rocker shaft fretting

hcoles · 04-26-2010, 09:16 AM

I rebuilt the top end on my 3.2 about 30k miles ago.
I have the engine out and was looking at a weeping rocker shaft.
I pulled the shaft out and saw fretting marks all around the shaft outboard of the groove. This was on both sides. I'm thinking the shaft must have been working itself around over time. I should have taken a picture. I guess I can still pull the valve cover and pull it out again. I found a nick in one of the turbo seals and replace it and reinstalled the shaft and tightened the 5mm fitting to pretty tight with a long handle "L" key. How screwed up is my situation? What can I do? Pull all the shafts and inspect? I'm thinking what could cause these fretting marks on the shaft when the shaft is "clamped" to the aluminum tower.

Flat6pac · 04-26-2010, 09:57 AM

Put the seal on the rocker shaft and keep an eye on it. You weren t tight to start with so youve worn the aluminum cam carrier unless you can get it to seal.
Bruce

hcoles · 04-26-2010, 11:55 AM

Bruce,
Thanks...it seemed pretty tight when I undid to get it out.. but I guess not tight enough. I've said this before, I don't like that whole rocker shaft design. I probably didn't do one or more things correctly during the rebuild. I guess what you are saying is if it the leaking stops we assume the turning is stopped.
Thanks much for your comment.
-Henry

304065 · 04-26-2010, 12:35 PM

"pretty tight" what is the precise torque measurement?

hcoles · 04-26-2010, 01:46 PM

when the rocker is not on the end it is not easy to get a torque wrench setup in there, but I'm open to ideas.... I know it is sort of lame and I should figure out a way to better estimate the torque, any slick 5mm hex tool you can suggest?
Thanks,
-Henry

Eagledriver · 04-26-2010, 04:47 PM

I don't think many of us torque these bolts with a torque wrench. I basically put as much torque as I can on them with a 4 inch allen wrench. I even cheat by putting an adjustable wrench on the end of the allen wrench to get a little more torque.

-Andy

hcoles · 04-26-2010, 05:04 PM

When I put the engine together I was able to put them in one at a time with a torque wrench and a long extension.... but I think I stopped because this method has an issue. The issue is the 5mm side, I think needs to face so that the bolt will come out with the engine in the car or engine together (e.g. oil cooler in the way), now that I say that, I'm not sure. I need to go look again. I agree that probably okay to use the "feel" method of torque, as you say about as tight as you can get it with a long L key and maybe a helper (end of a combination wrench). This is where the pro engine builder has the advantage. I'm worried about the shaft and will pull it out again and send a picture and see about getting another, I don't like that the cam housing is probably dinged up. No easy way to fix that I'm guessing.

aws · 04-27-2010, 06:33 AM

For years I used a allen wrench and a small box end to extend my leverage to tighten all the rocker bolts "pretty tight" I finally bought a 1/4 inch stubby allen socket set off of the Mac Tool truck and used a 1/4 inch torque wrench to get a consistent torque value. The originally number was 21-22 ft pounds but that can lead to grief by stripping the 5mm allen head, so the number for years has been 18 ft lbs. You need to use the RSR "o" rings and some kind of sealant on the shafts. I have used 574 on the side from which I installed the rocker and silicone on the other side to good effect. The other advantage is the 574 will lock the shaft in place if the bolt comes loose. They also need to be assembled dry.

aws

hcoles · 05-02-2010, 06:22 AM

update and plan - today I hope to pull all the rockers and inspect shaft/bushing wear. Then I can get a picture of the fretting and post here. I ordered a 1/4" drive 5mm socket from Snap-On guy and use that to install at 18ft-lbs. I'll order all new RSR seals and use red RTV to install dry. The rocker shafts are not too expensive so I'll replace those that need it. Any added comments on 574, e.g. what is it like to get the shafts back out later? Thanks.

Flat6pac · 05-02-2010, 10:29 AM

I ve never sealed a shaft except or RSR seals on a couple engines. I use excessive torque, snappy tight because I ve never seen 14#ft guaranteed to hold the second time the engine is built.
Bruce

Steve@Rennsport · 05-02-2010, 11:00 AM

JMHO, but I would NOT use any type of RTV in there.

