Came across this when I rebuilt my 250C, often a type 311 piston is listed as fitting the TY but there are a couple of minor differences.
The TY piston is made by ART but the 311 type is made by Izumi, thickness of the skirt is thicker on the 311 piston but the main difference I found was the TY piston has a chamfer from the skirt to the transfer cutout that the 311 doesn't, that seems to be where the piston hits the crank. I assume that the DT2 which is what 311 model code relates to uses either a smaller diameter crank or a longer connecting rod so the piston doesn't make contact
If you have your old piston you should be able to see the differences I've mentioned, if you put wrist pin into both pistons at the same time you'll see that the overall height & pin position are the same. I didn't try altering the skirt on the 311 piston but I think copying the chamfer will fix the problem you have
Yes, the DT2 crank is smaller diameter than the TY's
I have a keen interest in these too - in fact anything from the euro manufacturers that got little/no coverage in the UK press back in the day. Some fascinating machines
I could never understand why Bultaco didn't use/develop that engine more in their motocrossers, especially the big-bores, but I'm told it is a very heavy engine and that Pomeroy hated it. Apparently that meant end of story at the factory at the time, whereas the Brits (Malcolm Davis & Vic Allen) loved the last 400 prototype based on that engine.
Seemed to me to be a much better design than the chain-drive engine.
Some dealers back in the day took 125/175/250 Bultacos out to 325 using a new liner but it was a hec of a lot of work - press out the old liner, bore cylinder to take new 325 liner, open up the transfer ducts, split the cases to enlarge the crankcase 'mouth' for the new liner, machine head & combustion chamber adjusting dia & C.R. to suit larger capacity, then fit bushes on the 16mm gudgeon pin (of the smaller engines) to take the 325 piston (which used 20mm pin).
Bert Flood sold the kits in Australia & a local rider had it done on his Sherpa S 125 by our local dealer. But it always seemed a somewhat less than satisfactory practice to me, especially bushing the 16mm pin to take the 83mm piston. And if you didn't get the transfer ducts and head mods right....
These days guys seem to prefer boring out the 250 to take 76mm GasGas piston, giving extra 28cc. Don't know if they just bore the std liner or make new one. The Bul 250 liners are 4mm thick so that would only leave a 2mm thick liner if they just bored the liner. For me that'd be right on the limit. Don't know if the deck ht is correct or if you need to run a reedvalve with the GG piston either (ie if there's holes in the skirt.)
Another idea I've toyed with but never fully investigated is to use a 75mm KawJS550 watercraft piston, up to 1990 model which were pistonport engines (later models were reedvalve). Wiseco list them as having 16mm gudgeon, same as 250 Bul, but don't know if deck ht or ring locating pins are suitable. That'd give 21cc extra & more meat in the liner
That man Alan is a smart one, but here are some links with good information on the subject.
After reading these articles I decided to limit my overall efforts to the foot pegs. I couldn't convince my self cutting the frame would lead me to where I wanted to go. Many applaud the results. I just think I had more questions after reading a bit. I really like the first link.
For some reason that first website transposes "steep" to "spam", so whenever you see "spam", read it as "steep" or "steeper" to make proper sens of it.
Very good advice about the position of the kickstarter. I can't remember now whether it's the 1 o'clock or 2 o'clock position for the kickstarter they say not to exceed.
From memory its at the bottom of the stroke where the stop tab punctures the case if you have it too far forward.
Out of curiosity, can I ask why you need such a large amount of information? Are you restoring multiple Alpinas or writing a thesis on Bultaco Alpina frame geometry ?
Yeh, I wondered something like that too.
For what it's worth, I've had a go at summarizing the changes that I've gleaned over the years:
Alpina changes
M85 – near identical to M80 Sherpa, but with Matador gear ratios, longer seat & larger tank. One-piece tank/seat unit. Airbox under seat a la Sherpa. Full width 125mm dia front hub , mud-catcher alloy rims, round barrel & head, bolt-on footpegs, 2-piece header & midbox, triangular rear muffler. Single gusset at steering head (on centreline of tubes). Tapered fork-tubes (at top triple clamp). Alloy top triple, steel bottom, with built-in angular offset (a la Sherpa). Some had high-mounted front guard (early?), some low-mounted (late?). Late ones had recessed swingarm pivot (like early M91/2 Sherpa) & weld-on footpegs & the swingarm was slightly diff to match the recessed pivot. Not sure if they used the longer Pursang footpegs or shorter Sherpa pegs.
M99 – 325 version with square barrel & head, 60mm stroke.
