Cam Cap Question

I have often wondered how important are the locator pins on cam caps. I know about how heads and caps are line bored and are supposed to be a matched set....There are instances where some of us need new caps to an existing head. My question is this.....can a cam cap just be bolted on with out the hollow locator pins? If so it may give it just that extra bit of wiggle room to fit well. My reasoning is as follows: The cam would not move laterally as the half-moon bearing in the head portion would fix it's location and the cam cap would prevent the cam from jumping out of place. Any vertical discrepancy might be addressed either by adding shims or milling the cap. Any ideas on this anyone? Hopefully I explained it well enough

The cam caps are line bored from the end at the factory which is why they are numbered.

The twins don't have the "half moon" bearing inserts, the bearing surfaces are the head and caps themselves.

My guess would be the steel insert locator pins also provide mechanical support to the whole thing. You would not want the cap to be moving around against the threads of the bolts as the only support.

No, No, No !

What I am trying to do here is open a good discussion on this subject and maybe even have it go to a MYTH-BUSTERS status.......think outside the box everyone. :silly: There are a lot of really accomplished engineers and builders on this forum and I would love to hear ideas from you with reasons why. I think we all agree that these motors are extremely strong.....maybe even over-designed,

The more I think about this I am leaning to the conclusion that the two hollow locator pins are not entirely necessary. I agree with Bounty Hunter about the need for mechanical stability....but I wonder if the cam itself offers that stability and the cam caps only task is to keep the cam from dislocating from its position in the head. Another possible clue is the very low torque setting on the cam cap bolts....meaning that as important as the work they do is, they are not under a lot of stress.

Could it be that the pins are only used for the manufacturing process?

It would stop them from walking back and forth or chattering for lack of a better word. Definitely torqued to the upper end and line bored and honed together.

bluezbike wrote: Another possible clue is the very low torque setting on the cam cap bolts....meaning that as important as the work they do is, they are not under a lot of stress.

The torque spec (120 inch-pounds on mine) is the max they can handle before stripping. Just ask the hundred guys who have posted here about putting in heli coils when they cranked them a shade over the spec.

There are two forces acting on the cam caps, shear forces and tension forces. The bolts handle the tension forces and the pins handle the shear forces. If you don't use the pins you are asking for trouble. Kawasaki does not include engine parts that are not needed and every engine maker uses pins like these in their cam caps.

The dowels are like extra insurance for free. I have them on my aftermarket rods that I use in my small block chevy engines.

bluezbike wrote: an a cam cap just be bolted on with out the hollow locator pins? If so it may give it just that extra bit of wiggle room to fit well.

Leaving out the dowel pins is likely to cause a number of issues, but those aren't even relevant to your question. The real problem is that deleting the dowel pins will not help a random cap that was not drilled and line-honed to match the head.

The mismatch between any two random cam caps very likely goes well beyond the forward/back position enforced by the dowel pins. The center of the cam bearing circle could vary significantly in any direction. Up, down, forward, back, and even the angle of the cam axis relative to the plane of the cylinder head. So a random cam cap placed on a random head is unlikely to make a perfect circle, even if you never bolt it down. For example, If the hole was cut high on the head, and low on the substitute cap, you end up with a cam that won't even turn (even with no dowel pins). If the reverse, you have a huge amount of clearance. Other mismatches would give pronounced high spots and low spots...

If you really loved you head, but lost one cam cap, I think you'd have to have the all of the caps and cam journals for a single cam welded up, redrilled, and then line honed to make it really fit correctly.

Thanks DOHC, that really does explain it well....I thought perhaps that the vertical position would be consistent but it doesn't appear to be so. If it were I had then presumed that the other discrepancies would be handled up by the cam itself. Ah well, an interesting discussion I thought.