getting some revs out of the 041

[mcb]

im rebuilding an 041AV that i never use to give to my father for a primary firewood saw. ive got it apart and degreased right now, currently collecting dimensions and hope to plot out the timing this week.

i guess my first question is, what keeps the rpm down so low on these saws and how would you bump it up? ive got a machine shop, tig, porting equipment, etc.

 

[ironman_gq]

I think its the fact that the internals are heavy and exhaust timing is pretty low. lots of torque but not a lot of revs

 

[mcb]

maybe i can get a few grams off the piston by turning the crown margin for a popup and doing some radius work underneath.

mine has a points and condensor ignition.. anyone know how far these can rev before breaking up from weak spark?

 

[pioneerguy600]

Raising the roof/top of the transfer ports a mil or two would most likely raise the rpm but would also cause a small loss of torque. The old 041`s have plenty of torque so maybe a little trade off would be ok, that is one saw I personally have not played with the porting on them. It is also a saw we porters seldom discuss, the newer design saws respond much better and have better AV systems, the 041`s were bad for vibration and an increase in rpm may shake them to bits but I don`t know that as a sure thing.
Pioneerguy600

 

[blsnelling]

Lightening the piston alone isn't going to make it rev. Widen the ports and alter the port timing and it will.

 

[mcb]

i realize peak BMEP is a function of valve events. being unfamiliar with this particular engine im trying to understand the order of limitations.

im going to hold my timing questions until ive got the saw degreed and mapped out.

thanks!

 

[Oldsawnut]

That saw isn't designed for a lot of revs.... But on the bright side parts are fairly plentifull and cheap so feel free to experiment you might hit a sweet spot and worse case used cylinders are reasonable. Now the 056's can be turned up a bit

 

[synness4]

you my want to put new crank bearings and watch the that what I have had issues with my old 041 av that I ported I got almost 10000 out of it BTW were can I get more? anybody know?

 

[mcb]

that brings me to a question,, ive got all the fasteners out of the case halves as well as the dowels. i can pull the seams apart and shuffle the halves around but not get the two to separate. seems like the bearings are holding the case to the crank.

any suggestions on where to push on what in order to split the case? or where to source bearings and seals from?

 

[ironman_gq]

You need a pulled that pushes on the end of the crank and fastens to the case to push the crank out of the case. The bearings are pressed into the case

 

[Brmorgan]

Yeah watch for loose screws if you rev 041s out too far. Check your fillings while you're at it.

I've often wondered if the fact that both exhaust and intake ports are on the same side of the cylinder on these guys affects the RPM/torque range much. I don't know enough about 2-stroke cylinder design in general to make a judgment on that though; but for some reason it just seems like that design would waste more fuel than ports located across the cylinder from each other. I don't think you could expect to ever rev an 041 out terribly high or make some screamer out of one, but with some minor modifications you can make them hold a considerably higher RPM in the cut, which is what matters at the end of the day. This is the non-AV 041 I just built a few weeks ago; all I did was smooth out and polish the ports and remove the base gasket to bump compression up a bit:

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It pulls stroooong for 61cc. Tons of torque to dog in and take advantage of; I can lean on it really hard and it doesn't slow down much. Doesn't sound too bad either! I can't thread my compression gauge in to the spark plug hole where it is behind the handle so I can't give you any numbers on that, but I can tell you that I can hold it up by the recoil handle all day long if I want to and it won't drop. I have a ported 041 Super project in the works right now - I have it running and it feels super strong and sounds amazing, but I have to rebuild it again on a different case (better condition) and haven't cut with it yet. I didn't take pics when I did the port work, so when I tear it all down I'll take a bunch and post them. Keep an eye out.

you my want to put new crank bearings and watch the that what I have had issues with my old 041 av that I ported I got almost 10000 out of it BTW were can I get more? anybody know?

What exactly are you asking? More crank bearings, more 041 saws, more RPMs? Punctuation is your friend!

 

[mcb]

i slapped on an indicator and degree wheel just before getting ready for work and took some quick measurements.

serial number 9649254

piston diameter at crown: 1.727"
base gasket thickness .016" compressed
squish clearance (no gasket): .044@ quench pad, .034" @ circumf of bore (.030 margin approximately)


carb:
tillotson HS138A603 (stamped 1963, made in ireland)
diameter at choke plate .875"
diameter at throttle plate .805"
diameter @ narrowest point .675"
carb to intake spacer diameter .750" round, poorly transitions to rectangular

Port Timing (without base gasket)
Exhaust opens @ 108* ATDC
Exhaust closes @ 250* ATDC

Intake opens @ 67* BTDC
Intake closes @ 65* ATDC

Durations
Exhaust 142*
Intake 132*

port dimensions (piston end) are about .500 tall x 1.0" wide on the exhaust and .500 tall x 1.1" wide on the intake if i recall correctly.