If RSR rocker shaft seals and proper torque will not stop the leaks, you need another cam housing thats in better condition that the current one.

cgarr · cgarr's Garage

The shaft ends only expand .002 so they need to fit good from the start.

4sd911 · 05-02-2010, 07:42 PM

Quote:

Originally Posted by aws

For years I used a allen wrench and a small box end to extend my leverage to tighten all the rocker bolts "pretty tight" I finally bought a 1/4 inch stubby allen socket set off of the Mac Tool truck and used a 1/4 inch torque wrench to get a consistent torque value.

aws

AWS: Could you post the part no. of the torque wrench and 5mm allen stubby and brand, they should be mark on the tools. This combo does work in the confined space of the tower, correct?

aws · 05-02-2010, 09:34 PM

If Steve is nervous about RTV on the FAR side of the shaft bore on assembly I have used Curil-T. I do not use RTV on the shaft bore side that I am installing the rocker from because I do not want to push RTV into the engine. In my opinion the use of sealant on the rocker shaft bores stopped 99% of my leaks in that area. ALL the bores get scarred from dirt and grime on tear down and I have gotten in the habit of using carb cleaner and compressed air to clean as much of the dirt out as I can when I tear one down. The grooves don't make the cam tower unusable, just prone to leaks. The reason for the increased torque is not to stop the leaks, but to forestall the shafts coming loose. The 935's had tabs that attached to the cam tower bolts to keep the rockers from coming loose. Rather than going to that extreme I have found the increased torque to have solved the problem of the rockers coming loose. Saying that, on rare occasions I have broken a shaft (collapsed) on tightening the pinch bolts.
The shafts will come loose fairly easily with the 574, make sure the pinch bolts and beveled washers are removed, the rocker adjuster nuts are loose. Then I use a 5mm Allen socket seated in the shaft and tap with a small hammer.
I will look to see what the tool part number is and post it tomorrow
aws

cay-ahe · 05-03-2010, 04:56 PM

Anyone try or use these?

TurboKraft : Catalog Home : Rocker Shaft Lock Set [901 105 360 TK] - $360.00

Rocker Shaft Lock Set
[901 105 360 TK]

Another TurboKraft original.

TurboKraft’s Rocker Locks solve the problem of rocker shafts coming loose and shifting as the engine reaches operating temperature.

When the rocker shafts move in the camshaft housing, they shift to the side so only one end is supported. Not only does this create a huge oil leak, but the rocker arm is no longer completely supported and risks binding or breaking, causing a cascade of expensive engine component failures (rocker arms, timing chains and sprockets, valves, pistons…)

TurboKraft’s Rocker Locks and CNC machined of stainless steel so they will not corrode.
Their design correctly positions the rocker shaft within the camshaft housing to provide the greatest support of the rocker arm.

They are machined to maintain the expansion (flaring) of original rocker shaft to create the oil seal to the housing, though Motorsports Rocker Shaft Seals are strongly recommended for all engines to minimize the risk of leaks. (Motorsports Rocker Shaft Seals sold separately.)

-Installation is a direct bolt-in replacement for the original rocker shaft bushings and nuts.

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Inexpensive insurance! Costs to replace later can exceed 10.4 hours, plus gaskets, plus shop supplies, plus…

An essential upgrade for all racing engines and Turbos.
Fits all 911 engines 1965-1994

Sold per set. 1 set = 1 engine (24 pieces)

Walt Fricke · 05-04-2010, 07:30 PM

Keith

I've seen that advertisement. Looks like a very nice system, and neater than the systems which are based on attaching something on the cam carrier to head attachment studs in place of the usual washer.

But I've only once had a shaft come loose, and that was clearly because I didn't tighten things quite enough. Once I saw someone assert that the hardware could withstand 18 lbs/ft, and I used a torque wrench on rebuild, I've not had one come loose. Even if just tightening as much as I could when replacing a broken rocker at the track.

The problem I think most of us have is that these leak some. Mine all have despite the overpriced RSR seals. Yes, the shafts get reused a lot, and that doesn't help the cam carrier bores any. It probably doesn't help that I normally leave the hardware in when removing (and certainly when installing) the shafts. Once the Allen has broken things loose I use it to push tap the shaft out. Yes, the conical piece will try to expand the shaft end doing this, but my experience has been that it doesn't do that much - once things are loose they just push out.

