Lengthening the Frame - Worth the Effort?

[MikeJ]

Hi Professor -

I'm glad you asked. There are two reasons I want to try this....

First, mounting an engine in the front diamond places the engine attach points a few inches or more from the welds. This feeds engine vibrations into the tubes, which flex ever so little by their nature. I suspect the engine vibrations are not damped as well as they could be if the engine were attached to a (hopefully) more solid base. I want to use a 4-cycle, like Elmo is doing, but place the engine closer forward to the bottom bracket. And personal preference is to have the engine and noise behind me. (That's the real reason.)

Secondly, I read that a longer wheelbase provides a smoother ride. I want to use shock forks up front, just like Elmo and many riders. I would also like to place a 2.5 inch or maybe a 3 inch wide tire in back and run it a bit underpressure to absorb the shocks caused by highway joints. On one road I would like to ride I think the highway joints were purposely engineered in to produce the "bump-bump" ride for miles on end. I have a wheel adapter and sprocket from Jim of Manic Mechanic on order; I will hopefully be able to move the sprocket outward enough so that the chain will clear the tire.

I might think of a third reason later today.

But you use the HF engine with a wide crank? That is another good point to know. I can place that engine almost up to the seat post, minimize wheelbase, and not worry about hitting it with the pedal crank. Thanks!

Mike

 

[professor]

I actually welded another frame bar horisontally in the frame and the engine is bolted to that. Vibes are pretty low with the HF.
Good idea having the noise behind you. I have a twin muffler and tail pipe, plus added sound box on the intake to help quiet the engine and this stuff works BUT the general clatter from the engine is still there. Never thought of placing it down in a long frame (great idea from a noise viewpoint).
Beside the fat tire (or in place of) consider a Cloud9 seat and a suspension seat post- should be very comfy. Seatposts come in a great variety of tube sizes- all metric- measure carefully if you go that direction.
Yes, a long frame always rides better.

 

[Elmo]

If you are leery of frame cracks- make little gussets (triiangle bits) to web between the angles of the frame. Really, I doubt you will have any issue with stregnth unless you weigh a lot.
I placed the hf79 up in the frame and with a widened crank, there are no clearance problems. Is there another reason to go longer with the frame?

Wide pedals hurt my knees. I once put a pair of knee savers on my bike and they hurt. Of course with this bike you only have to pedal when you run out of gas or something breaks.
Elmo

 

[professor]

You guys got me thinking of a tandem!

 

[MikeJ]

Elmo, Professor -

Do you use a centrifugal clutch? I am assuming Elmo does, based upon his photo. But there is some more to Elmo's power train than what I saw. Maybe Elmo, you can post a photo of the left side of your engine?

I saw a photo from a very-low-budget bike where a V-belt was simply tightened via a tension idler (no centrifugal clutch) to transmit power between a V-belt sheave on the crankshaft and a belt-driven pulley like that found on a Whizzer. I am not going to rule out the V-belt option, expecially since I saw how Augidog mounted the driven pulley on his long bike's back wheel.

MikeJ

 

[MikeJ]

Tandem Bike? Absolutely!

I just looked at a relatively-inexpensive tandem bike from Toys R Us (personally, I'd go more upscale). But if you strengthen the horizontal tubes between riders, remove the diagonal tube there, remove the rear crank, place your engine in there, you would have the very same design Elmo has! Shorten that section and replace the front crank as necessary for a custom-length frame.