 

[mcb]

im starting to think my durations are way off after looking around the site. when you guys measure opening/closing, is it at X amount open or something? sort of like advertised vs @1mm/.050" on 4 stroke cams.

i still have to check transfer port timing too

 

[Brmorgan]

Well, you certainly don't mess around, eh? I wish I had the patience to set up like that. And it isn't that I don't have the equipment, which is the sad thing!

I agree with your observation about the poor transition in the intake block. I was unsure as to whether I should modify mine though, so I left it alone for the time being. I guess I do have a spare in case I bugger one up.

You'll also run into quite a roadblock in the muffler pipe right where it bolts onto the cylinder. It's quite an abrupt rectangular transition from the port to the pipe, and is rather restricted. However due to the pipe/flange joint design and the rather thin wall of the pipe, there isn't really any room to grind the inside out to port match it and/or taper the edges to smooth the flow. I thought of maybe building up some material on the outside with the welder and then grinding the inside out, but I'm not quite confident enough in my welding abilities. I don't want to completely grind away the original joint since I'd be worried about it cracking from vibration down the road.

 

[Frank Boyer]

I used 5mm longer fasteners on my 041 S and that helped keep things from falling out. They have a problem with the crank bearings wallowing out the case and the starter pawls hitting the plastic ring and wiping it out. Use loctite because they do vibrate a lot.

 

[mcb]

thanks for the tips. i built honda and acura race engines for a number of years so that stuff is all laying around the shop.

can anyone comment on the procedure for degreeing? do you mark the timing event at the actual degree where the port creeps open/closed or do you measure to some commonly accepted arbitrary point with a feeler gauge?

 

[mcb]

theres another thing my mind is still struggling to adapt from 4stroke ---> 2stroke.

on thumpers, your intake closing point has the largest effect on the rpm of your torque peak. so the piston passes bottom dead center and starts to rise but you still havent shut the intake for another 40-60 degrees in order to let the column of intake air which has accumulated inertia, force its way into the cylinder despite the rejecting tendency of the rising piston. radical cammed 4 strokes have a lopey/stumbly idle because the intake is hanging open for so long past TDC that the piston is spitting the charge back into the manifold port and the cylinder's low volumetric efficiency creates such little pressure that it can barely overcome the resistance of the other cylinder's compression strokes/valve springs, etc.

I know charge inertia exists on 2strokes as well, but it throws me way off upstairs because there are a number of things going on all at once. instead of the charge forcing its way into the shrinking cylinder volume, 2strokes are forcing charge into the crankcase. greatest vaccuum under the crankcase (if transfer ports werent there to confuse/complicate things) would be at TDC when the volume is largest, to generate the largest pressure depression. charge filling would start as the piston began to descend.

from there it all turns to mush as i need to overlay transfer ports and pressures simulataneously going on above the piston in order to figure it out, and my brain just draws a glassy eyes blank. ill have to look more when i get home.

 

[SpaayDawg]

that brings me to a question,, ive got all the fasteners out of the case halves as well as the dowels. i can pull the seams apart and shuffle the halves around but not get the two to separate. seems like the bearings are holding the case to the crank.

any suggestions on where to push on what in order to split the case? or where to source bearings and seals from?

Check out the start of my rebuild here:http://http://arboristsite.com/showthread.php?t=121397&highlight=041+rebuild

I was lucky enough to find both seals and both bearings at my dealer. I could not comment on where to find them anywhere else.

 

[mcb]

came real close to getting crushed in the tree a few hours ago. lot of factors influenced it but ultimately my bad judgement call was responsible. the top twisted and walked right over where i was.. i saw it and did some squirrel darting action fast enough to only have it knick my leg before crashing onto my garage from 50 ft... not a skinny top either. im amazed my garage took it so well. no camera on hand right now. pretty shook up.

 

[pioneerguy600]

Close call, glad you escaped serious injury, thats a killer situation , you were very lucky.
Pioneerguy600