RB20 big end bearing

[LeightonRB20]

Total novice when it comes to tuned engines! But here goes;

I'm running an RB20 with all the upgrades recommended by AF Rayspeed including running 4% mixture. On the way home from Tenby, the bike decided it didn't want to continue! Anyway, long story short, the big end has overheated and has given up. My local expert is removing it and after discussion with AF it is going back to them for an inspection as it has only done 400 miles. AF state in their literature that 4% mix is a must as any less can starve the crank of lubrication. I filled up in a Texaco station and use Silkolene oil.

So, to the question; WHY? I can live with these things happening if I can understand why and can do something to stop it happening again. I don't believe for a minute that AF will say that it is a manufacturing fault. Consequently, I will have to shell out another couple of hundred pounds and potentially wait for it to happen again!

Any thoughts gratefully received.

Cheers, Leighton

[speedy]

To be fair, I think you will find AF's to be honest with you and if it's down to their parts, they will sort it. A 4% mix is what I use and feel happy with. Several years ago on a newish big end on a tuned TS1 using Silkolene Comp 2, I had the same thing happen. Hd the crank rebuilt and then changed to Silkolene pro 2 and it never happened again. I never found out weather it was a faulty bearing that got really hot, a major air leak that was cured on the new rebuild or the oil not good enough.cheers,Speedy.

[LeightonRB20]

Thanks for the reply, Speedy. I am using Comp 2, so a switch to Pro 2 is in order. Fingers crossed!

[jonashford]

If u are over loading the engine ie changing up and down gear because of hills, wind or ur engine is over geared then u can cook ur big end, u should maybe consider lowering ur gearing. Also a new big end for the rb frank is only £20 fitted

[LeightonRB20]

I'm being told that I need a new crank. I guess that AF will advise on that. I hope it is just a bearing!

[jonashford]

u shud really only need a new crank if the key way is damaged drive sprocket splines or if its more econimical!

[speedy]

Thanks for the reply, Speedy. I am using Comp 2, so a switch to Pro 2 is in order. Fingers crossed!

No problem mi duck, but as I say, I cannot say what the contributing factor was that caused my problem. Oils are personal choice and I think comp 2 has changed since my issues,as have other oils. The other factors that have been mentioned need thinking about,ie, gearing and labouring of the engine. If yer crank is rebuildable, AF's will do a great job of it. Hope it is and good luck.Speedy.

[Scooterdude]

I know this is an old post but just curious as to what the outcome was? Did AF get it sorted for you?