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)

[jaredmcginness]

Hey guys,

Thanks for the advice. I cut about 30qty .015 thou SS shims at work today. Easy to stack. I added at least one between every joint on cylinder 1.


Here is a quick video of me finding full lift tonight.
(I think I did this right!) Preload to. 600 thou. Came out 500 minus .012. Turned the motor over 6 or 7 times and it stayed true.

https://www.youtube.com/watch?v=oZka98bGYMg...eature=youtu.be


(IMG:http://www.914world.com/bbs2/uploads_offsite/i.imgur.com-23209-1600909649.1.jpg)


Looks like .488 is my full lift, cam card said .495.

This was on the first try with the recommended 27.1cm Pushrod.... if my math works out... this is WELL within the +/-5% recommended. (1.39%)

Half is .244 and we will go from there tomorrow. Checking the valve alignment at .244.

(IMG:style_emoticons/default/beerchug.gif)


Edit: Adding some thoughts here to refer to later.

I believe I need to repeat these steps on the exhaust valve. (once I get a nice intake valve alignment.)
I am not sure if my Scat c35 is a dual pattern cam. Asymmetrical = dual pattern every time? My research suggests, yes. So most of our generic cams would be considered dual.

That said, I will repeat these steps and shorten my starting point for the exhaust pushrod 1mm (.039) as Raby recommends. Bringing the starting Exhaust rod length to 10.630.... and go from there.

Last thing here to figure... I am now doing the exhaust lift with the intake rod installed. Makes sense so I can monitor the entire rocker assembly alignment.