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Question Not your average Cam timing Question

Myself and Sand_man have been trying to figure out an issue we're having with timing my 79 930 (SC cams).

We do all the steps needed with the pin etc. on the right side, but when we go to tighten the nut and washer the timing is thrown way off.

First we tried to compensate but found that it is off by different numbers every time (anywhere from .05mm to .35mm). We even tried using a different pin location, but still have the same issue with it changing when tightened.

We tried different methods to tighten the bolt and hold the cam, but have noticed the sprocket itself is being moved by the nut and washer being tightened (chains are as tight as possible). It has even gotten to the point that when we undo the bolt and re-check with the pin in, the number goes back to where we wanted it

Anyone one have any thoughts on what we did wrong, or what we can do to prevent this movement, and get exact timing?

Thank you!

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1979 Porsche 930: 3.4L, SC cams, Twin plug, Leask WUR, Custom SSI turbo exhaust, Tial WG, K27HFS, and we can't forget the Zork (short lived depending on my homeowners assoc.)
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Old 09-28-2007, 09:48 AM
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To John's point, I have the newer style cams which I found much easier to torque to spec without moving the cam...John has the early style cams that use the large crows foot. I have found the earlier style much more awkward to keep secure while applying the torque.

One possible idea was to try and factor in some of this movement into the index hole selection crieria. For example, either retarding or advancing the cam ever so slightly so that once we've gotten it all torqued, the correct value reads on the dial gauge when we check it.
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Old 09-28-2007, 10:15 AM
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It just seems that no matter how hard we try to keep the cam steady, we can see the dial gauge jumping right before our eyes as we apply the torque.
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back in the saddle: '95 993 - just another black C2
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Last edited by sand_man; 09-28-2007 at 10:19 AM..
Old 09-28-2007, 10:16 AM
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You know....there are probably going to be some wankers who jump on me for this...but here's my 2 cents on timing cams with the early style nose (crow's foot /46mm nut)

-use the cam turning bar to get the timing where you want it, _._mm overlap @ TDC
-Lock the flywheel ...I use an A/C bracket with two bolts-one on the case and one on the flywheel
-take a 1-13/16" Snap-on Socket (or 46mm, if you can get it...I got mine at Sears), and tighten it to torque specs. (110 #-ft.) with a torque wrench
-Check your timing. if ok, move on, if not, repeat steps 1-3 until you get it right.

You may need to adjust it so that your timing is .1-.2mm 'backwards' so when the nut finally grabs and holds the sprocket, your timing is right where you want it.

Might get tedious, but at least you won't have that stoopid crow's foot slip off the nut, and your cam won't move a dot...

godspeed
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Last edited by YTNUKLR; 09-28-2007 at 02:13 PM..
Old 09-28-2007, 02:10 PM
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Yeah, I'll be one scott. I wouldn't use the chains to hold the timing while you torque it.

Guys the timing shouldn't slip that much while you torque the nut. Yeah the flange and chain sprocket can move sometimes a little when you do this,

On the later style if you are holding the timing sprocket with the tool, it won't move. I thought the 79 had the bolt and not he 46mm nut.

With the nut the spring washer should insulate the sprocket from moving. If it doesn't, try putting some oil between the 46mm and the sprocket.
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Old 09-28-2007, 02:42 PM
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Thanks for the replies, guys!

John's car is actually one of Porsche's "cross-over" models, so some parts are "old skool", some are new...in this instance, he's got the big ol' nasty crows foot!

What I'm thinking John, is that there is no way around it, you're/we're gonna have to better control our technique for holding that bastard...I mean it's obvious that it's gonna be trial and error to make it work out.
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Old 09-28-2007, 02:49 PM
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Sorry guy's I don't understand this sprocket and cam slip. If the woodruff key is in place at the cam, the sprockets are held firmly in position to the cam.
If all this is still slipping with the woodruff key in place, then the problem is at the drive sprockets on the intermediate shaft. Same type of issue.
We are talking keyed sprockets and shafts here.
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Old 09-28-2007, 03:42 PM
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I know it doesn't sound kosher but my method certainly works. The real crux of it is to check your measurements carefully (multiple times) after you arrive at the specified value, and see where they're at. If they're bang-on, and the nut is torqued, you're good to go.

