Thumper Cafe Racer

[humphrt]

Hey had an idea and was after your thoughts thanks.

Was thinking of getting a cb350 or similar frame(cafe racerish) and fitting it with a large single(thumper, around 50-60hp). Just for something different and because i can, or wanna try to anway.

Thoughts please

[vifferman]

You'd be better off getting a newer bike, summat with decent suspension and brakes, and fitting a big single into that. I've seen a few conversions where they took a Kawasaki 250 (can't remember year or model) and stuck an XR500 engine in. A cafe racer should be sporty and handle well. A CB350 is neither, and it would be hard to find a decent one to use as a donor. They're over 30 years old, y'know...

[koba]

What? Like this? (http://www.trademe.co.nz/Trade-Me-Motors/Motorbikes/Motorbikes/Classic-vintage/auction-180102140.htm)

Quick, Quck 27 mins to go....

[humphrt]

yeah like that, but i need a lil more money than i got right now.

well a 'cafe racer' type then with all the appropriate suspension. thats why i want feedback. what would be a better frame to start with? a Honda GB or what????? im just thinkin this through right now.

[Daffyd]

My son had one of those 250 Hondas (V3 - 2smoke) that had an XT600 slotted in.

Went like a cut cat, but had bad vibration probs, so bad the tacho needle broke off.

[Atomic]

Im halfway in with your idea. Iv got an Aprilia RS250 with a dead engine, just bought a Yamaha Raptor 660cc single last week, trying to put them together to finish my Yamarilla Super Mono project. About to place an order for an oversize piston kit, s/s valve kit and hot cams...gonna hand build a full system, carb and dyno tune and wow! I cant wait!

So yeah, go for it mate.

[Atomic]

My son had one of those 250 Hondas (V3 - 2smoke) that had an XT600 slotted in.

Went like a cut cat, but had bad vibration probs, so bad the tacho needle broke off.


Hmmmmm yeah iv been told I need to strengthen my engine mount points at the aluminium frame as the vibration will possibly cause fracture.

Bikes with steel frames are recommended.

[koba]

Hmmmmm yeah iv been told I need to strengthen my engine mount points at the aluminium frame as the vibration will possibly cause fracture.

Bikes with steel frames are recommended.

Very important.

It would pay to do lots of reseach on engine vibrations and the like.
You should also get an idea of tho the thumper vibrates and build the frame appopriatley around it, not quite as easy as bungin one in. TIG access is almost essential if you have an Alu frame. (which you do...)

A single downtube on the front would prob work best, I saw a guy with a honda RS125 based one that he had added a soingle downtube to and it seemed to work well.

Make sure the engine is kept in its sweet spot for vibes, if you plan to tune it to rev higher you may have to have it re balanced to a different factor.
If it has balance shafts LEAVE THEM IN.

There is a good chance lots of little aprilia bits on it aren't designed to cope with the vibes and you may find that beefing up things like subframes, brackets, footpeg mounts, fairing pieces, radiators, exhausts etc is needed - rubber mounts on certain things can help.

Have a good look at old heavy brit thumpers and see how much more heavy duty things had to be on them with their big vibratey singles.

Rubber on footpegs = must.

There is great potential in this kind of platform but it will take alot of development work to get it working ok, I had/have one and it never got close to even doing one lap at full potential but in the moments it was running sweet it handled better thn most bikes I've ridden, pulled HARD out of corners had feck all top speed, little low speed control and was bucket loads of fun, then it would break down.

[koba]

yeah like that, but i need a lil more money than i got right now.

well a 'cafe racer' type then with all the appropriate suspension. thats why i want feedback. what would be a better frame to start with? a Honda GB or what????? im just thinkin this through right now.

Keep it steel.

BSA?

[Atomic]

Very important.

It would pay to do lots of reseach on engine vibrations and the like.
You should also get an idea of tho the thumper vibrates and build the frame appopriatley around it, not quite as easy as bungin one in. TIG access is almost essential if you have an Alu frame. (which you do...)

A single downtube on the front would prob work best, I saw a guy with a honda RS125 based one that he had added a soingle downtube to and it seemed to work well.

Make sure the engine is kept in its sweet spot for vibes, if you plan to tune it to rev higher you may have to have it re balanced to a different factor.
If it has balance shafts LEAVE THEM IN.

There is a good chance lots of little aprilia bits on it aren't designed to cope with the vibes and you may find that beefing up things like subframes, brackets, footpeg mounts, fairing pieces, radiators, exhausts etc is needed - rubber mounts on certain things can help.

Have a good look at old heavy brit thumpers and see how much more heavy duty things had to be on them with their big vibratey singles.

Rubber on footpegs = must.

There is great potential in this kind of platform but it will take alot of development work to get it working ok, I had/have one and it never got close to even doing one lap at full potential but in the moments it was running sweet it handled better thn most bikes I've ridden, pulled HARD out of corners had feck all top speed, little low speed control and was bucket loads of fun, then it would break down.

All good advice cheers.
Fortunately I do have TIG access.
To some degree, ill wing it, if it works great and if not, well i will have learnt somethign!

[GaZBur]

Sounds like a good idea for a reasoably cheap F3 racer as well. Good luck, wish I had some welding skills myself!

[Bonez]

Keep it steel.

