Yamaha YBR Custom - Slipping cam chain

[NagaNaga]

I could really use some help here.

The top end in my YBR Custom (2010) stared making a strange sound on a trip recently. Bike was running fine otherwise.

So when I had some time I Decided to check in on the top end.

Rockers good, camshaft good, camchain all good. Bearings on the camshaft also good.

So nothing to suggest it would be making the winding wherring sound I was hearing under acceleration.

Whacked it all together and no start.. no compression.

Bent exhaust valve. But how? I made sure I set to TDC following marking on the flywheel and cam sprocket.

So, New valve in and no leaks. Back to finding out what happened.

It seems the cam chain is slipping on the bottom sprocket. But why? All was fine before I touched anything and I've done plenty of top end work on bikes before with no issues so what gives.

It seems the chain is slipping is roughly the same spot in its rotation. Timing mark on the sprocket must face up when in TDC and where the chain slips is when the mark is pointing left or forwards.

If I turn the engine over slowly it does not seem to do it but if i turn it quicker or use the starter it slips so TDC making on the sprocket is now off by a tooth or two.

Cam chain tensioner is working and has plenty of adjustment left in it. Cam chain seems nice and tight but something is amiss.

Wish I never went looking for this sound now!

I tried to get the flywheel off to get a look at whats going on but it will not budge. It broke my tool! I Buggard the threads on the end of the drive shaft in the process. Glad I have a die and tap set!

Anyway, If anyone has any ideas as to what the frick is going on that be very helpful.

My next step is to try and change the cam chain for a new one but if I cant get the flywheel off that aint happening

[Nobby the Bastard]

Cam chains dont slip if the tensioner is in place properly. You probably didnt check the timing properly with an outside bet on the chain jumping a tooth before the tensioner clicked into position properly.

You shhould always turn the engine over by hand a couple of times after messing with the timing stuff to 1) ensure the tensioner is doing its job and 2) the timing remains correct after a couple of rotations.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[NagaNaga]

[Nobby the Bastard]

Chains don't jump teeth unless the tension is wrong.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[NagaNaga]

[Nobby the Bastard]

It will not alter the fact that cam chains do not jump unless the tension is wrong. Your problem started when you took it apart. You are doing something wrong with the tensioner.

You clearly don't know how the tensioner works because, as you say, it's an auto one but you say you used the nut to tighten it up a little which you can't do with an auto one.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[WD Forte]

So 2010, ok, what mileage?

As Nobby says, chains don't slip unless there's significant wear or slackness
somewhere in the process.
They don't 'slip' anyway its not a belt, they jump teeth for the above reasons
Bent valves mean mistiming due to wear, slackness or user error.
Poor servicing/neglect on a high mileage bike wont help.
when did it last have a cam chain?
pics vids will help
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bikers smell of wee

[Nobby the Bastard]

Id be impressed to see the ybr125 that does enough mileage to get to the point where the cam chain needs to be replaced.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[WD Forte]

I cant recall a YBR needing one but 14 years of possible thrashing and neglect will wear anything out
____________________
bikers smell of wee

[Nobby the Bastard]

[NagaNaga]

Bikes done about 13k miles.

Was at 9k when i got it about 1.5 years ago.

I know what your saying about the tension but I am 100% doing it right

The tensioner adjusts its self with a spring but it wont go back in unless you turn it with a screwdriver. Is then locks in position so you can do what you need to, then with a screwdriver just give it a tap and the spring snaps it back to tension.

I just undone the bolts that hold it in a few turns to let the tensioner move out a little more and then tightened the bolts again. This has the effect of putting even more tension on the chain and its still slipping.

I am going to grab a different tool for the flywheel to get it off and have a look at whats going on in the bottom.

[Nobby the Bastard]

[Nobby the Bastard]

Pretty sure the bolt at the end of ann auto adjuster is to hold the tensioner in the smallest position whilst installing because otherwise it will be too extended to go in and then gets completely undone so that the tensioner plunger is pushed fully by the spring towards the chain.

