Maybe I didn't explain what I meant very well. After thinking about it last night, the first little movie of the valve train with valve bounce, the guys said that they can cure the valve bounce with a heavier spring. If you went through a few springs that could be made to work. What is staring you in the face is that the spring only went into a vibration frequency at 6200 rpm, after that it worked fine. It would be a safe bet that the spring would continue working well untill the next vibration frequency. It might be 1 1/2 or twice the speed it would do exactly the same thing. Whatever it was, it would not take long to figure out a simple mathematical formula to predict exactly what rpm it would do it next. The trick with revs is to have a spring that is not going to have a speed where it will stop working and start dancing. if your after revs, higher spring pressure is not always the answer.

All I could think of is that sportsters have a similar pushrod system and some of the parts might swap as I think they get a few more revs than the twin cam, but don't know as I don't know anyone with one to check bits or revs with, never owned one. If I was wanting more revs out of my twinky (which I don't because of the huge costs involved), would be spending a few hours in a Buell parts catalogue or S&S buell parts or someone else who specialises in high performance Sportsters to see what bits or ideas could be borrowed from them for the valve train. Maybe spend a few hours reading at the NHRS website taking note of what they do, bound to be others out there who race their sportsters at the track or the drags.

Its off topic but I can't stop thinking that all that crankcase pressure from two big pistons coming down at once pressurising a tiny crankcase, robbing power from the engine could be put to good use if it was turned into a two stroke, they're not my thing but am sure it would work a treat. If it could be made to work it would make some serious power, the rest of the drive train and the bike wouldn't be able to cope with it.

Better get back to work or will still be here at 11 tonight again.

I could be completely wrong and your welcome to think that way, but I would be following the instructions.

The amount of expansion that the motor has as it gets hot is not simple. The top of the cylinder would be hot, the bottom would be closer to the oil temperature, the cases would be close to the oil temperature. The head would be hot but so would the whole valve train to the oil temperature, so every thing is expanding but only by the metals coefficient of expansion times by the difference in temperature + or -. The coefficients are tiny numbers and depend on the individual metal type. The exhaust valve would be one of the hottest bits and expand the most, reducing the clearance, not increasing it. Thinking that the whole valve train stays cool but only the cylinder expands would not be a good idea to follow when setting the lifter clearance. There are a lot of different pieces of different metal types between the cam and the valve going through the motor, or going through the valve train. Two different paths of expansion and not short paths either with the valve and seat at the far end on this vintage Harley system in an air cooled motor. The guys at S&S would have been through all this stuff until they were sick of it. By all means set your lifters how you want but I won't be doing it that way. If the threads are 32/inch, if 6 flats is one thread rotation the lifter will have 0.794 mm clearance, it might need that much space to work properly and do what its supposed to right through the rev range. If it doesn't collapse (and mine hasn't so far) then maybe everything is working as it should and how it was designed to. A lazy lifter will still get you home. Not seen a dyno graph or anything else proving its even worth reducing the clearance. Do what you want with your own motor. Nobody has even come close to convincing me that its worth doing, if anything I probably won't bother even putting the limiters in mine. They seem like a backup device in case a lifter gets lazy and isn't functioning properly.

My 2 cents, I'm done, back to work.

hi , name dyno , i have been building engines for these bikes for 6 years , i have  2 dynos , i spend a lot of time makeing changes to engine builds my own as test  benchs  , and re running them few hrs latter checking for percentages of improvement or losses or nill change , i have spent weeks playing with lifters depths , travel limiters ,settings  etc ,  hydraulic lifters are there for smooth running and reliability  at normal operating temps and  rpms , i have asked questions to manufactures about , what oil presure do they need to operate at ,what is best oil viscosity at 180 temp range  then if i increase  lift , what lobe profile what spring presures are they designed to handle , i dont get a answere , i did experiment at drag strip , set push rods to middle of plunger depth in lifter , ran bike at strip and it ran 11.20 down quater mile , reset lifters to 1/4 turn of bottom and bike ran 10.83  20 mins latter , i all ways adjust lifter to over bottom depth to let lifter  bleed out quickly while oil warm , then reset just of bottom , i have been doing this for years , hydraulic lifters set in centre will bleed down while rpm s 5500  thru each gear eventualy will bleed down causeing loses of cam lift and duration , hence , poor performance at end of strip , dureing normal rideing they will not exibit this ,i have found the s/s with limiters cover my needs best , engines do grow , alloy has growth rate 2.5 times of steel at same temp but the cast sleeve has almost minimal growth at  say same temps , it is a dead metal , i do work in metal trades , used to haveing materials heat treated , case hardened etc , the en series of alloy steels to 4140 h/t for shafts etc ,  engines i have been involved with for long time , but last 6 years doing my testing on my own bikes ,  you refer to that you havent seen a dyno graph show that it is worth doing , i have  imfo on that when doing all gears runs under load to show losses after 7 seconds of running , on normal dynjet 250 , a 100 rwhp bike may take in 4 th gear 6.5 secs to run , what the run wont show you is that sustained high rpm ,they will bleed down , then what you wont here is the damage of excess clearance will do or allow lifter to pump up and maybe piston touch valve , recently i have few bad manufatured lifters in sets , , my own car eng builds for performance aplications are solid roller for accurate constant control , any way , there are setting for general use of rideing , and if chaseing bit more , then these are some options to help keep gains ,these are things that i have found in this area ,  cheers guys

Thanks for the info Dyno, cheers