A forum for owners of Yamaha TTR250 trail and enduro bikes!

hags · Member

Rolled backwards, now wont run.

texasT · Senior Member

Welcome hags!

If you had bike in gear going down hill, that sound you describe sounds normal to me. I think it was the gears of the bike making the noise. That is not good on a bike, especially a cold bike, but since you had been riding it for a while, gears were oiled up. I'll guess it may not be your problem of not running right, but not sure.

I wonder if you turned the bike upside down? ...4strokes don't like that too much.

How far backwards did you go, while in gear?

Did you lay the bike over and slide or were you able to jump off and hold it up?

Have you checked to see if you bent or pulled anything loose or pinched a fuel line etc.?

greg

TTRfan · Super Guru

Welcome to the forum Hags wink

A '93 will have a metal tank - perhaps the episode on the hill stirred up some detritus or maybe water/condensation in the tank and/or carb and may have blocked the jets?

If you undo the drain plug at the bottom of the float bowl, does the fuel run out clean?

Brian

TerryK · Super Guru

Was the engine turning over backwards when rolling backwards down the hill. If so the valve timing may have changed (chain jumped the sprocket)

brindabella · Senior Member

I assume (and hope for you) that it is something simple, and the bike is now going again.

However, there have been some anecdotes suggesting the ttr250 can have rare cam chain tensioner and "timing slippage" problems.
It would be nice if you could rule that in or out in this case please.

hags · Member

Hey guys, thanks for all the quick replies!!

It doesn't seem like a fuel thing but will drain float bowl to check. It is a metal tank. & while i didn't completely flip the bike, it did get laid down a couple of times & well & truly shaken up.

I was leaning more towards timing based on how it was behaving. I've downloaded a manual, but what is the easiest way to check iif timing has been thrown??

TT-R250M · Super Guru

First check & align the the rotor to TDC... (use a 14mm socket on the rotor bolt to turn motor clockwise with the engine in Neutral).

When the ''|'' mark on the rotor (NOT the ''H'' mark) is aligned with the stationary pointer is lined up (as pictured below), it is correct.

Note: the rotor does not like to stay at TDC because of the magnets so constant rechecking is required.

Make sure cam shaft lobes are facing away from each other like the pic below..

It should line up as shown in pic below.

IMPORTANT: Take note of how the ''E'' on the camshaft sprockets sit & all marks shown in red below.

The manual is not very helpfull for this part so line all marks as shown below...

Jarrah

hags · Member

Thanks Jarrah,

Got a chance to have a look tonight. drained the carb bowl first & flowed nice & clean so took the top off & sure enough, Exhaust Cam was way out... like 180 out. it'd jumped a whole lot of teeth...
Got it all lined up again, but turns out I've only got an owners manual, not workshop manual... so don't have all the specs I was after. ie, things like torque's for cam sprocket bolts & cover, cam chain tensioning & is there any adjustment needed for valve clearance?

I found the links to manuals but they are all for later models. is there a downloadable manual for a 94' model? (its 94', not 93' as I'd previously stated... dunno if theres any difference)

In saying all that,

there's obviously cam chain tension issues. I saw a couple of threads before on problems with the automatic tensioner. is that applicable to this model? and if so, whats the fix on that? maybe a link to a thread that covers it.

Thanks again guys. nothing worse than having a bike that just won't go & not knowing why.

Hags

TT-R250M · Super Guru

If the chain slipped as much as you say you will have bent the exhaust valves.

Checking valves clearance is something that hardly needs checking unless a lot of miles has been done or new valves are fitted.

The engine specs will be the same as 99-13 with only a few small insignificant changes. See HERE for more info.

If you want a manual, send your email in a PM and I will send the full repair manual through.

The auto tensioner is fitted to all TTR250's. The cam chain should be replaced and the spec's of the auto tensioner, cam chain, cam chain guides and sprockets checked. While you are there check the rings and cylinder. The tensioner needs replacing now and again and you cannot adjust for minor wear. It can also slip out of time momentarily and cause the valve timing to be momentarily out of time. You can buy an aftermarket tensioner like THIS.

This is what the company states about the auto tensioner...

This manual cam chain tensioner is designed to replace the automatic and hydraulic tensioners on high performance engines. The automatic adjusters can back out when the throttle is closed suddenly at high RPM. This allows the cams to go momentarily out of time, and can result in bent valves and/or serious engine damage. The hydraulic tensioners have a tendency to put too much tension on the chain guide under high RPM/high oil pressure conditions, resulting in premature wear. Both problems can be eliminated with the installation of a manual cam tensioner. No matter what the engine does, the cam chain tension will remain constant. A manual cam chain tensioner is a must for any kind of performance riding. These manual tensioner bodies are CNC machined from billet aluminium to exact tolerances for perfect fit.

