[sparky]

From my recent experience rebuiling my 968 engine I found the Workshop manual really doesn't explain the setting of the camshaft timing that well. I have prepared a technical paper that clarifies the relevant sections of the workshop manual. I am offering this paper, including it's 5 attachments (one chart and 4 photos) as a permanent reference for the 968 community.



cheers

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[flash]

great effort - i'd love to see more stuff like this from people who work things out



having seen this done at rs barn however, there seems to be quite a bit missing, though this may be all that is needed for adequate timing within factory spec - i'm not at liberty to discuss the details though, nor am i thoroughly clear on recollection - this is one of those "things that sets one shop apart from another", and while pretty handy with a wrench myself, i figured that when i installed new cams, i would just fly pete out to do it, so i didn't bother to write it down or memorize it



i would contact pete - in discussing this with him, i can say that it appears that a good portion needed to really set it right was left out of the manual - most shops don't even know about what is needed - i can also tell you that it sems that my engine was "off" from the factory, though it appears within spec per those instructions, and after he timed them, it was quite different, and noticeably improved



again, i commend the effort, but recommend trying to see if there are some critical things missing or that could be included - it may turn out though that the additional steps are for performance tuning, and not for standard rebuild - we had some similar "tricks" for tuning the mgb engines, and kept them pretty much to ourselves

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[RS Barn]

My first post in awhile!!!

Timing the 968 cams is quite a miracle to do correctly. The factory info leaves alot to be desired. Even if you follow instructions to the letter you can be .2mm off which exuates to 4-6 degrees.

The falicy of using the factory marks (---) three letter name, is just that -a gross misinterpretation of the dynamics required to do this correctly.

I've degreed in a few engines just to verify factory specs and how changes affects results.

I just checked cam timing from a newly touted shop in NY and found cams to be .0025" (.2mm) off.

I don't have a quick easy answer for the DIY or even experienced shop.

I just know it is a critical setting.

Pete

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[Cloud9...68]

Hmmm... This is kind of scary, for anyone who has gotten, or is contemplating getting, their variocam pads and chain replaced. For those of us who don't exactly live up the street from Pete's shop, is there an objective list of mechanics around the country who truly know how to set the cam timing correctly, so we don't end up with several hp left on the table? It's a little late for me, as I had this done a couple of years ago; I just hope my guy knew what he was doing...

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[sparky]

oops, I may have accidentally set off some unnecessary paranoia ...



Once you get the dial gauges set in place, and you understand what you're trying to do, it's not hard to find the true TDC of piston #1 using dial gauge #1. As indicated by RS Barn Pete, the tricky bit is trying to get the inlet valve lift to be within specification range (0.39 +/- 0.3 mm) using the second dial gauge.



Look again at the first photo of the camshaft drive gear. The wide keyway slot provides the adjustment range, it isn't a big range! As long as you have your coarse timing right (using the flywheel marks) all the fine tuning is about getting this cam drive gear locked in the right spot on the camshaft.



The worst that can happen is your timing ends up a bit out and you don't quite get max power. Even if that happens to me, I will simply vary timing experimentally (with no dial gauges and without pulling camshaft cover off again) by loosing the drive gear centre bolt and moving the camshaft gear a tiny bit on the camshaft, and testing power again... if it gets better good. If not, try again rotating the other way. the range in that keyway is not that big ...



so I'd say not scary, really ....

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[flash]

no, not scarey - i was surprised though at the difference, especially considering i am all but certain that mine was factory set, as it only had 22k on it when i got it, and i know all of the service since then, with no change in cam timing

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[Cloud9...68]

By "scary," I didn't mean scary as in fear of something breaking or blowing up as a result of not getting the cam timing perfect, I just meant that it seems to be very difficult to trust that the cam timing has been set correctly if for any reason the cams need to be removed. But I guess that the potential loss of even a few precious horsepower in these engines can be pretty scary...

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[tloof]

I recently replaced the variocam chain & sliders along with all the belts & seals in my engine myself. It requires making a few special tools to do so correctly, but isn't too bad to do. Instead of trying to mount the dial indicators to the head with magnetic bases like Sparky did, it is far better to go get two low cost adjustable dial indicator mounts from someplace like Harbor Freight that screw into a threaded hole. I made two metal mounts out of 1/4" steel flatbar that I drilled holes in to allow them to bolt on the head where the valve cover bolts attach, and also a threaded hole that the dial indicator mount screws into. this provides a much more secure setup and also allows easy adjustment of the dial indicator extension rods (these I made from 3/32" steel rod that I threaded to fit into the dial indicator plunger...one that was straight and 8" long, and the other a few inches long with a 3/4" long 45 degree bend in it that is rounded off so that it will fill well on the #1 intake disk that the cam lobe depresses). It is very simple to identify the exact TDC point with the dial indicator with this setup. You will also have to make a special air fitting to pressure up the variocam assembly, and this can also be made out of 1/4" steel flatbar by tracing the variocam oil feed tube flange mount onto it and then drilling the required holes so that it will bolt in place of the oil tube. Before bolting it on weld a straight 1/8" steel pipe threaded coupling onto that plate flange which will allow an air chuck fitting to be screwed into it and thus an air hose to be attached.



The procedure that Sparky gave can then be used to adjust the cam timing fairly precisely. As for RSBarn's mention of cam timing variances, it all comes down to either following the depressed cam lifter dimension that the factory manual gives or degree wheels will have to be mounted on the cam drive pulley to determine that exact degrees of cam timing that it moves when adjusting it...take your pick! I used the value given in the factery service manual and adjusted it fairly precisely (the value stayed the same after rotating the engine thru numerous times after the initial setting), but I didn't check it with a degree wheel to see if that matched the specs for when the intake valve actually was supposed to open or close.



