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Last week was the first time I took the Scott out on the road after a long rebuild (three years) I was a dream to ride ( the first time I had been on a Scott) well worth the all the time. everything worked fine except for a couple of small items. On returning back at base I noticed one of the plugs had a small amount of oil around it. I removed the plug, thread looked OK screwed the plug in finger tight then applied the spanner, this is where things went wrong. It just keep turning, stripped thread. No panic I had long since given up deadlines, so I drained the systen down, removed the radiator (thanks John no leaks) released the head bolts but head would not lift past the frame. Again no problem doubled nuts on the studs and unscrewed all the studs (well greased & new they came out easly) removed the head all I need now is to get the thread heli-coiled 18mm x 1.5 pitch.
The good news was just over a year ago I purchased a secondhand head from Gill (god bless the spares scheme) at the annual rally. Imagine my surprise when before griving the new head a good clean up I thought I should offer it up to the bike to check it fits (cause it will they are all the same) OH NO THEY ARE NOT. this one had smaller compression domes in the head about 68 mm diameter not 74mm as my head has, when the bike was turned over the piston lifted the head. Is this off a smaller CC short stroke? Well I was not going to be beaten so I re-machined the chambers to the same profile as the old one, wall thickness to water ways ended up the same as the original so I can only assume the same casting is used (apart from minor differences). Now all I have to do is make or buy new tubes as the old ones were craked or damaged. Does any one have 1″ x 26 tpi tap or die that they could loan me? The Die is not too important as I can screw cut the tube but I do need a tap to clean out the head threads. Can anyone tell me what is used to seal the threads of the tubes if anything. Any tips or tricks greatly appreciated.
Hi Keith. You must have bought a 498cc head I suppose but no matter if you have been able to machine it to 596 combustion chamber size. Could you please check on that hose spigot thread pitch again as I think it should be 20tpi and not 26tpi. If it is 20tpi I can lend you a 1″x20tpi tap if you pay the postage. Phone me to discuss. [number in front cover of Yowl] Regards. Brian.
Glad you got the Scott going at last and enjoyed the first ride out. As far as the threads on the cylinder head tubes goes I have made some previously and found that they were an awkward size being 1″ by 24tpi.
If I can be of any help please email direct.
Thank you for your reply, I have since re-checked the thread under a microscope after recieving Jon’s reply & he is right, it is 1″ x 24 TPI. It is the same thread as used on bicycle head sets, now all I have to do is find where I can get hold of a tap from. If I manage to get one I will make it available to members if required as I can’t be the only one that has come across this problem. I am also purchasing some brass tube to screw cut the thread on, so if there is anyone out there that needs some tubes let me know as while the machine is set it’s just as easy to make some extra’s.
Hi again. I have been out to the playroom again, and checked four cylinder heads and blind head water-domes. All are threaded 1″x20tpi, repeat 20tpi. All I can think of is that SOME but by no means all are 24tpi like yours and it is worth noting that cycle threads above about half an inch diameter do become erratic in pitch listings, with 20,24,and 26tpi being alternatives, so carefull checking is obviously necessary before attempting to screw in a new hose spigot. Regards. Brian.