BSA?You haven't had a close look at a GB have ya? GB frame with an NX650 engine would be just lovely.

[koba]

All good advice cheers.
Fortunately I do have TIG access.
To some degree, ill wing it, if it works great and if not, well i will have learnt somethign!

Cool!
I do believe this kind of bike can be made to work well on a tight track, however in most racing circumstances the original two stoke would be better in almost every way.
But pissing about building somthing is much more fun and as you say you are bound to learn LOTS wether it works or not.
Good Luck, post up some pics and a built thread if you can!

[koba]

You haven't had a close look at a GB have ya? GB frame with an NX650 engine would be just lovely.

Nope, Coz if I (my ever so humble personal opinion of course) was going to build such a beast for the road I would make it out of an old Beezer or somthing that has cheap rego and can comply to the standards of the time.

No, that doesn't mean it has to cost heaps - it could use a rotten old barn frame (http://www.trademe.co.nz/Trade-Me-Motors/Motorbikes/Parts-accessories/Frames-bodywork/auction-182594912.htm) or somthing as a base.
The idea of good rear suspension would be the stumbling point.

Each to thier own tho...

[98tls]

Have this lurking in the shed awaiting some time/$,NSR framed XL powered.Fwiw.

[FJRider]

RG250 (OR SIMILAR) rolling chassis's can take 500/650 British singles, or jap 500/600 (or thereabouts) singles. Certification is the biggest hurdle.
Its been done so often, plenty has been written about what problems there are...

[speights_bud]

Hmm i have a CB360 plonked in a CB250 frame in the gargre somewhere... should dig it out sometime

[doc]

Hey had an idea and was after your thoughts thanks.

Was thinking of getting a cb350 or similar frame(cafe racerish) and fitting it with a large single(thumper, around 50-60hp). Just for something different and because i can, or wanna try to anway.

Thoughts please


Now this is what I would like, if your talkin large thumpers.

[Ocean1]

Now this is what I would like, if your talkin large thumpers.

Very nice. Blown backwards I see.

Front don't inspire me, and the rear shock mounts look dodgy, but I would love to press up something similar.

Wot is it? Any links?

[humphrt]

wicked


Now this is what I would like, if your talkin large thumpers.

can i hear you say "animal".


Quote:
Originally Posted by Bonez
You haven't had a close look at a GB have ya? GB frame with an NX650 engine would be just lovely.

Nope, Coz if I (my ever so humble personal opinion of course) was going to build such a beast for the road I would make it out of an old Beezer or somthing that has cheap rego and can comply to the standards of the time.

No, that doesn't mean it has to cost heaps - it could use a rotten old barn frame or somthing as a base.
The idea of good rear suspension would be the stumbling point.

Each to thier own tho...

so can always fit modern shocks to an old frame though cant you? yeah im not really after a modernish frame(rg250) i really want it to be oldschool but still able to mix with the modern stuff in the corners.

[avgas]

Wot is it? Any links?
Half a harley - no really.
all custom - 1L from recall
Notorius - was in Robb Report a year ago.
Completely 1 off

[Dodgyiti]

The vibration may be an issue depending on how well ballanced the single is, plus the ones with counter balance shafts and the like would be what to go for. Or you can also, or as well, isolate the motor like they did in the olden days with isolastic mounts.

[humphrt]

The vibration may be an issue depending on how well ballanced the single is, plus the ones with counter balance shafts and the like would be what to go for. Or you can also, or as well, isolate the motor like they did in the olden days with isolastic mounts.

so im guessing that these mounts are rubber(or similar) that cushion the frame from the vibration? wouldnt this cause the frame to be less ridgid? which is not so hot on a speedy lil beast.

[xwhatsit]

so im guessing that these mounts are rubber(or similar) that cushion the frame from the vibration? wouldnt this cause the frame to be less ridgid?
Yup, and yup! By varying how much you torque the mounting bolts, you can choose between handling and comfort :laugh:

[humphrt]

ok now this may seem completely ridiculous :shit: how about a turbo'd single, i know the exhaust stroke once every four cycles isnt ideal. but lunacy is fun :laugh:

[Ocean1]

so im guessing that these mounts are rubber(or similar) that cushion the frame from the vibration?

Correct.


wouldnt this cause the frame to be less ridgid?

Just means you can't consider the engine to be a structural frame element. Rigidity in most planes is a good thing, you'd just have to design the frame to handle it alone. In theory that might mean more overall weight, however Mr Buell managed to produce one of the best handling, lightest bikes in it's class with an isolated motor.

[humphrt]

Mr Buell managed to produce one of the best handling, lightest bikes in it's class with an isolated motor.

Lucky Mr Buell has an R & D department, but im sure my millions from lotto last night will go towards it *gotta go check that ticket*.

[pritch]

The man who originated the isolastic mounts worked for Norton at the time.

I understand he left there when it became apparent that the future was bleak and he moved to the USA where he worked on the design of the "Rubber Glide". Which concept is spreading (or has spread) throughout the whole Harley range.

[humphrt]

ok so it wouldnt quite be a cafe racer but what about this frame?

http://www.trademe.co.nz/Trade-Me-Motors/Motorbikes/Parts-accessories/Frames-bodywork/auction-182667856.htm

trimmed down a little, with a big thumper in it