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MG MGB Technical - Exhaust valve cutouts

I'm fiting on of Peter Burgess' fast road heads and have filed out the cutout for the exhaust valve. I was just wondering how far I should be able to drop the valve before it hits the block to be on the safe side. I have one at 0.48 inch and another at 0,52 inch. This is with no head gasket fitted. Also can anyone confirm what the valve lift should be with standard rockers and a Piper HR270 cam?
Steve Church

Steve, if the cam is on the bench, meaure the long side of the lobe and the short side. Difference is cam lift. nswer x 1.4 is valve lift.
If cam is in the car and Piper don't say, use a dial indicator on the pushrod.
Art Pearse

Steve-
Valve lift with a Piper BP270 camshaft and OE 1.426:1 ratio rocker arms should be .405". If you have a cylinder head casting with the earlier 43cc combustion chamber, presuming an Original Equipment combustion chamber height position of .425”, the required valve counter bore is .0425" (1.0795mm). If you have a cylinder head casting with the later 39cc combustion chamber, presuming an Original Equipment combustion chamber height position of .375”, the required valve counter bore is .0925" (2.3495mm).
Stephen Strange

And, (cannot find where) but someone had a lovely write up with fotos of how to very accurately and carefully "mill' these cut outs. They used a router with a stone, made a jig, and thus carefully, bit at a time took material off, marvellous. I will try and find the link. Mike
J.M. Doust

I've filed out the cylinder top as documented on Peter Burgess website but am still not confident that I have taken enough out. How much meat is there in the block at this point?
Steve Church

Hi Steve

Valve lift approx 0.397" or 10mm
valve to head face should be approx 8 mm.
head gasket compressed approx 0.75 mm
as long as your cutouts are approx 3.5 mm deep you will be ok. Dont forget to slacken the rocker adjusting screws right off so you dont coil bind on fitment of head.
On a +60 the ex valves only just hit the block if not relieved so you do not need tons of clearance.

The top ring is what prevents one going too deep! Expose the top ring and it will snap in use.

Peter
Peter Burgess Tuning

This thread was discussed between 04/02/2012 and 06/02/2012

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