Engine on Swingarm or frame?

[billlaws]

I'm building a kart with rear simple rear suspension, but cannot decide where to put the engine.

Info - its based around a 250 6speed bike engine and will be only used off road.

I can either:

Mount the engine on the frame and try to line up the pivot point with the centre of the output sprocket of the engine (hard to get exact and would require a chain tensioner.

Mount the engine on the swingarm to remove chain tension problems due to change in length due to suspension. This does however cause problems with the gear shifter (motorbike engine).

Not having the engine on the swing arm would be better for the engine but could be a headache to get right.

Having the engine on the swing arm is less desirable but gives a much more reliable final drive.

Does anyone have any thoughts on this?
cheers
Will

 

[robbie]

A tensioner could be your easiest solution. Another possible solution could be a jack shaft. When you build the attachment point for the swing arms, build a mounting plate in between them for attaching your jack shaft bearings. Thread a rod through all four points to get them lined up as you weld everything together.

I've been thinking about this same problem for a mini bike I'm planning to build. I'll probably use a tensioner on the bike and a jack shaft on my next kart.

 

[billlaws]

I'd thought of jack shaft, the only thing is I'm trying to build the kart quite short and low. The problem with the bike engine is that I can only really run the chain back or about 45 deg down. So the engine would have to then be in front of the pivot. I think I'll try and get some engineering drawings of the engine so I can just get exact locations of mounts and the centre of the drive sprocket. Then as you say just use a simple tensioner to remove any inconsistency.

cheers

Will

 

[theo]

Build it somewhat like the edge sidewinder, engine at the side.

 

[billlaws]

I've also looked into that, It gives a nice short kart however a pretty poor weight distribution. The sort of thing I've got in mind is:
http://www.youtube.com/user/glassglowz#p/u/4/D6Lba_Zq3Lg

However I'm going to do better 4-bar suspension on the front and a stronger suspension setup at the rear. Will be a project log going up soon hopefully...

 

[theo]

He has now changed that set up to trailing arms.

 

[billlaws]

He has now changed that set up to trailing arms.

Is he on here somewhere? do you have any pics?
cheers

 

[motor_head]

it's not super hard to get the motor sprocket lined up with the pivot just takes time tacking it in and making sure it's right, as long as your withing 1/2 the change it chain tension won't even be noticeable

 

[modelengineer]

The ride will be so much better with the engine on the frame

It gives a nice short kart however a pretty poor weight distribution

The advantages outweigh any potential imbalance imo. I don't even notice the weight off the side while driving, and it can be balanced out if you put a car battery and steel fuel tank on the other side.

 

[theo]

Is he on here somewhere? do you have any pics?
cheers

No I don't yet. He is in the process of the conversion.

 

[billlaws]

I've had another much closer look into the sidewinder option and I'm still a little unsure of its suitability. The honda engine I've got is dimensionally a lot larger than seems to be used in the plans and is also a fair bit heavier (being from a road bike). Without offsetting the seat I dont think it would be that great.

How poor will the ride be if the engine is on the swingarm? the kart in the video I posted seems to track and handle relatively well. What I'm trying to avoid is a really long and thin kart. I only have a 44" rear axle. Has anyone built a really compact rear suspension unit which could fit behind the engine but not reqire CV joints etc?
thanks
Will

 

[Doc Sprocket]

The ride will not be horrible if you dial in the suspension accordingly. I am facing the same hurdle with my design plan, which involves a Yamaha Virago VX250 v-twin. I have looked at it every which way, including mounting the engine both sideways and backwards. At the moment, I'm considering the possibility of extending the engine's (tranny) output shaft a couple of inches, placing the drive sprocket clear of the gearbox so the chain can be run straight down, or even forward. This will, of course, require a support bearing.

 

[modelengineer]

I've mounted a REALLY heavy 500cc twin w/ 6 speed (also from a road bike) on the side of a 'winder. The engine weighs around 60kg (130lbs) I would guess from how difficult it is to move. and there are no issues with tipping/irregular handling/etc.

The ride will be much better with it on the frame, you won't need as strong a swingarm and axle since it won't get as much shock loading from a HUGE amount of un-sprung weight.

As long as you put the engine exactly in line with the suspension pivot you don't need much of a tensioner since the lenth of chain doesn't need to change with suspension movement.

That and the fact that if it's an air cooled engine then on the swingarm, behind the seat, is not the best place for airflow. If it's water cooled then you'd want the radiator exposed to air flow, so on the frame, so you need some sort of flexible coupling to account for suspension travel.

Also, the gear linkage will be much simpler (unless you're doing cables, then it's pretty much the same) and won't jump around as you go over bumps. I've seen a kart (not very well done) which changes down a gear every time he hits a really big bump. Not very safe.

Please, just put it on the frame it is better for SO many reasons.

 

[bajagokart]

If he has a go kart like mine where it is independant rear suspension, the whole rear end is it's own frame that just swivels! You mount your engine and everything gets mounted to an actual prt of the frame and all your drive train is independant but still all together apart of your go kart if that makes sense lol

 

[modelengineer]

If he has a go kart like mine where it is independant rear suspension, the whole rear end is it's own frame that just swivels

That's not independent suspension, lol. Sry.

 

[bajagokart]

its independent of my main frame, so it technically is independent of everything else

 

[modelengineer]

The movement of one wheel is influenced by the movement of the other, therefore not independent.

Think of a car with a live axle. That's not independent suspension even though one wheel can go up when the other stays where it is. The movement of one wheel changes the camber of the other wheel, therefore it's not independent.

 

[fowler]

independent means each wheel is independent of the other
in other words in old cars where the axil solid when 1 wheel hits a bump the other is afected where as independent is when the action of 1 wheel doesnt affect the other

the first pic is the axil on flat ground
the second is the solid axil hitting a bump
the third is the independent hitting a bump

 

[fowler]

modelengineer u submitted your post while i was writeing mine
bugger
but on the origonal topic
u could extend the drive shaft out a little and support it with a bearing the run the chain back to a jack shaft

 

[Doc Sprocket]

u could extend the drive shaft out a little and support it with a bearing the run the chain back to a jack shaft

Wish I'd thought of that!