PorKen

Has anyone tried using adding additional rollers to make the 16V cams adjustable?

I checked my cam positions against the crank, and found the left cam ~2 degrees (1 cam) advanced, and the right cam ~5 degrees (2.5 cam) retarded (total ~7 degrees (3.5 cam) difference between the cams).

I don't believe that my heads have been milled (which retards?) so this is just regular tolerances?

I've started thinking about a bracket to put an idler roller between the oil pump and the left cam (and possibly between the cams too) to adjust slightly the length of belt. Firstly to correct the tolerance. Secondly to try advancing the cam slightly to move the torque peak down a bit for my automatic trans.

There looks to be enough adjustment in the belt tensioner to allow for at least a few degrees movement, and the early US valve train shouldn't have a problem with valve clearance?

Any problems I'm not seeing here?

*Update*
~thread~start~

Jim bailey - 928 International

Added complexity for very little potential gain so if it is 230 hp or 240 ? does it really matter ? We also know that other modifications work .

ViribusUnits

Might you have a machine shop build you a modifyed key? Maybe even adjustable with shims?

I'm thinking a peice of metal that is thinner than the stock key for the pully, but the full thickness for the shaft. Then have a set of shims that you can place on eash side of the key for the wheel. You could then adjust the advance of the camshaft by adjusting the shims to one side of the thin key or the other.

I've never tryed it, but...

If you had a grinder, time, a peice of high quality bar stock, and a feeler gauge you could mess up, your could probably make it w/o the help of a machine shop. It would be a hand constructed job, so mass production would be out of the question, but your only looking for 2 units. Oh, and a pair of tin snips to cut up the feeler gauge...

PorKen

Jim bailey - I'm talking about driveability, not max HP. Moving the torque peak down a few hundred rpms would give that little extra push for the 3 speeders. Especially those cars with open exhausts which have raised that peak.

VU - I'm sure 2 or 4 degree (1 or 2 cam) keys could be made or bought (I'm not sure about the longetivity of shims).

Adjusting for the (minimal) stretch of the belt over time would require removal of the cam gears.

What I'm suggesting is just an extra idler roller on a bracket, nothing fancy, for ease of adjustment over time. The primary benefit I see is an increased smoothness with the cams syncronized (as is possible with the 32V cars).

Jim bailey - 928 International

Mark Anderson many years ago ran adjustable cam gears on the two valve engines very little benefit BUT they tended to break since they were modified stock gears that was not good with big cams ....it bent valves .

PorKen

Do you recall if he a used welded-on bolted arrangement?

How about 1 or 2 new keyways/notches machined in the gear (1/2 and 1/4 tooth) instead of my foolish rollers?

That wouldn't diminish the gear's strength much?

Jim V

If the cams are keyed onto the shaft, ofset cam keys are available thru any Mopar Performance dealer, they come as a set of 3 or 4 with different offsets. Don't know that they'd fit 928 cams though...

jpitman2

Some cam wheels (other makes) have 3 key ways in the centre for std timing, and + or - a couple of degrees, so you can play with the timing a little. If you could decide what was needed and design where to cut the keyways, find your machine shop.
jp

Jim bailey - 928 International

the adjustable gears were bolted together had slots machined into a flat circular plate . Bolts were tapped into the remains of the original pulley center hub / outer toothed ring .

PorKen

Jim bailey - thanks for the info.

There are 24 crank and 48 cam slots (square and round profile).

That makes 15 degrees at the crank, 7.5 degrees at the cam for each tooth of the belt.

I think what I'll do is have two additional keyways made in the cam gears, at 1/3 and 2/3 of a tooth to better syncronize the cams. Then use an idler roller between the oil pump and left cam for advance/retard experimentation, to see if it makes a difference on my car.

If it is beneficial I would have keyway(s) made in the steel (reversible) crank gear for changing the advance/retard.