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prop coupling problem

dexion7 - 21/4/11 at 10:55 AM

Description

Looking for help with this coupling problem.

The diff flange is max 50mm from the engine flange. The photo shows a donut coupling linking them but will chassis twist cause misalignment problems? Would mounting the diff flexibly or solid be best.

Already considered a cv joint but it won’t fit within 50mm.

Would a direct connection e.g. bolting the diff to the engine work if the diff was flexibility mounted?

Any other ideas or comments or ideas appreciated

Miks15 - 21/4/11 at 11:00 AM

Diff should be solid mounted but you need to make sure it ss close to perfectly lined up with the engine so you dont get any misalignment problems.

blakep82 - 21/4/11 at 11:04 AM

i'd keep the rubber donut in there, that will take account of any misalignment, twisting etc.
if you bolt them straight together, neither will last long IMO

the engine will vibrate, and the the diff will try to move.
you'll also have all sorts of shock going through everything when you pull away on full throttle for example.
the rubber donut will dampen this.

dexion7 - 21/4/11 at 11:11 AM

will the donut be happy with heat conducted from gearbox through coupling into it?

incidentally there are 2 donut types, rotoflex (springy) and this type which is pliable (from a bmw 5 series and used by nova racing in their coupling)

dexion7 - 21/4/11 at 11:19 AM

and what about the coupling that dax used to supply for a bike engined rush - the 'fingers' that fit into the engine sprocket?

would that work if the diff was flex mounted?

Miks15 - 21/4/11 at 11:31 AM

My BMW engine and box has a rubber donut which looks very similar to the one you have between the box and prop so should be fine.

Like blake said the donut which just take up the little vibrations and movements

dexion7 - 21/4/11 at 11:38 AM

quote:
Originally posted by Miks15
My BMW engine and box has a rubber donut which looks very similar to the one you have between the box and prop so should be fine.

the bmw gear box will run much cooler than the output flange of a though - waht temp will these donuts be ok with?

quote:
Originally posted by Miks15
Like blake said the donut which just take up the little vibrations and movements

in the bmw you have a long propshaft with 2 universal joints thus there is vitually zero misalignment potential on the donut and its purpose in life is to dampen rather than to accomodate misalignment.

Miks15 - 21/4/11 at 11:42 AM

The BMW has a two piece prop, the first of which is connected only with the donut, this then goes back to a bearing in a housing which is solidmounted , then there is two UJs between this section and the diff so there is the possibilty of some misalignment as the engine/box move about slightly under running. I know its not quite the same but it will experience similar loads.

Cant help with the temps though although i can't see why you output flange will run any hotter than mine? Theyll be doing similar speeds

[Edited on 21/4/11 by Miks15]

nick205 - 21/4/11 at 11:47 AM

Would it not be better all round to mount the motor transversely and use a chain driven diff - I thought that was how middy BECs were laid out?

dexion7 - 21/4/11 at 11:52 AM

quote:
Originally posted by Miks15
The BMW has a two piece prop, the first of which is connected only with the donut, this then goes back to a bearing in a housing which is solidmounted , then there is two UJs between this section and the diff so there is the possibilty of some misalignment as the engine/box move about slightly under running. I know its not quite the same but it will experience similar loads.

Cant help with the temps though although i can't see why you output flange will run any hotter than mine? Theyll be doing similar speeds

[Edited on 21/4/11 by Miks15]

thanks for the detailed explanation Miks. one further complication when comparing the two situations is that in the bmw donut i suspect there is a spigot spherical bearing to ensure that only angular, rather than parallel (the worst type) misalignment can happen. in my setup i might be more likley to experience parallel depending upon how any chassis flex manifest itself.

on the temps issue the dount is bolted direct to the engine drive flange (which is at engine oil temp) whereas in the beemer it would be connected to gearbox as well but this temp would likley be substantially lower than engine oil temp.

dexion7 - 21/4/11 at 11:57 AM

quote:
Originally posted by nick205
Would it not be better all round to mount the motor transversely and use a chain driven diff - I thought that was how middy BECs were laid out?

its a busa engine in a riot and Sylva supply a longer chassis for those wishing to fit a busa rather than an R1.

the R1 engine allows a much longer chain and if the busa is fitted transversely in a short chassis like mine there is very little chain length which i was told would make this drive system even more susceptible to damge caused by chassis twist. its also a turbo busa so i dont know if the chain would take the strain

Miks15 - 21/4/11 at 11:58 AM

Nope there is no bearing.

