JJ Cobas - Tiddler!
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JJ Cobas - Tiddler!

This is a discussion on JJ Cobas - Tiddler! within the Vintage Motorcycle Racing forums, part of the Caferacer.net Forums category; Got a message yesterday suggesting I should post this under the Racing section so here goes for those that find race bikes interesting. The bike ...

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Thread: JJ Cobas - Tiddler!

  1. #1
    Senior Member jalsteve's Avatar
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    JJ Cobas - Tiddler!

    Got a message yesterday suggesting I should post this under the Racing section so here goes for those that find race bikes interesting.

    The bike featured is a JJ Cobas and dates from 1989 and is one of several bikes Alex Criville used to win the World 125cc Championship that year. Today we call this championship Moto3.

    The spec of the bike as follows;-
    - Cobas TB5 all alloy chassis
    - Forcella Italia USD forks
    - Ohlins Rear Shock
    - Marvic 18 inch wheels (the bikes ran both 17s an 18s in period)
    - Zanzani Discs
    - Brembo callipers
    - Rotax 128 engine 40+ HP
    - 42mm Magnesium Flat slide Delorto

    Kerb Weight; I have no idea of but I can lift it with one arm to sit the bike on a foot peg stand! It weighs nothing!

    Before I start work on anything I will spend a hours looking at a bike, the parts fit and generally how the bike has worn, it misalignments and problems. It became clear that this bike had gone through a number of small changes each creating a knock on effect and in some cases more problems to fix. For example the rear shock wasn't correct for this bike, it was much bigger than the original as a result the exhaust could not be fitted in the correct position which meant the seat wouldn't fit. The bike had lots of little issues like this including a pair of knackered magnesium wheels which were full of cracks and poorly aligned, brakes likewise, the instruments didn't work and so on.

    After a month or so I stripped the bike and set to work. It was decided to re fit period Marvic streamlines and original spec Zanzani discs (from the original supplier Motobi Murko Zanzani in Italy). Whilst waiting for the discs, which did take a while to turn up, the frame and arm were checked for cracks and the sub frame repaired. The forks stripped and rebuilt with a few small mods too to improve them. The body work was completely restored, the fairing was particularly bad with pre mix contamination and the gell coat falling off, cracks and poor repairs everywhere. The engine had been rebuilt by someone I knew so a quick call to confirmed spec and condition. I just checked the top end and stripped out the clutch for a clean, checked the pump etc so a light touch. Saying that the Rotax 128 engine is super simple to work on. Then I got involved with all the fiddly stuff, clippons which had a crack, bent control levers, rear sets, steering damper and a clamp that was locked tight to the frame etc.... And that exhaust for which we made a new blown front section to clear the shock which also added volume, in effect we broke the exhaust back into its sections and rebuilt the exhaust so that it fitted into the void under the seat at the same time we took a slice out of the centre to keep the volume the same.

    The Marvic magnesium wheels I was asked to fit needed a lot of work, and had been fitted to another bike, although straight they had seen better days with lots of stripped threads, there were no hubs or bearing spacers so we remade all including the cush drive, we also made over size inserts to recover the threads. The wheels were crack tested prior to painting.

    So below is the finished result restored and back to race condition again. All the issues sorted and everything fits as it should.

    Name:  Cobas Creville lh side from front.jpg
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    Name:  Cobas Creville lh side tank cockpit detail.jpg
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    Name:  Cobas Creville rh side from rear.jpg
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    Name:  Cobas Creville rh side rear wheel.jpg
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    Name:  Cobas Creville rh side from front.jpg
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    Name:  CRIVILLE JJ COBAS.jpg
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    Last edited by jalsteve; 01-02-2016 at 03:42 AM.
    Lite the blue touch paper and stand well back!

  2. #2
    Senior Member jalsteve's Avatar
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    Quote Originally Posted by dirkchecken View Post
    i dont like it, i love it.
    You could hang on a wall like a picture.

    I was given a little racing 50cc Maserati in 2014 which when restored will be going up on the wall.
    Lite the blue touch paper and stand well back!

  3. #3
    Member racer61's Avatar
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    a proper restoration...so few people actually do them right. bravo, well done, terrific result.
    -parks61

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  5. #4
    Senior Member jalsteve's Avatar
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    Thanks Parks61.

    Restoration shouldn't be a compromise but to return a bike to the way it was. This takes a lot of research and building a vision of how the bike was in period, sounds easy but often its not. In this instance there are 2 other 1989 bikes claiming to be Criville's and they are different to each other in many details as is this one. The key thing is that the major parts are right so its all about working out chronology and reasons for change - All three bikes are correct as Criville rode 4 or 5 over the season. But to prove it meant collecting 100's of photos, period magazine articles many in Spanish, Italian and English then date everything, identify circuits and put stuff into piles. When one pile of stuff starts to look correct for the bike you have one just digs deeper into that pile, this takes months by the way and often the bikes owner is completely unaware. One must be mindful of (**) bodywork changes and repaints and in season up grades however there is usually a point at which the team dumps the bike and adopts a new chassis as No1 race bike, perhaps a geometry change or new arm, engine reposition and in this instance its the swing arm which dates the chassis to the 1st 3 races of 1989 and we know where the bike came from.

    For many guys restoration does become a compromise as non period parts find there way onto a bike. Sometimes this is for expedience or upgrade and there is nothing wrong with this but its difficult to say later this is the bike that...........!

    ** Many small GP teams would sell earlier generation bikes at the end of a season to provide a small income but its very unusual for a bike to be sold in sponsors colours or with special works engine parts. Why? Well if the bike is sold and some dickhead puts himself and bike into the Armco and is seriously hurt the old sponsor doesn't want his name plastered all over the press and the selling team loose sponsorship and likewise if a highly tuned engine proves unreliable after 75 races miles and a 40foot container of race spares and £1m to buy them is required to finish a season the manufacture doesn't want the world to know either. They are looking to advertise success not the dangers associated or the cost! So to find truly unmolested as raced championship competing or winning bike is very rare, we know the major manufacturers crushed their bikes for these very reasons, in my opinion it has little to do with technology falling to the opposition as Honda or another could simply buy the opposition's chief designer and often did.
    Last edited by jalsteve; 01-02-2016 at 10:44 AM.
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  6. #5
    Senior Member thechief86's Avatar
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    Awesome work, sir. Even as a fat guy, I want to ride this bike. I can't even comprehend 40 h.p. from a 128cc engine.
    It ain't easy bein' fat and greasy.

  7. #6
    Senior Member jalsteve's Avatar
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    Quote Originally Posted by thechief86 View Post
    Awesome work, sir. Even as a fat guy, I want to ride this bike. I can't even comprehend 40 h.p. from a 128cc engine.
    Me rather prosperous too.

    128 is the series number of the engine, the capacity is 125cc, The engine is rotary disc valve and yes a little over 40 horses at 12800 rpm. Seems a lot but remember these are GP engines and the guy who built them for Cobas was the same guy who built the Ossa 250 engines for Santiago Herrero; Eduardo Ciro. Not only were his engines fast they were reliable too with only one mechanical failure in the 89 season. Putting that power output into perspective, kart guys are working hard for 31hp 20 years later!

    The Rotax 250cc engine which is basically 2x128 engines and called the 256 Rotax (Tandem) is seriously quick and scary, I would rather ride a TZ750 in the wet.
    Last edited by jalsteve; 01-02-2016 at 01:27 PM.
    Lite the blue touch paper and stand well back!

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