My RB20 bites the dust

[carlos fandango]

On the way back from the IOW on the A34 trying to keep up with Eden and Yam-Lam my RB bit the dust coasted to a convieniently placed layby, tryed a kick and no comp, checked the plug and it looked like the piston was holed. So i was sat in a layby, and i was quite p1ssed off and very perplexed as to why it had holed? I had had it set up on a dyno, i know it was running rich, the rubber wasn`t split head and pipe weren`t leaking, my egt was at a constant 400 deg.
So over the two hours sat waitin for the breakdown truck and thinking of other things that it could be....timing .... dodgy egt..."bad fuel" .

Anyway stripped it today and got quite a shock.. got the head off and piston crown and head mashed up with bits of metal in it so thought its the rings?
Then i got the barrel off and the rings and pegs are all in place and complete so not the rings
so it looks like the crank big end bearings.

AF crank bought at the same time as the kit, it twisted about 6 weeks ago so took it back and had it welded, its only done about 1900 miles.
So what do you all recon the crank not up to the job? not fit for purpose? trading standards?

[rog60]

They'll probably use the 'welded up' as an excuse for invalidating the warranty.

So nobody stopped even though I bet the A34 was buzzing with scoots as it's the main North/South route

[bazman]

Have you checked the small end bearing? My mates ts1 bit the dust couple months back and this was due to the small end bearing collapsing !
Sorry to hear of this though

[paulc]

i'm guessing af have never heard of that happening before

[andylaw7]

look in the split in the conrod to see if any big end rollers are misaligned .been there twice

[sydduckett]

I was told that this was a problem with the RB kit as supplied by AF, so ended up getting the kit via Taffspeed. they supplied there own semi-race crank which i belive is the same as the AF version apart from the webbing? I also believe it started life as an indian part but im not that clued up on this sorta thing...

anyways i have murdered the RB, really smashed the arse out of it so to speak and its standing up very well. Would reccomend Taffspeed all day long as they offer quality service and parts. Found the opposite with AF, but each to there own..They are also very knowledgable about the RB and helped me sort out all the set up issues i had..

Sef

[Train Driver]

Reading all the posts about cranks it seems everyone has problems with AF cranks or copies of their cranks and everyone praises Mb and their alfa crank, i know where i will be spending my money.
Have heard good things about Jb's new cranks anyone used one yet, looking at getting a 62mm crank

[carlos fandango]

Heres a couple of pics.



I got the crank out today, and as i suspected its the big end. The bearings are in place but its the cage that has disintergrated.

I brought the kit and crank from the same dealer, it was dynoed by them. when the crank twisted after 1500 miles i took he crank back to the same dealer, who welded it. so its going back tomorrow and we`ll see what they say

[J1MS]

The bearings in thes RB engines need to be high quality and checked prior to assembling cranks.
When I build an engine with a new crank it is thoroughly Washed out with parafin.
If you use a glass bowl full of parafin then place the crank in it and try to spin holding only the little end as if turning an engine over for about a minute then let the parafin settle and there will normally be swarf washed out and sometimes a little grit from the grinding of the pin but alot of people think it's a new crank put it in. I always tell anyone building with a new crank to do this. A used crank is nomally just covered in old dirty oil and the parafin discolours but no swarf is evident the swarf that does come out is very fine usually but sometimes little slithers of metal from pressing the crank are evident. Try it next time you buy a shiny new crank. You might just be suprised ...

[Arfur]

Thats exactly what happened to my AF crank just the other week I didn't bother calling them as I knew what the answer would be.
No prizes for guessing what it would be...............................
It should be their slogan