16 replies to this topic

[supasamurai]

Hi guys. I just got a stage two kit. It came with a head and a set of roller rockers and a set of spacers for the rocker pillars. They fit in between the pillars and the head (I'm pretty sure). My question is, how do I know if I need the spacers? There are two things I could see needing the spacers for. One, maybe the valves are opening so wide that they are actually hitting the tops of the pistons? Or two, maybe the springs (that came mounted on the head already), are getting too crushed when they are fully squished? How can I tell if the pistons are actually getting hit? If I put this thing together, and figure that I do indeed need to use the spacers, is my brand new head gasket ruined? I'm in the US and if I need a head gasket, I have to pay lots of money to get it overnighted to me. If there was a way to figure out whether or not I needed them without wasting a head gasket, that would be boss.


Thanks!

[cradley-heathen]

i must admit im not exactly sure how you work out if you need them and what thickness, but its about getting the correct lift etc i believe, not about valves hitting pistons etc.

i think the valve lift and effectively the ratio itself can be affected by these spacers, get it wrong and the benefits are lost.

(as i say im not entirely sure on all this so im waiting to see what replies you get as i want to kow myself!)

[Guess-Works.com]

Basically, if you've had loads skimmed off the bottom of the head, then the position of the push rod in relation to the surface of the head will change by the amount skimmed..

So you need to raise the rockers ( or use shorter custom pushrods ) to offset the height difference.... otherwise you may find you run out of adjustment on screws, or the roller tips may actually come off the top of the valve on full compression.

[Pigeonto]

its quite a science actually but they wont affect the valve lift amount. Des Hammill details it very well in his A series tuning book which unlike alot of them you can actually see online. Lots to learn!! but its worth getting the geometry right.

[Wil_h]

The spacers will not affect the valve opening that much, but getting them the right height will optimise lift.

If you think about it you'll get more valve opening with the rocker moving through the horizontal, rather than above or below that point.

So not like this
http://www.britishca...of P1010496.JPG

But like this
http://www.britishca...of P1010530.JPG

IMO the spacers should only be needed if you have very long valve stems or massively recessed valves. If it was supplied as a kit I'd have thought that the supplier should be able to tell you whether you need them or not. I presume that they know what valves they have fitted etc.

Edited by Wil_h, 11 November 2011 - 09:28 AM.

[Guess-Works.com]

can't see the piccies Will...

[Wil_h]

I've edited so the links should work no.

by the way, I've never agreed with adjusting the rocker geometry owing to head or block skimming. I'f there is not enough adjustment in the rockers then you should get the appropriate length pushrods.

[Ethel]

Not this
http://www.google.co...=1t:429,r:0,s:0

like this
http://www.google.co...=1t:429,r:0,s:0


I'd say the rocker should really be "level" half way through the valve travel to get maximum lift with minimum side
load.

What's the other spline nut (not the S big end one) been pinched off do you reckon?

[Wil_h]

I agree, makes sense that the maximum lift will be gained with the rocker level at mid stroke. But will this make the most power? I think that there is an argument that having it level when closed, opens the valve more at the start of the opening.

You'd need to sit down and work it out, but I'm sure someone already has.

[Cooperman]

Skimming just a few thou off the head won't make much difference in rocker geometry terms, but with a very high lift cam and higher ratio rockers it can be a geometry issue.
It's best to get the rocker shaft horizontal at about 10% to 20% into the lift opening. The lift is unaltered as is the total amount of opening, and the power difference won't really be noticed. it's really about leverage loading.
With, say, a 12G295 head on a 998 it could be that the head has to be skimmed a lot, say 0.080". In that case rocker pillar spacers could well be needed.
Best thing is to do a trial build with an old head gasket and see what it all looks like when assembled. If you ae not changing the cam at this point it's highly unlikely that you'll need roacker shaft spacers.

[supasamurai]

Best thing is to do a trial build with an old head gasket and see what it all looks like when assembled. If you ae not changing the cam at this point it's highly unlikely that you'll need roacker shaft spacers.

I've still got the stock cam installed. So my plan is to put it together with out the spacers. Then I'll set my tappets and see how everything measures out?

[Cooperman]

If you do that it should be fine.

[twrminisport]

Skimming just a few thou off the head won't make much difference in rocker geometry terms, but with a very high lift cam and higher ratio rockers it can be a geometry issue.
It's best to get the rocker shaft horizontal at about 10% to 20% into the lift opening. The lift is unaltered as is the total amount of opening, and the power difference won't really be noticed. it's really about leverage loading.
With, say, a 12G295 head on a 998 it could be that the head has to be skimmed a lot, say 0.080". In that case rocker pillar spacers could well be needed.
Best thing is to do a trial build with an old head gasket and see what it all looks like when assembled. If you ae not changing the cam at this point it's highly unlikely that you'll need roacker shaft spacers.

Peter is largely correct (yet again)
With a 998 engine i had the stock cam installed. Then i fitted a 12g295 cooper head and found that because of the amount it had been skimmed i could not fit my 1.3.1 roller rockers. THis occurred because i was unable to set the clearances because they were too tight and the con rods were fouling on the rocker arms.

You will soon find out if you NEED the spacers because you will not be able to set the clearances.
You will know if you COULD DO WITH the spacers by looking at the information above

Notice the difference

Jesus

[supasamurai]

I don't have a cooper head, it's a bog standard 998 head that's been reworked. It's the "stage 3" head from mini sport.

So would I have a problem if I fit the spacers when I don't actually need them?

[Ethel]

That's a very good point Will, chances are you have more than you need when it's at full lift anyway.