lawnboy crankshaft machining

[Rear engine 86]

Hi there.

I am currently working on a new engine project for my gokarts and minibikes. I'm looking to install a 6.5 hp Lawnboy duraforce 2 stroke lawnmower engine.

I understand this is not a bolt on and go operation and that is half the fun

I would like to machine the stock crankshaft PTO end to a usable .750 dia from the stock .981 inch diameter and have a 3/16 keyway milled lenghtwise.

Has anyone done something like this and do you need to reharden the shaft afterwards? I would like to be able to mount my Tav2 and have one unique gokart/minibike engine.

I plan on starting a build thread soon. any advice or tips would be great.

 

[mckutzy]

It should for the most part not need any annealing/hardening. Just machine, or get the machinist to work it. Carbide tooling will cut it anyways.
Edit: I say this if there isn't any hole through the shaft for a bolt. It will be defiantly weaker if there is one.

 

[OzFab]

I have. I had to reduce a Honda shaft from 20mm to 3/4"...

Mckutzy is correct, carbide tooling is a must, HSS won't even scratch it. Take your time & do lots of thin cuts. For best results & minimal runout, turn it using a live centre

 

[Rear engine 86]

Hey thanks for the reply. I didn't think it would need to be hardened again but I will need to drill the 5/16 tapped bolt hole. I plan on mounting a comet 30 series driver as its part of the Tav unit.

I'm petty sure another member did this to his law boy project.

 

[Rear engine 86]

I have. I had to reduce a Honda shaft from 20mm to 3/4"...

Mckutzy is correct, carbide tooling is a must, HSS won't even scratch it. Take your time & do lots of thin cuts. For best results & minimal runout, turn it using a live centre

Thanks for the tips. What would a live centre be on a lathe?

 

[OzFab]

I don't understand what you're asking...

 

[rmm727]

Its in the tail stock. The link he provided shows one.

 

[mckutzy]

A live center on a lathe, is a center that has a bearing in it. It spins with the work being turned.
It would be necessary as there is an eccentric portion to the mas and would whip the crank about, potentially causing it to fling or bend when the tool touches.
Will need a similar setup to mill the keyway on the shaft.

Just off hand, coule use some V blocks and clamps, but would need to make sure it is parallel with the table and axis of travel.

 

[anderkart]

I would like to machine the stock crankshaft PTO end to a usable .750 dia from the stock .981 inch diameter and have a 3/16 keyway milled lenghtwise.

Sounds like your diameter would fit a 1"-bore driver now...

 

[Doc Sprocket]

We have an older, well-respected member by the name russ2251. He's not on much anymore, but may respond to a pm. He's kinda our resident LB DuraForce guru.

I believe his shaft solution was a bit simpler. IIRC he milled in a keyway (by hand if I'm not mistaken) and used .007" shim stock to allow 1" clutch use.

Try messaging him, you might well pick up some good and useful info. If you search on his username, you can see some of the stuff he's done.

 

[Rear engine 86]

We have an older, well-respected member by the name russ2251. He's not on much anymore, but may respond to a pm. He's kinda our resident LB DuraForce guru.

I believe his shaft solution was a bit simpler. IIRC he milled in a keyway (by hand if I'm not mistaken) and used .007" shim stock to allow 1" clutch use.

Try messaging him, you might well pick up some good and useful info. If you search on his username, you can see some of the stuff he's done.

Hi there.
I have sent Russ2251 a PM and also another member, Fast Eddie both a pm regarding the entire LB Duraforce transformation for kart/mini bike use. I understand most of the build and so far I'm having no real troubles.

However it would be nice for some feedback regarding how they run, perform and any problems that have cropped up after long term use.

I would keep the stock PTO if I could make it work but I need to mount a Tav 30 series driver. Another member has done this I believe.

 

[mckutzy]

If anything why not just offset the engine and connect it using a chain/sprockets that fit the motor and TC.

 

[Rear engine 86]

I appreciate the input but I don't quite understand what your trying to describe. I have found a local machiniest who can do my described work for a good price. I wondering if I have to press off the crank roller main bearings.

 

[OzFab]

They should stay in the case & the crank slide out of them...

 

[mckutzy]

Rear engine 86-If it was I you were referring to...

Im describing not for a mini bike, as no other vehicle described. No machining required, just move the motor over a bit enough to fit a chain and sprocket(s) that fit both the crank and the TC.
With this setup, this essentially is a variable speed jackshaft. Also take into account for rear sprocket alignment.

 

[Scout]

I remember Russ had built a few karts, one had twin engines on it. there were a few videos, but I can't find them on youtube.

 

[Rear engine 86]

I have spoken with Russ before hand briefly about the LB stuff a few years back but like another member was saying he doesnt seem to be on here much anymore.