Shimming Valve Springs

[Anonymous]

The next time I have the head off my bike, I am thinking it might be worthwhile to shim the springs for a bit more seat pressure and float resistance. If I wanted to do it, how much should I shim them and what do I use for the shims?

Thanks,
Mark

 

[Paul]

Mark, you have to measure the spring pressure when it is held in place by the spring caps. (ie when it is fitted in the head).
Also measure the gaps between the coils when the spring is at full travel (when cam has fully depressed the valve).
Then find out what the figures should be for your particular setup of cams & springs.
Then fit shims under the lower valve spring holder to bring the figures within your operating tolerances.
You need a spring pressure gauge/tool, feeler gauges & a vernier to measure the free/closed length of the springs.
Sorry if I've made it sound complicated it is easier than it sounds, but it is time consuming as you have to do each spring individually.
Personally I don't think it is worth it for a road bike.

 

[SqDancerLynn1]

Spring seat pressures are critical Could cause premature wear on the cams & followers

 

[massakins]

I used valve spring shims from my local auto part supply house (i.e. NAPA, etc.). But I agree with the others, I doubt you need it on the street.

And remember the higher the spring and friction loads in the motor, the less power that is available at the rear wheel. And the harder the load on the starter!

High lift cams require heavier springs at high RPMs, but not at lower ones. Probably more cases of motors that are oversprung than undersprung.

 

[Anonymous]

Hi Mark:

Read all the posts - they are reasonable. HOWEVER,

I worked with a guy that won the NHRA in 1988 - name Rick Stetson. Owned a machine shop in Framingham Mass called Harrys Machined Parts. After he won the NRHA title - all the street racers from NYC wanted him to build their $leeper$.

OK - Rick did my head work - less the blending and glass beading that I did. Rick said that

"Suzukis in general were sprung a little soft. On my 750 - 16 valve TSCC engine, he used 0.020" copper shims. I was also running a GS1100 intake cam with higher lift and duration than the stock cam. No coil bind or excess seat pressure. I know you have an 1100 engine so may be different.

Particularly pay attention to his comment "GS's sprung soft.....etc...." I had had "cupping" on the valve seats before his regrind and shim. I ran the bike the same amount of miles as the original rebuild, pulled the head off, and the valve seats STILL looked brand new. Valve float kills a seat quicker than a little extra pressure.

Anyhow - good luck. - Dieter