rocker geometry

Seight-V8 · Post by **Seight-V8** » Wed Jan 28, 2009 8:59 pm

hello all,

So i've been checking the rocker geometry.

As suggested i got some micrometer blue on each rocker face then, with a dial gauge dropped each valve by the valve lift my camshaft gives (12.11mm)

I recon that the rockers are about 0.5mm out from one side to the other.

So i am looking at about 0.25mm to move the rockers for them to be in the middle of the valve stem face.

Is this worth doing, as its looks as if i will need to remove some metal from the pillars to correct this.

cheers

scott

sidecar · Post by **sidecar** » Wed Jan 28, 2009 9:26 pm

Seight-V8 wrote:hello all,

So i've been checking the rocker geometry.

As suggested i got some micrometer blue on each rocker face then, with a dial gauge dropped each valve by the valve lift my camshaft gives (12.11mm)

I recon that the rockers are about 0.5mm out from one side to the other.

So i am looking at about 0.25mm to move the rockers for them to be in the middle of the valve stem face.

Is this worth doing, as its looks as if i will need to remove some metal from the pillars to correct this.

cheers

scott

I may have got the wrong end of the stick here but it sounds like you are trying the move the pedestals either nearer or further wasy from the springs and valves. This is not possible, you can only raise or lower the pedestals. lowering the pedestals about 1.5mm or 60" will help bring the max lift contact line more towards the middle of the valve stem.

You really should buy Des Hammills book, its all in there!

HTH,

Pete

CastleMGBV8 · Post by **CastleMGBV8** » Wed Jan 28, 2009 11:16 pm

But if you have the pillars machined, dont forget to have the oilways in the base of the end pillars re-machined as these will be lost when the bases are machined by 60 thou.

Kevin.

ppyvabw · Post by **ppyvabw** » Wed Jan 28, 2009 11:44 pm

Because I'm only an amatuer I have no idea what you're trying to do. I think what castle is trying to say, if you machine the pedastals you change the relationship between the oil ways in the rockers and in the heads because oil ways in the heads aren't square with the surface of the rocker pedastals things in the heads? Is that right?

CastleMGBV8 · Post by **CastleMGBV8** » Thu Jan 29, 2009 9:41 am

Adam,

If you look at the bottom of a standard rocker pillar there is a recess that allows the oil to feed from the oilway in the head up the pillar to the rocker shafts.

When you have 60 thou machined off the bottom of the pillars that recess all but disappears and you need to have it machined out to regain the proper oil feed to the valve gear.

This need to be done on the at least the two front pillars on each shaft or both ends as I did so if the rocker gear is switched from one head to the other you will still have an oil feed. My local machine shop did it for £30.00

Kevin.

kiwicar · Post by **kiwicar** » Thu Jan 29, 2009 10:52 am

I've said it before. . .

if you machine the bottom off the pillars to correct the geomitry you then need to use ajustable or custom length push rods to correct the preload, it is far simpler to put a set of lash caps on the valves of the right thickness to sort out the geomitry 80 thou or so should do it, with roller rockers this is a good thing anyway and use shims under the pedistals to set the preload and do a fine tune on the geomitry.
Again I've said it before but Mr Des Hemmill is only one source, there are many other authors who have written on rebuilding V8s and on how to tune them. I would strongly recomend reading as much as you can about rebuilding as many different V8s as possable. Mr Hemmell has many good ideas but tends to reach for the fully equiped CNC machine shop before exploring simpler cheeper solutions that will work as well.
Particullaly, if you are interested in the rover read about the Mopar small block (look at how they tackle the valve train in that engine), the Chevy small block and the Buick V6. All V8s are different but all are variations on a theme you can learn alot from the huge number of hours spent tuning these other engines.

Mike

sidecar · Post by **sidecar** » Thu Jan 29, 2009 10:52 am

ppyvabw wrote:Because I'm only an amatuer I have no idea what you're trying to do.

Not sure if you don't understand why the rocker shafts need lowering, I'll assume that is what you mean.

The shafts need to be lowered when a high lift cam is fitted in order to reduce the fact that the rockers start to sweep back on themselves. This sweeping motion pulls the tip of the valve creating side loads which wears out the valve guide. That's it in a simplified nut shell!

Pete

CastleMGBV8 · Post by **CastleMGBV8** » Thu Jan 29, 2009 11:16 am

Mike,

Just information.

I looked into the possibility of using lash caps on a Rover and got Real steel to check it out for me, unfortunately there is insufficient valve stem height above the spring caps to allow proper seating of lash caps, so had to go the machining route.

I think from memory that the lash caps required 20-30 thou more than was available with the rover valves, which is obviously different to the Chevy situation.

Also agreed that the pushrod length will need looking at but Scotts heads have had quite a bit machined off so it will all need a measure anyway once he's got the engine assembled. Think he was suggesting adjustables but they still may need shortening a little to give enough adjustment.

Kevin.

Seight-V8 · Post by **Seight-V8** » Sat Jan 31, 2009 3:17 pm

thanks for everyone help.

I understand now about adjusting the rocker shaft pillar heights, if i need to do it.

I was just wondering is it possible to work out, if you remove say 0.25mm from a rocker pedastal....how much this alters the rocker pad on the valve stem.

Not really sure that i need to remove material yet, but best to check first.

cheers

scott

mgbv8 · Post by **mgbv8** » Sat Jan 31, 2009 10:08 pm

You are trying to move the rockers "sideways" so the pads on the rockers sit central on the valve stem tips arent you?

Seight-V8 · Post by **Seight-V8** » Sun Feb 01, 2009 5:30 pm

hiya,

Yes i think i need to move the rocker arm position on the valve stem.

Think the only way to do this is raise or lower the rocker pillars.

I think i need to make it more central to keep the geometry right.

But i dont know how much to remove from the pillars, and how this will affect the rocker position on the stem.

Proberly got something to do with the 1.6 ratio and a calculation somewhere.

cheers

scott

mgbv8 · Post by **mgbv8** » Sun Feb 01, 2009 6:53 pm

So not sideways then. Are you saying that you have the valve stem tips moving off the inserts in the rocker arm tips then?

Seight-V8 · Post by **Seight-V8** » Mon Feb 02, 2009 6:18 pm

hiya,

yes i have the valve stem tips moving off the rocker tips.

I recon its only about 0.25mm....so just wondering if i can leave it.

or how much to remove from the pillar heights.

cheers

scott

CastleMGBV8 · Post by **CastleMGBV8** » Mon Feb 02, 2009 7:08 pm

How much lift on the cam?

Kevin.

Seight-V8 · Post by **Seight-V8** » Mon Feb 02, 2009 7:16 pm

hiya,

Its a piper 285 and info says 12.11mm lift.

cheers

scott

The V8 Owners Forum -

rocker geometry

rocker geometry

Re: rocker geometry