H2

I just spent the past 3 hours searching and reading old posts on replacing 928 S4 cam gears and hubs....and didn't find an answer to my question.

If one wants to avoid the tedious dial method for adjusting cam timing after changing to a new cam gear, it is usually recommended that you carefully mark and orient the new cam with the old "marks" or scribe marks inside the rotor holes on the old cam hub or "spyder" so as to be very close to the original cam timing.

I've done the above successfully, using PorKen's 32V'r tool. Easy.

HOWEVER, what does one do if you're also replacing the backing plate and the hub or "spyder"? (part no. 928.105.459.00). By replacing these parts you've essentially eliminated the "marked part" normally used to orient the cam gear to the cam.

I've ordered all the parts back to the cam and will be replacing these since the new cam gear I just put on seems to be occilating a slight bit (although the belt runs true). I want the cam gear to also run true and hope to eliminate all possible issues. It's unlikely that a brand new gear was delivered that wasn't straight...but I'm not sure how to test for this. I use a good tork wrench on all bolts so overtorking and distorting anything is unlikely.

In any case, I've heard that the cam gear backing hubs sometimes develop cracks so I'm replacing the driver's side unit. But I do not want to buy the tools to do the cam timing as per the WSM. Pretty expensive kit and a lot of PITA work. PorKen's tool is a snap for what I did before.

Any experience with the above? Is there a way to replace the backing hub and still maintain a close cam/gear timing orientation?

Thanks,

Harvey

the flyin' scotsman

Harvey.........if you take the cam covers off you can lock the crank and the cams before you take it apart keeping both oriented where you stop the engine.

You can then use the Porken tool to recheck after you installed all the new parts.

docmirror

I think he doesn't want to pull the cam covers, and have a repeatable cam alignment. Oui? This is going to be difficult. Here's what I would do. since there's no way to lock the cam in one spot, you'll have to find a way to mark the location just prior to pulling the gear and hub. We did this at Roger's house a few times, and it seems we've got it about right.

The hub is keyed so it will only go one location. It's the relationship of the hub to the gear that's of issue. So, before you loosen the big cam bolt, install three 5m x 15m in the hub to flange to lock them together. Then, remove the big bolt by using the old belt on the gear. It's okay if the cam moves around now, the small bolts will hold it in relation to the hub, which is of course, keyed.

Once the big bolt is loose, remove it. Now, you have to mark the gear and not move the cam after that. The trick is, the hub and gear will come off together! Now, use a punch, slide it in the cam tooth slot on the gear which has the indent on the back for reference. Dimple the backing plate of the gear shroud so it will act as the reference. Now, remove the gear and the hub with the three bolts. Do not move the cam from this point. If you do, you can reinstall the old hub and gear and re-align your reference dimple. Orient the new gear on the new hub, and put three bolts in just snug, not fully tightened. Install the new hub and gear on the cam, and use the same punch in the same reference tooth.

Now without moving the cam, loosen the three bolts, and set the punch point in the dimple on the backing plate. Now, tighten the three bolts carefully without moving anything, and I would recheck using the old assembly. The transfer measurement will be pretty accurate if you are careful when pulling the old gear and hub. You can always use the old gear/hub to re-orient the cam to the dimple if it gets moved. Now put in the big bolt and you're done.

<edit: I just noticed that you are replacing the backing plate. In this case, I think you're in trouble. If you can do it the way I described without moving the cam between the hub/gear swap you'll be okay. Otherwise, it's gonna be pull the cam covers.>

PorKen

Harv,

If you can wait until the end of the week, I should have your V2 32V'r. If you can't wait, I can loan you my V2 again, and/or send you an alignment bar for your V1.

Any way you go, you are going to be within ±1°. Really! No need to mark anything. Just put the new hub and gear on, and set the timing.

V2 L: 0° / R: -1°

OR

V1 L: +2° / R: 0°


(Updated V1 32V'r manual) (V2 32V'r manual)

Now, where's my beer -

H2

Thanks, PorKen,

I'll wait until the new tool arrives. I've got some other things I want to do on it anyway. Getting close to detailing time.

Harvey

H2

Thanks, Doc. That's a great blow by blow description. I'll follow it as I wad into this change. I'd not seen this kind of description before. I think it will work. I may or may not pass on the backing plate...I won't know until I get in there.

I really appreciate you taking time to write this up. Hopefully, others can learn from it also.

Harvey