Technical Preparation for Nogaro

RG 500 Setup
Main jets are 240s at the front and 250s at the back.
Starting gearing is 15/39.
Ignition Zeel 2
Exhaust valve Closes at 7300 (from 7800)
Exhaust valve Opens at 7200 (from 7500)

Piston Replacement

The new piston arrived, and before installing it I wanted to note the relative weights and dimensions :-

The old TKR piston  weighed in at 205 gms and the new Mikata Piston came in at 195 gms.

The dimensions were pretty similar, I hope the 10 gms difference doesn't induce any vibration. Having remvoed the carbs I put in 390 main jets, I mistakenly removed the float bowl on one carb as that is what I am used to doing and promptly found myself with 2 floats in my hands. They run on sliders, connected to the float bowl, and are released as you remove the floatbowl, in fact on the new carbs (VM34), you have a big nut covering the main jet so changing them is real easy. I also put some gasket silicon around the carb balance pipe as it may have been leaking air there. I won't start it again until it gets fine enough to take it outside..

I also have found a vendor for the rubber o'rings behind the RG 500 carbs. Simply Bearings in the UK seam to do two different o'rings that are about the right size, I have gone and ordered up 10 of each to see which is the best size. From what I can measure (difficult to measure a rubber band!), the Outside Diameter is 36mm, the ID is 32 and the approximate thickness of the ring is 1.75.

I ordered these and these.

Nogaro in a few weeks, and I still need to upjet the 500, change my wets onto different wheels, and change the Exhaust opening revs.

Cracked Piston

After Croix, I wanted to be 100% sure of the state of the 350 so I decided to remove the head and get a good look at top of the pistons. You may remember that the left sparkplug was a bit light, and the left was a nice chocolat brown (caramel). Well, the short of it is that the left piston had cracked quite severly but thankfully no bits had cracked off. The bore is not touched, but I will need a new piston.

The cause is obviously some heavy detonation, which could be (probably is) either a very lean carburation or some airleak. No reason to suspect an airleak, although when I put it back together, I will ensure that the reed rubbers are well sealed, as the new rubbers are not that great a fit around the pipe joining the two sets together, I don't know if this would cause just one side to go, but it's a plan.

The base gasket looked a bit tired aswell, (could it be leaking!) so this will get changed aswell.

Nogaro is my favourite circuit for seizing at the end of the straight, so I will be upping jets on the 350, and also the 500, just to make sure of know disasters. For info. Nogaro is about 100 meters lower that Croix, so normally I should running bigger jets as the air pressure should be higher.