PorKen

Using Mercedes camshaft Woodruff keys.

They come in many different degree offsets, and are only few bucks. (An easy to look up model is a 1980 300D.)


621 991 00 67
4 x 6.5 x 16mm offset 1.3mm keys
(dimensions measure slightly smaller)

Why am I bothering you with this?

If your cam gears don't line up with their marks (the right one is usually off the most), the engine will not perform as well as it could. I have found that just syncing the cams made the idle better and the engine produced more torque on the dyno.

Put another way, if you are off by 1/2 cam gear tooth, that is 3.75 cam degrees advance or retard (7.5 degrees crank), which can make a big difference.

After the cams are synced, advancing both cams will give more low end torque (2-3 degrees works well), and makes the automatic, especially, more fun around town.

On later models you could do like I did (here), or the hard way (here), for an adjustable advance.

...

You want to line up the cam, the gear mark stays where it is.

Scribe a line down the front of the cam in line with the cam gear mark, then find a Mercedes key to advance/retard the cam to line up with the mark on the head using a straight edge along the scribed line.

toofast928

Yep, I was able to advance the cams simply by using the slop (extra clearence) in the keyways. Tightened the cam gear bolt, and both gears never moved off mark. I am amazed how much 3.5 degrees moves to the power band. The cams only have this alignment issue when upgraded to the HTD T-Belt. Wish I never upgraded. Having the cams off mark is outweighs the benifits oh HTD.

PorKen

It's too late in the day. Can someone help me with the math?

928 cam gears are 23mm ID, and the OD is 144mm (crank gear is 72mm), so how many degrees do these translate too?

Part number | ID Offset
621 991 04 67 | 0.7mm
621 991 02 67 | 0.9mm
621 991 01 67 | 1.1mm
621 991 00 67 | 1.3mm
...

toofast928,

I had the same problem with both the square tooth belts and round tooth. ~2 degrees retard on the right cam, ~.5 degree advance on the left.

I believe the cam bolt does most of the work holding the gear in place.

jpitman2

23MM ID * PI = 72.2565MM CIRCUMFERENCE. 1/THIS = .0138395 *360= 4.98
ie nearly 5 degrees per mm of offset. 0.7mm = ~3.5 degrees AT CAM, 7 degrees at crank.
Is this what you wanted to know?
jp 83 Euro S AT, more interested as Ken goes on.

PorKen

Thanks jp,

Almost, I think. What I'm looking for is the number of degrees at the OD, 144mm, given the known movement at the ID, 23mm.

It should be some fraction, right?

Using your figures I think 0.7mm works out to ~1.8 degrees at the OD, or 1/4 cam tooth.

jpitman2

Ken,

Degrees are degrees, finish. if .7mm offset gives 3.5 degrees at the hub, it will still displace the outer edge of the wheel by 3.5 degrees, even if the wheel is 1000 miles in diameter. Sure the distance the timing mark will move will be greater, but it will stay the same no of degrees. To get the distance the mark moves on 144mm diameter wheel, multiply radius (72)* tangent of 3.5(.061) to get 4.4mm - maybe half a tooth? About what you were after?
jp 83 Euro S AT 48k

PorKen

Thanks, jp.

A friend of mine made this for me using CADKEY '97.



Note: one cam tooth is 7.5°.

jpitman2

Problem with diagram is you are using diameters (OD=144 above) instead of radius. when you use radius, the degrees will double. From the centre of the shaft, which is the point you are turning wheel around, to outside of hole is 11.5mm, and to OD of wheel is 72mm. Hence your 1.743 becomes 3.48, which was my figure for the .7 offset.
jp 83 Euro S AT 48k

PorKen

Okey, dokey, picture updated.

The second degree value is the offset key combined with moving the belt one cam tooth (eg. 7.5 - 6.45).

Part number | Offset | Degrees | Plus One Tooth Degrees
621 991 04 67 | 0.7mm | 3.483 | 4.017
621 991 02 67 | 0.9mm | 4.475 | 3.025
621 991 01 67 | 1.1mm | 5.464 | 2.036
621 991 00 67 | 1.3mm | 6.450 | 1.05

Eric Buckley

What's different on the US 16V L-Jet cars? Why won't this work on all 928's with non-adjustable cam gears?

jpitman2

IIRC, early cars had woodruff keys (half moon, or crescent shaped), later they went to square section keys, 4x4mmx16mm long. Just have to find correct key type from MB, if available.
jp 83 Euro S AT 48k

PorKen

Eric,

The L-Jet cars and up use a parallel or square key.

Parallel


Woodruff


I looked into it somewhat, and I could not find offset parallel keys. I did find places that might make them, but I ended up converting to the 32V HTD adjustable gearset, instead (which works with parallel or Woodruff).

(click here for 32V install thread)

toofast928

Hey PorKen you realize when you install the SC your going to have put the cams back on the mark.
How about developing a catch can, or converting the to MAF.

PorKen

toofast928,

I reckon with a supercharger, you'd want to retard a tad so the exhaust can breathe better. That's what the 951 guys talk about doing, anyway.

I only make things when I need them, so when ( ) I supercharge, then I'll make that stuff. I already have trouble finding time to work on the polished (Polish?) versions of the few worthwhile things I've installed.

GlenL

PorKen,

Have you sourced them yet?

Just the ticket for some low-cost tuning.