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Question Newbie rocker arm shaft questions

Originally posted in 911 technical forum, but was suggested to post here.

1. Why can't the shaft be removed, without dropping the engine, if the shaft bolt doesn't come out toward one of the center gaps? This would only apply to cylinders #1, #3, #4 and #6.
2. What problem(s) occur if the bolt is over tightened?
3. Clarify why the thinner flange needs to be inserted one way or the other.
4. Clarify why you shouldn't tighten the 8mm nut, only the 5mm nut.
5. If the rocker arm shaft falls out while the engine is running and doesn't obstruct the cam or valves, what happens inside of the cylinder?
6. If the rocker arm is causing a tapping sound, what is happening to cause the sound?
7. How does the rocker arm shaft effect oil leakage? In other words, what common mistakes cause the oil to leak and how is the oil leaking past the shaft? Please describe the oil flow around the rocker arm shaft.
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Old 09-19-2005, 08:40 AM
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so others know what has already been said, here is the other thread:

http://forums.pelicanparts.com/porsche-911-technical-forum/241671-newbie-rocker-arm-shaft-questions.html#post2129517
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Old 09-19-2005, 11:48 AM
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Razor,
I'm not an expert on these,but have just finished my 2nd engine R&R with some rocker issues thrown in,so here goes:

1)Shafts want to come out the thinner of the 2 bosses in the cam box.Even with engine out,this can be a pain.Guess it could be done in car,not sure,would not be easy.
2)If they are overtightened,they can bite into the soft aluminum & form a burr that will make removal difficult later,possibly leak by scaring the bore.
3&7)Flanges go in so as to make removal easier without disassembly of cam chain boxes off front of motor.Flange should be about flush with thinner boss when installed.Doesn't matter which flange,theaded one or bolt head one,just that it is flush with boss side.This is due to the placement of the grooves in the shaft.If grooves are out of position in the bores,side to side,IT WILL LEAK OIL,ask me how I know!
4)You only want to tighten the bolt,which squeezes the tapered cups into the shaft,which in turn spreads the end of the shaft.If you turn the 8mm cup to tighten shaft,it may/will gall the surface & not tighten properly.When you tighten the 5mm bolts the cup do not rotatate.
5)Not sure what a shaft falling out would doother than getting wedged into a bad spot & bending stuff in the rocker box.In the cylinder,not sure anything, per se,would happen other than that paticular valve not opening,wash down cylinder with gas,bakfire due to exhaust valve not opening,just not sure.
6)Rocker causing a tapping sound would be excess clearance of shaft/rocker would be my assumption.
7)Again,if the shaft isn't positioned correctly,the groove in the shaft allows oil the escape from the oil side out to the non oiled side.BTDT!
RSR shaft seals are also a worthy invesment.They are cheap insurance against leaks.

Again,I'm not an expert,but these are the things I have seen,done,researched during my time in playing with these beasts.Attention to detail is your friend!

Chris
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Old 09-19-2005, 11:57 AM
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RazorRacer,

I am far from an expert here, but I just finished my first rocker shaft assembly, and I can give you my $.02 worth until the experts show up here.

#1.) It sounds like you have given this some thought already, but I think that #1 and #4 would be interfered by the chain housings left and right, and #6 would be interfered by the oil cooler - not to mention being at the back of the engine compartment, and #3 may just be because it's at the back of the engine compartment. It's just much easier to work into the center of the engine.

#2.) Bolts stretch when tightened, and an overtightened bolt can yield, and eventually loosen up, and come out.

#3.) If you insert the rocker shaft through the thick flange side, you will have to push it throught much farther than if you inserted in the small flange side. The rocker shafts are not centered between the flanges, they are centered on the rocker arm, and are much closer to the edge of the thin flange than the thick flange.

#4.) Oil is fed to the rocker shafts through the rocker arms. If the rocker shafts are not sealed to the thick and thin flange, this oil will be let out inside the side covers where oil is not supposed to be, and may not be sealed up (it leaks all over the outisde of the engine).

#5.) If the rocker shaft comes out, the valve will stop opening and closing, and the rocker shaft will be free to move around where your cam is spinning (not good).

#6.) The rocker arm is the connection from the cam lobes to the valve stem. There is a small (0.1 mm) gap allowed between the valve stem and the rocker arm. If this gap gets too big, it will start to make a noticable tapping noise.

#7.) See answer for #4. Maybe someone will come up with a good diagram here for you.

