Hi all,
I’m checking the big end bearing on my DT400 twin shock. 
There is no up/down movement. 
I can rock the con rod slightly - please see video..
Is that an acceptable amount?

youtube.com/shorts/5rasfL6sNf8?feature=share

She'll be good until next time by what i can see. That's so long as it feels smooth to revolve but of course you're revolving mains as well so have to sort of feel any roughness through the conrod from the bigend. I'm sure it'll be good. Rocking is likely from the cage end bits wearing the rod very fractionally for the first few mm each end. I'll link a page i put pics on a while ago as easier than transferring the pics now i've found them. Don't let me scare you into pulling it apart this time though.

yamaha-enduros.com/index.php/forums/1968...wear-rod-rock#134470

My 2 cents worth is that you will be fine for a long time as long as it gets clean air, but that would be the same advice with a new rod
Doug

Thanks for putting my mind at rest…

RT325 - very interesting regarding the wear of the con rod that you describe. If everything is kept perpendicular during normal engine running, why is that wear taking place? Have I missed the reason? The cage doesn’t come into contact with the con-rod?

I think its just because the cage is floating on the rollers so it just gets centrifuged out to be always rubbing around the rod. That's always been my guess. Can wear the crankpin in a similar way over time--long time--'i think' if the cage is thrown upwards to rub on the rod then the inside of the cage is touching the pin. I must check my worn out one in the pic & see if that's possible but think so. My stuff is way past its use-by though.

Yamaha manuals have the correct method to check... usually 2mm "wobble" max at the small end...  you don't slide the rod, you wobble it and measure with a dial indicator.  

(In a pinch I've clamped a steel ruler to a stud and used it to gauge the wobble)

See the service manual in tech library

It's amazing how a rod will start to make noise when the wobble exceeds 2mm even though you can't feel any up-down play.

Another old school test is to pull up on the rod with one hand as hard as you can...  then while holding the up pressure on the rod tight, smack down on the end and listen for a metallic "click"
 

Just my experience, but noise is usually caused by going through the hardening in usually the top area of the eye of the bigend end of the conrod & the rollers also loose hardening & when the two rough surfaces pass each other you get the concrete mixer cycling growl every lap "extreme case". Learnt my lesson at work once when briefly in charge of the workshop & a TY250 came in like that growling & sounded typical rough or rusted mains, so after telling the mechanic to do the mains only it still growled so had to do it properly & rod hardening damage became obvious. Mechanic probably knew & thought that'll teach the smart arse--& it did haha. Never took that noise for granted after that.

Another quick test I was taught many years ago (+40) was the twist test....grab the little end of the rod and give it a twist. If you can sense any play while twisting it then this shows the big end needles are barreling (worn on their ends ) and in need of replacing.
-- Ray