Cam question; 3 or 4 rivets

[lcvaldetaro]

Hi,

I have a hot cam that was specially made for me. It is complete with the gear, it has 3 rivets on it.

My car is a 74 Ghia. I've read somewhere that the cams after 71 changed to 4 rivets.

Does that matter? can I use this 3-rivet cam on my motor?

[Phil69]

The only difference will be the oil pump drive shafts.

http://www.youtube.com/watch?v=uMSE0ATFjZg

[Marc]

The BODY of the 111 115 107BK pump which came stock on your `74 (with 4-rivet cam) is also thicker, and the boss which supports the shaft is longer (as you can clearly see in the video) - so you cannot use that pump with a 3-rivet cam. You will need a 111 115 107AK pump (do NOT get a 311 pump, although it has the correct depth and shaft protrusion the oil passages are too small to match up to the `70 and later cases).

It is possible to use the 111 115 107AK pump with a 4-rivet cam, by pressing the shaft deeper into the gear so that it extends far enough to engage the cam - people do that all the time - but because of interference between the body and the face of the cam, going the other way isn't viable.

There's a far easier way to properly align the bolt-on cam gear; it'll physically fit three different ways, but the one correct way puts the timing mark directly in line with the slot in the end of the cam.

[mji1198]

DANGER, there are 3 rivet aftermarket cams that have the same type of offset as the normal VW factory 4 rivet cam. The first time I came across this, it really threw me. When I'm building a VW engine, I always check the engagement of the oil pump shaft to the camshaft slot when half of the engine block is on the engine stand as it's easy to do and if there's an issue it's immediately obvious. When it's aftermarket, you shouldn't assume they think like the VW factory.

[Marc]

First I've heard of that. WHO, pray tell, is going to the effort to make odd-ball cam blanks to achieve this result? I mean really, if this was a viable way to fit the "deeper" oil pump, why would VW have gone to the effort to re-engineer for the 4-rivet design? I wish that they had, since I'm convinced that the incidences I've encountered of loose rivets on the late cams are caused by harmonic effects which the 3-rivet design avoids. If there's a good billet made that makes this possible, it'd be an excellent basis for hot-rod cams, allowing those who need a larger pump to use a stock 111 115 107BK rather than an aftermarket 111 115 107AKHD which protrudes further from the case.

..."citation needed"

[mji1198]

I've seen 2 3 rivet cams that were made "deep" at the camslot for the later oil pumps, I think they were from a Brazilian aftermarket supplier. I remember they had aluminum gears. I really scratched my head a lot after finding the first one. As many of us know, you need to be careful about aftermarket stuff. Years ago I got some bus rear wheel bearings from a supplier (the roller bearing) that wouldn't even fit, the maker of the bearing wasn't even brave enough to put their name on the box. I returned them with a letter describing the problem and never did receive an answer from them. I went back to using the local import store and buying the more expensive German FAG bearings. Often you get what you pay for.

In regards to cam rivets, I've never seen factory VW cams have a problem with this in the beetle style engines, but I've seen several of the type 4 engines with loose rivets. One got so bad it stopped running. I had a customer with a company rebuilt high performance engine that lasted only a few months.In this engine (beetle type) they used a fairly radical cam with some very heavy valve springs but they reused the old, worn magnesium cam gear, it just wasn't up to it. In building these fine motors for over 25 years I've seen some interesting stuff.

[Marc]

One could probably make the center part of the slot deeper in a 3-rivet cam billet (and provide a counterbore to clear the round part of the pump shaft) but that's still not going to provide clearance to the longer body of the "4-rivet" pump - the only thing it would be any good for would be a 3-rivet pump which had its shaft pressed deeper in the gear to extend its reach, so what's the point? All you'd end up with would be a cam that was unnecessarily weakened and a pump shaft that hung out further past its support.
When a 3-rivet cam uses a bolt-on gear it's not unusual for the clearance between the bolt heads and the pump body to very close (sometimes too close without grinding the bolt heads down) to a 3-rivet pump body - it'd never work with the 4-rivet pump, I was being facetious above.