I hope this helps - from one novice to another. I'm sure I still have a lot to learn, and an expert will help both of us here soon.

Rex
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Old 09-19-2005, 12:04 PM
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Good link:

Walking rocker shaft?!?
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Old 09-19-2005, 05:39 PM
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Here's a stab at a few of these:

You can get (in theory) any rocker shaft out with the engine in the car. I've replaced rockers at the track. It helps if you made sure that all the 5mm allen ends point inward when you assembled the engine, so it is easier to use the wrench on them, and ingenuity may be required (like inserting small sockets you can pry against, or removing the front end sheet metal on the left bank or inserting a long bolt whose head you can pry or tap against, and having shortened L shaped Allens, at least for the 8mm one), more so for some end ones than others.

A loose shaft usually anounces itself with quite an oil leak. I think that the small leaks which leave that part of the cam carrier so dirty over time may be due to the pressure of the oil: when the rocker rocks, it squeezes the oil that got in through the two holes in the rocker, and some must squirt out sideways along the shaft. But when the shaft moves enough to create an actual opening, well there is often a fair amount of pressure inside the engine along with quite a mist of oil, so quite a bit of it will fall on the hot headers and smoke up the joint muy pronto.

A loose shaft is apt to cause a ticking which grows in volume as the shaft works free from one end. Eventually the rocker may break, or the elephant foot may get knocked off, or the lock nut will loosen and the adjusting screw will back off all the way, or the adjuster can break. Quite a racket. But if you catch all this at the oil leak stage and poke the shaft back into position (after examining everything) and tighten it up, all should be well.

If you can't find a loosened lock nut or elephant foot in the cam carrier space after one of these adventures, and can't find it in or near the oil drain plate (or don't have one in your case to start with), you may be able to ignore it. I've gotten away with that - so I think it ends up safely sequestered in the bottom of the case, reasonably far from anything it can cause to jam. Scary, though.

In a well used engine the shafts should slide in fairly easily, at least if inserted in the same direction as removal. So much so that you have to try extra hard to be sure to tighten their hardware (as, for instance, putting the #1 intake in for cam timing purposes, meaning to tighten it later when you start putting all the others in.

I envy those who have achieved a zero weap oil condition. Despite adding the RSR seals I have never been able to do this. Ditto with the breather cover - always some grime outside after a while.

Walt Fricke
Old 09-20-2005, 06:42 PM
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Great info, Walt.

Do you think there are any disadvantages to the RSR seals?

Best Regards,
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Old 09-26-2005, 11:20 PM
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Well said, Walt!

Great info there..

I can add that I have seen two engines which had actually broken the cam carrier as a result of a walking rocker shaft..

The shaft gradually walked until eventually one end was out of the bore in the housing..

The offset bending load on the shaft now only supported at one end cracked the housing bore...

I have many times wondered whether to try some mods to the housing to eliminate the leaks..eg bushing them with a broze liner and an O-ring.

Another idea I had was to make a pair of bigger wedge plugs, such that the wedgeing was actually against the outer ends of the housing bore...the problem is the shaft would be allowed to float slightly unless all the dimensions were correct...and I'm sure if it was floating, it would gall the bore...

I now do my best to degrease everything before assembly, and use RTV in the bore, and in the grooves I put an ordinary O-ring.

The rockers then have to be prelubed through the hole..

Kind regards
David

Not easy at all..

RTV
Old 09-27-2005, 02:04 AM
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Andy

I worried that the RSR seals might make it harder to push the shafts out when you wanted to do that (at the track, for instance). Fears were unfounded - they push out as before. Which leads me to wonder just how much good the seals do - I should take a rocker shaft and do some measurement to see if the pinch bolts make the slot narrower along with expanding the ends of the shaft.

David

Egad - I didn't know a loose shaft could break the carrier. I've been lucky a couple of times, I guess.

The RSR seals are a flat sided "o" ring. You have gotten ordinary round cross section o rings to work? How?

I have wondered about bushing the cam carrier bores, though more in terms of restoring them to size. At some point the carriers may become expensive enough to make something like that worthwhile. Perhaps that could also deal with the wear that could lead to excess sideplay in the rockers? I've never paid much attention to that, but perhaps I should.

I suppose a guy with a machine shop could come up with things to stop the leaks. For instance, make flanged caps (or bolts) for the "short" end in the carrier. Slide the shaft in with hardware attached and an O ring in place, so when you tighten things up the O ring is captured between the flange and the vertical face of the cam carrier by the hole. That would keep the shaft from moving into the long end of the carrier, too.

