Rocker side to side play?

vreference · 10-02-2008, 12:42 PM

I keep finding mentions of Rocker side-to-side clearance issues from searches in the 911 and 930 forums. Although people have noted that it was responsible for their elusive noises I have yet to find any measurements. What is an Acceptable measurement? Bentley doesn't have a spec or procedure for this as far as I can tell. What's the procedure to fix this? My schematic doesn't show shims - just rockers and towers.

I haven't been around for a bit; my elbow ended up in four pieces and I haven't touched the 911 in two months. Physical therapy has progressed enough that I got under it with the intention of finding out once and for all if my clack is due to valve lash. I had planned on just setting 0 clearance and running it for a few seconds to see if the sound went away. Instead I found two valves that were now measuring to loose and decided to set them properly once again with complete confidence that this was finally the solution. Ironic that each time I feel confident walking away with repeatable measurements. Fool me once... After setting with a .004 feeler a hair tight I confirmed with backside which also agreed, once again, that things were perfect. I buttoned it up and my clack is still there. I think it's worth noting, through this whole process, the sound hasn't change in intensity or tone; through 4 or 5 adjustments now. The car still runs great, I have found no extra metal in the oil after 1000 miles. I keep thinking about breaking down and taking it to a shop but it's just not in my nature. I can't let this beat me. At the same time I can't enjoy driving the car with this clack following me around.

billybek · billybek's Garage

Can't help, but I am interested in finding the answer as well.
Bummer about the elbow. It is one of those most used body parts that you really miss when they are out of service.
Subscribed.

db_cooper · db_cooper's Garage

I did the factory training for 911 engine back in the 80's. As I recall, there is no real spec for end float on the rockers. Obviously, they should not be tight or excessive.
I believe the thinking was there is very little thrust from side to side and, therefor, little load.

Noisy rockers were almost always wear on the rocker shaft and bushing. This caused the clearnces to wander around. If you are having issues with the clearances changing, look at the shafts and bushings.

I used to, when making a valve adjustment on an engine with any mileage, remove the rocker shafts and rockers, insure they were in spec and replace 180* out from the position at removal.

You could remove your most problematic adjusted rocker and inspect. If it is OK, reinstall, again, with the shaft turned 180* on the "fresh" side.

dshepp806 · dshepp806's Garage

I, too, have this "sound" at ~9-10K on the last valve adjustment.....time to take a look.

I, too, have been researching the rocker arm threads to be prepared to gauge their integrity...

Best,

Doyle

vreference · 10-02-2008, 02:24 PM

I like it, cooper. It didn't really occur to me that the shafts/rockers could be removed for inspection with the engine installed. There is a bushing in the rocker-shaft bore then? If the shafts/bushings were oblong I'm still not sure exactly how that would cause my random measurments but I've been suspicious of the shafts for a while now; maybe I was on to something. As far as I can tell there is only one repeat offender; I will be overjoyed if the issue is obvious. I've been dreaming of rebuilding the topend only to reinstall and still have the noise!

fumanchu · 10-02-2008, 04:14 PM

Hmm,.... cylinder number three is the one that seems to clack just a bit more than the rest. I wish I would have done the 180 rocker change when I had the motor out last month. I have no leaks in the rocker area.... am I going to create a leak by disturbing and turning the shaft? If so, i will put up with the noise on that cylinder if necessary.

Shawn

RoninLB · 10-03-2008, 05:05 AM

Quote:

Originally Posted by vreference

. There is a bushing in the rocker-shaft bore then?

db_cooper was referring to wear on one side of the rocker shaft causing noise. He said to change the direction of the shaft 180deg.

The rocker arm has a removable bushing.

vreference · 10-03-2008, 05:37 AM

Quote:

Originally Posted by RoninLB

db_cooper was referring to wear on one side of the rocker shaft causing noise. He said to change the direction of the shaft 180deg.

The rocker arm has a removable bushing.

I'm just thinking that I may have a bushing that's severely worn. (which would be great) I suspect this noise more, than anything else, precipitated the sale of the car and there's no telling how long it's been run like this. Not less than 1084 Miles on my part. If the shaft is damaged I'd certainly consider replacing it as well.

db_cooper · db_cooper's Garage

The rotation only needs to be 180* rather than a "flip". Yes the rocker shafts and arms can be removed "in situ" with the valve in position for an adjustment. (loose) A 1/4 drive allen and the old fashioned "L" allen is what you need to loosen the pinch and a bar (screwdriver) to push out the shaft. It is very simple.

Once removed, don't turn the engine over. Do each rocker and shaft one at a time.

Once reinstalled, us a torque wrench and tighten the shaft to spec. Be sure the shafts are centered. Use a feeler gauge to find the slots on each side of the shaft as you install the arm.

When you remove the rocker and shaft, it will be very easy to see what I referring to.

If the rocker shafts are torqued correctly, they won't leak.

You will want to recheck the rocker shaft torque again after about 5000 miles, they may loosen after getting hot a few times.

