My port motor keeps breaking a valve spring. its happened 3 times this summer and its been the same cylinder each time. Ive had different mechanics look at when the spring gets changed and they can't find anything wrong. Anyone have any ideas what might be causing this. The motors were freshend about 120 hrs ago. They have a total of 450 hrs on them. The starboard motors runs fine. I have never broken a valve in that motor. Since new this is the 4th spring broken in the port motor. when freshen they told me they put everything back to stock except they did a 3 angle grind on the valves and some very mild head work. (not sure what that entailed). Hope someone can give me some ideas. Thanks.

Well I have trouble with lifters but I have not broken any springs. If everything checks OK I would be looking at what manufacturer of springs you have had installed. Harmonics to wierd thinks to springs. Hope it just picks up a miss and not tagging a piston with a valve.

Yea thats all that ever happend, just a miss developed. Theres never been an issue with a valve dropping and hitting a piston.

Is the installed height correct? Perhaps a valve with an incorrect keeper groove? Have you checked for spring bind on that particular valve?

Hi Todd, "mild head work" may mean that they may have done some bowl/pocket porting just underneath the valves to clean them up for a little better air flow which translates into more power---maybe 10-20hp.

I would for sure change the roller lifter on that one too. It could be contributing to the valve spring breakage due to harmonics induced by a weak or out of spec lifter.

Look at the valve guide very carefully. The BB Chevy has replaceable valve guides but sometimes the hole in the head isn't perfectly centered resulting in the replacement guide being offset.

A machinest will cut away the valve seat to match the offset valve guide so that the valve will seat. This may put a little side pressure on the spring if the spring pocket isn't also machined to be aligned with the new valve guide.

When Chevrolet builds the heads they install the valve guide without a hole and then machines the hole. The hole is not always perfectly centered in the valve guide when new.

Replacing the valve guides with an aftermarket guide that has a centered hole predrilled into the guide may leave the hole offset from the original location.

Sincerely
Dennis Moore

Mercury had a valve spring problem on the 1999 and earlier 500 hp motors. Racers changed to a comp cam spring. I think it was the inner spring that was failing.

I RAN 500 HP'S IN WILDTHING FOR 3 YEARS. I ONLY BROKE 1 SPRING IN OVER 200 HOURS PER YEAR. I WOULD CHANGE SPRINGS EVERY YEAR FOR INSURANCE. WE RAN STOCK HEADS WITH 140 LBS SEAT PRESSURE (VALVE CLOSED).I ALWAYS RUN HARD!!JUST TAKING ADVICE FROM EVERYONE THIS IS WHAT I DID AND IT WORKED. R.B.

Crane cam developed around 2000 or 2001 a new triple spring that should avoid harmful "harmonics" ( what ever the heck those are) They are for high life roller cams and I'm into my third season with mine - no problems yet.

I think the crane spring # is 99896 - 16. Call their tech line and tell them it is for a marine application.
904 258 6174

MAV