Suzuki Rebel 315cc bored to 350cc

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Cockney Rebel
Still in the Driveway
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Suzuki 2-Strokes: 350 REBEL 1972

Suzuki Rebel 315cc bored to 350cc

Post by Cockney Rebel »

Hi , I am interested in trying to get the the standard 315 cc barrels to the full 350cc has anybody tried this or know of the best way to achieve it. I have seen posts before of people using Yamaha R5 pistons and over boring the barrels or using GT185 pistons or even GT550 and cutting them down. Just wondered how far the barrels can be safely and successfully bored out.
dollydog
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Suzuki 2-Strokes: several gt250 ramairs

Re: Suzuki Rebel 315cc bored to 350cc

Post by dollydog »

hi mate, i rebored a pair of gt250 barrels to 58mm and put +2 ts125 pistons in to make a gt285, BUT, when i built my full size 347cc i had the liners replaced [by s.e.p. in kegworth] with 64mm liners. i used ts185 pistons and made a 4mm thick baseplate for each barrel out of aluminium plate [ts185 pistons are 4mm taller than gt250]. of course if you can find 64mm pistons with the same crown height you won't need the baseplates. you might also need to relieve the ledge inside the front of the crankcases by 1mm. 315cc barrels will NOT go out to 64mm, so new liners is your only option :D
cheers, dd.
p.s. you could always buy my 350 engine and save a lot of hassle and expense. but where's the fun in that? there's some photo's of it on here somewhere. just type gt350 in the search box :up:
GTS250 road registered. TS250 engine, Ramair frame.
GT250 big bang road registered. Both pistons fire the same time. USD forks.
GT285 road registered. Overbored - 58mm and TS125 +2 pistons fitted.
GT10 road registered. '65 T10 engine, GT250 frame.
Cockney Rebel
Still in the Driveway
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Suzuki 2-Strokes: 350 REBEL 1972

Re: Suzuki Rebel 315cc bored to 350cc

Post by Cockney Rebel »

Hi DD, thanks for the info very useful had a good read through some of your old posts too which are also helpful but couldn't see any photo's of your bike and engine. Understood most of your mods carried out apart from reducing the front ledge within the front of the cases by 1mm, is this in height or width and is this for piston clearance, and is this necessary if using the 4mm barrel spacers.

Thanks.
dollydog
Yeah Man, the Interstate
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Suzuki 2-Strokes: several gt250 ramairs

Re: Suzuki Rebel 315cc bored to 350cc

Post by dollydog »

the ledge was just thinned out - the piston hit it at bdc. the thickness of the baseplates won't make the blindest bit of difference, if you think about it. still the same crank and pistons, so piston still in the same place at bdc :) when i took my barrels in for new liners i also took the pistons in and told him i was using 4mm baseplates, so he ported the barrels to suit, plus gave me a mild porting job. it wasn't perfect, but a 3mm half moon out of the rear of the piston skirts sorted it. here's a photo of the bike, minus her clothes. yes, that's a kawasaki ninja 250 rolling chassis with my homebuilt engine cradle :D
cheers, dd.

halfbreed gt350:
Image
GTS250 road registered. TS250 engine, Ramair frame.
GT250 big bang road registered. Both pistons fire the same time. USD forks.
GT285 road registered. Overbored - 58mm and TS125 +2 pistons fitted.
GT10 road registered. '65 T10 engine, GT250 frame.
Cockney Rebel
Still in the Driveway
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Joined: Mon Dec 28, 2020 7:08 am
Country: United Kingdom
Suzuki 2-Strokes: 350 REBEL 1972

Re: Suzuki Rebel 315cc bored to 350cc

Post by Cockney Rebel »

That looks so good DD and though it has just rolled off the production line with everything in proportion and fitting well. Well done to you and the same look that I had in mind and was trying to achieve. Is that with the GT250 engine fitted as the heads look to have the ram air fitment lugs.
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markush
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Suzuki 2-Strokes: GT250/380
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Re: Suzuki Rebel 315cc bored to 350cc

Post by markush »

Hi!
dollydog wrote: Mon Dec 28, 2020 12:32 pm ...i rebored a pair of gt250 barrels to 58mm ...
Is that correct: you say you can bore a normal GT250KLM / ABC cylinder to 58mm?
How much is left of the wall thickness of the liner, did you determine that?
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Alan H
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Suzuki 2-Strokes: 4 x GT550s - J, M, A, B.
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Re: Suzuki Rebel 315cc bored to 350cc

