Mechanical sustainability with large engines?

[af6rf]

So I was all set to go for a chain-drive kit with the GX-50, and I talked to a mechanic friend of mine who rained on my parade. The concerns he raised are:

1) putting a 50cc engine on a system designed for a relatively weak human powerplant would lead to unacceptable wear on bike components, especially frame, forks and (obviously) brakes.

2) Lots of hills where we live, and without a variable-speed transmission even a well-made engine is going to have a tough time doing steep grades without putting a ton of wear on drive-train components and the engine itself.

He bet me dinner that I'd have trouble finding people who had put a lot of miles on a system such as what I've described without constantly making repairs. So let's hear it...!

 

[s_beaudry]

You should base your judgement off more then one opinion....

I am sure more then a few will chime in here with several thousand miles on thier MB's.

 

[af6rf]

<You should base your judgement off more then one opinion.>

Well yes. That is why I am here.

 

[kerf]

You don't mention which system you're considering. I'm running a Staton chain drive and your friend is wrong, the system is plenty robust after 1500 miles. From what I understand of the GXH50, it has plenty of torque for hills.

 

[af6rf]

I'm not familiar with that particular type of chain-drive system, but I'm not sure it matters in this case. The question is what sort of effect the forces exerted by the engine would have on the bike, especially since a rear-mounted engine would produce a very large upwardly-directed force on the rear fork. Any chain-drive system is going to produce force in this manner, no?

I'm not questioning whether the engine is capable of generating the force, there's no question the GXH50 is a pretty mighty powerplant for the application. What I'm asking is how much stress pulling steep grades, without the benefit of a VST, is going to put on the drive-train.

 

[kerf]

The bicycle I'm riding is on it's third engine, second drive unit, close to 2500 miles. Your friend is wrong, motorize one if you want to, while you think about it, I'll be riding.

 

[Happy Valley]

I think it's fair question. I recented stated in another thread:

Take two identical new bikes, same rider, location, and routing, motorize one and leave the other original. To my mind there is no doubt which will show more and faster wear.

My thinking is based on the grind of road wear, at more constant sustained speeds afforded by powered assist. I don't think engine torque is a big issue because the engines that are sized to be feasibly mounted at all don't generate that much torque in comparison to human power.

To illustrate, I had a conversation with a pretty sharp young mechanic at a local bike shop a while ago. We were talking about internal rear hubs and I asked him what he tthought of the NuVinci. He said "not much".

I wondered if he thought they wouldn't be rugged enough or something and said I knew guys who put them on MBs and they seemed to have no issues handling the torque. He replied torque wasn't the issue as a human rider was able to able to generate far more apllied torque on the pedal strokes than any small engine ever could. (He rides competitively and his stated dislike of the Nuvinci was weight and power loss.)

When I thought about it I think he's right about that. However I think road wear from more constant sustained speeds and vibration are other matters. I ride more with a motorized bike so that naturally means more maintenance.

 

[af6rf]

Wow, you have to swap an engine every 800 miles? That's like what, five tanks fulls of fuel? Thanks, kerf! In your own peculiarly hostile way, you've answered my question.

 

[kerf]

I didn't swap because I had to, all other engines are still on the road. I swapped in search of horse power, running 4.2 at this time. In quiet mode top end is 40, in loud mode top end is pushing 50. First time I've been called "peculiarly hostile" for giving someone what they ask for, takes all kinds I guess.

 

[Mountainman]

Where the rubber meets the road on a MB

some thoughts from a former bicycle shop owner

I am nearing the 15 hundred mile riding time on my MB
even though I know it's a good idea - due to extra vibration
I didn't use Lock-Tight on nuts and bolts when doing my assembly
NOT ONE THING HAS CAME LOOSE ON MY MB - to date anyway

I did break one spoke just a while back - I guess that's more than loose
cause -- I am not sure
I honestly do - hear about some broken spoke problems here on site
I have made an opinion in regards to spokes breaking --
I am leaning towards believing
that spokes today are not made as good as when I owned a bicycle shop
back then 1070-73 few spokes were breaking on newer bikes sold than today
at least that's the way I remember it --- long time ago

but -- in regards to drive units that are attached directly to spokes
this would have some extra wearing effect -- note - to keep an eye on

frame - again - should be checked occasionally for cracks - welded points
some here on site take about drilling into frame for certain mounting
that if done wrong -- could weaken a frame

here's a fact -- most of us know
give a wild boy a bicycle -- he can tear it up in no time
broken frame, broken spokes, worn out tires from skidding, bent handlebars ect.

how we treat our EQUIPMENT
MAKES A LARGE DIFFERENCE IN AMOUNT OF BREAK DOWNS - MB life

we could go on and on here -- BOTTOM LINE
small motor bikes have been ridden -- since way back when

if we buy a quality bicycle and engine - drivetrain ect
we should reasonably expect -
many carefree miles with some maintenance required

if you buy one -- Ride That Thing - Mountainman