Valve Preload AGAIN....sorry!

[Sidecarbod]

Hi Guys,

I've never been very happy with the valve preload on my RV8 as I used shims and found that it was impossible to set the valves up as accurate as I wanted to.

I am planning to buy a set of adjustable push rods from someone like Real Steel. (Unless anyone has a set for sale!)

My questions are:-

1. What is the advantage of going for the larger diameter rods baring in mind that the holes in the heads will need to be opened up.

2. I understand that the larger rods must be stronger but at what point are they needed?

3. Would it be true to say that the more clearance there is between the snap ring and rod seat plunger the sooner the valve will start to move off it seat as the cam follower starts to move? i.e. similar to running LESS clearance in normal tappet set up.


The reason that I would like to understand how the clearance effects the valves is that I would rather ensure that the valves are fully closed and this would mean running LESS snap ring clearance unlike a normal setup which would require setting up at the larger end of the specified range.

I was thinking of going for 40 thou, my motor runs V8 Development stageIII heads with whatever springs they use and a typhoon cam. I think that some of my valves are over 60 thou at the moment

Any help would be appreicated.

Pete

[mylesdw]

Originally Posted by Sidecarbod

Hi Guys,

I've never been very happy with the valve preload on my RV8 as I used shims and found that it was impossible to set the valves up as accurate as I wanted to.

I am planning to buy a set of adjustable push rods from someone like Real Steel. (Unless anyone has a set for sale!)

My questions are:-

1. What is the advantage of going for the larger diameter rods baring in mind that the holes in the heads will need to be opened up.

2. I understand that the larger rods must be stronger but at what point are they needed?

No advantage unless you are running very heavy valve springs and high revs. There is a disadvantage if they are heavier than standard because they add inertia which will cause standard springs to 'float' sooner.

Originally Posted by Sidecarbod

Hi Guys,

3. Would it be true to say that the more clearance there is between the snap ring and rod seat plunger the sooner the valve will start to move off it seat as the cam follower starts to move? i.e. similar to running LESS clearance in normal tappet set up.

The clearance makes NO difference to the timing. The only crucial thing is that there is enough preload to stop the plunger from hitting the snap ring; if it does this it will destroy the lifter quite quickly.

Originally Posted by Sidecarbod

Hi Guys,
The reason that I would like to understand how the clearance effects the valves is that I would rather ensure that the valves are fully closed and this would mean running LESS snap ring clearance unlike a normal setup which would require setting up at the larger end of the specified range.

I was thinking of going for 40 thou, my motor runs V8 Development stageIII heads with whatever springs they use and a typhoon cam. I think that some of my valves are over 60 thou at the moment

As above. The clearance is not at all critical for hydraulic lifters. They automatically adjust themselves to zero clearance every time they pass over the cam base circle; it is not the same as setting tappet clearances for solid lifters.

[demus]

Sorry to get slightly off the clearance subject but are these lifters servicable ??
I have one that if the engine stops in a certain place, ie with pressure on that lifter, its real noisy for a about 5 minutes. theres only one noisy one, and dont really want to change them all.... and the cam?

Cheers guys, sorry for the interuption:thumb:

[Sidecarbod]

Originally Posted by mylesdw

No advantage unless you are running very heavy valve springs and high revs. There is a disadvantage if they are heavier than standard because they add inertia which will cause standard springs to 'float' sooner.



The clearance makes NO difference to the timing. The only crucial thing is that there is enough preload to stop the plunger from hitting the snap ring; if it does this it will destroy the lifter quite quickly.



As above. The clearance is not at all critical for hydraulic lifters. They automatically adjust themselves to zero clearance every time they pass over the cam base circle; it is not the same as setting tappet clearances for solid lifters.

Hi Myles,

Thanks for the well explained replies to my questions, I suppose my next question is, is there any point in using adjustable pushrods with hydraulic lifters or are they just ment for solid lifters?

Cheers,

Pete

[russell_ram]

To quote Myles,

'No advantage unless you are running very heavy valve springs and high revs. There is a disadvantage if they are heavier than standard because they add inertia which will cause standard springs to 'float' sooner.'

I would add

The only time I could think you might want to use them with hydraulics is if you've modified you head so much that you can't get in the acceptable (say 20-60 thou) range with std rods. You're pretty unlikely to need their additional strength or rev capacity with a hydraulic cam in any case.

Russ

ps I'm pretty certain in the factory not a single engine was ever checked for lifter pre-load prior to being despatched - the tolerances on the std Rover parts are such that the pre-load will work every time.

[Purple AK]

Hi Pete.
I may be completely wrong here, And I'm sure Myles will put me right if I am But my understanding is that the pushrods need to be the correct length to allow the correct rocker contact with valve tip. This can alter if you have had, either the heads skimmed or the block decked. I see no need for adjustable pushrods, But only ones of the correct length. http://www.trickflow.com/product/for...ushroddata.asp

[Sidecarbod]

Cheers Guys,

I was just about to waist 140 quid! I'll find something else to spend it on! :thumb:

Regards,

Pete.

[mylesdw]

Purple Chris is quite right; the correct length pushrods are needed to get the correct rocker geometry. As also mentioned above, you only need to worry about that if you have taken a big slice off the head and/or the block or if you were running exotic stuff like a reduced base circle cam.