Itinerant Air-Cooled

I await your reply with one question:
If a cam lobe is pushing a lifter open on one side of the engine, then goes over to the other side to open another lifter, how is that not "twice as much" as a typical engine?

??? You ask me this question, and then answer it yourself in your next paragraph...
Why? Are you testing me, or just want it printed online to educate the masses? I have no problem with either.
Oh well, here goes... Let's use the #1 and #3 intake as examples. easy to pull, easy to view. Lobe#2 on the cam.
- On the #3 side, the lifter runs so far forward on the lobe, it actually hangs off the edge. On the #1 side, the lifter runs so far back, it hangs off of the back of the same lobe. The lobes on those type 4's are as long or longer than the cam bearings!
- Although 2 lifters run on the same lobe, the contact points are very much separated.
- Although 2 lifters run on the same lobe, the lifters contact different, separate, parts of the cam.
- Although 2 lifters run on the same lobe, the work and wear that is done is in 2 VERY separate places.
If we look at type 1's, I agree 7053%. Short lobes, both lifters contacting same spot, 2 wipes on same contact spot of lobe per revolution of cam, twice the work and wear in the same spot. Yes sir...
But we are not. We are talking type 4. LONG lobes, both lifters contacting DIFFERENT SPOTS, 2 wipes on DIFFERENT CONTACT SPOTS of lobe per revolution of cam, twice the work, BUT 2 different spots, which equals 2 single instances of work in 2 separate places...
Let me be clear. I FULLY understand what you are saying. However, my discussion on this thread is "work" and "wear" per lifter, per contact point, which equals ONE.
Your last comment, "Are you familiar with it?".
You are kidding, right??? My friend, I still have dreams about those Nazi drill sergeant teachers swinging around a cam without a gear like a ruler they were gonna rap on my knuckles to drive home a point...
Most respect and good to you, Walt.

aussiewalt wrote: intake as examples.#3 forward #1 back,
Although 2 lifters run on the same lobe, the lifters contact different,

That is the remarkable thing about Type 4 intake cam lobe wear. Even with the long lobes, the opposing side lifters overlap on the lobe. So we get those pretty arched wear patterns, looking like a cathedral stained glass window arch. Totally unique and annoying.

The exhausts, they don't even try the long lobe deal. You know why?
You know why the intakes still overlap, defeating the "purpose" of the long lobes?
Because the long lobes were not long to prevent wear.
They were long because the engineers had a mighty problem on their hands with exhaust ports exiting down between the pushrod tubes. They whole reason behind stupid camshaft lobe width differences and weird extra-tilted rocker arms on #3e and #4e was because they had to get #4's exhaust port down the middle between intake and exhaust pushrods, and they had to sneak #3's exhaust port just ahead of 3e pushrod. Go to the other side of the engine, and #1 has the wide spacing between pushrods and #2 has the tight bunched pushrods. Add a little mitigating offset (left side is one rod journal forward), and if you diagram it, the exhausts line up like a Type 1 and the intakes are kablooey. As a matter of fact, VW blew it here. The cam wear is *worse* on the Type 4 engines because the overlap area is at the outside radii of the rotating lifters. At least the Type 1s are centered on the contact patch so each side wipes the toe down equally!

aussiewalt wrote: If we look at type 1's, I agree
Walt.

Here is a page out of the book-that-is-eating-up-my-life showing the Type 1 rocker offsets but lifters aligned. Interestingly, the pushrods/tubes are required to go at an angle in the direction of the cylinder bank offsets, while the T4s are dead straight perpendicular. That's because the Type 4 pushrod tubes are designed to move in and out of the bores as the engine expands and contracts.
Colin

Zombie thread revival:

edit: most of my questions were answered when I realized this was a two page thread.....

I don't have a Type 4 cam here to examine, are any actual lobes longer (front to back) to accommodate this concept?

Robbie

What a beautiful illustration! Where's the book! Ian

asiab3 wrote:Zombie thread revival:

edit: most of my questions were answered when I realized this was a two page thread.....

I don't have a Type 4 cam here to examine, are any actual lobes longer (front to back) to accommodate this concept?

Robbie

Yes, look at a Type 4 camshaft. It has two looooooong lobes. They are the intake lobes (front one opens cyl.s 1 and 3 intake valves, rear does 2 and 4's)
Colin