled through it. the steel needs to be placed between the cylinder fins and then the rod threaded in.

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the biggest problem to overcome is the 13mm piston mounted on a 10mm wrist pin. parrisw machined me some trick bushings to make up the difference. these things are tiny! obviously they are 10mm ID and 13mm OD.
they are cup shaped so thay the bushing will retain the pin. the bushing is then retained by the stock 038 c-clip. i did use an 026 10mm pin because it was short enough to work without cutting it down.

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[volks-man]

the stock top cover does fit over the cylinder.
but, it is close all the way around. time will tell if this is a problem or not.

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the 036 intake boot won't do. the 038 intake boot is longer and angled enough to to make the transition to the 036 carb box. the one hang up here is that the boot needs to mount a bit crooked and a bit stretched on one side. i don't think it is a problem but it could result in premature failure of the boot over time. i am currently running a 036 carb on the saw.
this may change in the future due to an odd limiting of no-load rpm (may also be boot related).

later, the cylinder also needed trimming for the chain brake handle (i did not have it at first). the clearance is only needed when the brake handle is pulled back.
'madhatte' was kind enough to trade me lots of peripheral parts including the brake handle, muffler, and front handle.

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[volks-man]

somehow i lost my muffler pics.
basically, the 038 cylinder leans back on the 036 case. the top of the exhaust port is in nearly the perfect position to mate with the 036 muffler but the bottom is way too far forward.
the solution is to cut the rear of the muffler like a dog door flap. cut three sides leaving the top alone. i kept bending the flap in more and more till everything fit. after it fit i pounded the old corners of the 3 sides untill i could weld them to the dog door flap. bam! a perfict fit.
i also opened the outlet as far as i could and retain the spark screen and deflector.

here is a vid of the saw running. the log is 15ish inch yellow pine. i am running 3/8 on a 7 tooth at oscar's gtg.

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what i and others at oscar's eastern PA gtg found is that the saw will not turn over 12,400 rpm (no-load) no matter what you do with the H screw. though i find it a bit puzzling i am working on a few theories to remedy this:

the 036 carb may be far too small dimensionally.
the 038 intake may be angled so much as to restrict flow.
the small 036 case may be placed under a small amount of case compression near BDC causing an air cusion effect slowing the piston's travel.

the results of this project are both pleasing and a bit dissappointing.
the saw runs well enough and cuts o.k. but it does seem to be falling short of it's 72cc potential.

the initial project was undertaken as a 'proof of concept'. as such, i was unwilling to put any more time in to porting, tweaking timing, modding the carb box for a bigger carb until i knew the hybrid could work.
proof of concept is what it says... it proves that it can be done.
the next steps will be to improve upon the concept and create a screamer.

 

[blsnelling]

That is some awesome re-engineering you've done there! Thanks for sharing:rockn:

 

[Stumpys Customs]

Great job. Keep us posted.

 

[Bowtie]

Whether you make it a screamer or not, thats pioneer engineering at its finest!

I hope you knock it out of the park! That is awesome!

 

[pioneerguy600]

Thanks for sharing Volks, I was thinking of doing this transplant earlier this spring when I built a 036 PRO hotrod but it turned out so well I did not pursue it. Now I will have to get another 036 to mount that NOS 038 P&C to. I will keep an eye out for this thread to see how the RPM progresses.
Pioneerguy600

 

[parrisw]

Awesome work! Glad I finally got to see it. Happy for ya that it worked out ok.

 

[madhatte]

Holy cow! I had NO idea I was contributing to such an awesome build! EXCELLENT work!

(geeze, now I gotta get those parts again so I can try the same... D'OH!)

 

[logging22]

Awesome work.

 

[Steveo_supremo]

All I can say is WOW. Awesome work!

 

[volks-man]

thanks for the kind words fellas!

the worst part is wondering if i had done this or that would it have run stronger.
oh, well.

this thing turned out really light and nimble. if i can grab a few more rpm it could make one fine little saw.

also:
there are a lot of members here who helped with parts and advice. the project toook so long (i put it away for the summer) that i honestly have forgotten half of the names.
among them are the original thread guy russ61, parrisw, madhatte,
b200driver/sawdr, jacobj, and at least 10 other members.
thanks guys!

 

[Scooterbum]

Gotta love it when people think outside the box !!

Great work !!


Now ya' got me thinkin' again about that 038magII I have......hmmmm 064 top? Maybe 066 even?
Got a few layin' around.

 

[parrisw]

thanks for the kind words fellas!

the worst part is wondering if i had done this or that would it have run stronger.
oh, well.

this thing turned out really light and nimble. if i can grab a few more rpm it could make one fine little saw.

also:
there are a lot of members here who helped with parts and advice. the project toook so long (i put it away for the summer) that i honestly have forgotten half of the names.
among them are the original thread guy russ61, parrisw, madhatte,
b200driver/sawdr, jacobj, and at least 10 other members.
thanks guys!

Not a problem at all. Was glad to help out with something like this.

You got the hard part done. Its now easy to pop off the the covers, muffler and carb, get some timing numbers post them up for discussion. Then take the cylinder off for some work!

 

[2000ssm6]

Nice work! The 036 carb might get you by being stock. I'm thinking when it gets ported you will need to add a bigger jet or go with another carb. The 036 filter is restrictive also, if you are using it. I'd go with a velocity stack/foam type filter. However, hiding these parts under the oem covers will be tough.

 

[nmurph]

Gotta love it when people think outside the box !!QUOTE]

box, what box!!!

nice work volks......def rep worthy!

 

[willbarryrec]

Very bad ass sir!

This is what keeps me around this site!
Thanks for sharing your work!

 

[oldmar]

Glad I got to see that thing in action. Very impressed with the sandpaper machining, not many know that trick. Well done, sir.

 

[jockeydeuce]

That's the stuff I love!!.....What a sweet project!!