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Classic Bike Trackdays

New to me 1987 SDR 200
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Yellow02Z06



Joined: 14 May 2023
Posts: 21
Location: Michigan, USA

PostPosted: Thu Jan 23, 2025 4:55 pm    Post subject: Reply with quote

Hello @jamesP and @thump566 and others.

Couple things to share.

Mentioned I have SDR200 with me while staying in Southern California USA for a while, and I have been ripping up and down a section of Pacific Coast Highway near me, looking for top speed records for fun.

Got to 150 one day and then finally, in a tuck, 155kph (flat ground).

Went for it again, a few days later, got to 155kph, and engine locked!

I skidded bnut was able to stay stright (small fishtailing), but was able to quickly grab clutch....coasted to a stop a long distance, got my wits about me, and then tried to kick it and luckily it had unlocked, it started, and I rode back to where Im staying...albeit slowly.

So now I am going to need to take it apart, and proably will need rings, piston, hone or bore....

Re-looking into mods....

@James P, I have reached out to AEB, but also there is indeed Chinese listing for 230, 350, Lanza replica engines, and parts...

Any idea if a crankshaft kit would bolt in along with cylinder to get to the bigger bole and stroker based capaicyt without getting who engine?
_________________
1971 Kawasaki A7 350 Avenger (stock)
1973 Kawasaki H1 500 (mild mod)
1975 Suzuki GT250 cafe racer
1985 Yamaha RZ350 (mild mod/blue)
1987 Yamaha SDR200
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thump566



Joined: 28 Jun 2023
Posts: 51
Location: West London

PostPosted: Fri Jan 24, 2025 7:03 pm    Post subject: Reply with quote

Ouch, but glad you managed to stop relatively safely.

155 kph is pretty impressive for a Whippet running on skinny tyres.

Jams is in a far better position than I to recommend modifications as you will know if you have seen his SDR build thread.
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Yellow02Z06



Joined: 14 May 2023
Posts: 21
Location: Michigan, USA

PostPosted: Sat Jan 25, 2025 4:00 am    Post subject: Reply with quote

thump566 wrote:
Ouch, but glad you managed to stop relatively safely.

155 kph is pretty impressive for a Whippet running on skinny tyres.

Jams is in a far better position than I to recommend modifications as you will know if you have seen his SDR build thread.


Yeah I was pretty pumped about the 155kph, and the seizure was mild I think.

Yes hope James chimes in....
_________________
1971 Kawasaki A7 350 Avenger (stock)
1973 Kawasaki H1 500 (mild mod)
1975 Suzuki GT250 cafe racer
1985 Yamaha RZ350 (mild mod/blue)
1987 Yamaha SDR200
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James P



Joined: 31 Mar 2013
Posts: 189
Location: Sydney, Australia

PostPosted: Sun Mar 02, 2025 8:31 am    Post subject: Reply with quote

Yellow02Z06 wrote:

Went for it again, a few days later, got to 155kph, and engine locked!

Any idea if a crankshaft kit would bolt in along with cylinder to get to the bigger bole and stroker based capaicyt without getting who engine?


Sad Sorry to learn of your seizure, glad you didn't fall off.

Before you decide on any modification, you may like to assess the damage (which you may have done by now). Did the engine overheat in some way, or was there a non-heat-related mechanical failure?
For keeping an eye on temperatures, I recommend fitting EGT and CHT thermocouples, along with a suitable gauge/monitor, as well as a proper coolant temperature gauge instead of the standard thermo-switch and warning light. Monitoring all of these temperatures could easily mean the difference between continuing undamaged at a slower pace or being stuck at the side of the road with a broken engine.

I'll have to admit that I've never looked at the Lanza crankshaft for transplanting into an SDR. If you can borrow one or ask an owner to make some measurements, you can probably discern whether it is an idea worth pursuing. Alternatively, you could ask a specialist to make you an eccentric big-end pin for the standard crankshaft (you could likely get at least 60mm stroke that way). Whichever option you take for a long-stroke conversion, make sure that the replacement or modified crankshaft will fit in the engine case...or that there is enough material remaining in the engine case if you have to increase its inside diameter or machine a trench for big-end clearance. Also worth considering is the ability of the standard balance shaft to cope with the action of a longer-stroke crankshaft.

I also haven't looked seriously at increasing bore size to any great extent. However, the LA Sleeve Co did make a 72mm big-bore sleeve for the SDR (Part No.YA-5070B), supposedly for use with a standard crankshaft. Of course it would be necessary to modify the cylinder head accordingly...and I think it may be impossible to use the power valve (I imagine you'd have to modify the power valve spool to allow clearance to the piston and then fix it in position somehow). I don't recall whether the type of piston was specified, but it might be Kawasaki H2 750...or possibly a piston from one of the more modern 300cc European enduro engines.

