Walking rocker shaft?!?

[Mike the mechanic]

Hey guys, I have a little problem. I have recently rebuilt a motor, from 3.2 to 3.3 p/c's, gt2 cams, heavy duty valve springs and titanium retainers, big single turbo, etc.. The car kicks ass, but after a track event, the car started to leak a little oil. After checking it, I noticed that the rocker shaft in the intake side of cyl. #1 had slid out (partly)!! I took them all off, (only one had moved), installed rocker shaft seals, and re installed the shafts and torqued them to proper specs. The car has been running about 2 weeks with no problems, until last night, after another track session, another oil leak developped. It was the same problem; the rocker shaft has slid out partly. I know I torqued everything fine, and there is no visible damage to the rocker or the cam housing, so why would this happen and how can I correct it??
Thanks in advance!!

[cstreit]

I read from Competition Engineerings site that they recommend slightly higher torque values on the rockers than specified by the factory (something like 20 ft/lbs up from 13). Primarily to combat leaks, but perhaps this might also help your rocker shaft from escaping.

Check http://www.competitioneng.com/WaltsPage.htm at the bottom.

If the shafts aren't expanding enough I would guess either faulty torque reading or could one of the "cones" that expand the shaft be rusted or stuck to the shaft and therefore not push it outwards into the bore walls?

[Doug Zielke]

Good advice from Walt Watson, and thanks to Chris for noting it.
I used Walt's technique on my own engine, and there are no rocker leaks.
Walt also stresses that the rocker shafts and bores should be absolutely *dry* (as in "oil-free".) at time of installation. After things are in place and torqued down, squirt some oil into the rocker oil holes for start-up lubrication.

[Wayne 962]

When the engine is disassembled, if someone not experienced in the disassembly process takes it apart, they can tap the rockers out without properly loosening them. This can expand the bores, and make the rockers walk.

Walt does recommend the higher torque settings. I spoke with him on this issue (and others) before I wrote the book. Here is what I concluded:

- Torque the rockers to their factory specifications upon engine assembly
- Install the RSR seals to guard against leaks
- Increase the torque on the shafts if any of them leak after running the engine

Basically, the rockers are relatively easy to reach, so I don't recommend tightening them up further unless your needs require it.

-Wayne

[snowman]

Bruce Anderson mentions, in his book, that if the rocker shaft twists while tightening will leak or become loose. I noticed that while tightening a few of mine they twisted and did not feel right when torqued down. I added a small ammount of torque to get these ones to "grab", ie feel like they stuck, or took the tightening. Really hard to describe as it is a touchy feely sort of thing, but you would recognise it if you felt it. The feeling is like the thing is sort of sticking or stuck, breaking loose, turning, and then, grabbing hold. Unfortunately you may have to exceed the recommended torque to get the thing moving. Might be caused by buggered threads or whatever. I kinda think this is one for the tighten to the attained feel due to experience sort of thing.

PS whats a small ammount of additional torque? beats me.

[speeder]

Agree w/ Walt, and Jack, just started installing mine tonight and I'm going to make 'em on the tight side, within reason of course. Walt is right on the money about them being a common leak spot. I'm using 935 rubber seals also. And I wish that I could install them dry, but the ones that Walt rebushed for me are a little on the tight side, couldn't even install the shaft on the first one I tried. Tomorrow I need to match them up, maybe some of my shafts are fatter than others, use those on the old, (not rebushed), ones. Time to sleep, Goodnight.

[J P Stein]

Based on my meanders thru the 911 motor world, the "walking shaft" seems to be a fairly common problem. We each get 12 chances to screw the pooch during a rebuild. As a result, I researched this a bit and here are my observations....for what they're worth.

Mr. Anderson does indeed spend some time here. He states in a section of his book that the rocker nut should bite the shaft and cease turning (no longer need to be held from doing so) BEFORE ultimate torque is reached. He further states that if it fails to do so, the bore or the shaft is bad and will probably walk at some inopertune time.

A look at the shaft is in order here. The ends are chamfered and the OD of the shaft is ground. There is a sharp edge at the intersections. NO deburring is done here. As I see it, this sharp edge bites into the aluminum of the bore.....but not enough to permanently dent the bore. A fine balance of expansion by using torque on the bolt/nut, me thinks.

During assembly, I had 2 or 3 new spare rocker shafts standing by. Using Andersons installation guidance, I replaced a couple of them. I also used silicone grease on the RSR seals. I can report success here as none leak or have moved. I boogered up a couple other areas (my leaking #8 brg reminds me every day), but this wasn't one of them.

[snowman]

JP
Since the seals are desgned to work in oil, wouldn't oil be a suitable lube for them?

[J P Stein]

Originally posted by snowman
JP
Since the seals are desgned to work in oil, wouldn't oil be a suitable lube for them?

