Preloading Valves
- Thread starter hotrod92
- Start date
Pk in oregon
Member
Why? And how much?
No way I’d go .010.
Is there a mounting bracket for it that a guy can buy?
Flattop1 probably meant .0005 - .001 but, i'll say one thing.....we were at a race down by Arkansas last summer that, the smell of Ether was in the air so strong, about made me pass out!
. Ether my favorite no start 
1fasttiller
Member
They have almost no compression when cold but get them nice and warm and they seal up nicely 
Big Chris
Member
Remember fellas, we are not doing this to gain valve lift. We are doing this to control the "noise/rattle/resonance" in the valve train. The net result for those of you without dynos is that the amount the HP falls off as the engine gets hot, 2nd, 3rd, and even 4th pull is less than if the valve lash was bigger. If you set it just right you wont lose any power as you build engine temp. Those of you with dynos can "see" this phenomenon and easily test for it. Test the same engine back to back. Set the valve lash to .003-.004" make 3 pulls. Set the valve lash to .001 - .002" when the head is HOT ( >375°F). When the engine cools, the valve will go into a preload condition. Start both series of dyno pulls at the same starting temp. Change nothing else and observe the results.
If you are chasing the 238/242 lift rules, you aren't even in the right zip code.
My guess after all these years, is the power losses are not from a a diminishing valve lift but rather increasing noise, harmonics, bounce and float that occurs as valve lash grows. The slight pre-load on the valve spring suppresses the tendency of the valve train to "chatter" reducing bounce at valve closing. In short, the tight lash clearance grows into a "hot" clearance of .001-.002". This simply does a better job of controlling float & harmonics at high rpm than an engine that has .005" or more "hot" clearance.
Harmonics man, harmonics.
You can argue with me, or you can test it for yourself. And there is a balance, and without a dyno you are simply guessing. Too much preload and on the intake, and you create all kinds of problems with interrupting the intake charge. Too much preload on the exhaust and you lose cylinder pressure. Both result in a loss of HP. I tried setting up with a "measured" preload, but experience shows the best way to do this is to make an adjustment and test on the dyno.
Go to this thread, and start reading around post #43, much development went into this. This was 5 years ago and lead to a valve train / spring setup that kicks ass.
https://4cycle.com/karting/threads/take-a-guess-how-much-hp-gain-with-illegal-springs.54338/page-3
That's my $.02
If you are chasing the 238/242 lift rules, you aren't even in the right zip code.
My guess after all these years, is the power losses are not from a a diminishing valve lift but rather increasing noise, harmonics, bounce and float that occurs as valve lash grows. The slight pre-load on the valve spring suppresses the tendency of the valve train to "chatter" reducing bounce at valve closing. In short, the tight lash clearance grows into a "hot" clearance of .001-.002". This simply does a better job of controlling float & harmonics at high rpm than an engine that has .005" or more "hot" clearance.
Harmonics man, harmonics.
You can argue with me, or you can test it for yourself. And there is a balance, and without a dyno you are simply guessing. Too much preload and on the intake, and you create all kinds of problems with interrupting the intake charge. Too much preload on the exhaust and you lose cylinder pressure. Both result in a loss of HP. I tried setting up with a "measured" preload, but experience shows the best way to do this is to make an adjustment and test on the dyno.
Go to this thread, and start reading around post #43, much development went into this. This was 5 years ago and lead to a valve train / spring setup that kicks ass.
https://4cycle.com/karting/threads/take-a-guess-how-much-hp-gain-with-illegal-springs.54338/page-3
That's my $.02