have a 86 flhtc had new cylinders 10-1 pistons supposed to be 86 cubic inches when i run it up to 90-95 bending valves what can i do to stop bending valves-------HARLEY DAVIDSON
The other answers are on the right track, but are failing to include the other possibilities. You say you have had the heads done...WHO did the headwork? Were oversized valves installed? What valve springs are you running and were they packed for proper and even seat pressures for the cam lift? Were the valve seats cuts for new valves and if so, was proper valve stem height set? What cam are you running?...What is the TDC lift on that cam? Were ALL clearances checked when the engine was assembled?...Meaning valve-to-valve clearance during valve overlap, not enough clearance and the valves will hit each other...valve-to-piston clearance, this is where the cam's TDC lift specs come into play, if you don't have the proper clearance, the valves will hit the piston........MINIMUM of .060 clearance on both of these checks. What lifters and pushrods are you running?...stock lifters can pump-up at high rpm and lift the valve too much causing it to contact the piston or the other valve. Are you 100% postive you are adjusting the pushrods to their manufacturer's specs...different pushrods manufacturers use different thread pitches that require different adjustment lengths. As you can see, if the engine wasn't PROPERLY built and all clearances checked, you have a MAJOR job ahead of you, this require extensive knowledge and tooling. If you assembled the engine, take it to a reputable performance shop and let them check it out, if a shop did the work, FIND ANOTHER ONE!!! Building performance engines is not easy work and not for the novice.
I'm leaning toward the valve float or lifters pumping up idea. I wouldn't double up the head gaskets because you're asking for a leak, especially with your high compression. A good way to determine how much actual clearance you have between the piston and valve is to stick some soft modeling clay on top of the piston where the valves are, torque down the head, turn the engine over and take it apart. You will then be able to measure how thin the clay was flattened out to, giving you an idea of the clearance. If you seem to have plenty of clearance, then it may be valve float. If you've swapped out the cam, also compare the timing as well as the lift. The actual lift may not be a problem, but if it's opening sooner or later than stock, that may be when the valve and piston collide.
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sounds like the high compression pistons dont have enuf valve relief( 2 little depressions on the top of the piston to keep the piston from smacking the valve). youll have to change brand of pistons, with more valve relief, or lower the compression ratio. next time before you completely put the heads back on, do so with out the head gasket and turn engine over by hand to see if the valves and pistons collide. (no head nuts either) if they collide, you will see the head rise up on contact. this could also be the lift and duration of the cam you are using. specifically the duration. if the valve stays open too long the piston will smack the valve that way too also at high revs, if the valve springs are weak, will cause the valve to float causing the piston to smack the valve
The harle pretty well covered it but if i was you i would do a valve clearance check on the engine and turn it by hand and if you have resistance stop .. ok the way you do this is to take some sylicone and glue some solder to the top of the pistons where they are making contact and put the engine together and turn it over and mic the solder and that is your static valve clearance ..I like to have around .080 on mine and if you have that kind of clearance then yes you may be floating valves .. camshaft profile has a bearing on when this occurs and what springs you run and the head set up has to be right on .. sounds to me like a pretty mild evo though and if you used wiseco pistons they usually have enough relief that you don't have these problems .. i got one set up simular to yours that is a 84 evo and it runs like a raped ape for what it is and has for the last 26,000 miles and it has been turned over six grand too on rare occassions but not often..
