RH4 Head query

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Feb 14, 2004
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This might be a silly question but I have an 850 with an RH4 head and it has HP1 stamped next to both the left hand inlet rocker spindle cover and the right hand exhaust one. Is this standard?

I recently had it bored to +20 and had to have the valve pockets in the new pistons machined, appears that the head has been planed in the past.
Could it be HPI? There used to be a shop in California called HPI that did a lot of Norton work. Don't know if they still exist. Perhaps they milled the head and stamped it with their ID?? Has the bike been in New Zealand its whole life?
RH4 Head Quey

Thanks Ron, yes the bike was brought to NZ from the US about 1984. Have had another look at the stamp marks, the H and P are in upper case, the third figure is just a vertical line so could be an I.
Have had a surf for HPI. Only mention i can find is on INOA site under a description of a members bike. They were based in Stanton and are said to have made cams as well as doing porting, head planing etc for performance.

Does anybody have any info on the HPI cams - markings for identification etc - just in case there was more work done when mine had the head plane?
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