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Discussion Starter #1 (Edited)
Willard & (MX hotsaw project)

I should have joined this great site years ago.
My name is Willard Holmen, I'm a 62 year old tree climbing arborist out of Manitoba Canada.
I may seem a bit of an odd ball as my interests are building log cutting MX engine hotsaws for timbersport speed cutting competition.

I'm presently on a 2 saw build project one is a 1982 YZ125 I originally built 36 years ago. The other is a 1983 Honda CR250R.
Both these engines are right hand ignitions which I have reversed their engine rotations with PVL bi directional analog ignitions in order to get the PTO on the right hand side for normal sawchain rotation.

Power to weight ratio is key in these 2 builds as I'm using lots of carbon fiber and grade 5 titanium.
The 1983 CR250R is new to me and I love this engine as it shows lots of potential. Very similar to a TRX engine.
Next winter's project I'm planning a crankcase build for the Honda carved out of 3 inch thick mic 6 aluminum plate.
Here's some pics, first from 36 years ago with the '82 YZ125 build, rebuild in 1989 then onto PVL ignition, Mikuni SBN carb and the '83 CR250R.
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Welcome to the home of the 250R; .NET

Very cool stuff Willard. BDT Motorsports has built quite a few 250R based engines for the Saw Team's locally. If I recal correctly; some of them compete in the USC Pomona, CA.

The use of CF + Ti is awesome...both excellent materials with high strength to weight ratios. I have built quite a few parts over the years from 6AL-4V Grade 5 as well CF in many configurations from sheet to bagged vacuumed parts.

Keep posting, very interesting stuff...!

Carlos
 

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Discussion Starter #6
Thanks guys!
cmorris these bikesaws are used in speed cutting competition making a number of cuts through a horizontal positioned log.
Most events starting the saw is included in the cutting time. So the engine must start on the first pull and be at WOT rpm immediately into the wood.

Carlos, I got quite a bit of advice on this latest project from Nathan a TRX builder out of Oregon. He keeps reminding me to call you or Arlan, Lol.
Nathan hangs out at a chainsaw forum where we do alot talking. He has a sweet Banshee and a 1969 Camaro.
I'm definitely stay on board here sharing my project progress and my travels this coming summer at some competitions.
 

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Thanks guys!
cmorris these bikesaws are used in speed cutting competition making a number of cuts through a horizontal positioned log.
Most events starting the saw is included in the cutting time. So the engine must start on the first pull and be at WOT rpm immediately into the wood.

Carlos, I got quite a bit of advice on this latest project from Nathan a TRX builder out of Oregon. He keeps reminding me to call you or Arlan, Lol.
Nathan hangs out at a chainsaw forum where we do alot talking. He has a sweet Banshee and a 1969 Camaro.
I'm definitely stay on board here sharing my project progress and my travels this coming summer at some competitions.
seems pretty cool sir thanks for explaining
 

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Thanks guys!
cmorris these bikesaws are used in speed cutting competition making a number of cuts through a horizontal positioned log.
Most events starting the saw is included in the cutting time. So the engine must start on the first pull and be at WOT rpm immediately into the wood.

Carlos, I got quite a bit of advice on this latest project from Nathan a TRX builder out of Oregon. He keeps reminding me to call you or Arlan, Lol.
Nathan hangs out at a chainsaw forum where we do alot talking. He has a sweet Banshee and a 1969 Camaro.
I'm definitely stay on board here sharing my project progress and my travels this coming summer at some competitions.
That's cool. I was surprised a few years ago to the interest locally in SoCal for level of Chain Saw Competition...very interesting. Keep posting...!

Carlos
 

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I’ve been following along it’s super cool stuff. I have watched that on TV but never suspected 250r motors! Super cool!
 

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Discussion Starter #10
Honda CR250 motors have the most versatility in custom mods more then any other brand.
The days of highly piped porting is giving way to 8000K big bores with high drive sprocket gearing on the sawchain.
Here's a 330 Sphinx with lots of ports.

63792

63793

63794
 

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Arlen (LED) has been involved in this sport for quite a while. I have watched his saws cut in local logging shows and on TV. Pretty cool stuff and super interesting to me as I grew up in a logging community.
Welcome.
Loren
 

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Discussion Starter #12
Yes I'm located up in an area of logging and every little rodeo or festival has a wood cutting competition.
Arlen is making off the shelf hotsaw pipes and cylinders too. But he has business ties with a fellow down in California who is solely in the business making hotsaws.
 

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Yes, fully aware of the Local Hotsaw activity, I was quite surprised years ago. I understand the pursuit of higher performance; if you wan't to beat the competition, you must step outside the box, the standard, and develop your own path forward. Doing what everyone else does, does not equate to Wining IMO.

Carlos
 

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Discussion Starter #14 (Edited)
Yes, fully aware of the Local Hotsaw activity, I was quite surprised years ago. I understand the pursuit of higher performance; if you wan't to beat the competition, you must step outside the box, the standard, and develop your own path forward. Doing what everyone else does, does not equate to Wining IMO.

Carlos
Well said Carlos.
That hotsaw builder in California I'm not sure where he is but he is solely a Honda CR250 man .
At one time a few guys up in Wisconsin, Michigan area were cutting Rotax jetski and snowmobile engines in half to make the rule sanctioned single cylinder only hotsaws. Sanction will always stand for single cylinder only.
Now the CP Industries Honda big bores are now taking over from what I can see.
But there is one other contender out of Europe making good gains with the Wankel kart engines and their becoming the ones to beat.

Me I like Hondas and am going my own path with it. No vertical cylinder for me, mine are horizontal with reversed crank rotation with the last year 1983 CR250R and 1982 YZ125 right hand ignition motors.
Still lots of testing in the future.
But I feel with the major piston thrust with its large flat skirt wearing on the same type of surface below the exhaust port and allowing minor thrust on the open intake ports allows room for more flow modifications
The 1982 YZ125 has road race porting with a 3mm piston pin offset towards the exhaust. In testing it worked great. But long term and extra hp will decide whether to go to a zero offset pin or not.
I do plan to run them both on alky/nitro as I had experience with it almost 40 years ago.
I think the advantage of a horizontal engine design with methonal is there won't be any repercussions with the fuel puddling in the crankcase starting fires or something.

Like you said following someone else won't make a competitor a winner.

BTW Carlos . The way things are going Internationally with the Cor virus I may have to cancel my families California spring break trip first week of April.
It pretty well looks at the moment I won't have any choice.
 

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Discussion Starter #15
To add about my way of doing things. With my design seeing the standard hotsaw engine profile is vertical.
My horizontal profile is great ergonomics with a lower center of gravity. Handle positioning is much better to steer the saw then with the saw steering the operator due to a high left hand top handle position.

Better view of the log. No exhaust header pipe interference with the log allowing able to cut from either side of log. Center of crankshaft closer to log with less waste of bar/chain length being more efficient in cutting and saving power.
Fuel and bar oil tanks up front for better balance and less thermal heat.
Vertical saws have their fuel tank rearward above the ground level mounted exhaust pipe.
 
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