something to do over the holiday

[dollydog]

well, apart from drinking, playing santa and eating like a pig
here's the first mock-up. 3mm aluminium plate will be used as a pattern/template for the final 10mm thick plate. wish me luck
cheers, dd.

mock-up:

[jabcb]

What are we looking at? What neato project are you envisioning?

Good luck & have fun. Whatever it is, it's way beyond my skill set.

[tz375]

RG250 top end on a set of GT250 cases perhaps?

That will be quite a trick to get the RG crankcase porting to work on and older bottom end. They are interesting barrels for sure. Transmissions on RGs used to be a bit fragile IIRC but the handling was streets ahead of and RD Yamaha.

[jabcb]

Looks like it could be a 76/77 GT250 crankcase.

[dollydog]

jab, easy way to tell the difference between the 76/77 gt250 crankcases and these ramair cases are the oil feed bosses - just below the barrels you can see 3 of them, the other is tucked up in the right corner. the later cases have an oilfeed right in the middle, as the later centre main bearings are fed by the oilpump. on earlier ramairs the single central main bearing is fed direct from the gearbox, hence you get 4 symmetrical oil feed bosses
cheers, dd.

[jabcb]

Yes. For 76 Suzuki switched transmission oil lubrication from the center main crank bearing to the right main. I was aware of that.

Was thinking it was a 76/77 crankcase based on the oil pump area. I wasn’t aware that the GT250s have a plate between the oil pump & crankcase.
Took a look at the online parts diagram. And the plate is the same for 73 thru 77 models.

The T500/GT500 has the same center main transmission oil layout. It looked so easy to screw that up with sealant when I was assembling the GT500 cafe build motor.
Using transmission oil for the right main avoids that issue.


Looks like a fun project. An early GT250 crankcase with water-cooled top end.
77 was the last year for Suzuki two stroke street bikes in the US. You have options for a lot more different fun projects in the UK.

[dollydog]

sorry i haven't updated this thread for a few months, but boy have i been busy the first change was moving to plan 'b' and that was to take the rg250 top end off and put it away safely. after my mate sent me a load of photo's of his conversion and all the machining it took i sort of chickened out. he used a gt380 bottom end with rg250 top ends and it took him 5 years to finally get it to run. at my age i haven't got 5 years to spend, so i went for plan 'b'. still using the same 250 ramair bottom end but - say it quietly - a yamaha rd250lc top end. had the spigots under the barrels machined so they fitted in the gt top crankcase. threaded some 8mm aluminium round rod and filled the 8 fixing stud holes. then the difficult bit, drilling and threading the top crankcase to take the rd barrel studs. this worked perfectly, but it meant i had to cut the rd cylinder head in half. easy conversion on the aircooled as they are separate heads. anyway, the heads are now off to be faced, so i can weld a 3mm plate on the end of them. what about the thermostat and inlet/outlet for the coolant? all in order. i'll bring you that in the next post, with photo's
cheers, dd.
p.s. the waterpump is fitted under the engine and it's off an audi

[dollydog]

finally had confirmation off the bloke who's machining my cylinder heads. they'll be ready to pick up next tuesday. then they are off to the aluminium welder to get the side plates and inlet/outlet pipes welded on. i'll post some photo's then. in the meantime i've got the left side exhaust built and attached to the micron, but due to these bank holidays my 38mm exhaust bends haven't arrived, so i can't start the right side yet. but i'm getting there slowly. it's never taken me this long to build a bike from scratch. once the heads are sorted including squish gap, compression ratio etc, will give it a whirl and if it just fires, and there's no reason why it won't, i'll strip it all down again and fit the new crank, get the frame and swingarm powdercoated, crankcases aquablasted and probably a hundred other jobs before i rebuild it as a bike, not just a frame and engine. it's just taking soooooooooooooo long
cheers, dd.