I've been testing my rear engined BEC and I get quite a bit of vibration from the drivetrain. I think its because the sprocket adapter isn't perfectly lined up.

Its a zzr1100, with a freelander diff. I have one of the 12 spline adapters but it the homes dome match up with the freelander diff.
I've drilled new ones but dont have a mill etc so eyeballed it. I think it's pretty close but there is some definite vibration.

The diff and engine are rigidly mounted to a subframe with no space for a driveshaft.

Can anyone suggest a solution?
All I can think of is finding a machine show that can drill the holes in the freelander output to perfectly match the sprocket adapter.

Thanks!

Apart from getting every thing lined up spot on how about a rubber donut like on some production cars

That was the original plan, but I found it difficult to find an off the shelf part that fitted.

To mount the output flange direct to the diff' they have to be very accurately aligned. If not the misalignment won't only cause vibration but will damage either engine or diff or both in time.

Are the diff and engine rigidly mounted to the same frame?

Yes, both engine and diff are bolted directly to the same frame with no rubber bushing.

So it's seeming like flex during use, or does it happen while on light throttle too?

To me it would seem logical to isolate them via rubber mount because you don't want to load the bearings in ways they're not designed for, but if not you need to align them to within a gnats ass of perfect and brace everything to prevent twist winthin this unit of parts.

Thanks for the suggestion...

The car hasnt been on the road yet. I just have the rear on axle stands and have engaged 1st gear while idling so that the wheels spin. I can see the frame rhythmically 'bouncing' as if something is off-centre or balanced badly. As there is no load and the engine is running slowly I dont think flex is causing it at the moment.

this will probably come down to which is easier..

to bush both the engine and diff will need a complete redesign of the subframe.
having the output shaft drilled accurately by a machine shop might be quicker cheaper and easier.

as previously mentioned, Instead of soft mounting the engine and diff, it might be easier to install a rubber flex disk beaten the output shaft and diff like you see in a lot of RWD cars.

The problem here is they are all three bolt pattern and the output flange cant be a complete circle. It needs gaps so the bolts from the other side have space to 'float'. So this solution would need need a three bolt pattern drilling in both flanges, and some of the flange cutting away.

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Originally posted by nick9one1
Thanks for the suggestion...

The car hasnt been on the road yet. I just have the rear on axle stands and have engaged 1st gear while idling so that the wheels spin. I can see the frame rhythmically 'bouncing' as if something is off-centre or balanced badly. As there is no load and the engine is running slowly I dont think flex is causing it at the moment.

this will probably come down to which is easier..

to bush both the engine and diff will need a complete redesign of the subframe.
having the output shaft drilled accurately by a machine shop might be quicker cheaper and easier.

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wheels are fitted and were balanced once

That's a good point though. I'll pop the driveshafts out and confirm the problem is definitely the engine/diff alignment

quote:

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Originally posted by nick9one1
Thanks for the suggestion...

The car hasnt been on the road yet. I just have the rear on axle stands and have engaged 1st gear while idling so that the wheels spin. I can see the frame rhythmically 'bouncing' as if something is off-centre or balanced badly. As there is no load and the engine is running slowly I dont think flex is causing it at the moment.

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Solid connection from engine to diff, without anything (donut or otherwise) just looks, with best engineering , like its not going to be perfectly aligned and will be relying on the sprocket adaptor being a floppy fit on the splines to compensate for unintentional misalignment, which will cause an issue somewhere down the line. If the Adaptor is solid on the output shaft, even more so.

A bike engine will vibrate like crazy running it like that. Its due to not having a flywheel to dampen it out. Scared the crap out of me first time I did it with mine during the build.

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Originally posted by adithorp
A bike engine will vibrate like crazy running it like that. Its due to not having a flywheel to dampen it out. Scared the crap out of me first time I did it with mine during the build.

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