Perhaps Pete from RSBarn could shed a little light on the most precise method to use in order to best do this job so that we can all achieve the greatest power this engine is capable of?

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[RS Barn]

It actually comes down to where Piston TDC is. Piston stays at TDC for approx 8 degrees of cam timing.

You are right about degree wheel which can tell crank degrees vs cam timing. Long process of figuring out basic timing vs torque timing in factory information. The degree wheel goes on crankshaft!!!

I will be glad to discuss offline with anyone (well most) attempting to do this himself or clue his shop in.

Pete

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[FRporscheman]

Sparky-

Thank you for providing us (me) with such a valuable article. I have had 968 cams out twice, and both times I just did my best to make marks and put everything in the exact way it came out. I yearned for a clear method to set the timing.

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[sparky]

my pleasure FRporscheman, let me know if you find any improvements to be made.

man that's some stable of porsches you run ... the his / hers balance must be a challenge ?!

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[SpeedRacer64]

[quote name='sparky' post='42873' date='Oct 25 2007, 04:04 AM']my pleasure FRporscheman, let me know if you find any improvements to be made.

man that's some stable of porsches you run ... the his / hers balance must be a challenge ?![/quote]



No mention of where the "best" setting should be for maxium gains?



Tried and True....advance to increase low end...retard for high end performance....



So where does the BiG LiTTle 3.0 like to live?



LuKe

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[RS Barn]

I can discuss cam timing specifics with anyone who plans to use the Factory guidelines and calls me.

There is someone at Renn---- telling people the timing doesn't matter. His theory is the cam belt sprocket was marked by the factory after setting the timing correctly. This is true for the original belt. Any change, belt,pulling Cams to change pads change "Everything"......

The correct cam timing relates to intake cam location in relation to Piston TDC at cam overlap.

Pete

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[sparky]

Pete - I am keen to learn what you are hinting at. I tried to call you on this topic a few months back, but never got through. What is best number to ring you on? And what days / hours ? (I will be calling from Australia!)



[quote name='RS Barn' post='46492' date='Jan 29 2008, 01:14 PM']I can discuss cam timing specifics with anyone who plans to use the Factory guidelines and calls me.

There is someone at Renn---- telling people the timing doesn't matter. His theory is the cam belt sprocket was marked by the factory after setting the timing correctly. This is true for the original belt. Any change, belt,pulling Cams to change pads change "Everything"......

The correct cam timing relates to intake cam location in relation to Piston TDC at cam overlap.

Pete[/quote]

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[RS Barn]

Sparky,

I am here most weekdays from 10AM-6PM Eastern standard time.

If I'm not here Max can explain to you.

I think I have a simplified procedure written down somewhere I could send.

Pete

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[kwikt]

After researching over the last month, I am finally going to tackle the cam chain and pad replacement this weekend. Got my pads, chain, rollers, belts etc. I even have 2 dial indicators and a homemade tdc dial indicaor adaptor that screws into the #1 spark plug hole. The cam timing procedure seems to be similar to that of a 911 which I have done numerous times. If...If I run into a "slight" snag, would their be anyone on this message board that I can call this weakend to offer some advice. Thanks!!!!!



Kevin

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[SpeedRacer64]

[quote name='kwikt' post='46531' date='Jan 29 2008, 11:22 AM']After researching over the last month, I am finally going to tackle the cam chain and pad replacement this weekend. Got my pads, chain, rollers, belts etc. I even have 2 dial indicators and a homemade tdc dial indicaor adaptor that screws into the #1 spark plug hole. The cam timing procedure seems to be similar to that of a 911 which I have done numerous times. If...If I run into a "slight" snag, would their be anyone on this message board that I can call this weakend to offer some advice. Thanks!!!!!



Kevin[/quote]



Pete



Thank-You again for the information/instructions with respect to cam timing, very insightful....Good Luck and continued success with the site...looking forward to the coming changes.



Be Well



LuKe

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[kwikt]

Is the camshaft gear suppose to slide off or is a puller required? Thanks!

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[blue968]

[quote name='sparky' post='42130' date='Oct 8 2007, 04:50 AM']From my recent experience rebuiling my 968 engine I found the Workshop manual really doesn't explain the setting of the camshaft timing that well. I have prepared a technical paper that clarifies the relevant sections of the workshop manual. I am offering this paper, including it's 5 attachments (one chart and 4 photos) as a permanent reference for the 968 community.



cheers[/quote]





Hi Sparky,



I was wondering if you have a how to on changing the timming belt,rollers and water pump?? I think the hardest part is setting the camshaft to the crank but i was hoping to get some help before attempting it.



thank You

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[sparky]

The workshop manual descriptions for removing / replacing the camshaft & balance belts is pretty good. Once you have them removed the water pump is pretty straight forward: just undo all the bolts/nuts around the perimeter and gently prise it off. Clean up / remove the old gasket remnants and fit the new pump. Then follow the manual on how to get the belts properly aligned.



There is one slightly tricky bit - setting the balance belt tension requires a long 27mm spanner and a special Porsche tensioning tool, or at least good experience to know what is right tension. Not that I'm that experienced, but I tensioned it without the tension tool ... at first it was too tight and noisy, so i loosened it a tad and the noise reduced accordingly. An very experienced mechanic friend suggested the tension should be such that I can twist it through about 90 degrees with my fingers. That's where it is now, and it's working/sounding fine, but this week I'll take it to the local Porsche workshop to get it properly tensioned with the proper Porsche tool.

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