'81 KTM 250GS rebuild

[Olddog]

Howdy everyone,
I've just picked up a 81 model 250GS



which i want to give a bit of a freshen up so i can ride it on a charity ride next Easter, we'll be riding from Sydney to out past Fords Bridge on as much dirt as possible. My mate will be coming along on a 1949 B31 BSA so it'll be a slow trip and debateable which one will actually make it

Anyway, the bike is in relatively good condition, it needs a new barrel as the old one has lost a lot of fins, and the crank was seized on the bearings due to old 2 stroke oil. I filled the crankcase up with a mixture of brake fluid and thinners and it loosened right up and the bearings are smooth.
While i have the motor out i thought i'd drop in a new piston and ring, plus gaskets and seals. Now I'm new to KTM 2 strokes, having played mainly with IT's, YZ's and RM's and on these bikes its wise to replace the crank seals. I've found an engine rebuild manual at the KTM 495 site but it doesn't show crank seal replacement? Probably a stupid question but do these motors have replaceable crank seals? Looks to me like maybe they are relying on a bearing seal?
I ask as I'm struggling to get the flywheel off, i think if i put on more pressure i'm likely to crack it, and i'm wondering if i should even bother? I'm wary about applying heat to area in case i damage the motoplat ignition as well.

The wiring is pretty seriously hacked, so i'm planning just run the engine straight off the dynamo and leave the lights as cosmetic only.

Anyway, any advice is appreciated!

Cheers

OD

[ozktm151]

Welcome to the club olddog. Looks pretty good your find there. Most parts are available if you are prepared to go overseas. Check out Penton Parts and KTM Klassiker on the net. They supply some quality parts. Read your manual a couple of times so you can understand how the engine comes apart and goes back together. The manual should have plenty of photos that will help. You probably will need a new rod kit and bearings for gearbox and crank. Most likely the main bearings are a 3 piece bearing that requires careful set up. Al at Penton parts has new bearings or you can get 2 piece roller bearings from your local supplier.

Crankcase seals are both in retaining rings. The ignition side is behind the motoplat. Motoplat has a left hand thread that could be your problem as they are not too hard to get off usually. Drive side crank seal is in a ring that is accessed after the main bearing is taken out of the case. If you thought the flywheel was hard to get off the the small primary drive gear should be harder to get off.

Clutch requires delicate work to get it going somewhere near a Japanese one. Think about getting new plates. We have used Honda ones that the tabs have to filed a little. Helps a bit. The gear box internals should be ok as it is quite strong. Check the bearings inside the gear cluster. Check the magnesium engine cases for cracks around the area where the swingarm buts up to the case as sometimes the metal washers have disappeared which then puts more force on the case itself. Also check around the primary drive bearing area for cracks as this is another potential weak spot and the engine does not run well with cracks in the cases.

Wheels and brakes should be pretty good depending on the workout they got. Check the axle locating lugs on the forks as they are more often than not cracked by over tightening. The fork legs are difficult to weld. Rubber mounting between carb and engine is probably perished. Get a new one. The rest is just like any other 30 year old bike. Have fun they have pretty good power and handle ok for what they were.

Cheers Bill

[oz555ktm]

  Yes Wecome too the KTM Family .

   The 250 look good and bill has given you some pointer  .

    But if you need Help just ask and some one from the KTM Group ( Family ) will allway step up to Help..

     We all Just Love to See More KTM out on the Track or in the Bush or at a Show and shine ...

   Dennis Oz555ktm

[Olddog]

Thanks for the info Gents and the welcome, much appreciated! That Klassiker site has an amazing amount of gear, I'll have to get the credit card ready.
Bill, with the lywheel, do i use a puller to remove it or is the flywheel also on a left handed thread? I found that the nut was left handed and managed to get that off ok, the manual isn't exactly clear, probably due to it's being converted from Austrian or something.

Thanks again

OD

[ozktm151]

OD you need a puller but I am not sure where you can get one. Maybe Penton parts.

Bill

[oz555ktm]

Les  at VMX Unlimited in Oz

 www.vmxunlimited.com
            or
 The Klassiker Austria
           or
  Your KTM shop   Part Number   (520 12 009 000)

[ozktm]

Welcome to the clan...
Billy C has given you many pointers.
I am just down the road at Wollongong if you need a hand. Bill/Dennis and myself have had these bike for years and put many of them together over that time.
I have Rod kits, main bearings and gearbox bearings are available through the bearing services (i use SES here in wollongong, SKF dealer). In fact i am picking up a couple of sets today.
I have manuals for the 250 available in pdf to help. Both chassis and engine spare parts manuals too.
I will have my motor in pieces this weekend if you wanted to look at what goes on. These things don't just throw together like a jap motor. There is a lot of measuring an checking for the main bearings in particular. You will require a special puller for the bearing inners.
I have been using the flat roller Mains that Bill mentions, but i am shifting back to the three piece specials for a few reasons.

Cheers,

[Olddog]

Well i gotta say i do appreciate the advice, however i'm starting to worry that this little engine might just be a bit beyond my ability when it comes to setting up a new conrod etc. I can do a lot of stuff but when it comes to that stuff I think I'll be better off leaving it too the experts. Can you guys recomend an engine builder? r do any of you do rebuilds for people? Just might be the smartest move.

Cheers

Bill

[ozktm151]

History says none of us has totally built an engine for somebody else but there has been a lot of help over the years. That we can certainly do. Adrian (ozktm) should be closer to you than Den or myself and would help you get the engine together ( pretty sure hey Adrian) and we all can offer lots of advice. If I can put one together if you take it step by step you will be able to as well. Hang in there.

Cheers Bill

[ozktm]

No problem,
We can get a rod fitted no problem, just need all the bearings, gasket kit, newer top end you said you wanted, rebore.
Then it's time to fit it all together.
I can build it for you with you looking over the shoulder to see what's going on.

Any other problems we strike, i think i have enough bits to get us by.

Regards,
Adrian

p.s. give me call on 0 Four 27 967299 if you want to talk about it.

[Turtle.Inc]

Watch these blokes olddog , next they will be teaching you secret handshakes and wanting you to hang out with em drinking hot chocolate

[TooFastTim]

it needs a new barrel as the old one has lost a lot of fins

Not necessarily. A new barrel is the easier option but a good man (and there are many on these forums) can weld new fins onto the barrel if you can't find a replacement.

[09.0]

Watch these blokes olddog , next they will be teaching you secret handshakes and wanting you to hang out with em drinking hot chocolate

Ha ha. When they ask you " If you went to a party and got really grunk and woke up the next morning from behind a couch with your pants down and a sore arse , you would tell anyone?". Don't answer yes as you will get heaps of invites to Ktm parties! 

[Canam370]

[/quote] and got really grunk


Grunk? That cant be good

[bigk]

Current model YZ250 rod is the go, just need to bore the crank webs to take the bigger pin.
K