Valve train geometry advice.

[j-f]

I'm currently setting the valve train on my 1641cc engine. Camshaft is from Loïc Charpentier (A french engineer) with 8.90mm lift at the lifter and 12.70mm at the valve with bugpack 1.4(ish)-1 ratio rockers.
Here is the spec card from the camshaft.


This is the first time I play with ratio rockers and I don't know if I set it up correctly. I read and follow the excellent "all about performance air cooled VW engine 3" from Hot vw's.

Here is what I ended up with. As the valve are stainless steel I use lash cap.

At O lift.


Half lift.

Pushrod and rocker at half lift.


Full lift.


The length of the pushrod is 27.1mm.

I don't know if the tip of the rocker is correcty set up with the valve stem? What do you think guy's?

Thanks.

[modnrod]

The rocker arm "wipe" pattern looks to go across the cap OK, but the rocker nose itself seems too close to the valve.
Have you tried it with rocker post shims to raise the whole assembly up? It will "fix" the nose-to-valve distance. I remember having to use them with high ratio rockers.

Then again, it has definitely been a while since I did it!  It could be perfect!

[Jim Ratto]

My advice-
at 50% valve lift, the middle of the rocker pad should be contacting lash cap and the pushrod and adjusting cup screw should be in same plane, or imaginary line. From your pictures, you're not quite there. From the last picture it looks like you're near full lift (judging by spring) but your rocker pad is still on "low side" of pad profile (the side it's on when cam is at 0% lift).

Plot where you need to be without piushrods first. Mount rockers (make sure adj screw is centered in travel) to head with no shims and using a light checking spring, open valve (using your hand on rocker) until dial indicator shows 50% total valve lift. If you're not seeing the center of rocker pad contacting lash cap @ 50% then you either need to shim off head or you need less tall lash caps. If the rocker pad is contacting more towards rocker shaft @ 50% lift, you'll need to raise rockers off head with shims. After you get the relationship between rocker pad and lash cap happy, then determine your p/r length (I do it @ 0% lift but with prescribed lash).

When checking total valve lift for measurement purposes or to check coil bind always use the real springs and always use a good HD pushrod. Otherwise your numbers will be off, sometimes as much as 0.030-.040" optimistic if you use a light checking spring, and 0.030"-.040" shy if you use and adj pushroid against real springs.

Good luck. That's the fun part of motor building.  

[deano]

I think I would try shortening your pushrod slightly... and try it again.

[Taylor]

I wouldn't shorten it. The adjuster looks like it is about half way out already.   Shim up the rockers.

[nicolas]

I wouldn't shorten it. The adjuster looks like it is about half way out already.   Shim up the rockers.

yep and make sure the oil still gets  from the pushrod to the hole in the rocker. only fine-tuning is done with that screw. 

[j-f]

Thanks all for the advice, especially Jim.

I already try to shim the rocker mount, but I was wondering if I can put as much shims as I want or if there was a limit? It looks like I will have to shim it about 5mm to get it right.

I don't check the thickness of the lash cap. They are from Bugpack.
The cup screw is already centered in travel.
I use the inner spring of my dual springs to make adjustment.

Good luck. That's the fun part of motor building

Yep, I already feel that I will have to spend a few moments on the work bench to sort this out  Not really a difficult job, but time consuming and lot's of trial and error.

[Jim Ratto]

Cool. I wouldn't say there's a limit to shim thickness, if geometry is correct, it's correct. On a 2276 I did 2 years ago (K motion, long valve motor), it ran .200 thick pads under rocker stands.
be careful running pushrod too short. If the adjusting screw is screwed too far into rocker, at high rpm, with decent spring pressure, you can expect the cup to snap off the adjusting screw. I've had it happen. I try to run the screws so you see approx 3+ threads above lock nut when it's seated. You want to leave some room for backing it out, but you don't the cup hanging way out there, with no support behind it.
When I do geometry on ratio rocker motors I use a felt tip pen and make a hash mark on side of rocker pad to align with where it contacts lash cap @ 0%, 50% and 100% lift, and when you've got it shimmed right the 50% mark should be in the middle of pad, and other marks equidistant from there. And make sure pushrod and screw are in same plane @ 50% lift.

good job

[fish]

Jimbo, thats exactly what I do and aim for in a "Perfect World" and spend hrs to achieve but with todays difference in tolerances even between rockers, stands, shafts etc. its hard enough getting geometry right let alone perfect.

J-F, my concern is if you are setting geometry with the case halves already buttoned up, that you have just wiped the cam lube of the measuring Lobe otherwise you are close to ideal geometry as it stands with maybe a .050" rocker stand shim.

At half to full lift I prefer for the pad to ride slightly higher on the nose of the valve which seems to minimise valve guide wear.

Here is a diagram which I will not take credit for:

[RFbuilt]

fish awesome diagram! where'd you get it?

[j-f]

Thanks all for all the great advices, very instructive, but get me a bit more confused 
I used a shim of 2.4mm under the rocker shaft to try to make the rocker pad contacting the lash cap more from his center rather then from his low side as my first pictures show and as Jim suggested to achieve. It just seem to push the rocker more on the outside of the valve. I leave 2 turns on the adjusting screw when the cup is against the rocker arm.
I used a fairly thick shim in order to have an idea of how much it can influence the relation of the rocker pad and the valve.


I talked with my engine builder who sold me the camshaft etc. He advice me to check the lift not at half lift, but at 1/3 of the lift. He use to do it this way because the valve acceleration is more important at this moment rather than at half lift. 
(Sorry if it my explanation is not very clear, but as I'm french spoken, it's quite difficult to translate )

[fish]

fish awesome diagram! where'd you get it?

I can't remember where I got it mate, it makes a lot of sense when you see a diagram.


j-f thats why setting geometry is no picnic, it takes time and a lot of trial. seems you were much better off without the shims, just get your pushrod length and you ready to go.

[j-f]

fish awesome diagram! where'd you get it?

I can't remember where I got it mate, it makes a lot of sense when you see a diagram.


j-f thats why setting geometry is no picnic, it takes time and a lot of trial. seems you were much better off without the shims, just get your pushrod length and you ready to go.

Thanks Fish 

[TexasTom]

Before you hang this up and just go with it, try this ...
Use a permanent marker to color the top of the lashcap, replace the rockers and run through a full cycle of the engine valvetrain ... 2 full turns.
Pull the rocker back off and look at the pattern produced.
The more shim you use the further the pattern will travel towards the top of the valve stem/lashcap.
You want the pattern right in the middle.
Interestingly, in my experience this will produce the most lift at the valve!

I like using the marker as it helps me determine exactly where the contact is being made.
Good luck with it!
TxT

[Jim Ratto]

one thing I forgot to mention...
don't do these checks after you've done the final assembly on the lower end. By checking over and over and rolling motor over and compressing spring, you're wiping cam lubricant off lobe and lifter faces.
If you've done all these checks after you buttoned bottom end up, be sure to re lubricate the cam and lifters with moly.