Hi All,
During the last couple of weeks I have been involved with an A10 "Rocket or RGS " replica
the chap who bought it recently asked me to try and solve a misfire!!!
(can you see this is going to be a long story??)
After going through all the usual and unusual things to no avail including compression testing changing mag and carb
I thought the compression pressure was kinda high I read 175psi on the kickstart, so I started the bike on the good cylinder and then checked the misfiring one, compression was erratic????
So I took off the head for a look see!!! the exhaust valve spring on the misfiring side had lost all its tension and was only barely closing the valve
On further examination I saw that it was fitted with an unmodified A7SS head!!!!
The pistons had been clouting the head around the edge of the combustion chamber!!
I decided after looking at the bores I had better lift the cylinder block for a look see
silicone goo instead of a base gasket obvoiusly hadn't helped
The cam/followers are in a sad state and the bores had been scored by the shrapnel flying about
Nothing for it now but a complete reconditioning of the engine
Most of you will know that the 650 alloy head uses different caps collets bottom collars etc than the rest of the range
I have a spare 650 head which is bare and would require a complete recon to use
All this adds up to a considerable sum on top of any labour costs and the top dollar price paid for the bike in the first place
I probably shouldnt say any more until the owner goes back to the seller with the photographic evidence and the estimate for the rebuild
To return to the original topic I would think from this that fitting an unmodified A7SS head to an A10 that has 7.5 or more comp pistons is not too good an idea!
Either modify the head to 650 spec (not cheap) or use flat topped pistons and the consequent poorer breathing of the 500 head with smaller valves
Regards
John O R