Yamaha TRX850 Enthusiasts Forum

Hi Folks

Had a great day out on my bike today right up to the point when it lost power which at first i thought was running out of petrol
When I pulled over it became obvious that the engine was making some horrendous noises ..... ratlling , clattering , knocking ..........truly dreadful

Now Im assuming the crank has gone and Ill have to get it in bits and sort it out but the question is why ?

It had plenty of oil in and I wasnt thrashing it excessively , it just imploded
I will rebulid it but I dont want it happening again if I can do anything to prevent it

Thanks

Chris

Assuming (?) it is a crank failure - you'll probably find it's dropped a few teeth off the cam drive sprocket on the crank Who last checked the valve clearances,etc? If the cam retainers are over tightened they tend to either shear down into the head or strip teeth from the sprocket on the crank. I've had the same experience recently - some bolts in the head over torqued & some only finger tight

Hope this isn't your problem as cranks second hand are getting hard to get hold of, £1000 for a new one from Yamaha!

zednine wrote:Hi Folks

Had a great day out on my bike today right up to the point when it lost power which at first i thought was running out of petrol
When I pulled over it became obvious that the engine was making some horrendous noises ..... ratlling , clattering , knocking ..........truly dreadful

Now Im assuming the crank has gone and Ill have to get it in bits and sort it out but the question is why ?

It had plenty of oil in and I wasnt thrashing it excessively , it just imploded
I will rebulid it but I dont want it happening again if I can do anything to prevent it

Thanks

Chris

Could it be that the camchain was at end of life and it jumped a tooth or two on the sprockets? Mine had just one click left on the tensioner when changing it at 40kkm. Easy enough to take out and check....
Mates speed3 did this....

Update .........

Took the alternator cover off and discovered the 3 screws holding the alternator on had unscrewed ( not me by the way ive never had the cover off before ) ...........

Alternator is trashed etc so I was quite releived

However ......... big problem is that there is a few mm " play " in the crank end ...... both up and down and in and out ...... ie I can grab hold up the end of the crank and lift it up and down and push it forwards and backwards

This cannot be right and the only assumption I can come to is the end of the crank has broken off ........ is this unusual or have we come across this before ?

Thanks

Chris

No point playing `guess the severity`, time to get the motor out and strip it down is the only way you`ll ascertain just how bad it all is.
If the crank moves that much, that`s why the alternator bolts shook out!

Mincehead wrote:No point playing `guess the severity`, time to get the motor out and strip it down is the only way you`ll ascertain just how bad it all is.
If the crank moves that much, that`s why the alternator bolts shook out!

Id have to disagree mate ........that engine was perfect before the alternator came loose

In fact amongst the Trixies round here it was the quitest and smoothest ..... but like you say its gotta come out ........ let the fun begin haha

That`s what I meant though, likely the alternator bolts coming loose were as a result of the crank vibration, perhaps even allowing the rotor to hit the stator etc.
These things can happen pretty quickly when you consider the crankshaft would have been spinning at 8000 + revs!

Have you tried dropping the sump & seeing if you have any 'surplus material' in there? First place i'd look & whether or not your engine was quiet before, if you have that much play in the crank you have a problem that needs sorting (couple of mm is a lot!)

ive had a few trxs and must admit, this was the quietest, sweetest sounding engine i've heard. I was gobsmacked when i read this

Well the day started sweetly .......... engine was out and on the bench in just under 2 hrs



Head removed and no problems found



Ancillaries taken off and still no isuues ........... mmm what could be the problem ?



Think Ill have a peep inside the crankcases ...... just on the off chance .......... oh bummer



Anyone selling a crank ?

Chris

fook

Ferk a rook, NEVER have I seen one break like that!
Beyond repair that-un, you need to ascertain the viability of re-using your crankcases too by the looks of it.

I do ? ..........whats happened to them ?

This is getting worse lol

On the left of the picture, the cranks been doing a grand jod of grinding the inner edge away from the looks of it.
I suggest you get it split and have a damn good inspect and clean, there will be metallic particles throughout the motor, carried around in the oil.

Ah I see what you mean ........well the other side is exactly the same and its very even ....... id think thats factory machinibg of the cases mate ....... could be wrong but Im fairly sure