i got the fst high compression piston and cam installed. my mechanic says there is not enough space between the piston and valves. intake and exaust. it's properly timed. has anyone else had this problem? please help.

 

I'm not real sure about the Raptor, but I know some piston/high comp. head combo's require that the top of the piston be machines a bit to allow for the valves. I would call the manufactuer and ask them what's wrong.

 

Have your mechanic call FST.

 

i finally got up with mickey dunlap. he said the valve springs have shims that have to be removed. the mech. understood and everything is right in the universe once again.

 

Valve spring shims have nothing to do with the clearance between the piston and valve.

Removing the stock hardened steel shims from the spring pockets can and will cause two major problems. 1) Instant wear on the alum. spring cup 2) too weak of installed spring pressure.

Spring pressure should be no less than 50 pounds and no more than 63 pounds. Too much and the rockers fail too little and the valves bounce and float. Each spring is checked for the correct spring pressure and then shims are added to achieve that pressure on the installed valve. Valve clearance is determined after and it is a separate issue.

 

these are not stock springs. these are stronger springs from fst. this thing runs like a gelded ape now. i'll keep my fingers crossed. thanx.

 

Raptor720,

Have you had a chance to checkout the titanium valve springs for the Raptor offered by Alba?

Thanks.

 

DO NOT USE TI valve springs!!!!!!!!!!!!!

Ask ALBA to provide the useful life for the springs. You will discover that the springs will wear out in a matter of hours. They are used for drag racing only. Sure they are slightly lighter BUT, who cares. Go with TI valves if you must, lighten the rockers, go to a roller cam chain and alum gears, lighten the crank and balancer BUT don't go with TI springs. I will be really pissed if ALBA is telling people that the TI springs are the thing to have.

 

Raptor720,

I found out about the offering from Alba from their ads in Dirt Wheels under the Raptor upgrade section. I've read a few posts that the stock springs can be improved but I am not sure where to look for replacements.

Checkout their ad to see for yourself.

 

I could not find a good spring set from any supplier. After dealing with the problem on the 400ex and the need to hard face the rockers, I did not want to face the same problem with the Raptor.

I tested many springs and found that the stock springs at the installed height provide 32-35 pounds of seat pressure. That is too little for any application -- the valves will float and/or bounce. On the other hand, the "performance" springs produce over 60 pounds of seat pressure -- way too much for a number of reasons. 1. Can cause the valve stem to break 2. can cause the rocker to gall or the cam to gall 3. wastes potential hp 4. is just the wrong thing to do

The best installed spring pressure is 50-55 pounds. Depending on the cam lift, the full lift pressure must also be considered. What I did was have a spring manufacturer make a set of springs. If you are interested, let me know what cam you are using and I will (e-mail) you with info on how to order the correct spring set.