Setting deck height for 9:1 compression Options

[technicalninja]

Important point!

Verify camshaft base circle is concentric.

See this thread.

http://www.914world.com/bbs2/index.php?showtopic=373021

You're all modern so I'd bet BIG money you're fine.

Not checking this while the engine is on the stand IS a mistake however!

[Chad911sc]

It is a new Web cam that is advertised as base circle concentric. I should be ok, but will double check. That is interesting though that the stock cam was designed as such.

[technicalninja]

ALL camshafts should be "base circle concentric"

If I saw an advertisement like that I would ask "Are there other options?"

This is so commonplace that checking this stuff is usually NOT done!

I found it via a "fluke"

In a normal application with normal valve adjustment clearances, it wouldn't matter.

Because the T4 expands differently than a "normal" engine AND you fit steel pushrods most specs call for zero lash and that is where this type of deviation could create disaster.

This IS NOT something you can verify via paperwork!
HAS to be checked via a dial indicator IMO.

Paperwork that stated "base circle concentric" would be a red flag for me!

I'd hope what you found is a notation of "asymmetric lobes".

THAT is Ninja approved!
I'd pay MORE for that...
(IMG:style_emoticons/default/ninja.gif)

[Chad911sc]

I’m off this weekend and will be back at it.
Can you explain the procedure using the dial indicator to check the cam?
I will do it on Saturday and make sure it is right. I am using the chromoly push rods so it needs to be perfect.

[technicalninja]

Drop dead simple...

Set up dial indicator so it replaces the pushrod into the lifter.

Rotate engine through 720 degrees.

You will notice needle movement through whatever degrees duration the camshaft says it has. Let's say 300 (big cam). the other 420 degrees is the base circle, and the needle movement should be VERY small if it is noticeable at all.

For use with zero lash the "runout" or variation should be .0002" (two ten thousands) or less.

Many dial indicators don't read that small.

What you are looking for is a solid needle during the "not on lobe" or base circle portion of the rotation.

My stock cam had somewhere between .0022" and .0024".
You would definitely see needle fluctuation with this much runout.

I'd check lift during this procedure as well. Tip of lobe to base circle multiplied by 1.3 should be very close to what the cam card says for lift.

Watch Karr's videos on setting up both pushrod length and rocker arm geometry and shimming. Good stuff!

Edit: You can find ultra-accurate dial indicators; they are expensive and "finicky" to use.
A normal cheapy version will work fine for this. Most are good to .0005.
You should see almost no movement on the base circle.

[technicalninja]

Just had a post from Jack Standz in my base circle thread about aluminum performance push rods.

OMG this is the way to go!

https://vwparts.aircooled.net/ACN-Heavy-Dut...p/acnhdalpr.htm

I believe this shop is no longer in business but I'd search BIGTIME for those pushrods.

[Chad911sc]

You can get those custom cut aluminum push rods from Germany. The same place that I bought my 10mm swivel feet adjusters from, offers them. I had already purchased the chromoly ones, so I didn’t get them. They say that they are much quieter and expand at same rate as factory, so they are better. Stateside tuning is the place to order if interested.
I did the base circle test on Saturday and it was successful, no movement on the cam lobe until the lobe starts it rise. The lift number on my 86a shows 436 lift on intake and exhaust side per the cam card, I’m only coming up with 418.6 ?
I had to stop there because when I pulled out my new Web lifters for the cam, I realized I was sent hydraulic lifters instead of solid ones. I’ll have to wait until I get the solid ones in before going any further with my build. I used one of my original lifters to do the test.

[zig-n-zag]

Type 4 rocker arms have different ratios for the intake and exhaust. Intake ratio is 1.36 and the exhaust ratio is 1.3.

A matched set of connecting rods can vary in length up to 0.010” due to the manufacturing process, but all the rods in the set will be the same length.

[GBX0073]

Just had a post from Jack Standz in my base circle thread about aluminum performance push rods.

OMG this is the way to go!

https://vwparts.aircooled.net/ACN-Heavy-Dut...p/acnhdalpr.htm

I believe this shop is no longer in business but I'd search BIGTIME for those pushrods.

with John from ACN no longer selling I went to Tabari Andrade on Facebook
He may be able to help with something even better.

[rfinegan]

let us know...
CB has a set that look tempting
https://www.cbperformance.com/product-p/1627.htm

[rfinegan]

or this one...
https://www.cbperformance.com/product-p/1624.htm

[GBX0073]

Rob
Great Find your always a great reference for Parts
Back when I was looking CB did not have these offered

[Chad911sc]

Stateside tuning has these available now. It only took about 5-7 days for my swivel foot adjusters to get to Fl. Super nice people as well….

[Chad911sc]

Thanks Zigzag!!!
I feel better now that my numbers match the cam card….

[Chad911sc]

I ended up taking .002 off the top of the piston that had the deck height of .033 thousands. I then used the one heavy wrist pin that I had to place into that piston and all my weights are nearly identical. I then went back through all the other pistons and cylinders and switched them around until I came up with deck heights now of .035 on three of the cylinders and .040 on last one. Now I have a spread of .005 across my heights instead of the previous .007