964 cams on 993 engine??

[mmasse]

I am rebuilding my 993 (Varioram) engine. I am planning to convert the friction style 993 sprockets to the mechanical 964 ones. The problem is that my 993 cams do not have the woodruff key on them.
I could get a hold a pair of 964 cams, but my question i:s are those interchangable? Can I use 964 cam on the 993 engine? What's the difference?

Thanks for your inputs.

[Nine9six]

While I am not familiar with your application, what would prevent you from having a woodruff key slot machined into your existing cam? Is the specific area designed to run a sprocket? If so, does the term, "friction style 993 sprockets" infer that the sprocket is a press fit onto the camshaft? If so, why not grind the area to accommodate a slip fit clearance (.0005 per inch of diameter) and have a woodruff key slot machined into the area?
Proper sequence is to machine the woodruff key slot prior to grinding to slip fit the sprocket.
HTH

[mmasse]

the 993 sprocket is only kept in place by the force of the cam sprocket center nut. The sprocket is not pressed into the cam. So, clearance is already the correct one.
actually, machining the cam is another option I am not so sure where to have it done, though

Will any small machine shop be able to do this? i am afraid a big shop will not take such a small job.

Thanks

[KTL]

Take a look at the parts diagrams and you'll see the early 993 (with 993 part number cams) had a woodruff key and used the same sprocket and drive flange as the 964. Maybe that answers your question? The only difference I see in part numbers for parts that go on the end of the cam, both cams having the woodruff key, is the big washer that goes under the camshaft center bolt has a different part number between 964 and 993

As far as the cams go, I can't answer that in terms of profile/performance difference. I would bet the cam profile was changed to reflect the needs of the Varioram system? Even the non-Vram 993 has a different cam than 964. Porsche had to change something to go from 250>270>282 from 964>'95 993>V-ram 993

If you switch to 964 cam housings, I think everything will bolt up fine and you'll eliminate the hydraulic valve lifters/adjusters too..... I'm sure there's more than just switching cam towers- like valve covers are completely different too. Looking at the diagrams for the 993 & 964 chain box cases, there's some subtle differences there too.

[Nine9six]

...which is why I recommended the machining of a woodruff key slot, rather than swapping cam shafts. Go the quick easy route and eliminate any guess work.
Yes, both camshaft and sprocket will need machining. Small job, so any small automotive job shop should be able to perform the work. Cam shaft gets milled; while the sprocket gets broached.
I would want them to be a reputable shop. Maybe a custom cam grinding shop will take the work.
You are correct. A big shop wont bother with this 1-2 hr job.

[mmasse]

Nine9six

I just got a call from the machine shop. He was about to machine the groove for the key, but he first fitted a 964 sprocket and trust washer, and according to him once you do this the sprocket will sit a bit far out. He mentioned that the edge of the 993 cam has bit of a shoulder at the end which makes the sprocket to not fit completly in once the trust washer and alignment shims are

I guess that's why you mentioned that the sprockets need to be machined as well. could you please be more specific about this? What the job that need to be done to the sprockets?

Thanks

[mmasse]

picture of the 993 for reference where you can see the shoulder mentioned by the machine shop

[Nine9six]

Originally Posted by Nine9six

Ask your machinist, to define how far is "a bit" from proper alignment

I said the sprocket will need to be machined in order to have the corresponding woodruff key slot broached into it, if it doesnt already have a woodruff key slot.
From my previous post:"Cam shaft gets milled; while the sprocket gets broached."

Prior to machining anything, I would have checked for proper alignment by setting the cam into place and checking alignment with a straight edge, to the corresponding drive sprocket.

I suspect the woodruff key slot would need to be properly located for TDC reference of the cam lobes to the TDC marks on the sprocket. But I fugured you already knew this.
I hope this helps...

[mmasse]

I will try to explain better. The shoulder the machinist was refering to is the outer edge (red circle on the first picture- 993 cams).

The second picture is the 964 cam. You can see how the outer edge is square when compared to the 993 cams.

I thinkg the point that the guy from the machine shop is making is that the sprocket will not sit correctly due to the rounded edge. It is not really an alignment issue, but a problem with the shape of the end of the cam not providing for proper support for the sprocket. Now, should he push the sprocket inwards to make it sit properly, then it will clearly not align with the intermediate shaft.


any thoughts on this?

[rsscotty]

You have to have the rounded end of the 993 camshaft welded and then machined to look like your 964 cam picture.

[mmasse]

Any idea who can do this job?

