Adjustable cam gear

[lmcchesney]

This is regarding my 96x78 rebuild project. We will be using adjusted 2.0L D-jet FI system and gave up trying to find the ultimate cam. I went with the Web Cam 73 grind and lifters. My mechanic, Denny @Autocraft Engines, said he cannot obtain the best cam advancement with the stock cam gear and suggests to go with an adjustable stright cut cam gear. The costs approx. $260.
Question:
1. When I use the timming on my simulator for a 73 grind I am using 0.05 lift and 224° duration and intake centerline of 103° and lobe center angle of 108° with +5° advance. Are these correct?

2. Are all adjustable cam gears stright cut?

3. Who is the best source to obtain the cam gear from?

4. If you use a stright cut cam gear, do you not need a stright cut crankshaft gear?

Thanks,

L. McChesney

[Dave at Pelican Parts]

1) Webcam quotes the specs as:
0.426" total lift
262 degrees total advertised duration
224 degrees of duration at 0.050" lift
The info I could get did not specify lobe centers, "intake centerline" (huh?), nor advance.

2) I would be surprsied if the adjustable gears were only available in straight cut, but I don't know for a fact.

3) I don't know who you'd get the gears from.

4) A straight-cut cam gear requires a straight-cut gear to drive it on the crank.

--DD

[SGB]

My understanding is that the cam gear attachment is the weakest point in the type-IV. I bet Jake Raby has stories.... I would wonder what additional (or reduced) stresses might be created using straight cut gears. I don't really know what an adjustable cam is- what is adjustable? I would hesitate to get very radical if it is FI. Go for drivability and as wide a power band (even with a reduced peak output) as possible to make the most of our car's low redline.

[silver2.0]

There is an advantage to straight cut gears. I rebuild industrial transmissions for a living, and on any helical-cut gears that have any real load on them, there is a thrust bearing, that takes up the SIDE load from the helical gears. The way that the helical gears work, the more load applied, the more side thrust there is on the shaft. As you can see in the instance of the cam shaft, there is not tremendous load, but you will all but eliminate the side load with straight cut gears. By the same token, you have at least 2 teeth taking a load at once, and there is more surface area per tooth on a helical cut gear. They are stronger.
To answer the question of why would you use an adjustable cam- That is just so you can dial in your cam perfectly. If you want to adjust your valvetrain a couple of degrees, it can be accomplished with this adjustable cam gear. Although, you will not get quite as much adjustability with a single cam, as opposed to say, a twin cam motor with adjustable pulleys, or gears.

[Stock93]

I have a dial a cam gear that is a helical cut adjustable cam gear.

[Stock93]

Heres another picture. I didnt buy it and really havent been able to find out much about it. It came in a core motor I got.


John

[lmcchesney]

Kevin,
Thanks for your input. The mechanic wants to preserve low end torque and thus wants to set the cam to +3°. I did some math of the gear configuration secondary to your input and came up with exactly the same results. Depending on which sector you align, the tooth degree variation is 1.28°. I'll take this back to Denny and see if we can get the approximate timing.
I appreciate your thinking.
L. McChesney

[Zeke]

Originally posted by kdfoust
I'm a little rusty with my differential indexing and it is a Sunday night and all...BUT.

How much does he want to adjust the timing? The gear is 56T and there are 5 screws (or rivets) in the stock gear to cam setup. So, each tooth on the gear is 6.4 degrees apart (360 degrees/56 teeth). Each bolt hole is 72 degrees (360 degrees/5 holes) apart. If you offset the gear one bolt hole on the cam you move the timing .2 teeth (72 degrees/(6.4 degrees/tooth)=11.2 teeth). The .2 teeth that's leftover from the 11.2 teeth is the offset you get. It's about 1.3 degrees. So the way this figures is that you get increments like this (rounding off) available in the plus or minus direction:
1.3, 2.6,3.9,5.2,6.5 (<-one full tooth move@6.5) degrees.

Does this make sense to anyone else?

Have fun,
Kevin

Yeah, that's prety clever. I've not seen that idea in 2 year's woth of reading 3 BBS's

[lmcchesney]

The Web Cam and Web Cam Gear bolts are not equal distant. Therefore, you cannot use our method unless you redrill the cam and gear. You can align 3 of the five but redrilling results in an oblong hole. It seems you have to dril five complete new holes and then worry that structual strength is adaquate.
L. McChesney