O yeh i forgot the box ran on the same oil as the engine in bikes. The box would still run fairly hot on the beemer but like you say i suspect it wont quite be as hot.

Johneturbo - 21/4/11 at 12:00 PM

quote:
Originally posted by dexion7
and what about the coupling that dax used to supply for a bike engined rush - the 'fingers' that fit into the engine sprocket?

would that work if the diff was flex mounted?

I'd like to fit something like that on mine to take out some of the vibrations/slack.

it sounds like a cush drive that's on Mbikes rear sprockets

Do you have any more info on that part Dexion?

nick205 - 21/4/11 at 12:02 PM

quote:
Originally posted by dexion7

quote:
Originally posted by nick205
Would it not be better all round to mount the motor transversely and use a chain driven diff - I thought that was how middy BECs were laid out?

its a busa engine in a riot and Sylva supply a longer chassis for those wishing to fit a busa rather than an R1.

the R1 engine allows a much longer chain and if the busa is fitted transversely in a short chassis like mine there is very little chain length which i was told would make this drive system even more susceptible to damge caused by chassis twist. its also a turbo busa so i dont know if the chain would take the strain

Ah ha - now I understand!

dexion7 - 21/4/11 at 12:03 PM

quote:
Originally posted by Miks15
Nope there is no bearing.

so on the beemer does the gearbox drive flange hold the donut and the other flange of the donut goes straight the the solid mounted bearing you mentioned earlier - what about the hole in the center of the donut (40mm i think), does this sit on a spigot on the gearbox flange or what method do they use to ensure that the front prop does not teld to flail around its centre line?

dexion7 - 21/4/11 at 12:12 PM

quote:
Originally posted by Johneturbo

quote:
Originally posted by dexion7
and what about the coupling that dax used to supply for a bike engined rush - the 'fingers' that fit into the engine sprocket?

would that work if the diff was flex mounted?

I'd like to fit something like that on mine to take out some of the vibrations/slack.

it sounds like a cush drive that's on Mbikes rear sprockets

Do you have any more info on that part Dexion?

ive heard it described as 'excellent' and 'nasty'!

basically they make a propshaft flange and bolt hardened steel pins into it which mate with the teeth on the circumference of the original engine sprocket. this apparently alllows for minor misalignment (the amount of acceptable misalignment presumably depends on the clearance between the pins and the sprocket teeth). ive not actually seen one but i understand that the sprocket is deemed to be a consumable item.

doubt if it would introcude any cush drive effect though

MK9R - 21/4/11 at 01:45 PM

Theres a guy on here called paul telford who did exactly the same thing, he spent a lot of time and effort trying to sort it out. I cant remember his login though.

dexion7 - 21/4/11 at 02:08 PM

quote:
Originally posted by MK9R
Theres a guy on here called paul telford who did exactly the same thing, he spent a lot of time and effort trying to sort it out. I cant remember his login though.

hi Austin - that is guy is me and im still trying to sort it!

MK9R - 21/4/11 at 02:11 PM

quote:
Originally posted by dexion7

quote:
Originally posted by MK9R
Theres a guy on here called paul telford who did exactly the same thing, he spent a lot of time and effort trying to sort it out. I cant remember his login though.

hi Austin - that is guy is me and im still trying to sort it!

arh, ok, bugger! good luck!!!

Mr Whippy - 21/4/11 at 03:44 PM

my worry would be that the rubber flexing very quickly if there is much of a misalignment. That would heat the rubber up and I mean a lot! To the point it failed

I'd suggest you make a cradle that supports the engine and diff rigidly so that they are effectively locked together , once they are aligned then they should stay that way with the rubber coupling just damping out the engine vibrations to the diffs bearings.