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.

dgmattingley

Hi,

I would check with your machinist, I believe it is easy for them to machine the groove into your current cams. I'm going through the same rebuild process right now, although my cams had the grooves. I just ordered the 964 sprocket setup from a used parts suppiler. Good luck!

cheers,
Don

Pete Debusmann

I answered this on Pelican. The 964 cams are different. 993 cams have a groove machined in the first bearing journal. I think this is to get oil up to the hydraulic lifters. Also the shape of the cam lobes is different due to the hydraulic lifters. You can use a cam designed for hydraulic lifters in an engine with mechanical lifters, but not the other way around. It is easier to just get a keyway machined in the cam. Dave Coleman in WV did this for my cams.

Pete

Steve Weiner-Rennsport Systems

You cannot use a 964 cam in a 993 engine unless you convert to 964 rocker arms without hydraulic lifters (besides all the machining for keyways).

The ramp profiles are different; you can use a hydraulic cam in a solid rocker engine, however you cannot use a solid rocker cam in a hydraulic engine.

bobt993

Have you pulled the cams yet? A good deal of the 993 cams have the key way already. All the cams I have removed have had the notch for the woodruff key already. Also check with Steve Timmons if you plan to use solid rockers. It is advisable to have the lifters/heads setup for the lack of using the hydraulic oil passage. As Steve stated the hydraulic cams have a pre-load built into the ramps for the lifters.

mmasse

Thanks for all the input. I will stick to the 993 cams and have the keyway machined.

Unfortunately the keyway is not present on my cams (they are '97)

B

bobt993

^^^ 97,98 likely missing. Seems like 95,96's have them. Your other option is to write an email to Instant G. I think he has some moderated cams you can swap out with him that give you a little bit more torque/hp. That opens up the option to re-map your ECU a bit for the upgrade and pick up yet more HP. 97/98 ECU can be re-mapped which Steve Weiner can provide.

mmasse

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.

Have anyone faced this issue when doing this job?

mmasse

Picture of the 993 cam where you can see the shoulder mentioned by the machine shop

berni29

Hi

My 993 has the early style cams and sprockets, and the sprokets do not fit fully on the cams. I guess they are a bit more than half on! Def looks wrong but it isn't. You may have to do some re shiming to get them parallel.

Edit, I have some pictures of the cams and will have to have a look and see if mine have the shoulders.

Berni

NineMeister

Yes, but there is an easy fix. Have your shop turn down the last 5/16" of the cam so it is parallel, then make and shrink (or loctite) on an oversize steel sleeve. Then turn down the sleeve flush with the location diameter for the sprocket. Leave the end of the sleeve square to give the maximum support for the sprocket.

As others have mentioned, it's a relatively easy fix to cut the woodruff key slot however don't forget that the slot is also an indication of the correct cam position for installation; the key is set at the top of the vertical centreline with the cams at TDC.

NineMeister

Sorry to break it to you Berni, but the accurate end location of the sprocket is critical. Without the full diametric support of the end of the cam the sprockets will run eccentrically when installed, causing harmonic problems and possible failure of the chain tensioner.

berni29

Hi Colin

They basically went back on the way they came off and were original to the engine along with the sprokets. Perhaps I expressed myself badly, but if you look at the following link from pcarworkshop mine looked exactly like the ones in the picture where he is putting the locking pin in.

http://www.pcarworkshop.com/index.ph..._timing_Part_I

All the best

Berni

mmasse

Berni,

I guess the problem is generated when you change the sprockets for the 964 ones. The original 993 sprocket is a one piece part and has plenty of diametric support.

Colin,

Thanks a lot for your input i will talk to the machine shop and provide this alternative. It should be much cheaper than a set of new cams!!!

NineMeister

There is no problem with the end-relief 993 cams if used with the one-piece 993 sprocket, only if using them with the 911/964 two-piece sprockets. Of course, the 993 sprocket does not have a locking pin.....