Yamaha kt100 homemade chainsaw hot-ish saw

[McLeach]

I wanted to wait till I made it into the "its gonna happen" stage of the build to post.

I just sold my McCullough SP125. As it was a collector saw, no matter how bad I wanted to use it, I couldn't feel good about really rippin some stuff up with it. I wanted an even bigger saw that I could really run the piss out of, break, and do whatever with. Hence a homemade build.

My brothers an I had talked about a hot saw here an there, but I kinda want one for practical use too. So, where do you get a 2 smoker that is double the power if a sp125 and doest weigh as much as dirtbike? The only motor I could find suitable is the yamaha kt100 kart motor. Thats what I started everything with. Brand new motor was almost 900 bucks. Yikes! Bought it anyway. I'm an engineer and I do well enough to fart around with a silly expense once in a while. I saw another guy had used this motor on a saw and wow did it rev to the moon!

I felt the tilted back angle gave me the most room to work with, and the cooling fins should convect better this way. Second, air filter needed to be something available anywhere. Thats an element from a VW bug. I 3d printed the box out of ASA filament. This stuff is impressive.

 

[McLeach]

I work at an aluminum rolling mill, so I have lots of sheet and plate all over hell. Plus, did I mention I'm somewhat of a machinist/ cnc programmer?

Here's some progress.

The bottom plate will work as an anti vibration mount, and there's the air box with the lid on it.

Meanwhile, after looking at the homemade chainsaw bar post that was on here, I decided to go for it and make the bar from scratch too. The specifics on it are on that thread.

 

[McLeach]

Here are some more random parts.
Pulley for a timing belt pull cord.
The split oil/fuel tank. It only holds 12 oz of gas, so yeah... it was not easy finding a good place to fit even that much. One of its shortcomings for sure.

 

[McLeach]

Fast forward. This is where it is now. I need to mount the skid plate, remake the full wrap handle a little tighter around the saw, and do a bunch of small stuff like fuel/oil routing...
The oil will be run generously off the exhaust pressure. Bar oil and fuel should deplete at about the same time.

Using a heat gun, a spring, and schedule 80 grey pvc, the bends turned out perfectly. And yes, the stuff is going to be plenty stiff.

Its really easy to do, and cheap. Trying to cut a little weight where I can.

 

[The Shooters Apprentice]

This looks pretty cool so far.

 

[McLeach]

Her's a little bit better of a mockup. The skid plate is waffled on the bottom and will bolt through into the wrap around handle. That'll stiffen up that bottom plate a bit. Its meant to be springy for comfort and when I plop the saw down on the ground.

Will probably be a while before its finished. Things left to do:
Kill switch
Oil/fuel caps
Bar oil delivery
Remake wrap around handle
Fuel line to tank
Pull cord
Chain
Exhaust port

Then The gambit of tuning the engine.

 

[av8or3]

Subbed

 

[freeasaburt]

Impressive! Looking forward to future updates.

 

[Bill G]

It looks really good!

 

[.22er]

Nice! thanks for sharing

 

[cookies]

Thats really neat. I've seen what those engines can do on a shifter cart, that saw should scat.

 

[Bill G]

Something that I have always found interesting about the KT 100 and the Comer K80 kart engines is their physical size and the cooling fins. Take a look at them compared to a Mac 101 or West Bend 820. The Yamaha and Comer are smaller in displacement but much larger in physical size. They should run a lot cooler.

 

[rocketnorton]

sub

 

[McLeach]

Finished the full wrap handle. Was going to put 1/4" aluminum strip inside the pvc and then press it flat with heat. I tested it and lost a lot of rigidity. Went with delrin inserts and bed blocks. Turned out quite nice. Pretty surprided how firm it is all the way around, and without any little supports up top. Quite pleased with it. And it'll be really easy to replace if it takes a real hard hit.

I can hold the saw anywhere I want, and it doesn't bend, even under that much weight.

 

[McLeach]

I haven't done my research on a specific chain yet. In the least, it hast to be .058 .404. Thats what both my guide bars take. Maybe one day they'll grow up to be .063 .

Anyway, the sprocket is 10 tooth and will see 15000 rpm. Saw should have ballpark 15hp. Wood will certainly be random pine.

I would value some of you fine folks's opinions.

 

[sean donato]

Any fan cooling plans for it? In the kart application they get plenty of air passing over the fins to aid in cooling when the kart is in motion. This thing will get hot quick without air flow, even with the big fins. May not be an issue for cookie cutting or saw races with short run times. Also will you be running a tuned pipe?

 

[McLeach]

No, I had considered milling down the fins and going fan cooled, but decided to give it a shot as is. I dont imagine it'll have a duty cycle long enough to have heat problems. Or at least I doubt I will last long enough for it to get too hot. Only one way to find out. Its not pushing a 300lb kart.

I do have a pipe for it, but am trying to keep it tidy, as a work saw. If I went that route, I'd go 250cc. Maybe the next saw. This one is my first build and will def see updates throughout its life. Smaller airbox, bigger oil/fuel tank mainly.

Finished the 3d printed throttle today. Trying to decide on the bar oiling and now have to wait on a couple things in the mail. Really annoying how you can't even get simple stuff like tygon fuel line anywhere but online these days.

 

[McLeach]

The bar oiling system has really been a pain to decide on, be it exhaust powered, or an old school thumb plunger.

What if I ran a T-fitting off the impulse tube and used another diaphragm pump to run the oil. I was going to go with cooking oil anyway, so it might be thin enough.

Would it be ok to run a second pump off the crank impulse tube? Or would it mess up the fuel delivery to the carb?

It'd be a pretty dang nice way to run the oil to the bar.

 

[McLeach]

I wonder if I put a nipple in the spacer between the carb and piston, I could run a vacuum style impulse pump from there. Then it'd kind of be on a separate system.

 

[frank_]

I wonder if I put a nipple in the spacer between the carb and piston, I could run a vacuum style impulse pump from there. Then it'd kind of be on a separate system.

kart pulse pump maybe ? with a tap off the exhaust expansion chamber and silicon pipe (like the aeromodellers use)
very impressive build