Just checking, am I correct in that the pinion gear and ring gear are matched as a pair. Case in point I have a 3:07 ring from a MGC but the pinion gear is not to be found, I was told that a stock B gear would work, is this true?
"Matched ring & pinion set" is the correct statement and are usually sold as such. Even if you find another MGC correct pinion for your 3.07 ring gear, that doesn't make it a matched set.
The last operation in manufacturing a ring and pinion set is to run them together in a bath of lapping compound. This process provides the final finish to the surface and defines the contact pattern. If you run an unmatched set I would think you are looking at a lot of gear noise.
Mark, I suppose if you "really" want education, you could try a test fit? If you you have concise manual, follow it explicitly on how to "read" pattern and adjust accordingly ? Perhaps even "best effort" , may require, lapping in. If that produces usable match, (unlikely), you could flush meticulously, and put in new bearings ? roverman.
Odds are your pattern will be less than perfect. But, these parts are cut to precise tolerances so the real reason for running them in is to smooth out tooling marks and minor warpage from heat treat. The processes are very uniform from part to part so the chances of an acceptable match might be quite a bit better than you think. At any rate, the "print" on the contact pattern is the final arbiter. A decent pattern at good clearances and you're good to go. Something odd... well that'll probably make noise. But it could still hold up reasonably well in some cases.
JB
As to the question about the stock MGB 3.9:1 pinion gear working with the MGC 3.07:1 ring gear, no way! The pinion gear angle and diameter for a set of helical bevel gears is different for every ratio and the ring gear thickness also varies. You'll definitely need the correct MGC 3.07 pinion and then you'd have to check the gear mesh pattern very closely when assembling.