YZ250F (1979) Transmission Problem

[BadgerMan]

I picked up a complete and running YZ250F (1979) this past weekend. The bike looks really good but has not been ridden since 1985. I drained the fuel, cleaned the carb, and it started right up and runs great. So, before I rode it, I changed the transmission fluid and then discovered that it won’t shift beyond second gear and into third. I was a bit confused by the spring loaded locator pin in the oil drain plug having never seen one of these before. A couple questions:

1. does the transmission have to be in a certain position when you put this plug back in?

2. could mis-assembly of this plug cause shifting problems?

3. could a weak or stiff locator pin spring cause shifting problems?

4. is there anything I can do from under the RH side cover to fix the problem or do the cases need to be split?

I am just trying to rule out the simple stuff before I pull the engine out and tear it down.

Thanks

 

[TRexRacing]

I do believe you removed the wrong bolt to drain the oil.One is for the spring detent of the shifter drum and the other is the drain.Get a manual and be sure as I'm going by memory and that's not something you should rely on.The good thing is if I'm right your problem is an easy fix.

 

[BadgerMan]

Yeah, I have a manual on order.

That was the only plug I was able to find on the bottom of the crank case......I'll have another look tonight just to be sure.

I hope you are correct.

Thanks

 

[Patman]

I believe there is only one bolt but it is a multi tasker. It's been a long time and wasn't even my bike but neutral might be a good place to start when reinstalling it.

 

[TRexRacing]

Might help,might not.The drain on my '80 YZ465 is at the very back of the case in the middle.lemme go out to the garage and see if that Clymer junk has anything about a '79 250.I'll be back in a few.

 

[TRexRacing]

It is a 2 purpose bolt.There are 4 parts including the bolt itself.Is that how many you had?The manual refers to it but has absolutely no info other than to make sure none of the parts fall into the drain pan.Try reassembling with the trans in neutral this time.That's all I can do for ya,sorry.Oh and I hope you didn't buy a Clymers manual 'cause they bring on the black hole suck .Search ebay for an OEM manual.I got one for my 465 for $20 US shipped.

 

[BadgerMan]

It is a 2 purpose bolt.There are 4 parts including the bolt itself.Is that how many you had?The manual refers to it but has absolutely no info other than to make sure none of the parts fall into the drain pan.Try reassembling with the trans in neutral this time.That's all I can do for ya,sorry.Oh and I hope you didn't buy a Clymers manual 'cause they bring on the black hole suck .Search ebay for an OEM manual.I got one for my 465 for $20 US shipped.

Yeah, I have all the parts (plug, spring, washer, pin) and yes I ordered a Clymer manual. Oh well, live and learn. I assembled it in neutral (I think) and still no shifty. I’ll try again before I tear it down.

Thanks.

 

[jsantapau]

I had a strange problem once on an old RM with the shift detent/oil drain setup. the spring/detent had a sloppy fit in the bolt and would wedge itself not letting it shift, you can easily isolate it by leaving the bolt out and seeing if it will shift by hand,engine off obviously.

It shouldn't matter whether it is in gear or not when you change the oil but.. you may need to install it loosely to help hold the shift drum in place when splitting or assembing the cases

if this bike has been setting for 20 years you might have a shift fork or slider gear rusted in place what was the oil like?

 

[Patman]

Might it be the difference between there being a crush washer and no crush washer?

 

[TRexRacing]

Good point.

 

[BadgerMan]

I had a strange problem once on an old RM with the shift detent/oil drain setup. the spring/detent had a sloppy fit in the bolt and would wedge itself not letting it shift, you can easily isolate it by leaving the bolt out and seeing if it will shift by hand,engine off obviously.

It shouldn't matter whether it is in gear or not when you change the oil but.. you may need to install it loosely to help hold the shift drum in place when splitting or assembing the cases

if this bike has been setting for 20 years you might have a shift fork or slider gear rusted in place what was the oil like?

Yes, I just tried and it will shift through all gears with the bolt/spring/pin left out. The oil was pretty black when I initially dumped it but nothing indicating moisture inside.

 

[BadgerMan]

By the way, here's a picture of the beast....just like Hannah's!

 

[TRexRacing]

Hey ya wanna buy a double leading shoe backing plate?I believe it'll fit and is a huge improvement.I switched to a 43MM fork and my old one won't fit so it's just collecting dust.Lemme know.Nice bike BTW. :)

 

[BadgerMan]

Hey ya wanna buy a double leading shoe backing plate?I believe it'll fit and is a huge improvement.I switched to a 43MM fork and my old one won't fit so it's just collecting dust.Lemme know.Nice bike BTW. :)

Thanks and thanks for the offer. I need to see if I can get the bike shifting properly before I spend any money tricking it out. Still, it runs great and it makes me smile even though it's only a two-speed. :laugh:

 

[julien_d]

Looks incredible for a 79, very nice find!

 

[jsantapau]

sweet bike

 

[Uchytil]

That's a nice bike, much better than the ones I start with for restorations. Gonna race it? Check out michiganvintagemotocross dot com, and, yzworks dot tripod dot com. And BTW, if you want to show off (or sell) the XR let me know.

 

[BadgerMan]

That's a nice bike, much better than the ones I start with for restorations. Gonna race it? Check out michiganvintagemotocross dot com, and, yzworks dot tripod dot com. And BTW, if you want to show off (or sell) the XR let me know.

I gotta getting it shifting before I blow any money restoring it. Yeah, the restored XR is nice......I don't plan to part with that bike as I have owned it since 1987. I raced it (D14 enduros) for several seasons back in the day.

 

[TRexRacing]

Well is it fixed?

 

[RedGreen]

Well is it fixed?

oh, it's fixed alright, and it rips!!

check this out:

http://www.dirtrider.net/forums3/showthread.php?t=173589

:cool:

 

[BadgerMan]

Well is it fixed?

Yeah, it seems to shift OK presently. I pulled the RH side case, the clutch, and the shift mechanism and everything seemed to be in order but the shaft that the shifter star thingy attaches to was not rotating freely. I noticed that the shaft that the star attached to had some kind of washer/spacer that was deformed and was interfering with the opening in the RH half of the crank case. I was able to use a pick and kind of reform it to eliminate the rubbing. I reassembled everything and was happy to find that it shifts through all six gears. We’ll see how it holds up. If I keep the bike, the entire engine should be gone through including fixing the transmission problem properly.

By the way, it is pretty impressive for a thirty year old bike. It hits so hard in the midrange that I had to check the markings on the cylinder…..I thought it might be a 400! Sure enough, it is marked “246cc”.

 

[TRexRacing]

You oughta ride my 465.have fun.

 

[BadgerMan]

You oughta ride my 465.have fun.

I would love to :nod:

BTW, if I happen to stuble upon a YZ400F, I am gonna snatch it! :laugh:

I still need to replace the swingarm bearings and pins and then do a shock oil change. It also needs a lower chain roller so I need to find an adaptable aftermarket part. Then, the bike will be raceable.

 

[TRexRacing]

Check allballs for the swinger bearings.They have an interesting set up for the thrust bearings.

 

[BadgerMan]

Check allballs for the swinger bearings.They have an interesting set up for the thrust bearings.

Thanks, I just ordered a swingarm bearing kit and two chain rollers (upper and lower).