500 heads on a 650

[moley]

Hi Folks

What effect would 500 heads be on a 650 engine !!

I am helping a m8 rebuild his g12 and he has 500/600 heads on the motor.

Thanks

[Eric]

It would think it would make a significant increase to compression ratio, but what other effects including not causing something to crash into something without modification I don't know.

[petert120r]

500 heads wouldn't fit on 650 barrels - smaller bore. If you tried 600 heads on post '60 barrels you'd have problems with the top spigot - different OD. Are you sure someone hasn't fitted 500 or 600 matching heads and barrels and a 500/600 crankshaft into a G12 crankcase? Count the fins on the barrels. 650 = 8, 600 = 7, 500 = 6.Edited by - petert120r on 02 Apr 2010 4:08:37 PM

[Don Madden]

The original question concerned G12 but there were three different top end designs for the 650 top end.

1958 only used a longer stroke crankshaft in what is essentially a 600cc motor. This G12 used the 600cc 7 fin barrels & heads with a special piston that had the pin location higher to compensate for the longer stroke. The cylinder top spigot was 3in with recess in head to match. As in all 500cc/600cc the exhaust port is 1-1/2in. & the vertical spacing of the inlet manifold is also 1-1/2in.

The 1959 650 had a new barrel with 8 fins & the top spigot is 3in. The head resembles the earlier type but had a port size of 1-3/4in. & the vertical stud spacing is also 1-3/4in. The recess for the spigot is 3in to match the barrels. The piston resembles the 600cc but the pin location is different.

The 1960-up barrels are also 8 fin but the spigot is 3-1/16in OD. The heads have a recess to match & the exhaust port is 1-3/4in. The manifold studs are angled, not vertical orientation. The pistons are flat top, protuding into the combustion chamber, unlike the earlier "carbuncle" type & have a pin location differing from all previous types.

So there are three different types of barrels, heads, pistons & manifolds & I have no idea what is fitted to the engine in question but many of the mixed arrangements could lead to disaster. Drawings of the various piston types are available in Christian's Archives.

Cheers, Don.

[moley]

Thanks Don very good description of heads. Barrells are def 8 fins and are 3" spigot. vertical studs on manifold with 3" to match barrells..so all looks like 59 . To be honest i knew 59 was a one year only head but i recognise 650 heads as the diagonal studs and perhaps the extra fins underneath i think this is where i have got confused. The pistons are the early carbuncle type !! i have had the engine to bits today as it was very tight to turn. found that someone had not put the bearing race fully home and also you could not turnt he new cams by hand - so gently reamed the bushed..all fine cheers for help

[moley]

oopps number on manifold 025091 and heads 02507 ( might be missing one there) ta