The long end could be filled with RTV. Or its cap could be made like a long cylinder, with a flange on its end, and an O ring, etc. Then machine the carrier so there is a smooth end surface and the shaft holes are all exactly the same length.

Guys with such hardware would be less likely ever to install the shaft incorrectly, too.

Me, I suspect I'll live with the small leaks.

Walt
Old 09-27-2005, 01:22 PM
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You can remove the rocker arms with the engine installed in the car. Is a work of the hell, but you can do it. If you lift the car using a lift gate would be better. Need to remove the engine black surroung sheet metal from both sides. Remove the valve covers., loos the valve ajusting screw to release the tension and then loose the shaft allen bolts, the take the shaft aou and the rockers.
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Old 09-28-2005, 10:40 PM
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Retro-engineering exercise:

With my keen 20-20 hindsight, perhaps Porsche could have used a single, long rocker shaft to support each set of three inline rocker arms, then included the spaces between the rocker arm support bosses as part of the "wet' area. Removal of the rocker shafts from an installed engine could be faciliated by sealed passages into the chain box.

I'm not an engineer nor German, but I slept at a Howard Johnson's last night.

Sherwood
Old 09-29-2005, 10:07 AM
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Thanks for that on the RSR seals, Walt.

Quote:
Originally posted by 911pcars
With my keen 20-20 hindsight, perhaps Porsche could have used a single, long rocker shaft to support each set of three inline rocker arms, then included the spaces between the rocker arm support bosses as part of the "wet' area. Removal of the rocker shafts from an installed engine could be faciliated by sealed passages into the chain box.
This is like a 2v/cyl BMW engine, though their rocker shaft extraction situation is quite different. I wonder if some of it didn't have to do with the racing cap type valve clearance shims they wanted to use on the racing cars; I have not used these myself but I understand that the rocker has to be removed to change shim, is this correct? if so, a valve adjustment would be really tough with a single rocker shaft arrangement, not to say it's easy on an RSR with many rocker shafts! Not only that, but would the rear bumper area need holes to get the long shafts out?
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Old 09-29-2005, 10:36 AM
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I'm with Sherwood. Going from VW engines to 911s was a kind of shocker as to the amount of time it takes to install or remove all the rockers. Of course the 911 OHC system itself is better than the pushrods.

A single shaft might prove problematic if, even with the adjusters backed all the way off, you still ended up with pressure on one of the three rockers on a given shaft - might be hard to shove it along farther. But maybe there is some happy sweet spot with the cam where this doesn't happen. I am pretty certain there is no such spot on the cam (would vary with the cams, too) which allows you to remove the cam itself without removing at least some rockers, though if a guy were just swapping cams it might be interesting to know how few rockers you could remove out of the six involved there.

The more I think of retroengineering, the more I think switching to 993 style cam carriers makes sense where these matters are concerned. But I don't think there is power to be gained there, so it's way down on my list.

Walt Fricke
Old 09-29-2005, 10:41 AM
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I think the RSR style valve stem end cap/lash setting system involved compressing the valve spring (and pushing the valve down along with it) to give you the room needed to swap caps.

Come to think of it, a single long shaft (and especially a casting keeping it in the wet area) is apt to interfere with spark plugs, no?

Walt Fricke
Old 09-29-2005, 10:52 AM
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Though not ultimately as rigid (maybe), Porsche also could have designed a a two-piece saddle and cap arrangement like many other engines use. With this method, with either short or long shafts, rocker shaft end movement and retention could be taken care of by simpler methods. With a long shaft, some machined flats on the shaft could allow periodic rotation to even out shaft wear.

The BMW arrangement required a special tool to compress the valve springs and relieve tension to remove the cams. A similar tool for the retro-designed Pcar engine would be needed for a long rocker shaft, sorta like the individual valve spring compressor tool sold by Sir Tools.

Sherwood
Old 09-29-2005, 11:39 AM
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I believe that the 935 used a rocker shaft retainer system to prevent the shaft walking under high valve spring loads and rpm



checkouk this thread Rockershaft retainers
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Old 09-30-2005, 03:40 AM
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rocker seals are the only way to go!! well woth the h-e-l-l- as I did it too. was not fun,some of the bolts were in the wrong way,but like said a thikin and a little trying it will be done.
Old 10-03-2005, 07:21 PM
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