M115/116 – extra frame tubes above swingarm pivot (like late M91/92 Sherpa). Frame seemed lighter, perhaps thinner gauge but still mild steel. Top shock mount moved rear-ward (on bracket behind the rear frame tube). New tank-seat unit. Airbox on right side (somewhat like M107 SD Matador) under removable cover. Angled/offset inlet manifold. Conical 140mm front brake, chrome-lined. Stepped gusset at swingarm pivot a la late M91/2 Sherpa. Pursang alloy triples & non-tapered fork-tubes to suit. No angular offset in triples (which is why these & later Alpina’s steer so differently to Sherpa’s) with 20mm less overall offset. Shorter wheelbase. Shoulder-less alloy rims. Dual gusset (folded over) at steering head. New longer seat; slightly new colour scheme. On these models the rear central-downtube was recessed for the swingarm pivot (like the equivalent model Sherpa) which I believe enabled the engine to be mounted about 15mm further back. I’m lead to believe the fork-tubes are longer than Sherpa ones too but not sure when this occurred. 350 engine had 64mm stroke, bigger crank (wider and larger dia), different crankcases to suit & diff stud spacing from earlier 325 engine (if I recall correctly).
M137/138 – much lighter Cro-mo frame, said to be 8 lbs lighter; very thin gauge which fractured everywhere, despite extra gussets/tubes under the airbox. Left side shifter, right side brake, Mk8 pursing rear hub (chrome-lined), one-piece header/mid-box, boomerang/clubfoot rear silencer, sidestand attached to swingarm (instead of frame), new swingarm (20mm longer?) with what appears to be lugs for passenger pegs. Longer wheelbase, more ground clearance. New clutch cover. My 137 engine has square barrel & head & duplex primary drive.
Later models (165/6, 187/8 & 212/3) had completely different frames, swingarms, tanks, shocks etc to the earlier Alpina’s, with rear engine mount bracket hung from swingarm pivot. These are similar frames to the 158/9 Sherpa’s and very different bikes to the early Alpina’s. Forks, triples & wheels look to be about the only things in common with earlier Alpina’s. They were said to have gone back closer to the Sherpa, but maintained the Pursang triples & Matador/Frontera gear ratios. M165 & 187 250 models appear to have the shorter 158 style Sherpa frame, with wheelbase specified as 50”, whereas 166, 188, & 212/213 models have the longer 159 style frame, with wheelbase specified as 51.6”.
Bultaco brains trust, feel free to correct it where required
According to one of the Sherpa books I have, apart from the tank, it also got alloy (mud-catcher) rims, a longer bash-plate, steering stops, larger reinforcement gusset at the steering head, & relocation of the VIN to the right side of the steering head (from left side above the swingarm pivot).
It doesn't indicate when, and I don't know how accurate the info is.
Thanks for the replys. The bike in the photo link does look very similer bar the rear mudguard loop. I was hopping it was one of the 64 model as that the one my grandad used to have plus i think the frame number is only 2 numbers long so looking good. Is there anyone that would know about sprite frame number?
Its only a minor difference so you'd think yours would be legitimately P65 eligible.
Charlie, the bikes you're talking about were built in-house at Hodaka R&D. (The Hodaka R&D guys were keen on trials). The 1st one used a Saracen frame with a special Hodaka engine, said to be about 175cc, with a Cotton tank.That frame was single front downtube as per Saracen. (If I recall correctly the parent company of Hodaka also imported/distributed Saracens)
Curt Alexander in Hodaka R&D then made 6 frames based on that modified Saracen frame of the prototype but with double front downtubes. When built up they used production Hodaka motors - 100/125. They were called the Bullfrog but were never a production model.
On the other hand, the bike pictured in Scot Taco's post is often said to be a Wassell or Wassell-framed Hodaka Wombat. It was actually built by Sprite. If you know Sprites it is very easy to identify as very similar to their Sachs-engined trials frame. It was sold by the Gemini distributor Terry Faust, who was also the Canadian Hodaka distributor. In the US it was sold as the Hodaka Challenger & in Canada it was known as the Sprite Avenger.
They used Sprite frames, swingarm, wheels/hubs, forks & yokes etc, with Wombat 125 engine and aircleaner. The tank may well be from Wassell, which is probably where the confusion comes from, but it is the same tank as used on the Sprite MX models.
The story from Frank Hipkins sons (Steve & Paul) is that Frank was sent a Hodaka engine by a Canadian Oil/Gas company to be fitted into a rolling chassis for use by their remote workers. It was not originally intended as a competition trials bike. Frank modified an existing chassis to suit the Hodaka engine then those Sprite rolling chassies were sent to the Canadian Hodaka distributor to be fitted with the engines. Sprite were said to have built about 150 of them, in batches of 75 (but I wouldn't be surprised if that figure was considerably exaggerated).
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Rickman
in Twinshock
Posted
That's beautiful. Very tasteful!