Valve Spring Shim Height

[MX Dave]

Hello,

In the next couple weekends ill be fitting some Genuine XR8 valve springs to my T.

Just curious if its really really necasarry to adjust shim height etc. alot of people have gotten away without changing seating heights.

and also alot of people say the heights need to be checked!

Im also still on the hunt for a member to loan me there atomic tool, Ill gladly pay you.

Thanks in advance guys,

Dave

[MX Dave]

Can anyone share there experience/s?

[riptide]

I can't tell you about your situation but I put BF valve springs in the cold side of my BA motor. I measured them before fitting and they were 3m/m longer than the BA ones and the same wire diameter so I guess they give more seating pressure. I made up a tool and replaced all the cold side springs with the cams in place. I still have the BA springs on the hot side and made 420rwkw on the dyno without any noticeable float. I didn't worry about shims because the lifters are hydraulic. Not sure if it's the right way to do it but it seems to go ok.

[johno]

What shims are you talking about?

[JVK]

Installed height relates to spring seat pressure.If you check the measurement between the spring seat and the bottom of the installed retainer with a inside mike and it is close to the reccomended

specs you should be ok .Some will flame me for my comment for sure but lots do it.Obviously perfect is best.

Sorry about the loan tool cant help you there.I know $500 is a big deposit to tie up but they have to make sure they grt their tool back,you cant blame them for that.

[JVK]

Shims are sometimes requierd to bring valvesprings up to the desired installed spring seat pressure for optimum function and performance.

[johno]

I know what shims do, but cant see what hydraulic lifters have to do with shimming the springs. The valve stem length is the same regardless of what shims etc are fitted. Only issue would be getting coil bind on max valve lift if the springs are too long, or shimmed up too much.

Or am I reading riptides comments all wrong?

My old motor has GT springs on it.

[riptide]

I think I see what you're getting at...the shimming would correctly tension the valve in the closed position, right?

Would you like to know the length of my BF springs or is there more to it than that? I could measure one tomorrow.

Edited 24/11/11 10:01 AM by riptide

[johno]

In the valve closed position, that gives you closed seat pressure of the spring. I think a lot of engine builders measure

spring tension at a certain valve lift as well.

Coil bind is the main thing to look for if installing larger/longer springs. If changing cam profiles(higher lift), this should be checked.

[riptide]

Hey johno, I see you're in Mt Gambier. I lived in the campground out past the Blue Lake for a few months in about 1990. Worked at Kruger Engineering

Edited 24/11/11 10:12 AM by riptide