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

pekkal · Member

Exhaust cam timing badly wrong?!

TTR-Tony · Newbie

Suppose it is possible the cam chain tensioner is bad and the chain was loose enough to allow the exhaust cam to jump teeth?

TTRfan · Super Guru

TTR-Tony wrote:
Suppose it is possible the cam chain tensioner is bad and the chain was loose enough to allow the exhaust cam to jump teeth?

That sounds a plausible explanation.

Is the cam chain tight pekkal?

Brian

pekkal · Member

The cam chain seems tight. Less than 2mm of play in the chain between the intake and exhaust sprocket. I'll check the tensioner later today. Strange.

pekkal · Member

The bike runs! I loosened the timing chain and rotated the cam in to position.

The tensioner seemed to be OK. Chain was tight, the srewdriver "rewind" and release worked and I was not able to push the tensioner chain guide in. So I quess the "lock" in the tensioner also works.

I'm still totally puzzled on how this could have happened. If the tensioner was broken and chain loose then a kickback could make the chain jump. But with a working tensioner it does not make sense. confuse I'll remove and examine the tensioner later. Maybe I should consider a manual tensioner (http://www.ebay.com.au/itm/Manual-Cam-Chain-Tensioner-Yamaha-TTR-225-230-250-NEW-/390253625908)?

Pekka

barra8 · Guru

pekkal wrote:
The bike runs! I loosened the timing chain and rotated the cam in to position.
The tensioner seemed to be OK. Chain was tight, the srewdriver "rewind" and release worked and I was not able to push the tensioner chain guide in. So I quess the "lock" in the tensioner also works.
I'm still totally puzzled on how this could have happened. If the tensioner was broken and chain loose then a kickback could make the chain jump. But with a working tensioner it does not make sense. I'll remove and examine the tensioner later. Maybe I should consider a manual tensioner (http://www.ebay.com.au/itm/Manual-Cam-Chain-Tensioner-Yamaha-TTR-225-230-250-NEW-/390253625908)?
Pekka

It can only be a buggered chain,tensioner,cam chain sprockets,guides
To check your tensioner...It should release without any catching-tight spots.Same with winding it up. Any catching or tight spots & i'd replace.
If you want to buy one of those manual tensioners by all means do so as these are much better (in my opinion)
......................
Jarrah.

pekkal · Member

Hello again,

The tensioner is ok. Works nice and smooth.

I was browsing the web and found this picture: http://www.totallyttrs.com/Used_parts/Camcover4sale2.jpg In the middle of the cover there is a piece of plastic held in place by a cross head screw. My head cover does not have this! I'm quessing that this is an additional guide for the camchain... Could well be the reason for the jump!

That part is not listed in the parts catalogs. Maybe I'll buy that cover from totallyttrs... Or maybe one of you guys have dimensions for it so I could build one?

Pekka

-- Edited by pekkal on Thursday 15th of November 2012 07:00:24 PM

barra8 · Guru

I'd be looking more along the lines of worn cam chain. It may not look worn but the problem with just looking is that really you would have to take the cam chain off to check this properly.

The only things that can make the chain slip are...

Worn cam chain.

Worn cam chain guides.

Worn cam sprockets.

Worn tensioner.

Worn crankshaft drive sprocket (highly unlikely)

My guess is either tensioner or cam chain but could be all of the above also (except maybe Worn crankshaft drive sprocket).

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

Jarrah.

-- Edited by barra8 on Thursday 15th of November 2012 10:10:07 PM

barra8 · Guru

It seems alot of ttr's came without the bump stops from the factory. Not having this would cause no dramas. It is just a pre-cautionary measure that does not touch or ''ride'' the chain it merely sits there looking good.

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

Jarrah.

pekkal · Member

The cam chain is 30 hours old (according to the previous owner). Should have said that in the first post. Sorry. I'll check the guides again but the do not seem to be too bad.

Pekka

brindabella · Senior Member

regarding the TTR cam chain, an internet trawl can come up with stories of high mileage owners who have replaced the cam chain multiple times, plus an owner who had exactly the same problem - exhaust cam "leading" the intake cam.

the fact that the chain is relatively new means it has been replaced - but maybe the previous owner didn't also replace the cam sprockets. if not, the chain may be "riding high" in the sprocket teeth. plus if (say) the guide was a bit worn and the (perhaps, but unlikely?) the oil pressure to the tensioner was low then you have a cause.

probably at the transition from intake to compression, when the pressure on the intake cam lobe is released (and the exhaust valve is closed, so that cam is "loose"), a little wave is sent along the chain (eg like flicking a whip) as it takes up some slack, and the chain momentarily lifts over the exhaust cam sprocket, allowing it to skip forward under its own inertia.

and that would be why yamaha have seen fit to put that little "bump stop" in place (presumably in later models?) - it would not normally touch anything but could interfere with that momentary wave that happens with a worn chain/sprockets/tensioner and so be a factor in increasing reliability.

well who know - its one theory, anyway.

so it would appear from stories in this and other forums, that if we keep our bikes for a long time, we can look forward to the swing arm being sawn by the drive chain, the starter sprag clutch breaking up, an oil leak developing in the decompressor plug, the carb inlet developing a leak, and the cam chain wearing out (in an otherwise highly reliable bike).

oh well, forewarned is forearmed!

barra8 · Guru

If the chain has been replaced recently then this would not be the cause of the problem- You may want to replace it though incase it has streched from the ''slipping teeth''.