AFA bolt vs. nut...the change-over was '81. I just rebuilt an '82 and it still had the big nuts (pun not intended) on the cams.
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Old 09-28-2007, 03:56 PM
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Right or wrong, I use the same method that Scott uses; a 1-13/16 socket from sears with the fly wheel locked. Several local shops use this method as well. I tighten down as much as I can with the crowsfoot and hold back on the cam, verify the lift, then to get the final torque value I break out the socket. It's much easier to remove the nut this way too.
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Old 09-28-2007, 06:29 PM
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I'm nor sure I understand the problem here either. As 2.7RACER points out, everything is keyed so the parts cannot turn relative to each other. I am wondering if the problem is just that the dial indicator moves when you tighten the nut - not that the timing is changing, just the cam is rotating slightly from the torque. I tighten my nut with the crow's foot and hold the cam with the socket. While tightening, I don't pay any attention to whether or not the cam moves slightly - I am holding the torque with the socket, not the chains. Then I spin the engine over a couple of times and check how well I did at setting the timing. I don't try and hold the cam and check the timing without turning it over once. I never understood the need for the instruction in Wayne's book to hold the cam from moving.

It could also be that your sprocket and pin are worn out and not a tight fit anymore - and the sprocket is turning relative to the cam.
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Old 09-29-2007, 06:33 AM
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if you have the chain preloaded in the direction of rotation with tension against the pin, it shouldn't be a problem. if you have slack in the chain, ie the pin is loose, it will never be repeatable.

After you insert the pin, you will have to rotate the the cam in the opposite direction of rotation while holding the crank steady. this will retard the cam. check timing/lift. if too retarded, advance the pin one location and verify again. at this point you know that the slack is removed from the chain and you can begin tightening the cam nut.

i do have to comment that i find the design completely insane that the nut is not self tightening with the direction of rotation...
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Old 09-29-2007, 08:02 AM
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Quote:
Originally Posted by 2.7RACER View Post
Sorry guy's I don't understand this sprocket and cam slip. If the woodruff key is in place at the cam, the sprockets are held firmly in position to the cam.
If all this is still slipping with the woodruff key in place, then the problem is at the drive sprockets on the intermediate shaft. Same type of issue.
We are talking keyed sprockets and shafts here.
Even with the woodruff key and the pin inserted, before the cam nut is torques the sprockt and flange can move independent of one another to some degree
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Old 09-29-2007, 01:05 PM
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I use the same basic technique as Scott.

A couple of things to note.
I ONLY have the #1 or #4 intake rocker installed, never all six on a side.
I lightly oil the cam threads, nut and washer.
Over the years I have made and modified the wrench and holder. The holder is a modified milled (not stamped) version. The wrench is a modified SnapOn 46 mm offset box wrench (3’handle) with a ” socket welded on for the torque wrench.

With this issue, I would carefully inspect the toothed hub, pin and sprocket for wear at the pin surfaces. The pin should fit ‘tight’ in the sprocket and need a screw to remove it (a sparkplug works). I have disassembled some engines where the sprocket and toothed hub were so worn the builder installed two pins in adjacent holes (and had incorrect timing).

The spec for the pin to toothed hub (Porsche calls this a ‘sprocket carrier’) is 0.000 to 0.0.029 mm. The spec for pin to sprocket is 0.032 to 0.610 mm. I would run these clearances as tight as possible consistent with correct cam timing.

I never adjust the cam timing exactly where I want it on the first try.

I use a solid tensioner when measuring. I never use the chain to restrain the cam sprocket. That always gives a poor adjustment.

Always measure many times, particularly after you have the normal chain tensioner installed and all the rockers. Never turn the engine counter to the normal CW direction. If you go past TDC, continue two more revolutions.

At you first service (and occasionally thereafter) you should measure the cam timing after torquing the heads and rocker arm shafts and adjusting the valves.

Best,
Grady
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Old 09-29-2007, 04:46 PM
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You guys have been great with the advice. I undertsand completely about how this really shouldn't be so much of an issue, provided all the gear wood-ruff keys have been installed: John is confident all the keys are there.

As for the wear condition of the actual sprockets, index pins, and related hardware...I don't know. When I did my engine, these parts were carefully inspected by the machine shop. John will have to provide his input on this area...I'm not sure how much mileage is on these parts. The chains are new...cams are new.