On the other hand, these leaks have not been obnoxious. Just a cause of more work cleaning grime off an area where it doesn't do any harm at the next rebuild. Only the leak when a shaft got loose caused a luckily very obvious leak (onto hot race headers, smoke, etc.).

The only marking I've noticed on the part of the shaft where the rocker does not rock has been a lighter colored band around where the ends expand. I figure these are fatigue marks from the expanding. Which are eventually going to break on installation. Leading to some fussing around and grumbling, but no real harm, as you know when this breaks.

I had been advised to apply some sealant to the far end shaft hole before insertion. This would keep the sealant out of harm's way, but would only help seal that end. I've tired adding some sealant (I think I used some Gaskacinch I had handy) to the near end of the shaft itself, thinking some of that might follow it in. None of this seemed to help at all.

What I'd really like to do is find a set of used 993 cam carriers that didn't cost an arm and a leg, and convert to that style. Would do away with all this fussing around, and speed up disassembly and assembly a great deal.

Walt

cay-ahe · 05-06-2010, 05:45 AM

Hi Walt,

I'm going to try these things. I will probably never know if they help. I just had the obvious leak lots of oil on the headers...... oil, smoke, hot headers, not good. This was a first for me. If I don't experience this again that will be ok with me.

The 993 cam carrier idea is great. Thanks

chris_seven · 05-07-2010, 02:34 PM

Very interesting.

Looking at the PET and several different volumes of the Workshop Manuals may be helpful.

The tolerances of the bores/shafts are toleranced as follows:

B – Bore 18.000 - 18.018 (0.7086” - 0.7093”)

W – Shaft 17.992 - 18.00 (0.7083” - 0.7086”)

Clearance (Cold and Untightened) 0 - 0.026 (0 - 0.14”)

This clearly shows that very little wear is allowed and that any damage will probably result in problems.

The tightening spec for the rocker shaft bolt is 156 inlbs which is only 13.0 lbsft.

The recommended torque spec for an M7 x 1.0 pitch Grade 12.9 cap head bolt is 260 inlbs (21.3lbsft) Dry and 156 inlbs (16.2 lbsft) Lubed.

It seems that 18lbsft is a bit too much and perhaps this overtightening could cause some bore distortion particularly in magnesium parts.

PET 6.0 shows the same part numbers for the shafts, bolts and bushes from 1965 through to 1989 for all 911s. The Turbo and the 964 also use the same part numbers.

One other point that I noticed looking through this information was that Volume 1 of the Workshop Manual describes the bolt as a 6mm Cap Head Bolt.

The Pet describes it as a Pan Head bolt up to the 964 when it is described as an M7 x 48 pan Head screw.

The method of setting the axial location using a feeler gauge in the groove also seems quite important.

hcoles · 05-07-2010, 04:13 PM

very good info and discussion,
the cap screw has an M5 hex head, so I assume it is a M5 bolt, the "nut" side which is not supposed to be turned, just held is an M8. I have an M8 L key cut down to hold that side.
The cool tool is a HAZET 8501-5 - this is a slim 1/4" drive socket. I got one of these, borrowed. A 3/8" 5M socket will work if you have the type that has a surface for a 3/8" box wrench.

BTW - when I subtract the max bore from the min. shaft I get 0.026mm or just a bit over 0.001" - probably as you say 0.0014" with a decimal error. I always remember 25.4 microns to the mil.
At the max. material conditions it might be a bit difficult to get the shaft in. I expect they do a good job of hitting the center of the tolerance, that's the least they can do.

Walt Fricke · 05-07-2010, 11:03 PM

Chris

Nobody who has more than one rebuild under their belt uses the feeler gauge method to set the shafts in their proper location. Takes way too much time, is unnecessary, and isn't even exact, as it requires you to move the shaft after you stick the feeler in.

One end should be flush, and one end indented, so to speak. When in doubt as to which is which, just hold the shaft against the outside of the housing and you will quickly see. The housing is wider, so to speak, on one side than the other. Wide is, obviously, the indented side.

If you somehow get your ends mixed up, you will quickly see the error of your ways, as the pinch part will pinch your rocker, which won't want to move when you try to set the lash.

Walt