Valve Float

kurly154

New member
I have a modified clone. running isky .310 246 dur. cam and 1.3 rockers. Running just the outer spring from the green stripe dual spring kit. It started to float the valves turning 7700-7800 rpm. Do I need to put the inner spring back in to increase spring pressure to turn more rpm? what should the installed height be for these springs? All advice is welcome. Thanks.
 

mikey56

New member
valve float comes from the filters not maintaining contact with the cam lobes. increasing the spring pressure will help, but you might also look at your gearing. depending on the spring pressure from the green stripe outer, you may want to consider going to a heavier spring set. be sure and check your valve lash, the use of the ratio rockers and your gearing.....that will help!! also, you have already got the right spring height for the springs you have installed, the addition of the inner springs shouldn't change this.....
 

kurly154

New member
I played with the gearing all day. Everybody else was turning 8k plus. I could only turn 7800 and it would float. Had to keep dropping the rear gear. The inner springs for the dual springs look tighter wound and appeared to coil bind where just the outer spring doesn't coil bind. I had lash set where isky recommends at .005 cold. Looking to have a different head built for this motor. Looking at nr racing 14cc with 27 and 25mm valves ported and milled .050 with dual 55lb springs.
 
We run 33lbs springs on our open motor and its hard to keep it under 8000 rpm's, but we are running a NR-274 cam .
 

mikey56

New member
what i'm looking at running next year along the same lines as being discussed....looking to turn in the 8 grand area.... but, to cure your valve float, change the springs out to stiffer springs (like the 33's mentioned bove). your hitting the upper popwer band and anything after that is wasted....you need to get the valve train working....i'd start with a good set of 32 or higher valve springs, replace the keepers in case they had worn out, look at the heads of the valves to make sure they haven't mushroomed, check your pushrods for straightness and i'd even crack the block open and look at the cam and lifters to make sure they are wearing..

springs will wear out (no definitive time line or useage)....but they will wear out and get weaker from constantly turning above 5K....you could jsut be suffering from weak springs and that will cause valve float. spring pressure has to push against the rocker, which pushes agaisnt the pushrod and keeps the lifter face in constant contact with the cam lobe.
 

kurly154

New member
This motor has 4 races on it since it was built. What is the spring pressure of just the outer spring from the green stripe dual? Can the valve stems mushroom even if using lash caps? I didn't think they would. Everything in this motor has 4 races on it. Oil changed every time it comes off the track with fhs62r oil.
 

mikey56

New member
nto with lash caps....but the springs i'll have to check on. oil changing is good, but not the cause of valve float....
 

Flash06

New member
You need more spring pressure with that much lift, also make sure when you are done running the engine, after you purge it you need to turn the motor to tdc to relieve some pressure from the springs before storing if for the next race. I run the dual green stripe with the 315/260 with 1.2's and have no problems with valve float or anything anywhere close to wear and tear from too much spring pressure. I have actually run 60lb duals in a motor and never had an issue with too much spring pressure, it's just good insurance IMO.
 

SMALL ENGINE CAMS

New member
Hi kurly154,
Thanks for running my cam! I would recommend using both the outer and inner spring and an installed height of .950" for your setup. You should be able to turn well past 8500 rpm.
Tim
 

kurly154

New member
Correct me if I'm wrong. The lighter the valve train the higher you can rev before valve float. Correct? I ask this because I'm using ss valves, aluminum retainers, raceseng s1 billet rockers and chrome moly pushrods.
 

kurly154

New member
Thanks for all the advice. Looks like I'm going to tear it down and recheck my installed height with the inner springs back in. Should I go ahead and get a new set of springs since I've ran the outer by them self?
 
Its a lot harder with 1.3 rockers. I bet you could run 1 to1 ratio and be ok. I tried a 1.3 on my S/A and it floated a little over 8000, with stock rockers it will go 9200..and the 1.3 didn't really help it, so I just went back to the stock ones..
 

PD Power

New member
If the outer spring does not bind...but the inner does bind....then reduce the height of the guide which the inner spring sits on.
Put the inner back in, and voila...this SHOULD clear the valve float.
 

RadialFin

New member
Did you lose time when you dropped the rear gear?
 

kurly154

New member
I'm going to listen to Tim. But this cam and springs were designed to work with 1:1 rockers right Tim? Also what can I use to cut down the guide where the inner spring sits?
Radialfin I'm not sure if my time dropped. They were pulling me out of the corners but I could catch them by the end of the straight.
 
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