Hello again folks
I have 2 cylinder heads here - can you please help me identify them.
They came with a 650SS bottom end, but the vendor could not tell me if they were for an SS.
I am struggling to attach pictures due to allowable file size but they can be forwarded to an email address on request.
I would like to know what they are, and what various engines they might fit.
Generally:
Head 1 has barrel spigot recesses, 37.5mm inlet valves, 33mm exhaust valves, 30mm downdraught inlet ports with studs in the horizontal plane, 35mm exhaust ports.
No casting marks except a P and Y on the underside of the bottom fin.
Head 2 is the same except 42mm inlet valves and a much increased squish - no spigot recesses and the gasket mating face is much closer to the underside of the bottom fin. No casting lettering at-all.
They both have rocker oil feeds tapped into the side ribbing between the rockers plus they retain the top oil feed tapped holes.
I suspect they have been used for racing as they both have teeped lettering on them - one has "RH10" teeped above the offside ex. rocker cover, one has "BROWN" teeped neatly around the head-steady mounting hole,plus the absence of any casting i.d. marks.
They both look excellent save for one exhaust port thread.
All opinions welcomed, hopefully someone will make a positive identification. Let me know if you want some photos.
cheers
Bruce
The RH10 head is standard…
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Well RH10 is a marking use…
Well RH10 is a marking used on 850 Commando engines. The downdraught head supplied with 650cc and smaller Dominator engines had no squish in the chamber at all, and it also had some of it's hold-down bolts located closer to the centerline of the bores than 750 or later heads.
If you have a 500-650cc cylinder for a Dominator, a 750 or 850cc head will not bolt onto it because of the different locations of some of the bolts.
If you have two heads with a squish area in the area close to the intake valves, then it sounds like one head would be for an early 750 that had the cylinder spigots, and the other is for an 850 Commando.
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The RH10 head is standard 1974 Commando. The three holes in the top of the head are for the Commando head steady, which is why they relocated the rocker feed to the side of the head.
The following link has pictures and descriptions of several heavy twin heads with detailed descriptions that should help you determine the application for the other head.
http://atlanticgreen.com/nhth.htm
Attached to the document above is a supposed factory letter that explains all the Commando heads - RH1 through RH10 - with corresponding part numbers.
Good luck!
BillT