Gearbox suggestions needed, please.

[Sserpent]

Hi Guys.

As I've posted in the Introductions section, I've got a Yanmar L100 and a Suzuki VL125 Intruder and I intend sticking the one into the other. And no intruder jokes please!
Some advice on a gearbox would be very welcome.
I'm looking for a pre-unit gearbox, ideally with a kick start attached but that's not a necessity. I don't have any particular preference other than ease of integration. Any suggestions would be greatly appreciated. As would any fitting advice and/or pit falls to watch out for.
This is my first build, so I'm going for easy as opposed to clever.
I'll leave clever for my next build.
Do all the pre-unit gearboxes come with built in clutches? Also, if anyone knows where I can get information on the ratios of the boxes that would be welcome as I'm not having much luck. Not knowing which gearboxes to look for doesn't help.
I've had a look at the gearbox threads, but other than a Enfield gearbox, I couldn't really find mention of anything else that would suit my application.

What I really want is a CVT, but reading the CVT threads this looks too complicated for me right now.

I'll try and post pictures of my build as it progresses, but I've already forgotten to take pictures of the Suzuki before I stripped it, so it'll all depend on me remembering to take pictures in all the excitement.

Thanks
Neil

[OilyPhil]

Hi Neil, the pre unit gearboxes you are likely to find in the UK are 50-60S british gearboxes, all will be 4 speed, kickstart and will have gearchange on right. The three main types are BSA, Norton/AMC and Burman. None have the clutch built in, you will have to source a seperate clutch. The clutch will have a sprocket attached so it is relatively easy to sort out drive to it from your engine.
The good news is that all are readily available (EBAY/AUTOJUMBLES/OLD BIKE MART). Most have a top gear ratio of 1:1 and can range from 1.751:1 1st gear (BSA RGS with an RRT2 close ratio gearbox) to around 3.2:1. Dont worry too much about gearbox ratios, just get a common gearbox (I like the STD BSA gearbox, mainly cos Ive owned several A10s) and adjust your gearing to suit by changing primary and final drive sprockets.

Other alternatives involving cutting the gearbox off a 2 stroke and using the gearbox/clutch mechanism, but Ive no idea about ratios, but suspect top gear will be 1:1, using a jap 2 stroke should net you 5 gears and if you get one from a early bike you will get a kickstart. Most of these clutchess will be gear driven so will be harder to mate to your engine.

Hope that is of some help, Phil

[Sserpent]

Thanks Phil.

Bother, I thought/hoped pre-unit gearboxes had built in clutches! I went around a bike jumble a few months ago just to have a looksee at what's around, and could have sworn I saw a gearbox with built in clutch. Stupidly I didn't ask the seller any questions! Do you know of any pre-unit gearboxes that have built in clutches?

Thanks
Neil

[OilyPhil]

Hi Neil, heres a pic of a BSA swing arm gearbox as fitted to A7/10, B31/33 therefore fairly common. This one is viewed from above and does hava a clutch attached. The final drive sprocket is inboard of the primary sprocket on the clutch drum.

.
They mount on a pair of brackets and pivot on the bottom mount for chain adjustment. Normally all gearboxes are sold without clutches as they are considered a seperate item, but can often be bought as a pair. Indeed brand new BSA clutches are still available (at a price!, see ebay, search for "bsa clutch") but are very common second hand. If you need dimensions I have one fitted to my RGS and am happy to measure it for you.

Phil

[Sserpent]

Aahh! Thanks Phil. Now I understand how it all fits together! I saw the clutch lever thingy on the gearbox and thought the clutch was in the gearbox!
That potentially presents a new problem for me. Do these clutches need to be run wet? I was going to investigate making the primary drive belt driven, to be able to run it dry, but if the clutch needs to be wet that'll put an end to that idea.
Don't worry about the dimentions thanks.

[sbrumby]

They are supposed to run wet but they seem to function OK dry. The biggest problem you will have is getting rid of the cog on the clutch basket and replaceing it with a belt drive, and by that I presume you mean toothed belt, as the pulleys are aluminium. My big Yam runs with the same gearbox in the previous pic but I run mine with double V belt, still a lot of machineing though.

[OilyPhil]

Have a lok at this site http://www.bobnewbyracing.com/ , probably costs a fair amount though! Id be tempted to run the clutch dry (Ensure the rollers are well packed with grease) and fit an o ring chain, if it works then you can convert to belt drive later (it would certainly be cheaper to change ratios with chain)

Phil

[Sphere]

I think Anorak_Ian has one of those and it's well over 400 quid.

[Sserpent]

Thanks Guys.

Yes, I was planning on running a toothed belt. Thanks for the link Phil, I'll send them an email, but as I'm a on super tight budget, I suspect it'll be too expensive for me. The belt driven clutch solution does look like just the thing though.
I thought of running an o-ring chain at first, but then thought that since the chain is going to be fairly short, it’s going to do fairly large number of revolutions (a lot more than the final drive chain). This will cause a lot of wear of the links. So I suspect that’s why they run the chains wet. Does anyone have any experience running an o-ring chain as a primary drive?
I must say the news that you can (possibly) run the clutches dry is welcome. How many mile have you done on the dry clutch sbrumby?

[smokyjoe]

The old Harleys and Indians that had a primary chain all ran them "dry", they had an oiler that leaked a bit of engine oil from the pressure bypass to a squirter that would give the chain a little lube. Messy, but effective. I'd make sure that running the clutch dry that the right friction material is used, some of the wet clutches are cork! that would smoke quickly if run dry. (done that inadvertently) The other thing is that with a wet clutch more efficient heat removal takes place than dry, something to consider. It was common to run the old Indians with a geared primary with a "dry" chain in racing applications as the chain has less loss than the gears and ratio changes were easier. Most of these old dry clutches ran asbestos friction linings, I think most modern ones use a kevlar/ceramic mix.

Good luck, I look forward to see what you come up with!

[sbrumby]

The big Yam did a few thousand miles, I havent used it for a while now as I have three and can only ride one at once. The plates on the BSA box are cork but they dont seem to mind being dry and dont smoke. If you take the easy route and put an o ring chain on you will find that it stretches the chain, the diesel engine puts out a lot of force when it fires and this stretches the chain. The Yam originally was built with chain but that would stretch 1" in 1000 miles. Slightly bigger and heavier than you are proposing (300kg 15hp) but you will still see it. the good thing about chains is they are cheap and easy to change ratios. So I advise go with the chain and get it right then convert to toothed belt or v belts as I prefer.

[hzoltaan]

Hi All,

I have the urge to build a small (5-6HP) light commuter bike to beat the buses/trams and for the fun of it.
I saw a big range of engines on internet (chinese yanmar clones) and I happen to have a Java350 and a GS450 frame around.

Now, I would rather not cut the frame like it was done in a bike-buillding topic, which a really nice built though. Here authorities do not like frame modifications...

So, my big question is, how do I fit the engine AND gearbox into the frame. Would that be possible that a dry clutch / CVT transmission from a scooter would fit? I'd imagine taking the dry clutch / transmission off a stronger scooter and put it on the engine... Any ideas? Maybe a readily avilable CVT transmissions, or a very compact gearbox...? (since the power is low I was considering to chop off the gearbox of an old 4-10 hp 2 stroke moped)

All ideas are welcomed.

Thank you
Z

[Sphere]

Assuming this is Katowice Poland, you could also consider a bulky frame like Ural and the like? In general I think there are a lot of myths surrounding the regulations of converting bikes to diesel and practice where it's not so bad after all.

It might be worth it to find out exactly what is allowed in your country.