Main Motorcycle: '08 Sprint ST
Join Date: Nov 2009
Location: Sydney, Australia
Other Motorcycle: '06 Daytona 955i
Extra Motorcycle: Husqvarna Terra 650
I don't think the head work made the most HP difference. I suspect it was the TB and exhaust matching work, reinforced by the dyno session. The headwork, as it turned out, was a good idea despite the bike performing very well. I had overheated the bike and it seemed at least a couple of the exhaust valves were not seating correctly.
My advice was that the re-seating of all the valves using a CNC 3-way grind would give a great result in terms of the torque and rideability of the bike, so I guess torque more than anything. Mention was also made of long term reliabilty and fuel efficiency. It was also a chance to inspect all the valves and seals, a couple of which (seals) had to be replaced. I took the opportunity to do some DIY port work. I cleaned up as much of the poor casting marks as I could, and some of it on the exhaust side was pretty bad. I've already mentioned the intake throats but I guess that's mass production for you.
The work was done by a specialist cylinder head guy here in Sydney so I guess that's irrelevent to you. The machining, including refacing the head was about $350 and my mechanic charged me about $400 to strip and reassemble the head and re-shim everytyhing. I did, however, have to re-shim again slightly after torquing the head back on the motor so would probably save the shimming until the end. Just make sure to measure all the shims with a micrometer to check them and have quite a few spare sizes on hand. I made up an excel spreadsheet which really helped me figure out what shims I had and what I needed. Often you can shuffle them around limiting what you have to buy/swap for this job. I'm happy to share it with anyone who wants it just PM me.
I got to have a good look at both the top end and bottom end of the engine. The top end looked brand new. The bottom, ie the crankshaft bearing shells had some minor wear marks but certainly nothing to worry about. I'm expecting this engine will last a long time with reasonablr care. I was advised to try to ascertain which bearings were in there should I ever need to replace them but there were no discerning marks on them at all so I'm not sure how the process would work if you ever needed to order replacements from Triumph.
I know I could probably have thrown all that money at a new bike but I love this bike. It fits me, I love the way it goes, handles, sounds. I now have the bike I love optimized to be as good as it can be. And if I wore it out, I'd re-build it or do it to another one. I now have so much familiarity with these bikes, including the special tools so, I guess, I'm invested. I think it's a good way to be.