Spinning at Bedford

A few weeks ago I took the 7 out to Bedford to see how it performed on the track. Preparation consisted of borrowing Ben's garage (thanks Ben) to try and get the suspension set up reasonably accurately - I think I did an OK job, but regret not corner-weighting it - maybe a job for the future, or maybe for a professional. I'm not sure how accurately I'd be able to do that at home.

I'm happy to say that performance was excellent. Cornering grip, even on cheapish T1Rs, was very good - I was surprised at how much better it was through the corners than many of the other cars there. Straight line speed was no real surprise - it was excellent, obviously, and even on the main straight (and through the corners, when I got the lines right) it proved able to stay with a Porsche GT3 RS, which isn't bad for something I bodged together in my garage. Top marks to the GKD design there. Braking was strong, but under very heavy braking it seemed to lock the front left much sooner than the front right (and then veer quite hard to the right) which I'm attributing to the lack of corner-weighting. Steering was on the heavy side; I suppose the weight of the big engine doesn't help here. I guess it'll be an on going task to try and figure out a way to improve that, maybe using rose joints instead of ball joints up front, perhaps a change of steering rack? I think less rear toe might improve turn in, but there's a balance to be struck there with cornering stability. Overall I'm really impressed with how it performed and look forward to seeing how performance improves with a corner-weighting, and perhaps better tyres.

Unfortunately there were two spins. The first was harmless, due to an ill-judged mid-corner gear change that unsettled the car and left me looking backwards down the track at a Boxster bearing down on me at 70 mph; the second wasn't so good.

The second spin looks more expensive. The first sign was a knocking noise...

Expensive noise.

Unfortunately at the time I attributed this to a loose exhaust silencer and carried on, but realised at the end of the day that it was coming from the engine. Further investigation and sump removal revealed that it had spun a big-end shell:

The spun bearing (number 6).

The spun bearing dissolved itself in the oil.

And left some parts of itself attached to the crank.

 The hope is that the crank will clean up in-situ, and then a fresh set of big-end bearings and a few oil changes should get it back to full health fairly quickly and cheaply. If the crank damage proves more extensive then it's engine out to remove the crank for a regrind, at which point the time and money cost will start to stack up...

Whilst investigating I also discovered that the idiot who previously worked on the engine has shimmed the intake valves to the same spec as the exhaust valves, so this will need fixing too. Not a massive or expensive job, but irritating nonetheless.

Hopefully the car will be back on the road soon - it really depends on what I find as I inspect the crank.

I would recommend other builders using the BMW straight 6 to refresh their big-end bearings and use upgraded (ARP) bolts. Apparently the big-end bearings are a known weakness in these engines, especially when driven hard as they will be in these cars. If done preventatively it should only be a few hours and around £150... if done after spinning a shell it could be a lot more if a crank regrind is required.