It's not an additional manual adjuster.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[NagaNaga]

[Nobby the Bastard]

First off, it's a bolt head and not a screw so I don't know how you are using a screwdriver on it and secondly it's not a manual adjuster, it''s to lock the plunger in it's retracted position to install it and then should be released.

https://i.ebayimg.com/images/g/yJIAAOSw8blmWZbV/s-l140.webp

If it's actually a screw head it's a replacement manual adjuster and it would need a little more than a tweak to adjust the chain. You note how the manual one below doesn't have the huge body that contains the spring?

https://i.bosity.com/product_img/275/67008661/67008661_9_image.jpg?x-oss-process=image/resize,p_100/watermark,image_d2F0ZXJtYXJrX2ltZy8xNzExMTQwMi9kZWZhdWx0LnBuZz94LW9zcy1wcm9jZXNzPWltYWdlL3Jlc2l6ZSxQXzk5,g_nw,x_0,y_0
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[NagaNaga]

Watch this

https://www.youtube.com/watch?v=k2vltxH2qZw

Then stop typing.

[Nobby the Bastard]

Do you not get the point that you are having to hold it back against the spring so that the screw has an effect in the first place?


The fact that you are having to hold back the spring negates the need to manually adjust.


What I think you need to do iis make sure you don't just turn the engine and hope the tensioner works immediately and watch and hold the chain against the cam sprockets so they don't skip.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[WD Forte]

That tensioner looks pretty typical to me

why did the chain jump?
A chain can only jump a drive cog if slack or worn or the drive cog teeth are worn or its subject to a high enough mechanical resistance to prevent normal function.
Misaligned timing can cause this if say valves contact the piston.

13k sound like a very low mileage for its age if correct,
less than 1000/year
MOT history may help confirm this
Not accusing anyone of lying but old bikes can have a very interesting history of folk swapping stuff about which the current owner may not be aware of.
Examination of the drive has to be done
____________________
bikers smell of wee

[Nobby the Bastard]

Are you hearing the clicking you would expect from an adjuster being released?

Are you working the engine back and forth a few degrees after releasing the tensioner and then checking the timing?

is it possible that the chain was slack on the wrong side of the engine so when the slack is taken up the timing is wrong? If so take the tensioner out, redo the timing without moving the crank by moving the cams over and working the chain over and then reset the adjuster.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[NagaNaga]

[Nobby the Bastard]

I'll be willing to bet that the slack is on the opposite side of the chain run so when you put the adjuster in it becomes apparent thaht the chain is a tooth or two out of timing.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[WD Forte]

Enough slack talk! what about the subframe?
Nobody ever mentions the subframe dammit !
____________________
bikers smell of wee

[Easy-X]

Having rebuilt a 125 top end fairly recently (RC125 of a similar year) I can say tensioners are funny things but nowt you can't figure out in 5 mins with it off the bike. I don't recall doing anything other than releasing the spring to let the plunger do its thing. There is a ratchet in there as well so it springs out but not back in.

If the plunger thingy is working then... I dunno, are the tensioner guides in correctly? They should only go in one way but if the plastic's worn or damaged maybe in upside-down or wrong side.

Regardless it'll be one of those things where a mate will come along and spot the problem straight away, I know that's not much help
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Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[Robby]

If the crank or cam gears locate on the shaft using woodruff key, then a sheared key could explain the problem. It will allow the sprocket to rotate on the shaft.

[NagaNaga]

Something has to be off with this engine...

I got a tool to pull the flywheel off so I could get in there and see what was going on with the cam chain on the bottom end....

It will not budge a mm. I have watched a few people on YT taking flywheels off including a YBR and they just pop right off.

Mine seems to be welded in place or something!

I think, I am just going to buy an engine... I just cant be bothered trying to figure out what the hell is wrong with this thing if its not going to cooperate.

Found a cheapo untested engine on ebay and as long as the bottom end is good it will do. The top end I can swap from my engine if needed or swap any other good parts over.