Hi all
Does anyone know if the M4 engine will fit in 425cc crankcases? Or, will the barrels & pistons from the M4 fit a 425 bottom end?
Ta
Mike

Barrels and pistons are interchangeable across all engines apart from the 435 as far as I'm aware form my fiddlings.
If you're upping the CC of a 425 I would maybe worry about whether the crank could take it?
If you want an engine to look like a 425 but with more power why not just use an M4 and put a 3 stud stone mesh on it
The 'in keeping' thing to do would be to get yourself a 425 big bore kit, I think RAF did a 500cc one?
Or to be in keeping with my recent face ache rant. Leave it the hell alone and live with it

Thanks Sam!
I have great sympathy with your rant, I share it.
However, I'm using Gerty as my everyday car & finding the 425 a tad slow, mainly in acceleration, the 48mph flat out I can live with but would like to be able to pull out of side turnings without needing a 3/4 mile gap
Anyway, I ask 'coz if I just dump the M4 in then I have to change the headlight bar to accomodate the external dynamo. A. I don't have a cranked L/h drive light bar; B. don't have a 6volt external dynamo & C. the spare wheel carrier won't fit and as there is no boot well the spare will be in the way.
So, as I have an M4 & a spare 425 with a dynamo I thought maybe a little mix and match...?
And the 425 in the car has just started spitting oil everywhere....

Will not fit


Will not fit

The only thing with the mixing and matching is that it never actually runs that well. You can head swap m28/m4s but it's just messy. If you're really that worried, 602 it! I have a spare cranked LHD headlamp bar if needed.
And I hate to see M4s pulled to pieces If you're ever thinking of selling it...

Could be your answer then!

Seems fairly conclusive! Thanks Roy, saves lots of spannering to find out
Guess I'll live withe the 425yness of it for now.
Sam, you can have the M4 if I don't put it in the AZU - depends if I can work an M28 into that without disturbing the peddles/master cylinder - summer project

You can keep the chassis mounted pedal-box if you either use a pre-May68 AK350 exhaust system (which is a bit small for an M28) or adapt an M28 crossbox and swan-neck to come out on the right-hand side (as pre-May68 AK350) and then just use a normal torpedo and a short (van/mehari) tailpipe.
The other thing you will need is a clutch cable from a Oct67-to-May68 AK350. This is very difficult to find as it is different to every other model. (The AK350 was the first model to use the later type gearbox, in Oct67, and therefore only model to have it with the chassis-mounted pedal-box, up to May68). I can dig out the part number if you want to do a search, or I have a spare new one that you can borrow, to get a copy made.

I suspect the alternator'd be a bigger visual give-away than the number of studs on the finger-filter.

Thanks all!