They're kind of like O rings. I like silicone grease on O rings as it will neither melt nor wash away(unless there is oil pressure against it...like on my #8 bearing). Since I had to lube the things to get em' in.....what the hell....an extra bit of sealing can't hurt, I figure.

[ChrisBennet]

Maybe you machinist types can answer this: Do you oil a shaft that is press fit into a hole or put it in dry?
Do you suppose this is why the shafts are supposed to be put in dry?
-Chris

[snowman]

Press fit items can be lubricated using lube specifically designed for this application. It is my understanding that a press fit, or interference fit is an undersize hole, by the tune of about 0.003" typical. But this depends on the size, material, application. A sleve fit is the same size or slightly oversize hole, which is what I beleive the rocker shafts are. This too can utilize lube. I am not a mechanical engineer so I do not know all the ins and outs of the subject by any means. The rocker arm shafts are held in place by a pinch bolt, ie a tappered bolt that expands the ends of the rocker arm shaft out against the bore, creating an in place interference fit. My words may not be technically correct but I think they are close to the correct ones, at least in meaning, if not correct. Since the rocker arm is not pressed into place, but expanded after they are in place, any lube would interfere with the expanded ends, biting into the bore and holding. A very small ammount of lube on the seals probably is not enough to interfere though.

Hope this makes sense to you.

[5axis]

Originally posted by ChrisBennet
Maybe you machinist types can answer this: Do you oil a shaft that is press fit into a hole or put it in dry?
-Chris

It depends A better way to look at it is, do you plan on ever taking it apart again? Our usual press fit is no more than .001" or in mold/toolmaker speak "a half per side". With hardened tool steels and pins there is not a lot of "give". Remember when you are ramming components together, something has to move.
If you were to lube the conical nut and bolts you should generate more expansion force. And that still is not a clear cut answer. When I disasembled mine, they were freakin tight.. and that's very tight. Hope that helps a bit. LOL

david 89 turbo cab

[snowman]

Well cleaned up, the rocker shafts should slip in with finger pressure. Note I did not say slip OUT with finger pressure. Crud, junk and wear, ie a ridge may develop with time, and hold these puppys in place. Just like glue. But they are not press fit in the beginning. They are slipped in and then the expansinon bolt tightened. This expands the outside of the shaft into the bore and may even make a minute (microscopic) impression in it. At least thats my take on it.

[ChrisBennet]

Originally posted by snowman
Well cleaned up, the rocker shafts should slip in with finger pressure. Note I did not say slip OUT with finger pressure. Crud, junk and wear, ie a ridge may develop with time, and hold these puppys in place. Just like glue. But they are not press fit in the beginning. They are slipped in and then the expansinon bolt tightened. This expands the outside of the shaft into the bore and may even make a minute (microscopic) impression in it. At least thats my take on it.

I guess I didn't word my question too well but what I was trying to determine is whether you would lube something (like a press fit pin) that you didn't want to move (like a rocker shaft).
I think lots of people lube the shaft to keep the seal from tearing but according to Bruce Anderson the shaft is supposed to be put in dry. I couldn't find anything on the rocker shafts in my manuals.
-Chris

[Doug Zielke]

If I understand your question, Chris, I did not put any lube on the rocker shafts or the rocker arms at re-assembly. This per the advice of Walt Watson, the reason being you have a better chance at keeping the shafts tight the first time around.

When you use the RSR seals, it does make it a bit more difficult to get the shafts in without tearing them. Just make sure they are seated very well in the shaft groove, and watch carefully as you push the shaft home.

After the bolt is torqued, I squirted engine oil into the rocker arm oil holes for start-up lubrication.

[snowman]

You absotutely need somethign ON the rocker arm seals themselves. It is possible to lube the seals and not the shafts. IF dry the seals will most likely tear or be damaged on installation. There may even be enouth on the seal itself, without adding any, but I would at least wipe the seals with oil on my fingers as I installed them. When a o ring seal is dry it is almost always history.

[ChrisBennet]

I've installed over a hundred of the seals dry without any problems (from the seals at least ). I could see how it would be easy to pinch or tear them though.
-Chris

[snowman]

Its possible you may have damaged the seal and not know, as the seal isn't required in most cases. ITs generally not advised, eg the seal on spin on oil filters, or any other rubber, silicone, whatever seal to do them dry. Thats what all the books, instruction sheets and mfg spec sheets state anyway.

Sort of like a Porsche engine, a contradiction in itself.

[Mike the mechanic]

Thanks for all the replies guys! All very informative and insightful. Snowman, you da man. The walking shaft was the one, the only one that didn't "grab" while torquing. I actually had to hold the 8mm side with an allen wrench, even at the final stages of torquing. I replaced the shaft with a spare I had lying around, and bingo, it tightened up with ease, no slipping of the 8mm side, and all is dandy. Oh and I did also torque all of them slightly higher than factory specs.
Thanks!