bulonda 420cc

[fatboyracing]

Question for everyone,
Will a xl350 honda motor fit into a bultaco 250 1974 sherpra frame I would like to try this mod ,has anyone tried this ? I am about to purchase a sherpia bike and I have heaps of xl motors. The forks are the same size as honda and shocks are the same length the big difference is the frame weight I recond it will be 30 kg lighter then standard XL when finished. The light weight chrome olly frame will make a big difference to the over all riderbility (if there is such a word) I hope you guys can help or maybe give me some suggestions

cheers
Fatboy

[tony27]

I think you'll have the spanish mafia putting a price on your head if you do, saw a sherpa fitted with a motorsport motor in a cockies shed years ago

[GD66]

There's an XL350-powered Bully running in WA, the South African rider Rob Wickes rode it up front at Narrogin at the 15th Anniversary meeting. It's owned by Mark Thomas : from (admittedly ravaged) memory, the lower frame rails had minor mods, but it was otherwise a relatively straightforward  insertion.

[VMX247]

Believe there are pics of it on the 15th Anniversary topic on vmxwa site.
It hammers along too !! 
cheers S&A WA

[firko]

There was couple of XL powered Pursangs racing in NSW and Qld a few years ago. If the swap is anything like fiting an XL to a Montesa or CZ it'll be a nightmare. Not sure about the Sherpa frame though Shane.
Are you building a motocrosser or trials bike? The steering geometry of the Sherpa might be a little squirilly for MX but it might work OK for dirt track.

[Davy123]

http://www.avcmc.iinet.net.au/201104/xl350.html

[fatboyracing]

Thanks guys for the info looks maybe not too bad of a project I will take lots of picts for everyone to see how it goes.
I am going to start today by taking some measurements to see how tight the motor will be.
The steering stem is a lot more layed down then orginal xl I hope this will make it turn alot easier then original
The back brake pedal will be a challenge
I dont no how it will handle on the MX track Mark but hopefully it will be alot lighter and will turn more like a MX bike then a road bike.

Cheers
Fatboy

[huskibul]

 Don't like being a stick in the mud fatboy but  that bulonda that davy posted has a 74' pursang frame, owning both a  pursang and  sherpa believe me the sherpa frame/swingarm is nowhere near as strongly built as the pursang, id be a bit skeptical if it would handle that motor

[fatboyracing]

Just had a measure up of the frame swingarm etc I think that Huskibul is right the swing arm is pretty light weight for MX so I have also got a Pursang swing arm that is a lot stronger and longer and should fit with a small spacers on each side. The motor should fit in to the frame ok. But I will wait until I pick up the frame next week to measure the motor properly.It is very light chrome olly frame abit like a push bike compared to a XL

cheers
Fatboy

[Rossvickicampbell]

yastill won't beat the YZ FB~!!!  But keep on trying 

[BultacoMacca]

Fatboy, I could be wrong, but a 74 sherpa might only have a steel frame not chromemoly. (Pursangs from 74 on had chromemoly).
Feetup Dave would probly know.

[ola_martin]

The Sherpaframes often crack at the steeringhead with original engine in trials riding. It's flexy and weak. I'd only imagine what it will be like with a honda 4 stroker on a mx track. 
 I also think it's regular steel.

If you're going to put in all the work of building a special i think you'd be better off getting a Pursang frame to start with.
For mx use that is, if you're building a trialsbike you're on the right way.

Whatever you do, put up pics....

[bazza]

XL259 with 305 big bore might be better fit and power?

[David Lahey]

There are loads of mid 1970s Alpina frames that noone wants that have a frame that is lightweight (especially compared with a Honda XL350 frame) and the same main frame geometry as the Sherpa T but they have more frame elements around the mid section which make them more robust. The riding stability they enjoy over the Sherpa T is due to having a longer swingarm and Pursang/Frontera triple clamps (more trail).
I'm talking about Alpina models 116/117 and 137/138. which were made 1974 -1976.
I suspect a Sherpa T frame would fall to bits pretty fast with an XL350 motor in it unless it was only used on smooth roads. Sherpa Ts are probably the most flimsy of the mid 1970s trials bike frames, especially the front downtube/top tube/steering  head area.

[fatboyracing]

Sounds like I maybe barking up the Wrong tree, sounds like I might need a pursang frame They are hard to find in tassie. I know nothing about bultaco's steel, chrome olly etc but I am listerning to you guys any one go any more suggestions? I have about 5 complete 350 motors no 250s and would really like to make a special.

cheers
Fatboy