[Mike Juzenas]

Hi Mario,

As we discussed via email, I have backdated the sprockets on my 96 993 rebuild, it worked perfectly fine, and the car has been running for over 20,000miles since the rebuild. I checked the cam sprockets for alignment, they were almost perfect, so I do not think the shoulder comes into play.

How about you check it out by doing a dry-fit of the parts on the engine, and see if that shoulder really makes a difference. You can also machine the sprocket so it fits over the shoulder, but like I said, in my case it worked perfectly.

Same as for the front taper - why would that be an issue? The stress of the sprocket is taken by the inner spocket locked to the outer, so that little bevel on the tip of the camshaft is not a problem, at least to my thinking.

Cheers,

Mike

[mmasse]

Thanks Mike

[Nine9six]

Originally Posted by rsscotty

You have to have the rounded end of the 993 camshaft welded and then machined to look like your 964 cam picture.

I completely disagree with this approach, and the heat that will transfer into the body of the cam shaft will warp it to hell and back! If you are looking for ways to scrap your camshaft, by all means, do as recommended above.

As long as 75-80% of the bore of the sprocket is in contact with the OD of the camshaft end, you will be fine.

Mike is correct!

[mb911]

the funny thing was I was wondering what it would take to switch to hydraulic lifters in my 964 as I hate the sound of my valvetrain by comparison. On my turbo I never heard it because all you heard was the turbo. aside from that why not just do a complete swap with someone. I am sure I am not alone in my thoughts

[mmasse]

After discussing with Mike, I tend to think that I am over-thinking this issue. He has done it and run the car for 20,000 miles with no problem. I guess I will stop worrying about this and do as Mike did!

[KTL]

Originally Posted by Nine9six

I completely disagree with this approach, and the heat that will transfer into the body of the cam shaft will warp it to hell and back! If you are looking for ways to scrap your camshaft, by all means, do as recommended above.

You sure about that statement? How are cams hardwelded w/out being destroyed?

[Nine9six]

Originally Posted by KTL

You sure about that statement? How are cams hardwelded w/out being destroyed?

Kevin,

YES! In this instance, I am... And please dont take my comment out of context.

I am not saying you cant weld up a cam. I am saying its not that simple; and in this case, not applicable or practicable.

Tell me something. Considering the application, do you think the cam end should be welded up, stress relieved, machined and ground to size?

If so, maybe you'd like to chip in to help pay for all the added pointless process steps?

I do like your attempt to needlessly spend someone eles's money...

Oh, and is the shop mmassee is using, a cam grinding speciality shop, or a small machine shop that may be thinking as you?

BTW, could you please explain the process of "hardwelding" I have never heard that term before and I am always open to learning something new.

nuff said...

[mb911]

ok I personally have welded up a cam shaft for a reburn engine (patent testing) and we did run out after building some of the lobes up as much as .600 run out was almost none existent but that was one camshaft for straight 6.

[KTL]

Hey take it easy and spare the attitude. Who died and made you moderator?

My intent isn't to needlessly spend someone else's money. Don't put words or intent in my mouth. I wasn't endorsing the welding method with the comfort of "spending someone else's money" needlessly. I was simply questioning how you believe the cam would be destroyed by welding on it, when you apparently know, based on your last post, that welding can be done on a cam.

I didn't take your comment out of context. I asked the question because hardwelding is indeed a process that is done on cam lobes to use an existing cam as a "core" but its profile cannot be reground to creat the desired profile. If the lobes can be welded, the bearing areas can certainly be welded. That's why I asked the question. Read & learn

Web Cam Inc. - Performance and Racing Camshafts

Read #6

Web Cam Inc. - Performance and Racing Camshafts

Go down to the bottom of the page and read the bold.

http://www.elgincams.com/c-por2.html


Hardwelding on the sacrificial cam provides the foundation on which the weld material is built-up. Then the cam is re-ground to the desired profile. Here is a set of SC cams that were hardwelded by WebCam to create a 911S profile.

S Cams for Carbs- Webcam 149S Hardweld

Look at the second picture in my sale ad and you can see the difference in color on the side of the cam lobe. The brighter metal is that which was built on top of the original lobe, which you can still see. Hardwelded cams are typically used for racing applications and/or stiff valve springs because the welded cam has a greater hardness than a new billet cam.

And I would suspect rsscotty suggested it because he's done it before. He's associated with Rothsport Racing and they've got a pretty good reputation when it comes to engine builds, race prep, fabrication, blah blah blah etc. etc.

I added something very constructive to the initial post in my own first post by pointing out that the first 993 cam used a woodruff key and 964 sprocket flange. Proving that at some point the 993 engine was keyed and then the designers chose to do away with it for some reason.