Post by Alan H »

Cockney Rebel wrote: Mon Dec 28, 2020 7:55 am or using GT185 pistons or even GT550 and cutting them down.
Gt550 pistons are the same as the 315 pistons. Just the stroke is different.
Think of how stupid the average person is, then realise that half of them are more stupid than that.
dollydog
Yeah Man, the Interstate
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Suzuki 2-Strokes: several gt250 ramairs

Re: Suzuki Rebel 315cc bored to 350cc

Post by dollydog »

no, that's the gt250 engine and sleeved out to 64mm. it looks even better with the ramair covers on. makes the gt350 look like a standard ramair gt250. the gt250 liners are very thick. way, way thicker than any of the others. easily went out to 58mm. can't remember offhand, too many years gone since i did it, but it leaves either 3mm or 4mm of liner. i think i'd err to 3mm, which i decided was the thinnest i was going to risk. i did loads of mods on the 285. bottom end is ramair, but barrels are gt250a, but i slugged the rear stud holes with ali and redrilled them at 65mm centre to centre so i could use ramair covers and heads. i wanted the 250a barrels because of the extra transfer ports [i've since been told i shouldn't have bothered, but hey ho]. milled the ramair crankcases to match the barrel transfer ports. milled the heads out to 58mm and just sloped the squish band down to meet the original. apart from that, standard 26mm mikunis on it and standard jetting 112.5 main jet, #30 pilot, my own electronic ignition and probably a ton of stuff i've forgotten :D
cheers, dd.

look carefully, you'll see the 4mm baseplate:
Image
GTS250 road registered. TS250 engine, Ramair frame.
GT250 big bang road registered. Both pistons fire the same time. USD forks.
GT285 road registered. Overbored - 58mm and TS125 +2 pistons fitted.
GT10 road registered. '65 T10 engine, GT250 frame.
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markush
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Re: Suzuki Rebel 315cc bored to 350cc

Post by markush »

Thank you for your response.
dollydog wrote: Thu Dec 31, 2020 2:33 pm i slugged the rear stud holes with ali and redrilled them at 65mm centre to centre so i could use ramair covers and heads. i wanted the 250a barrels because of the extra transfer ports [i've since been told i shouldn't have bothered, but hey ho]...
I have also thought of that, but I assumed that the new drilling for the stud bolts located further inside would touch or open the additional transfer ports of the ABC-cylinder.
Why you shouldn't have bothered about these transfer ports?
Was there an opinion that they have no performance advantage?
dollydog
Yeah Man, the Interstate
Posts: 630
Joined: Fri Aug 11, 2017 7:09 am
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Suzuki 2-Strokes: several gt250 ramairs

Re: Suzuki Rebel 315cc bored to 350cc

Post by dollydog »

yes mark, that was exactly it. a well known [to me anyway] tuner reckoned if you take the huge steps out of the ramair barrel transfer ports, then the ramair engine is easily as good as the 250a. i seem to remember breaking through somewhere when we redrilled, but we certainly got round it. just can't remember what the hell we did. unfortunately i didn't do a thread on that rebuild, i just wrote it all down in a notebook somewhere. just wish i could find it instead of having to rely on worn out neurons :D
cheers, dd.

the gasket on the photo exactly matches the transfer ports in the crankcases. this step needs removing for better flow :)
please ignore the reed conversion:
Image
GTS250 road registered. TS250 engine, Ramair frame.
GT250 big bang road registered. Both pistons fire the same time. USD forks.
GT285 road registered. Overbored - 58mm and TS125 +2 pistons fitted.
GT10 road registered. '65 T10 engine, GT250 frame.
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markush
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Suzuki 2-Strokes: GT250/380
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Re: Suzuki Rebel 315cc bored to 350cc

Post by markush »

I did the same with my GT250/380 cylinders. The transfer channel tapers towards the cylinder bore, so that the flow velocity in it increases up to that point. Especially if the cylinder is drilled wide up to 56 ... 58 mm, the transfer channel is shortened and its exit cross-section is increased, which reduces the flow velocity. That is why the widening at the lower end is important in order to maintain or restore better flow conditions.
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