Valve Train Geometry with Cam., Beating a dead horse. Options

[jaredmcginness]

Hey guys,

Making headway on my 1911 build (no pun intended).

I have a few valve train questions. I've researched this a good bit the last few days and read a couple informative threads on here with some info (including one by @nditiz1 that went through a very similar issue)

I am trying to not over complicate this, so my tiny brain can make sense.

I was having an issue with my rockers, posted a photo of my heads on the 914world facebook group and got a great response from J. Raby with a lot of helpful info.
It seems I bit off a bit more than I can chew with valve train geometry.
(I understand he wrote a dissertation about Valve Geometry a number of years ago, but I cannot seem to find it.)

It does not surprise me that the fella/shop who built my bottom end didn't go into too much detail about this. He basically laid the numbers out and said "If I have X amount of cam lift, we need to machine the heads for dual springs to achieve X amount of clearance. All there is too it."

Maybe there is a bit more involved than that. (IMG:style_emoticons/default/smile.gif)

Specs:
-1911 (96x66mm)
-51cc heads - fresh.
-Scat c35 .495 Lift
-Scat solid lifters
-Scat dual HD springs, head machined.


Recommended additional purchases by Jake:

All available at Type4Store
-911 Swivel Foot / Machine rockers .060
-Solid Spacer and shims. Byebye rocker spring.
-8mm HD studs for strength.

Question:
With all of this added, it seems like the heads will be much more sound, and be able to handle the possibly over-sized lift on the cam.


-I have seemingly completed a proper valve adjustment using the "Lobe per lobe" technique. (I.E. Intake 3 fully open, adjust opposite rockers on 1) I cannot find a lot of info on the right way to do an adjustment with a large cam. Thoughts?
My TDC mark on the flywheel doesn't match up with the valves due to the ramp of this cam. (I think I understand that right)


-Does this geometry affect my pushrods? They SEEM to be working fine at their length. Do I need "chromoly"? Is this for strength and + cut to size?
I read all these threads on the Samba of guys running large cams with stock rods. (probably my engine builder posting that stuff (IMG:style_emoticons/default/biggrin.gif))

I would just like to do this right the first time.


(IMG:http://www.914world.com/bbs2/uploads_offsite/i.imgur.com-23209-1599592477.1.jpg)

(IMG:http://www.914world.com/bbs2/uploads_offsite/i.imgur.com-23209-1599592477.2.jpg)


Sounds like this motor is going to run like scat if I don't wrap my head around this and study a bit more. I'm really proud of what I have learned so far building this 914.
But I am just at the tip of the iceberg.

Feel free to just tell me to use the search function. (IMG:style_emoticons/default/beerchug.gif)

[nditiz1]

Hey Jared,

I myself need to go back to my notes on my build thread to refresh, but the idea behind the rocker geometry is to ensure you have good angles and at the same time check that you are getting max lift.

So for my particular build of the 2056 I wanted to go with swivel feet adjusters as they look neat and will last longer. In my case I did not know what type of cam was installed. I was also to much in a hurry to do all the calculations to figure out exactly the total lift, but based it on a few quick checks. Once I had that down it allowed me to ensure I was within spec for that max lift. You on the other hand know what those are since you have that cam info.

I haven't read your post on the FB page yet, but the items that Raby wants you to get will make everything more concise. If you go with swivel feet adjusters you will most likely need to clearance the rockers to allow for more adjustment and you can also get the sides clearanced for the spacer kit. The spacer kit is always a plus as the rockers will not shift, which makes the impact point more accurate which will be less stressful on all the parts. The last about the 8mm studs is also good as it will help strengthen the same moving parts.

You can add spacers underneath the rocker shafts improving the angle and at the same time correcting the lift tolerances, but sometimes this can fix one thing and ruin another. The key to the geometry is getting the max lift height while making sure your angle is perfect at that max height (so in between the stroke). If you look at the pictures in my thread I have one showing what the angle should be as well as where it was hitting on the valve itself (almost center). I did not get it perfect, but I also did not want to get chromoly pushrods. I was able to have the guy that clearanced the rockers to remove the end of the pushrod and trim it slightly to the measurements I gave him. The angle does not have anything to do with the power you will gain from ensuring you have max lift at each cylinder, but more so that you are wearing your internal parts less. The more aggressive the angle the faster your parts will wear.

As I said in the beginning, I need to go back to my notes as I know I spent hours figuring it out and reading over Raby's method. Hopefully I didn't remember anything incorrectly on that. I'll see if I can find a copy of Raby's method.

Just remember to not stress if it's not perfect as far as the angle goes. Just don't leave max lift on the table and keep them all within a close spec of each other. One more thing, I have 2 adjustable pushrods you can barrow if you need to get custom chromoly rods made. On that topic of chromoly, if you go that route you are able to run 0 lash as the rods do not expand like the stock ones do.

Edit - sorry read your post again. The heads should be able to handle the load.
I don't know about your TDC and aggressive cam. Something doesn't seem right there. The Samba confirms using the back of the lobe technique and not TDC for the C35 cam SAMBA C35 . If the pushrod is anywhere on the back side of the cam lobe that valve will be closed. You should be able to set the intake and exhaust accordingly to the stock settings. As I mentioned before, chromoly p.rods would be 0 lash.

[jaredmcginness]

First, thank you for the awesome and thought out response, absolutely a huge help.

Just remember to not stress if it's not perfect as far as the angle goes. Just don't leave max lift on the table and keep them all within a close spec of each other. On that topic of chromoly,
if you go that route you are able to run 0 lash as the rods do not expand like the stock ones do.

I will have to read Jake's post and decide if I think that I need a different length PR. If so, I will take you up on your offer. I suppose zero lash is a nice benefit, makes adjusting things simpler and quicker (and probably a lot quieter)?
If that ends up being the main benefit, I can live without.

The Samba confirms using the back of the lobe technique and not TDC for the C35 cam SAMBA C35 . If the pushrod is anywhere on the back side of the cam lobe that valve will be closed.
You should be able to set the intake and exhaust accordingly to the stock settings. As I mentioned before, chromoly p.rods would be 0 lash.

I read through that thread and its seems I did things exactly as described.

I found this Vintage Speed YT video for a simple valve adjustment. I just went out to the garage and adjust as is done in the video...
I ended up being - at most - .005 out on an exhaust valve. Not bad for eyeballing the valve opening and closing!

I turned the motor over 5 or 6 times and my new numbers stay true at .006I and .008E. So it looks like I am all set on my adjustment for now. I feel a lot better about that. I was firing in the dark last time.