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1989 DT200R No Compression...

Discussion in 'Technical and Troubleshooting Torque' started by Browncoat, Aug 22, 2008.

  1. I bought this bike today and it only lasted the day... I was putting it through its paces accelerating in 5th gear when it made a distinct POP sound and the engine just died. Its got spark & fuel but I then pulled the plug stuck my finger in the plug hole and cranked it over and felt no pressure/compression at all.

    Doom and Gloom! I know..

    I'm going to strip the motor down for a look see but I really need a workshop/repair manual so as to check/compare tolerances. I cant find a manual for this bike anywhere online.. anyone know where I can get one?

    I reckon the guy that sold me this lemon musta had an inkling this was coming..

    Thanks people.
  2. Try somewhere in the UK that sells Haynes manuals. As far as I know, the DT200 was pretty similar to the watercooled DT125 which was very popular in the learner market over there. I'd be very surprised indeed if Haynes didn't do a DT125 manual.
  3. Here ya go. Australian source too.


    According to a quick Google, the DT125R manual covers 75% of the 200 as well. Apparently, the wiring layout and forks are different and, obviously, the top-end dimensions are different. Procedures and basic component layout are pretty similar though. Allegedly the Yam factory manual consists of the DT125 manual plus a 20 odd page supplement to cover the differences in the 200.

    Should get you started though.
  4. Thanks PatB,

    I'd just made a trip to my local Yamaha dealer and found out about the 125 manual and the 200 supplement. 85$ gone.. still should be helpful.

    Good googling PatB, I searched for hours and never found the link you provided. Perhaps thats a commentary on my googling skills.. :)

    Now I just hope the repair bill doesnt ruin me..
  5. Even a full top and bottom end rebuild on a cooking single pot stroker shouldn't break the bank. If you're lucky and it's just :shock: a holed piston with no collateral damage, you'll have enough change to feed it decent oil :grin: .
  6. Whilst I know of course the battery has no effect on compression I am curious as to what symptoms a flat battery would give with this 2 stroke? I'm starting to strip it all down and noticed the battery has bugger all acid in it, the multimeter shows .5 of a volt.
  7. Depends on the exact nature of the electrical system. Most likely effects would be weak or zero spark at kickstart engine speeds and/or, if it does start, a tendency for the engine to die if the lights are switched on.

    I can't imagine a battery being that expensive for a DT. Get yourself a new one for the best possible chance of avoiding trouble. The lack of acid does rather point to a neglected bike. I hope it was cheap :) .
  8. It was cheap :oops:
  9. hey mate im in newcastle too...i work just on 2 strokes road mostly..but i have an old dt too...when lookin for parts u can be use blaster pistons and parts(yamaha quad with the same engine as a dt200 except air cooled) do a search..there r heaps of aftermarket bits for them as they are hugely popular in the states, stroker cranks reeds u name it...all cheep too
    if u need a rebore or hone go to better spares in islington is your modle the crank case inducted on or does the carb come out of the barrel..if u need any more info gimmie a call 0406726252
  10. Thanks Twinrock,

    Mine is crankcase inducted.

    I might indeed give you a call when I get into it further. I just scored a new job at Onesteel (wont have as much free time on my hands) so i'm wondering if I should attempt the rebuild myself or just take it somewhere.. Any suggestions on who does good work for a good price?
  11. I would personally do the work myself. To replace a piston & rings on a 2 stroke is no more difficult than adjusting the valves on a 4 stroke. In fact I would rather replace a 2 strokes piston & rings than adjust the valves on my VFR 400 :)
    From memory Yamaha Australia parts are quite expensive. I would try twinrocks source as they seem a lot cheaper. I miss my DT 200. Great little bikes. Suspension was a little basic which is a bout the worst thing you could say about them.

    PS If the battery is totally dead then the bike will run quite flat as the powervalve is electronically controlled. Does the powervalve cycle when you switch the key on? If not then the bike will go about twice as hard when you fix that problem. Well it feels like it anyway :grin: :grin:
  12. I've never had experience with powervalves before, can anyone provide a laymans lesson for me? At first I thought that the powervalve was another name for the reed valve but that doesnt seem to be the case. Also the service manual I found is for the UK version and it talks about the powervalve being "pegged" and says not to worry about it because its doing nothing..

    And no the powervalve doesnt cycle when I turn the key on (I'm guessing it must be audible?). In fact nothing worked (lights, blinkers, horn) until I started it.
  13. Briefly, the power characteristics of a two stroke are partly determined by the port timings (that is, the moments at which the rising or falling piston opens and closes the inlet, transfer and exhaust ports in the cylinder walls). The exact relationships between port timing and power are something akin to black magic, understood only by grizzled sorcerers such as Stan Stephens, but there are some basic rules of thumb.

    One of these is that, for good bottom end grunt, the top of the exhaust port should be fairly low down the cylinder wall, whereas, at higher engine speeds, the optimum position gets higher up the bore. In a traditional two stroke, tuned for maximum power, the port is generally set as high as possible without making the engine totally unmanageable. As a result, a hot traditional stroker will generally pop and fart and misbehave at low revs, giving bugger all power. When the revs rise to a point where the port timings start to work, though, it feels like you've hit the giggle switch and all the power comes in with a rush. This is that wonderful two stroke phenomenon, the "powerband" and it's really exciting when it all works right :grin: . It does make a bike hard to ride to its full potential though and can also get very exciting if you're careless enough to hit the powerband while cranked over in the wet :shock: .

