Derbi GPR Nude

[SQL]

Head is a little battered but its the best condition 3MB head that has been on ebay for a while that has been cheap, its all getting sent off to be done rebore and tidying the head up too, it should run fine if worse comes to worse 2 metal head gaskets then the rubber one sorted.

The clearance shouldn't be an issue really.

[_Iain_]

Oh it wont cause it to run badly or anything like that, however if i was going to all the aggro of building the motor back up with the intention of keeping it & using it then i'd want everything specced up perfectly to get the absolute maximum i could out of the engine.

I think even if you get the squish 100% perfect on a race motor it barely accounts for 2% of peak performance. The fact that I know my H100 piston is scratched irritates me. The engine runs well, but I know it isn't perfect inside & this annoys me - I'd love an excuse to tear it all down & spec everything correctly
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Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[SQL]

I haven't got a piston yet lol will get one when its being rebuilt. as it will all be done as one unit making if better, the topend is being tuned and fixed, the botton end I am splitting (Phowar) and replacing main bearings etc and changing the conrod.

[_Iain_]

[SQL]

[P.]

Erm... yeah don't remove the pump. If its for fun, just fill the tank and leave it. Not heard of many DT's going pop due to oil pump failure.

[_Iain_]

Paddy said something about using engine braking on premix bikes usually ends in bang. If that's true then I wouldn't go premix if using the bike on the road - an autolube pump is extremely simple & would probbably be more effort to remove it and blank the hole off etc than to just spend 30 seconds priming it & adjusting the cable so the timing marks line up.

Plus - you've gotta carry a backpack with a bottle of two stroke & a measuring cup of some sort everywhere you go , then sit there working out precisely how many ML of two stroke you need for the amount topped up & mixing the fuel up on the forecourt. IDK, sounds like hassle - My little honda's done about half a bottle of two stroke over three tanks of fuel - perhaps consider fitting a smaller two stroke bottle if it's all about weight saving etc? I'm sure you'd get a few tankfuls from a 500ml bottle.
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Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[evoboy]

Running premix on the road is fine. But youll need to upjet slightly due to the oil weakening the mix slightly.

You can do damage by using the engine braking while running premix, but its not much different to using engine braking while running the pump. Both wont be feeding enough oil/fuel mix in at high rpm with no throttle input. On mine i normally give it blips of throttle with the clutch pulled in, or, roll with the clutch in instead.

Who uses engine braking on a 2stroke anyway?!
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Suzuki GT250 x7------- Fazer 600------CB250RS------Aprilia Rally 70----- Bandit 600

APT Motorcycles

[SQL]

As said just toying with idea based purely on weight saving. I may leave the pump on it but I have no idea if it even works yet as when I got the bike it had been seized but when i removed the 2 smoke tank it was half full so it don't add up. mainly why I said premix only as I have a 25 gallon tank that I can use for my premix

[_Iain_]

As I said when you bought it, the bike was owned by a rich downie & daddy was going to buy him another bike at the end of it anyway, so it diddnt matter if it was bodged...he also killed a mito & another GPR the same year.

It was in our warehouse at delta in bits for over a year after my ex boss's son decided he'd bounce it off the limiter in the snow when it had trouble starting. He also diddnt put any anti freeze in it, hence no radiator. When it worked he would redline every single gear every day from cold and always ran it on either £3 a bottle carlube or his dads chainsaw oil because he'd spunked all his money on MDMA and anodised bar ends.

Thats why it siezed. I assisted in removing the cylinder at the time and found bits as much as an inch of piston ring in the expansion chamber.

Hence why I said to Paddy to consider the engine as an absolute write off, bin it and buy a second hand motor. Captain spacktastic also had a play around with the gearbox oil & changed the clutch himself, so I wouldnt trust that either. Look at the tyres - he had a 150 rear fitted "because its a superbike and they race them like that, makes it corner well good at 130mph or more. I've had 140 out of it down bluebell hill tho"

IMO having seen the guy ride & work on it I'd not be keeping it, just stuffing a new engine in it, MOT & sell, then buying a non monged DT with the profits - it'll turn into a real expensive ballache otherwise.
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Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[SQL]

I am completely rebuilding the engine anyway.

the 150 tyre seems to be a common thing people do because it has a 4" rim on the back it is standard 110/140.

If I lose interest in doing it ill sell it with the V5 (If it ever comes) and all/most of the bits to get it as a half decent project.

[_Iain_]

Whatever you do dont oversize the rear and not the front.

Every bike i've ever done that on cornered like a sack of shit, it's to do with the profile of the tyre - either the front or the back of the bike will end up dropping in faster
____________________
Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[SQL]

Update time!!

Case has been split the crank is perfect so is the big end bearing, the stator side main bearing has a slight rumble but I have mains to go in it.

Gearbox looks good too

Tommorow goes back together and then pics

[SQL]

Took the engine apart and the mains were fuggered but I got some new ones and seals

https://i.imgur.com/OHlpXVL.jpg

https://i.imgur.com/miJOktf.jpg

https://i.imgur.com/aiajnHC.jpg

Bigend bearing was perfect no play in it

https://i.imgur.com/PHuDana.jpg

Old mains looking shagged, were very notchy


New mains in and seals in

https://i.imgur.com/q4uDO59.jpg

Nice new seals

https://i.imgur.com/YrH4xRZ.jpg


Powervalve open
https://i.imgur.com/7ZkPxdS.jpg

and shut
https://i.imgur.com/1teL89X.jpg

And a few nice random shots

https://i.imgur.com/kx0X8qD.jpg
https://i.imgur.com/SCuISEH.jpg
https://i.imgur.com/o0kCbIX.jpg
https://i.imgur.com/2TQTJ1A.jpg
https://i.imgur.com/rp3DNzJ.jpg
I really like this photo

https://i.imgur.com/d6Ck9Cn.jpg
https://i.imgur.com/aufLW6w.jpg


Things to do

Sort out the engine covers and polish the PV cover, head studs need to be put in, then bolt everything up tight and put in engine in frame

Have learnt quite alot about building up the engine too

[_Iain_]

Did you use loctite when fitting those bits of selector mechanism behind the clutch? I promise you it will cause huge amounts of pain if you diddn't

Looking good. You need to get this done!!

Edit, have you used instant gasket to put the cases back together?
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Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[SQL]

[SQL]

Also I now need a little end bearing and pin/circlips

Any ideas?

[_Iain_]

[SQL]

I can't find them seperate cheap, I have a piston matched to the 3mb00 topend just need new circlips and small end and preferbably gudgeon pin.

[_Iain_]

Lolwut?

A piston kit comes with a little end, gudgeon pin, circlips, rings and usually a little end bearing.

No point buying pistons seperately or running used pistons, one leads to £££ buying the rest of the kit the other leads to engine faliure.
____________________
Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[SQL]

I bought a complete barrel with piston but I lost the circlips like a tard and the littleend just needs replacing

[evoboy]

[lukamon]

possibly stupid question; why are 2 stroke mains always exposed crankshaft side? wouldn't they last longer in the gearbox side, staying oiled? or even a sealed greased bearing?
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killa wrote: Im an ass man myself

[SQL]

2 stroke main bearings are oiled with the petrol

https://upload.wikimedia.org/wikipedia/commons/3/31/2-Stroke_Engine_ani.gif

[_Iain_]