Rocker geometry.

Dixie6789 · Post by **Dixie6789** » Thu Mar 20, 2014 4:44 pm

I have installed a "stump Puller" CAM with 11.9mm lift into my 4.6.

Would you guys suggest taking some material off of the rocker pedistals so that I can improve the geometry? Roller rockers are just too expensive.

I will be using adjustable rods so the pre-load on the lifters wont be a issue.

As per instructed by Realsteel I have had the heads machined to fit double springs and installed shortened bullet guides. At the time I didnt really read up on the geometry. Didnt want to do the bases on the heads due to a built in angle, seemed easier to do the pedistals.

thanks Mark.

crayefish · Post by **crayefish** » Thu Mar 20, 2014 5:41 pm

What would you expect to gain from this? Perhaps if you have exhausted (excuse the pun) every other performance mod and are looking for those last few hp from your race engine, but otherwise seems like a lot of effort for very little gain.

But then again, who am I to stifle creativity?

Dixie6789 · Post by **Dixie6789** » Thu Mar 20, 2014 5:55 pm

It's nothing to do with gaining BHP, it's about getting the best reliability out of the motor.

If the Geometry isn't good, it can put side loads on the valves which wear the guides quickly, and puts un-necessary strain on all the valve gear.

1.5mm taken off the pedestals will make the rocker arm work centrally over the valve top and reduce stress.

However, this mainly for very high lifts, so I was asking what others have done with a mild high lift CAM such as a stump puller at 11.9mm.

Ta Mark

crayefish · Post by **crayefish** » Thu Mar 20, 2014 6:12 pm

Ah gotya. Thought you were trying to get a tiny bit more valve lift by modifying the geometry or something

Dixie6789 · Post by **Dixie6789** » Thu Mar 20, 2014 6:15 pm

Just don't want to get too anal and do stuff that isn't really required for a road car. Sometimes you can get carried away, when keeping it simple can be better.

However, that doesn't include shiney things, they are allowed!!

ChrisJC · Post by **ChrisJC** » Thu Mar 20, 2014 6:32 pm

If you alter the pedestals, will you also need to alter the pushrods?

Chris.

Dixie6789 · Post by **Dixie6789** » Thu Mar 20, 2014 6:35 pm

Thanks Chris.

I have adjustable push rods. So should be easy.

Did you skim your pedestals?

Mark

cammmy · Post by **cammmy** » Thu Mar 20, 2014 7:29 pm

Got Des Hammill's book here mate. He says remove 1.5mm from the pillar or boss for 11.90mm of lift

ChrisJC · Post by **ChrisJC** » Thu Mar 20, 2014 8:58 pm

At one time I shimmed the pedestals because I'd skimmed about 2mm from the heads!, but no, all my engines currently are on standard pedestals and pushrods. But then my cams are Piper 270 (in the Landie), and H180 in the Rangie.

Chris.

kiwicar · Post by **kiwicar** » Fri Mar 21, 2014 9:07 am

Hi
I would do it if it makes you happy, on a cam with that little lift it is really not worththe bother for any performaance or wear reason but it will also do no harm especiallly if you have the machinery to do it yourself. If you are going to have to pay someone to do the work then I wouldn't bother and put the money into the building society and save up for roller rockers. The other way to sort out the geomitry here is to buy a set of lash caps. Personally I would also just use the adjustable push rods to measure the correct length and buy some pushrods that are the right length and stick the adjustable ones on ebay.
Best regards
Mike

Dixie6789 · Post by **Dixie6789** » Sat Mar 22, 2014 9:32 pm

what are lash caps?

While the head was at the machine shop being skimmed, my man took 1.5mm off the bases for no additional cost.

M

kiwicar · Post by **kiwicar** » Sun Mar 23, 2014 6:52 am

Hi
lash caps go on top of the valve under the rocker, they come in various thicknesses, used on some ohc engines to set valve clearance but in this case they will alter the geometry by extending the effective length of the valve.
best regards
Mike

topcatcustom · Post by **topcatcustom** » Sun Mar 23, 2014 9:25 am

Mike I don't think there is really a sufficient amount of valve stem above the collects on a Rover V8 for lash caps, but I may be mistaken.