Last word I got from John was that he was going to give YTNUKLR's method a shot. I do remember having my flywheel locked up when I went for the final cam torque.
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back in the saddle: '95 993 - just another black C2
*SOLD*: '87 930 GP White - heroin would have been a cheaper addiction...
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Old 09-29-2007, 05:16 PM
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I was not able to get to this today as I was stuck at a house I am helping rehab. Thanks for all the info guys. Mike Bruns From JB racing PMed me and gave me some pointers as well. The keys are definately installed, as they were a bit of a pain to get in since the cams are brand new so I know this was not forgotten. Sprockets did have quite a few miles on them, but still are within tolerences.

Tomorrow I will be doing the following:
1. Oil the face of the spocket, washer, nut, and threads on cam.
2. Lock the flywheel
3. Figure out a way to hold the cam so it doesn't move at all (this will be the trickiest part)
4. Tighten up the chains even more (I doubt this will be possible b/c they are already so tight)

Mike also reinforced that the timing will change and I will have to compensate for this. Hopefully using the oil will help keep this range around the same, unlike the huge differences I was getting before.

Thanks again for everyones input. Sand_man and I tried a many different ways to get this to work, but now I feel confident having some more techniques in the "bag of tricks"

I will let you guys know which way worked the best. Wish me luck!
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1979 Porsche 930: 3.4L, SC cams, Twin plug, Leask WUR, Custom SSI turbo exhaust, Tial WG, K27HFS, and we can't forget the Zork (short lived depending on my homeowners assoc.)
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Old 09-29-2007, 08:34 PM
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Good luck, John!

Subscribing for information purposes. I may have to do this procedure very soon.
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Old 09-29-2007, 09:44 PM
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Well I couldn't sleep with this on my mind, so it is now 4am and I have the Left cam Timed!!

Motor oil, Motor oil, Motor oil!!! I followed the procedure outlined in Wayne's book, but this time I covered and smothered the sprocket, washer, nut, and threads on the cam. I could tell immediately that the nut wasn't grabbing hold of the cam like it did when Sand_man and I first tried (which moved the cam before the washer and nut could get tight enough to hold it).

I just used the torque wrench on the crows foot, and a breaker bar on cam holder. Then i just kept my eye on the dial gauge and watched for any movement. On the third try I advanced the timing to 1.73 and settled at 1.69 (optimal was 1.70 max, but i didn't want to push my luck)

BEWARE! Make sure you wipe off ALL excess oil from the nut and the crows foot tool! The crows foot is not the best designed tool and when you add oil into the equation a large steel crows foot could slip and head towards the lower waist area (depending on how your standing). Luckily I was not injured when this occurred

Thanks everyone for all their input thus far! at least now there will be a thread on this, for future re-builders (i already searched and there was not)
I will let you guys know how the right side goes tomorrow.
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1979 Porsche 930: 3.4L, SC cams, Twin plug, Leask WUR, Custom SSI turbo exhaust, Tial WG, K27HFS, and we can't forget the Zork (short lived depending on my homeowners assoc.)
05 Boxster S: For the Track.
06 Dodge Ram 2500 Power Wagon: Tow Vehicle

Last edited by AngM018; 09-30-2007 at 12:52 PM..
Old 09-30-2007, 12:11 AM
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AWESOME! Just make sur you don't time the right cam 180 degrees out, and you'll be the golden boy! LOL! Well done!
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Old 09-30-2007, 05:12 AM
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Quote:
Well I couldn't sleep with this on my mind, so it is now 4am and I have the Right cam Timed!!
Way to go John! It sounds like Grady's advice to lightly oil the nut and washer was what you needed.

During my first cam timing, I couldn't get everything correct in my mind. It kept me up at night until I just got up at 2:00 am, went down to the shop in my bathrobe, timed my cams correctly, and then went back to bed.
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Old 09-30-2007, 05:29 AM
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Congratulations John,

I have been following this thread so that I will know what to do when I get to that stage on my rebuild (should I have similar issues).

I got it......lots of oil on sprocket washer, nut and cam threads, then remove ALL the oil from the nut and crowfoot tool and put a cup on to protect your jewels (just for added protection).

This would make sense to eliminate as much friction as possible between the sprocket, washer and nut.

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Old 09-30-2007, 05:48 AM
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