It all points to either the cam sprockets guides worn or the cam chain guides.

It also could be a broken crankshaft tooth or badly worn but highly unlikely.

I'd be replacing the lot myself as one slip too far of the chain could spell ''DISASTER''

Of course it's up to you which way you go.

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

Jarrah.

TTRfan · Super Guru

Good bit of research Jarrah! It's good to learn something new every day wink

I now understand why Mr Yamaha fits the "slider" in the cam cover.

I stripped one out just now for Pekkal (that screw was tight!) and am surprised how substantial it is. The bean counters at Yamaha wouldn't have let the part be included if it didn't do a necessary job. It would certainly help prevent the chain jumping from the "whip" you describe.

I am not convinced that the camchains on the TTR wear out any more quickly than any other bike and don't think I would class it as a weak point. Perhaps I have been lucky but I have stripped and repaired a lot of engines and the camchains, tensioners and sliders have nearly always been absolutely fine.

One of the reasons for the forum is to help owners with problems so it is highly likely that many of the problems faced and represented here are not necessarily common. Just my take on things.

See pics of it below:

Camchain slider2.jpg

Camchain slider1.jpg

barra8 · Guru

Brian wrote:

Good bit of research Jarrah! It's good to learn something new every day wink

I now understand why Mr Yamaha fits the "slider" in the cam cover

I stripped one out just now for Pekkal (that screw was tight!) and am surprised how substantial it is. The bean counters at Yamaha wouldn't have let the part be included if it didn't do a necessary job. It would certainly help prevent the chain jumping from the "whip" you describe.

I am not convinced that the camchains on the TTR wear out any more quickly than any other bike and don't think I would class it as a weak point. Perhaps I have been lucky but I have stripped and repaired a lot of engines and the camchains, tensioners and sliders have nearly always been absolutely fine.

One of the reasons for the forum is to help owners with problems so it is highly likely that many of the problems faced and represented here are not necessarily common. Just my take on things.

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

That sure is what it's for Brian wink The reason i did not mention this is that some older models do not have this - therefore it should not cause a problem if all else is good.

I am just saying that if it was my engine i'd be replacing the lot to be sure. I would also be looking into fitting the bump stop as this could come in handy. That said fitting a manual cam tensioner solves that problem as when it's at spec...it stays at spec for quite some time.

TTR's ( & alot of other bikes) can have the 'whipp' problem if all is not maintained is all i'm saying.

Not sure if you or others relize but i have been helping alot of people but maybe not many people like me anymore on this forum from the ''rocket scientist'' so may be best to leave yaz to it once i finish my bike. I will leave my pics & threads up for all but maybe best to leave the ''helping'' up to you.

It may well be something ''highly unlikely'' but fixing the ''likely'' seems best & checking for the unlikely.

Anyway here is a pic of an old 1994 fitted with the ''bump stop''...

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

Jarrah.

TTRfan · Super Guru

barra8 wrote:
Not sure if you or others relize but i have been helping a lot of people .....so may be best to leave yaz to it once i finish my bike.
Jarrah.

Hopefully you will be with us for quite a bit longer then Jarrah wink

barra8 · Guru

TTRfan wrote:
barra8 wrote:
Not sure if you or others relize but i have been helping a lot of people .....so may be best to leave yaz to it once i finish my bike.
Jarrah.
Hopefully you will be with us for quite a bit longer then Jarrah

Glad i have one or two that don't dislike me. wink Maybe i'll stay longer but if everyone dislikes my help or company then there is not much point.

I do like this forum & all on it but maybe the forum don't like me so much - just saying how i feel & the replies i get...... Paintork out wink

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

Jarrah

pekkal · Member

I highly appreciate all the help and comments from all of you! (including you Jarrah) It is great to have such an active community helping each other! I hope I have not offended anyone by just thinking aloud and trying to figure out the root cause of the problem.

I'll will triple check the guides and sprockets again but they do not show signs of wear. I would not like to open the engine and replace a bunch of parts just to be sure. Specially as the PO has already done that 30 hours ago. I'll fit the "slider" and a manual tensioner and see how that goes. It's my bike anyway... wink

Pekka

nikroc · Member

I must have missed something along the way BUT I will say that although Im a new member the help and advice I've recieved has been bang on. I have even been reading around other threads (Jarrah) and have really enjoyed peoples passion and commitment to ttrs,not to mention the willingness to share expierience and how to's..

barra8 · Guru

Thanks pekkal & nikroc,

Good to know that not all dislike me wink If i took a vote i guess i'd be staying so maybe i'm over-reacting. blankstare I don't try to be a burden to anyone,just help when needed. Good to see people appreciate the lenght some of us go to to help

Do whatever you think is best as your the one looking at the parts wink Glad your fitting a manual tensioner

Good luck wink