Valve adjustment procedure for aggressive, overlapped cams...

Jason Porter · 08-24-2004, 08:13 AM

This will work for any cam, but is especially useful for cams with overlap. I'll be writing a tech article on this when I do my next valve adjustment.

The engine is laid out as follows:

F---1---2--F
L---CAM---A
Y--3---4---N

By the same formula(if you can call it that)above, valve layout is as follows:

F---1e-1i-2i-2e
L---CAMSHAFT
Y--3e-3i-4i-4e

By this formula, we see that the valves for cyl. 1 exhaust and cyl. 3 exhaust share the same lobe, ans so on. So if 3e is at maximum lift, then 1e is at maximum clearance.

Therefore, in fast easy terms, take off both valve covers(best during oil change), rotate engine until #3e is at max lift, and adjust #1e. Then rotate engine until #3i is at max lift, and adjust #1i, and so on.

Then start at #2e at max lift, and work your way back down the other side of the engine. I understand if this isn't layed out as simple as it is, but I can adjust my valves in less than 20 minutes with an overlapped camshaft, and experience no problems.

robinaube · 08-24-2004, 04:10 PM

Jason,

I use a similar process for valve adjustments that I learned when I did Type 1 motors. This process works for all Type 1, 2, 3 and 4 motors because they are flat engines with single cams down the center with shared lobes.

Step 1 - Put the engine at TDC on #1 - Pull off both valve covers. Wiggle the rockers on one side. Three will be free and one slightly open. Adjust then three valves on that side. I then move to the opposite side of the engine and adjust the one valve that is across from the one you didn't do.

Step 2 - Rotate the crank 360 degrees so that you are at TDC for #3 - Adjust the remaining 4 valves.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Hey, Rob... I have found that you run into problems when one valve on a cylinder is open. I think the rocker stands are not strong enough or solidly-mounted enough that the spring pressure on the one rocker arm causes the clearance on the other rocker arm to be off. (Larger than expected.)

I have checked this on three motors so far, and found it to be the case in all three.

--DD

john walker's workshop · 08-24-2004, 05:36 PM

what the heck is wrong with doing them the normal way? two at a time at TDC for each cylinder.

Jake Raby · 08-24-2004, 05:44 PM

When a cam has a very tight lobe separation, or overlap due to early intake opening I adjust this way..

Start at #1 exhaust... Rotate the engine till #3 exhaust is at full lift. This means you are on the heel of the base circle on #1 since they share the lobe.... Do this for every other cylinder and its easy and fool proof..

Jason Porter · 08-25-2004, 06:22 AM

Thanks Jake. Overlap on a cam can cause up to a few thousandths misadjustment using the TDC/2 valve method. Ask Scooter311. He used the TDC/2 valve method with his 86 Webcam, and had clatter and power loss like you wouldn't believe. I gave him this procedure Jake and I are talking about, and he's had no problems. As Jake said, it's foolproof!

John Rogers · 08-25-2004, 08:43 AM

When I had the stroker four I adjusted the valves the way the cam maker (Crower) said to do it. In my case it was engine hot and the piston at TDC.

Jason Porter · 08-25-2004, 08:44 AM

You can adjust anyway you want with proper results if the cam doesn't overlap. Crower makes Type 4 cams?

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Engine hot? In a 914??? Must be nice to have asbestos arms....

--DD

Jason Porter · 08-25-2004, 09:07 AM

Must be hydro

Scooter311 · 08-25-2004, 11:26 AM

Oh oh, my ears are ringing........
A'yup, the outlined procudure is correct for overlap - I also bribed a buddy to turn the roadwheel while I kept the feelergauge between the rocker tip and valve stem top. I found the point where the clearance was 'loosest', had him rock the wheel a tiddly bit back and forth to make certain, all the while with the feeler gauge in place - I wanted to be ABSOLUTELY certain.
It is pretty quiet and smooth - I'm very pleased.

Jeff (Scooter311)

John Rogers · 08-25-2004, 12:24 PM

Crower makes cams for just about anything, including type ones and fours. The adjustment was not as bad as you might think as the engine had headers that were insulated with heat wrap. Hey, I used to adjust the valves on my 1969 Z28 with the engine hot AND running!

Jake Raby · 08-25-2004, 05:53 PM

If you were running steel pushrods, thats was why they recommended to do it hot.

I set my steel pushrods at zero lash cold or .003 when warm..The pushrod material dictates expansion and contraction- steel PRS stay the same length when they warm up. Aluminum PRs grow with the engines temperature and ned more lash to keep from tightening up if the engine runs too hot.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

That brings a question to mind... How do Nickies affect the valve clearances? They would seem to grow more than the cast-iron cylinders, so wouldn't you need to use tighter cold clearances on a motor with aluminum cylinders?

--DD

joseph222 · joseph222's Garage

Quote:

Originally posted by Jason at Pelican Parts
Overlap on a cam can cause up to a few thousandths misadjustment using the TDC/2 valve method. As Jake said, it's foolproof! [/B]

Jason,

Using your method, what cold lash are you setting with these "aggressive" cams?

Jason Porter · 08-26-2004, 11:39 AM

Pending climate .006", but if you're in a much hotter climate, like the SW desert areas or something, then probably .007"...IMHO

3D914 · 3D914's Garage

Jason,

You're right on with this method. This is the method elluded to at the end of the PP valve adjustment article. It doesn't rely on find TDC, is much faster, and can be done quickly with one person.

Thanks for clearing this up.

Jason Porter · 08-26-2004, 11:51 AM

No problem, I'll be doing a full tech article in the next 2-3weeks, complete with pics of procedure...and twins!

joseph222 · joseph222's Garage

Quote:

Originally posted by Jason at Pelican Parts
Pending climate .006", but if you're in a much hotter climate, like the SW desert areas or something, then probably .007"...IMHO

Interesting. Same setting my local guru suggests (.007).

I've got an aggressive Isky cam and I tried their valve lash settings (.013N - .015X). No power and sounded horrible. I'm going to give your technique a try.

How do you determine when a particular valve is at full lift? Visually only? Placing hand on rocker and feeling it? Both? Dial indicator? LOL.

Jason Porter · 08-26-2004, 12:18 PM

Visual, and you'll feel the maximum tension if the spring in your feeling really zen with your engine. Me and my engine spend a lot of time together, so we're pretty emotionally attached

Also, if your a couple of thousandths (.002-3") below max lift, it's not crucial, as the "heel/bottom" of the cam is much wider than the top of the lobe. BUT, BE AS CLOSE AS POSSIBLE, or you will have some seriously loose valves.