Hitchcocks Forum

Hi guys
I have a 2004 bullet 500 with a 5 speed and electric start. I have, over the last 6 months, turned it into a racing scramble bike.I have put on a 21inch front wheel and knobby tyre, a top triple clamp and MX bars, removed the electric leg, fitted folding mx footpegs, fitted a scrambler seat, longer hagon shocks, custom rear 58 tooth sprocket, 520 chain conversion, electric ignition from electrexworld, chopped the guards and a few other things to make it race ready. We had a scramble event on Sunday and I raced the bike all day. The only gripes with the bike were bad down shifts and the want for more power.

What I am planning on doing is getting high volume oil pumps, 8.5:1 piston, comp cams and replacing the 28mm mikcarb with a 30mm amal. Would this be enough to make a reliable motor with a bit more punch? Am I missing something?

The words "steel con-rod" come to mind if you're using that bike in competition. There are all sorts of tuning goodies available, but a less-fragile bottom-end is essential.



A.

And forget the high capacity oil pumps, the engine doesn't need it. The Rickman brothers raced 500 Bullets back in the day and didn't use them. You might add Competition cams and a 3-keyway crankshaft timing pinion for extra tuning possibilities. Have a look in the Accessory Catalogue on the main site for more ideas. If you race it, you will break it but these bikes are cheap enough if having fun is your goal!

REgards, Mark

From what I have gleaned on here and other sites, the standard oil pumps are fine with the original floating bush big-end. The high volume pumps are better if you have a roller big-end, due to the oil exiting the bearing more easily.

Comp cams and bigger carb will be a bit pointless without gas flowing and opening up the head.

Only time you'd need the oil pump upgrade is if you switch to a needle roller big end..

Hi Josha, there is no need to overtune the engine but build to its strengths. I used to motocross with an AJS 30cs 600cc twin. It had 6 to 1 compression and was tuned for reliability and lowdown torque. It was well able to hold my team mates highly tuned singles and won in the unlimited class. It also went eight seasons without any major rebuild. Remember ; in order to win you first have to finish! Finally the redditch scramblers were available with an array of different compression ratios to suit differing conditions and the tuning notes state standard cams are better as they pull better from low revs. Vince

I found a guy here in Melbourne Australia that purchased a 90125A high tensile forged British steel conrod matched with a roller big end (RE13) 5 years ago but never used it. I have bought it off him for $350 AUD which is a steal compared to retail price now. So that's one major part off the list. Next is a piston, once the bank account has recovered.

Don't forget the steel con-rod is heavier than the alloy, consider getting the crank re-balanced when it is stripped for fitting the rod. As this bike is being used as a scrambler you could also get the flywheels lightened while you're at it.



A.

There is no need to change the balance factor when switching from an alloy conrod to a forged steel one, at least I never have. The same goes when swapping pistons, too. Lightening the flywheels - and restoring their original balance factor afterwards - is a VERY good idea, though. Regards, Paul.