    The Yamaha powervalve system is a means by which the effective position of the exhaust port in the cylinder wall is changed dependent upon engine speed, to allow the port timings to be optimised for both low and high speed running. So you end up with an engine that is useable at low speeds but which will still deliver the goods at high ones. There's generally still a noticeable powerband but it's not as sudden and vicious as it once was. A mate of mine races an RD350LC (non powervalve) in historics, against another guy on an RZ350 (powervalve) and it's noticeable that the RZ is easier to get off the line and is more manageable accelerating out of corners because of the lack of anything explosive happening at 6000 rpm.

    Powervalve position was determined by a little electronic box of tricks and a servo motor. One of the checks for a healthy powervalve is that, when the ignition is switched on, the black box will cycle the servo motor through the full range of movement of the powervalve, which you can hear it do. A flat battery will certainly prevent this from happening.

    The "pegged" powervalve referred to in your manual is a UK feature. Over there, when the DT was new, learners were restricted to bikes of no more than 125 cc and 12 bhp. A DT125R with a functional powervalve put out 20-21 bhp at quite a lot of rpm (I forget exactly what). However, if the powervalve was fixed in the low speed position, the engine would give decent low end torque (good for learners) and would give a power peak of 12 bhp at ~6500 rpm. So, for 99.9% of bikes that went to the UK, Yamaha left off the black box and the servo motor and fixed the powervalve in position with a peg. The lecky bits were available from Yamaha dealers and could be purchased, after you'd passed your test, on production of your full licence. The restricted bikes were quite frustrating to ride as they'd go well off the line and accelerate acceptably up to about 6000 rpm, then they'd just start to feel as if a powerband was about to happen and then it would all be over and you'd be droning along at 6500 with nothing more to come.

    The conversion was quite expensive and so many riders never bothered to fit it. Instead, you could take off the powervalve cover (round plate adjacent to the exhaust port), twiddle the powervalve to the other end of its travel, tighten and replace cover. Five minutes with the bike's standard toolkit for an instant 70% power increase :LOL: . Bugger all low down but it went like a bastard at the top end. A few folk also cobbled up manual systems with choke cables adjustable from a handlebar lever so their bikes could be civilised around town and little demons out on the road or the dirt. It does point up, though, that even if a new battery fails to get your PV working, the bike can still be fun (if a little savage) without it.

    Anyway, there ya go. A (very) potted account of Yam powervalves and a bit of UK biking history thrown in :grin: . Good luck.
  14. Great explanation PatB!

    Much appreciated.
  15. hey i would suggest graham morris motor cycles if u want i can have a look at it and evealuate the extent of the damage and any other possible near future failings..i can also rebuilt it for you..let me know if i can help..blaster pistons will still fit
  16. Yeah Twinrock, I remember Graham Morris from along long time ago when I rode a ZXR750, I used to buy tires from him.

    I am going to have a look myself to see whats failed. You will probably hear from me sometime down the road though, I appreciate your offer to help. Do you have the equipment to properly measure the bore, piston & rings? I'm not completely useless with mechanicals though i'm not quite sure how to tell how many rebores(if any) the cylinder has had and what size piston and rings to use.
  17. what u need to do is take it to someone who does rebores..ie better spares..he can look at your barrel and see what size will be needed to go to to remove the damage..eg say you are on stock bore..66mm i think,,there is damage to the bore take it to him and he will say ok .50mm is needed to remove it..then u call up ur piston suplyer..and order .50mm over size ..ie 66.50mm then take the barrel and the piston back to him and he will rebore it with the correct tollerences.. u will more then likely need a new head and base gasket also..then just a matter of putting it back together ..they are quite simple..but dont take it for granted be very carefull when re asembley..and all should be good..as i said im happy to show u , guide u ..
    p.s u will have to remove to powervalve b4 u give it to the machinist..
  18. Cool, that all makes sense Twinrock.

    Another couple of queries about this DT:

    When I bought it the previous owner had disconnected the oil injection system(apparently he had it tested and it was working but he just didnt trust an injection system), he was just premixing the oil/fuel in the tank. The oil light was on the whole time I was riding it and I just assumed it was because he'd disconnected to oil mix system. Does that sound right or is/was the oil light telling me something else? Anyone have much experience with oil injections? are they reliable?

    Thanks again
  19. The oil light only comes on when the oil level in the tank is low. Nothing to do with whether the pump is working or not. Where you mixing the oil in the fuel?
    As for the oil injection, I don't trust them either. I would much prefer to add the oil myself as then you are absolutely certain you are getting enough lube. Too late when your engine seizes or the bearings wear prematurely to find out the pump isn't working. The pumps main job is to try and limit the smoke when you are pottering around town and the engine is not really working. If you use a good quality 2 stroke oil at the right ratio there is virtually no smoke once the engine is warm and you're giving it a caning. Don't sit there for 10 minutes blipping the throttle to warm it up. Get on it & ride it gently until the temperature comes up.
  20. Yeah oil was added to the fuel in the tank.

    I just found where I was losing compression. There is a hole in the piston that my pinky finger can fit through.. can I get away with rebuilding just the top end or will this now necessitate doing the bottom end as well? My concerns being any piston material(grit) that may be in the crankcase.

    P.S. what causes holes to burn through pistons?