Monoposto Racing Forum

Hi,

Does anyone know what size bore the Formula Vauxhall Junior brake and clutch master cylinders are please, or does it matter? I cant get to my car right now to check the numbers on the side of the castings and wanted to order new ones, unless of course new seals can be bought from somewhere?

Regards,
Matt.

Master cylinders are the sort of thing that get changes to suit a particular driver, or a change in pad/caliper/design etc, so best to check on your own car as everyone else might have a different size. It's a compromise between feel, pedal movement and how hard you have to press. Some people like a firm pedal that barely moves (big diameter, lots of hydraulic advantage) whereas others forego some firmness to have a pedal that moves a long way and gives them feedback that way (small cylinder, less hydraulic advantage).

Also, I've heard (and found from experience to an extent) that rebuilding master cylinders rarely lasts long, and it's cheaper and easier in the long run to just buy new cylinders if possible. Doesn't seem to matter how clean your workshop is or how careful you are - maybe the repair kits are just lower quality???

If they are Girlings, then Raceparts have a good selection (of cylinders and seal kits) and might be able to help.

Thanks Tristan. As it turns out, it was cheaper to replace the whole master cylinder than buy a seal kit anyway!

I dont suppose you know what cylinder compression the FVJ engines should ideally produce? Mine range from 175psi on three cylinders to 200psi on the fourth! I am unsure what the E16SE vauxhall engine should be running or what the level of tolerance should be, and I just can't seem to find any info on the t'internet

There isn't really a correct figure, as it depends on how warm each cylinder is, the speed of cranking, and quality of the gauge and the fittings etc. It's not a case of saying normal atmospheric pressure is 14.7psi, so in a 10:1 compression ratio engine you'd expect 147psi.

Anything around 175-200 is going to be okay. It might be that three cylinders need the valves lapping in or the bores lightly honing, but equally it could be a bit of carbon build up on some rings that s stopping 'perfect' sealing. If you were going to take the engine out or to bits anyway, it would be a good idea to do those things, but if weren't planning on then I wouldn't change your plans based on 175-200psi.

Thanks.

Those figures were taken with the engine cold if I remember correctly. I'm planning on taking the head off for an inspection/overhaul anyway, just because i've never actually had a good view of the internals of this engine so it's still a bit of an unknown to me!

Not only that but the Fern's 8v Junior seems SO much quicker than mine on the straights, so I ought to freshen my engine up in order to give myself as much of a chance as possible!