......................................................................

Jarrah

TT-R250M · Super Guru

I see you are in Australia- if you find out that your valves are bent and need some I would be happy enough to go as low as $30.00, postage would be about $15-$20 for THESE.

They are in great condition and would be a shame to see them go to waste.

Jarrah

TT-R250M · Super Guru

Oh, your head cover may not have the bump stop fitted as it is an early model so check for this....

TT-R250M · Super Guru

If you need to buy cheap OEM parts and don't mind waiting for 2-3 weeks they can be bought HERE.

Keep in mind that if you want to replace the starter clutch and assembly you will need all parts. Also the 99-13 clutch has 7 plates but the plates still fit the 5 or 6, the basket is too big and the clutch cover would be needed to fit the larger clutch basket and clutch boss. The front sprocket drive shaft is slightly different to accommodate the digital speedo. Other than that the only difference is the 99-13 oil breather on the head cover (that can be blocked).

Enjoy!

Jarrah

hags · Member

Would I be able to tell if there is valve damage without taking them out?? or is taking them out the only way to really check?
I just turned the engine over by hand from the rotor bolt.
I'd rather not have to take the whole top end off if possible...

I'll try get a photo of the sprockets tonight.

-- Edited by hags on Thursday 13th of June 2013 04:48:36 AM

hags · Member

If the exhaust valves were bent, wouldn't that be pretty noticeable even just turning the engine over by hand?? maybe exhaust cam didn't rotate out as far as I thought... it seems to turn over fine with it all lined up again.

Here's where they where when I took the top off. this is just a little bit past timing mark on the rotor, so intake lobe is up a bit higher than when mark is lined up.

TTRfan · Super Guru

Wow - you are lucky not to have suffered valve damage blankstare

TT-R250M · Super Guru

Can we see a good pic from the cam chain side like the one below please.....

TT-R250M · Super Guru

If your cam chain jumped the cog AT ALL, it will most certainly need replacing. If you try to use it again with the auto tensioner, it will jump again but this time while the engine is in motion and bend the valves or worst. To check or replace the cam chain guides it is easier to take the head off. While your there you might as well replace the piston and rings or at least check them. If you have gone that far it is a 10 minute job ''each valve'' to check.

There is a reason why the cam chain jumped and not just because it went backwards. The engine can turn backwards without causing the chain to slip but...if the chain, guides or tensioner needs replacing, it will slip.

Cutting corners with an old engine like this will lead to bigger problems further down the track. Best to fix it before it becomes an expensive bottom end rebuild.

If you do not want to remove the valves you can check if they are seating properly by pouring fuel (solvent) into the ports to see if it leaks through the valves. If it leaks after leaving it sit for some time the valves will need to be replaced and or re-seated. Of course you would need to remove the head to do this.

I will be here to help you if need be so do not be afraid to take it apart. Before, dismantling the engine I would suggest to re-fit the head cover and give the engine and surrounding area a good clean.

ps. I have a spare cam chain guide here that I would be happy to let you have cheap if you need it (the one that bolts on).

Jarrah

TT-R250M · Super Guru

To remove the valves use a large G-clamp (called C-clamp in the US) like this......

Place the G-clamp onto the valve surface (making sure it has a plastic cover), now using a socket that is the same size as the valve spring retainer- Compress the spring just enough to remove the cotters (keepers). Once the valve spring is compressed enough, tap gently on the head with your hand or a rubber mallet to make the cotters (keepers) fall out. Once they fall out remove G-clamp.

Important: Make sure that the valve stem does not come in contact with anything while compressing the spring. In addition, DO NOT compress the springs too far.

Here is some vids that you may find useful..

In this one I would not use pliers but still useful..

Enjoy!

Jarrah

TTRfan · Super Guru

Excellent Jarrah!

I have a really nice valve tool but now use a technique very similar to that shown in the last video instead - much quicker wink

Brian

noeyedear · Senior Member

Great stuff and the you tube video has come at a perfect time as I have a valve job to do after the cam chain jumping

thanks jarrah

TT-R250M · Super Guru

TTRfan wrote:
Excellent Jarrah!
I have a really nice valve tool but now use a technique very similar to that shown in the last video instead - much quicker
Brian

No problems Brian

I mentioned not using pliers as some people are not as skilled as others and could cause damage.

ps. the second vid was meant to be this one...

Enjoy fella's. wink

Jarrah