Depending on how keen you are and what characteristics you want from a modified engine, there could be a few options for replacement cylinders from other bikes...although engine case modifications may be necessary and the donor engine should have a crankshaft stroke fairly close to that of the SDR to keep port durations sensible. If you fit a much longer conrod, you may be able to use a thick (i.e. 10+ mm) cylinder base spacer as an adaptor between the SDR engine case and whichever cylinder you choose.
Although I haven't looked in much detail, I know there are some 175cc water-cooled go-kart engines which are quite powerful, whose cylinders may suit your requirements. Also, consider looking at the latest aftermarket kit cylinders for two-stroke Vespa and Lambretta scooters - most of these cylinders are air-cooled, but some are water-cooled...and outputs in the range of 30-50ps are now fairly common for engine sizes of 180-265cc in this sphere. None of this stuff will be very cheap of course.

Naturally, after you have decided what to do with the crankshaft and top end, there is carburettor/intake, ignition and (perhaps most importantly) exhaust to think about...

If you don't want to do extensive modifications, you could investigate whether anyone has achieved significant output increases from WR200 enduro engines. The WR200 (also the JDM DT200WR) top end will fit an SDR engine case with slight modification (to either the WR cylinder spigot or the SDR engine case mouth) - slight modification to the transfer passages in the SDR engine case is also necessary to match the cylinder completely, but is not necessarily essential for the conversion to 'work'. If there is any likelihood of you wanting to return to standard SDR engine spec, just machine down the OD of the WR200 cylinder spigot. Even with such a 'straight-swap' conversion, you'd still have to find or make an exhaust to take better advantage of cylinder porting modifications. However, it may be possible that contemporary SDR race pipes (e.g. SS Ishii) would work.

On the topic of SS Ishii, that firm published some drawings and other details on how to modify the standard SDR engine for SDR Cup racing 'back in the day'. From vague memory, it involved fitting a TZ750 inlet rubber and YZ125 34mm carburettor, modifying the SDR cylinder ports and cylinder head and fitting the SS Ishii race exhaust. I think the recommended ignition system came from one of the contemporary TZ250 models; 1RK or 2KM perhaps (no lights though!), with a custom-made stator base plate. There are some stiffer clutch springs available as standard Yamaha parts (e.g. 90501-20361 for YZ80-125, TZ125, IT175, RD250/350 etc.) to use in conjunction.

I'm not sure whether any of this will be of use or interest to you - let us know!

Regards,
James
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James P



Joined: 31 Mar 2013
Posts: 189
Location: Sydney, Australia

PostPosted: Sun Mar 02, 2025 8:38 am    Post subject: Reply with quote

James P wrote:

On the topic of SS Ishii, that firm published some drawings and other details on how to modify the standard SDR engine for SDR Cup racing 'back in the day'.


For your info/interest, here is a link to my earlier post which itself has a link to the details in question: http://diffrentstrokers.com/phpBB2/viewtopic.php?t=2454&highlight=ishii

Regards,
James
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Yellow02Z06



Joined: 14 May 2023
Posts: 21
Location: Michigan, USA

PostPosted: Mon Mar 03, 2025 3:34 am    Post subject: Reply with quote

Thks James P, and sorry for those typos, I normally check my posts, texts etc. for typos/wrong spelling...

Well I am back home from my long California trip (where I had my little SDR 200 fun and incident) but I started working on my 1976 RM100 first (oil leak, needs a crank half)...

Meanwhile I bid on a Jackal on Yahoo Japan and did not get it, but I bought one from Gecko in the UK....so at this point I am thinking that without the capability to bolt on a cylinder and/or slide in a crank I will just try to run it/optimize it with the Jackal after I get any cylinder / ring / piston needs sorted

I guess I really should do a temp guage though...

I keep getting these urge to do something wilder but in reality I probably be able to continue to enjoy it and especially if the pipe makes the difference I expect it will...

Since I have an RZ350 with a good 60 HP and an RG500 with a good 85-90 I should just ride those when I want something faster water cooled 2 stroke wise...
_________________
1971 Kawasaki A7 350 Avenger (stock)
1973 Kawasaki H1 500 (mild mod)
1975 Suzuki GT250 cafe racer
1985 Yamaha RZ350 (mild mod/blue)
1987 Yamaha SDR200
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