RT I'm horrified, I thought you were a purist

Much as I'd love to just wang in an M28 there's the pedal box issue which is the reson for the arty exhaust - which being stainless I'd quite like to keep!

Plan is a hybrid M4/28 - M28 crank case with M4 heads and manifold.

I'm slightly saddened as the M4 does sound lovely but the hybrid should give a bit more umph.

What and where are valve guides?

Why its probably your heads that are Fubar.
( that reads a bit "dandy"! should be- "why? its probably.....")
the bottom end is fine so why change it? its barrels and rings and heads that are probably to blame, Itll need carefull set up to make sure the heads are fine with M28 pistons and that the valves are ok with the pistons and the cam profile

but as youve been told the valve guides are the weakpoint on that engine so why add the weak point to an otherwise decent engine?

where is the pedal box and why does it interfere with a M28/1

Think you'd need to fit the M4 pistons to avoid hitting heads.

My M4 got M28 pistons and .4mm off the barrels and valves don't hit, at least not whilst idleing and speed. Maybe they'll do under load when the engine gets hot, haven't been there jet.

I have a spare M4 so I'll get that apart and have a look at the heads and valve guides on it.

I know that the exhaust on an M28 would fowl the pedal box on a piston pedal car, I think that's partly why they have such a mad exhaust system.

Sam,
you keeping some chickens under the bonnet?

ken

They've come home to roost...