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!

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.

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.

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

Yeah, I'll be one scott. :D 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.

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.

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.

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. SmileWavy

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. ;)

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.

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.

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...

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

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 ½” 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. :D

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

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.

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!

Good luck, John!

Subscribing for information purposes. I may have to do this procedure very soon.

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.

AWESOME! Just make sur you don't time the right cam 180 degrees out, and you'll be the golden boy! LOL! Well done!

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.

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.

Grady, is it possible that you could snap a photo of the cam timing tools you use and made to do timing your way.
I think I can envision correctly what you procedure is and the tooling you crafted and use, however, a picture is worth a thousand words and your pictures and words are worth a ga zillion words to me and probably most here also!!

Thanks in advance Grady if you are able to post some pictures here.

Take care!
Bob

I finished up the ride side this afternoon.

I found that not only is the oil important, but keeping the chain extremely tight (more than you think you should) will also help out a whole lot. Luckily I found two mechanical chain tensioners online for cheap. They made this process so much easier.

On the right side instead of having to over compensate (choose a higher value) than the left side, I had to under compensate (a lower number than I wanted). It ended up being so spot on that I only had to go down one degree (started at 1.69 and achieved 1.70).

The crazy thing is, I put the guage back over on the left side and the timing actually changed a degree to 1.70 which worked out perfect!

I will be sure to check all the timing again after the chain tensioners go in.

Thanks again for everyone who gave thier input. I do hope this thread will help out others just like it did for me!

AngM018, what & where did you get the two mechanical chain tensioners? I need to buy two also for a rebuild.
Thanks!
Bob

picked them up on evilbay. I have been religiously watching ebay for Porsche parts/tools since january, and this was the only set I have seen. I dont think they are too expensive to buy new, but well worth the cost.

Thanks John! Can you post a picture of these mech tensioners? Do you know if Pelican sells these or where they can be bought?

Thanks alot!
Bob

Here's what mine look like. They are from Pacific Designs Inc.

http://forums.pelicanparts.com/uploa...1191258788.jpg


Here is what our host sells. These one's look better made than mine, but its not like they will actually be left in the engine, so I doubt it would really matter.

http://forums.pelicanparts.com/uploa...1191258915.jpg

Part #: STROMSKI-SR011
Price: $82.00 for the pair

thank you John!
Bob

I'm a bit late to the thread, but perhaps not too late...
There is considerable play between the pin, the sprocket and the nothc in the drive flange. This fact accounts for the movement observed by some posters while tightening the cam nut or bolt. Keeping the mechanism loaded in one direction while changing the setting and tightening fasteners minimises this effect.
FWIW, my procedure for timing the cams:

Preliminaries: Initially set the cams slightly advanced (keyway slightly to left of vertical). Not too much or with hot cams/high compression/tall pistons you'll get interference. Have all rockers installed and all valves adjusted. It does make a difference. Torque both cam nuts/bolts every time. It also makes a difference. Install mechanical tensioners. If unavailable, use C-clamps to pull the idler to the chain case. Tension chains tight, but not dead tight. Install degree wheel and determine TDC with dead stop method. Pulley works, but could be off. Install and zero indicator, obviously :) Lubricate the threads and surfaces that slide (side of the nut, under head of bolt) with a moly lube. Porsche are even very specific which lube is approved, but I use what comes with the ATP rod bolts or CV joint grease.

Procedure: Turn crank to desired lift. Long handled wrench on pulley nut works well. Crank will be beyond TDC. Holding the crank with the wrench, loosen the nut/bolt and slowly turn crank back to unload the pin, move pin to next hole until it slides in. Reverse direction on crank and keep pressure on while torquing the nut/bolt. Turn back until the indicator is at 0, then forward to desired lift as before. Repeat until as close to spec as possible. Final check by turning forward a whole cycle. My goal is to get within at least .05 mm. Advanced cam is better than retarded. Finally, if in doubt, check piston to valve clearance by threading a wide nut on a valve cover stud and using a prybar repeatedly push the valve open to feel the play while slowly turning the crank past TDC. 0.020 in with stock valve springs. At .010 you can usually hear contact noise at around 6.5 G due to float.

Couple hints: There should be no axial play between the cam and the sprocket.
When using a nut, be careful that the huge wavy washer is centered. The hole in it is large enough to allow it to get caught on the lip of the sprocket. Result: The nut, while torqued, will come loose.

Has worked well for me. I'm sure there are other methods which work just as well. I'm not preaching gospel.

I pulled the right side cam tower and replaced it due to a rocker shaft boss failure. I left the left side completely buttoned up... haven't touched the cam or anything. I'm now at a point where I'm ready to re-insert the right side cam, rockers, shafts, etc and time it. Most of you guys have pulled both sides and are starting from scratch with the left cam, then the right, etc. Am I ahead of the game because I didn't touch the left side? Or, do I need to re-time both sides. What's the procedure in my case where only the right side needs to be timed?

Thanks.

-Troy

Here's what I'd do:

Install your dial gauge on the left bank/#1. Ensure left-side chain is tensioned up, or clamp the idler arm to the top of the chain housing to tighten the chain. With your rockers backed off on the right bank (don't want to ding a valve while messing around over on the left bank), turn the engine to Z1/TDC overlap on #1. Take a reading of the cam timing on the left bank. Ensure both that you can repeat the measurement (by turning the engine thru 720' a couple times) and that the measurement is within specs. Now time the right bank as closely as possible to the reading you took on the left. Don't sweat it if you use different techniques to tension the chain left vs. right; on the stock DME cam a minor variance is not going to have any impact.

Most first-timers seem to get confused about the orientation of the cams during the timing process. Here's a way to improve the process above if it makes sense to you. With both chain covers off, turn the engine to Z1 and make sure the dot or '911' (or other PN stamping on the snout of the cam) on the left-side cam is pointing up. If pointing down, turn the crank through another 360. Now turn the right-side cam by hand (with rockers backed off) to the same orientation - markings up, so it is the same as the left. Now keep this rough timing by pinning the cam to the sprocket with the dowel pin and hand-torquing the bolt. While taking measurements on the left, the right will stay rough-timed. After finishing taking measurements on the left, set your dial gauge on the right and turn through 360 on the crank. You'll be on-cam on the right bank/#4, and ready to fine-tune timing.

Exercise extreme caution with the woodruff key and dowel pin, they WILL throw themselves down the chain case at the slightest opportunity. Often a good idea to stuff a clean shop towel down there. Saved my bacon on my latest build.

Is your left-side cam housing ok? Hate to see you going through this again in a few months on the left bank.

Thanks Dave! Great advice... and that doesn't sound bad at all. I've been dreading the cam timing part of this job.

I had been chasing an oil leak on that right side for some time, ended up putting RSR seals in there and, I think, over-torqued the sleeves causing the boss failure. The left side looks good, although I am gonna go back in and re-torque everything to spec just to make sure. Was real lucky I didn't do a ton of damage.

-Troy