The bushing is a press fit in the rocker arm. It should not be loose and floating inside the rocker arm.

Flieger · Flieger's Garage

he could also use the RSR seals as extra leak protection

ZOA NOM · ZOA NOM's Garage

The spec is in Wayne's rebuild book, and I can't recall it off the top of my head. I highly recommend the RSR seals, tho.

vreference · 10-07-2008, 12:57 PM

I'm afraid I didn't find much wrong with the rocker shaft that I suspect may be making my noise. The wear looks pretty acceptable to me. The only anomaly I saw was wear on the rocker tip (hoof) the picture didn't come out very well but I believe you can see the dot in the center of the tip. I was surprised by the amount of metal that appears to be removed. I imagine it would be measured in thousandths - 1 or 2 maybe? The tip of the valve did not appear to have the same mark but did show signs that it spins; I don't know if that is indicative of a problem or not. Unfortunately I wasn't able to remove 4 or 6 shafts to compare parts as I need a shorter allen wrench.

KobaltBlau · 10-07-2008, 02:43 PM

rocker looks great (can't speak to the side clearance of course); your noise could be a broken valve spring, see if the noise matches the description here: Engine noise diagnosis help Please - apparent valvetrain

RoninLB · 10-07-2008, 03:02 PM

was a test of valve to guide performed?

If you have any with play chances are they're contributing to noise.

vreference · 04:37 PM

Quote:

Originally Posted by RoninLB

was a test of valve to guide performed?

If you have any with play chances are they're contributing to noise.

Yes I've heard that suggested. And the #5 does wiggle by hand, it's certainly easy to see it moving back and forth. Some people have discounted the possibility that this is the cause of the noise and I ended up deciding it was wishful thinking. But here's a question; The foot of the #5 rocker had lines from, what I have to assume, can only be the valve rubbing against it through the throw of the rocker. They go all the way across the hoof. You can just barely make them out in that picture as bright lines that are at about a 45 degree angle (Because the hoof was rotated when pulled they were perpendicular to the Rocker shaft) Is this movement normal or does it indicate excessive valve guide wear? It will smoke like a... I guess stuck pigs squeal not smoke? Anyway it'll smoke a lot if it was parked with a cold engine so there's no doubt the guides need attention.

Also no, I'm afraid my sound is not very intermittent for the broken valve spring hypothesis. I've heard it go away at very low idle speeds (which does seem to coincide with the valve guide theory) but the engine very rarely sounds normal.

Apologies; I'm not trying to beat a dead horse. I'm just very afraid of pulling the engine only to have somehow missed the issue and put it back in to find that I still have a Carrera Diesel. Compression Test, Oil Pressure, And listening to the Case and Chain housings lead me to believe this is valve train related and I'd like to get it narrowed down before the engine is pulled.

KobaltBlau · 10-07-2008, 05:56 PM

Yes, the valve spring issue seems much worse in a particular year range your car isn't in anyway.

db_cooper · db_cooper's Garage

Reinstall the rocker shaft with the wear on the opposite side from removal. You could use a micrometer and measure the shaft to see if it out of round. If possible, measure the rocker bushing too. Even a few thousands wear or out of round will amplify at the adjustment end and make the clearances move around (noisy). Deflection of the valve in the guide with movement by hand is not really a good sign, you should measure it with a dial gauge. There is a spec for it.

Easy enough to reinstall and see how it sounds with the shaft turned.

vreference · 10-08-2008, 06:34 AM

I'm afraid I've already reinstalled (rotated 180 degrees) with no change. I do have an older Micrometer caliper but the difference was beyond the device. You can't feel the edge with your fingernail. I don't have a way to measure inside diameter on-hand but the bushing looked pretty good.

The next thing I'm interested in confirming is that, normally the hoof stays perfectly centered over the valve-tip (by way of the geometry of the hoof "mechanism") and the wiping marks I have on the hoof indicate excessive valve guide wear. If the valve is actually moving that much then I don't doubt that the valve/guide is making the noise. The divot in the center of my hoof could actually be wear from the edge of the valve tip although that's pretty scary and might be a stretch.

WERK I · WERK I's Garage

Quote:

Originally Posted by db_cooper

I did the factory training for 911 engine back in the 80's. As I recall, there is no real spec for end float on the rockers. Obviously, they should not be tight or excessive.
I believe the thinking was there is very little thrust from side to side and, therefor, little load.

Noisy rockers were almost always wear on the rocker shaft and bushing. This caused the clearnces to wander around. If you are having issues with the clearances changing, look at the shafts and bushings.

I used to, when making a valve adjustment on an engine with any mileage, remove the rocker shafts and rockers, insure they were in spec and replace 180* out from the position at removal.

You could remove your most problematic adjusted rocker and inspect. If it is OK, reinstall, again, with the shaft turned 180* on the "fresh" side.

According to Wayne's book, the axial play limit of the rocker is .5mm. If it is excessive axial play, the tic will become louder as the engine warms up due to the viscosity of the oil.