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Rocker arm shaft jump out??

My tech man just rebuild my engine, after running 100KMs, I find oil leak from lower side engine cover, when my tech man open it, he find the Rocker arm shaft jump out, he said he tight them up with spec. why they can not hold on place?
need help~~~
Appreciate your input!

Old 11-11-2013, 04:53 AM
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Spec works on new but you have steel shaft in aluminum housing using expansion of the steel for the seal. After new, spec is out the door on this item.
Bruce
Old 11-11-2013, 04:58 AM
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Flat6pac. thanks
so I can put more torque??
Old 11-11-2013, 05:20 AM
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There are many old threads on this topic (search: walking rocker arm shafts / rocker arm shaft torque), and as Bruce said, the general consensus from the pros is that the torque needs to be higher than what the book calls for (most seem to agree on 18-20 foot pounds). Here are a couple of links -

Rocker arm shaft installation?

RSR rocker shaft seals
Old 11-11-2013, 08:01 AM
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Thanks Ronnie's.930~~~
Old 11-11-2013, 08:23 AM
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John Walker gave me a number...it was a LOT higher TQ then stock, i thought the bolts would break !.....they did not. As per usual, J.W. knows what he is talking about.
You might add the RSR "O " rings whilst there.
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Old 11-11-2013, 11:14 AM
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Turbokraft sells rocker shaft locks that will prevent this from happening.
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Old 11-12-2013, 07:31 AM
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Thanks!!!!
contact Turbokraft, seem rocker shaft locks out of stocked......
Old 11-12-2013, 08:25 AM
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Yeah but they will have some made if you call them to order them. The reason these move is that the bore gets expanded a little bit each time these are installed and tightened.
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Old 11-12-2013, 11:21 AM
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Here's one of the pro recommendations if people need to see it to believe it

"Competition Engineering - CE's war on oil leaks"
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Old 11-12-2013, 12:04 PM
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Applying too much torque to any fastener is a dangerous and poor strategy that often result is a disaster and needs some thought if it is to prove useful.

The reason bolts fail is that the preload developed during tightening exceeds the Ultimate Tensile Strength of the material.

Once this value has been exceeded the bolt will neck down and eventually fail.

The torque measurement is a fairly crude measure of the preload in a bolt and significant variations occur depending on how the bolt has been lubricated.

The lubrication of the area under the head being equally as important as the lubrication in the thread.

If you examine an M7 bolts there is reported data to show the influence of lubrication.

If you have a bolt with a measured coefficient of friction of 0.1 then the torque needed to apply a preload equivalent to 75% of the materials Yield Stress (normally considered max load) would be around 20Nm which is around 14 lbsft.

If you reduce the lubrication so that the coefficient of friction is 0.2 then you would need to apply 42Nm - around 31 lbsft - to achieve the same preload.

The tightness of the bolt, hence the axial load developed would be the same in both circumstances.

If you don't lubricate the rocker shaft bolts at all then the increase in friction will result in an increased torque but no extra grip of the shaft in the bore.

If you lubricated the fasteners with an advanced thread lube such as that supplied by ARP you could well snap the bolt.

I have worried for a long time about advice that simply says overtighten the bolt.

Some better measurement and a lubrication procedure would be a good idea.
Old 11-12-2013, 11:26 PM
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Chris,

Keep in mind the M7 rocker shaft bolts are 12.9 property class so they've got some extra "headroom" for additional tightening. 12.9 bolt generally can handle 21 ft-lb dry or 19.9 if zinc plated. http://www.metricmcc.com/catalog/Ch10/10-1027.pdf

But I certainly don't discount your concern about overtightening when people install them oiled or with antiseize. Lubricant on the threads will substantially reduce the required torque. So I don't doubt many of these bolts are technically overtightened. However time has shown that the bolts don't break. Not saying that makes it proper. Just pointing out that these bolts rarely snap. Instead they get stuck/stripped hex tooling!
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Old 11-13-2013, 05:52 AM
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Kevin,

I agree that cap heads are Grade 12.9 and that the 75% of Yield is conservative but I 'like' to worry.

The only point I am trying to make is that as this seems a serious issue it must be worth trying to come up with a 'procedure' backed up with measurements which prevents damage.

The change in the bore of the carrier for example can only be caused by removing the shafts with the bolts still partially tight.

There is just not enough radial movement of the shaft caused by tightening to cause the Aluminium to yield so if the bore diameter increases it must be due to pushing out material with the shaft.

I have a few old carriers so I will measure the bores accurately and see what variation we get.
Old 11-13-2013, 07:31 AM
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This guy nick fulljames has a great engine build series on youtube. In the link below he presents very interesting views on the origins of rocker leaking, why he doesn't "buy" RSR seals and his custom made solution. Don't know if they're for sale or just for his customers.

Nick Fulljames on ageing 911 rockers! - YouTube
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Old 11-14-2013, 05:40 AM
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This video has been around a while and some of the comments made are interesting but I am not sure I am in complete agreement with all of the ideas presented.

It is certainly true that the majority of problems come from poor assembly and subsequent removal of damaged shafts.

The early shafts with the 6mm bolt probably don't clamp very well and would need replacing but I don't imagine that there are too many left in service.

The next generation of Rocker and Shaft also have significant issues as they are a steel on steel due to the lack of bush in the first generation Investment Cast Rockers despite having the M7 bolt.

This galling will damage the surface of the shaft and it is likely that the bore of the carrier will also suffer damage due to the surface protrusions caused by this galling.

Once scored the bores of the shafts will then be likely to leak.

The video shows a method to repair the damaged shaft which involves using an oil stone on the outer diameter - a practice I would never follow.

Later cast rockers are always bushed so this type of damage is much less likely to occur.

The lack of clearance between the bore and the shaft can, however, still make shafts difficult to remove and some galling can occur when shafts are removed using high levels of force.

The shaft seals that you are describing have been sold by Autofarm in the UK for many years.

AUTOFARM | Rocker-Shaft Oil Leak Solution

They are said to be patented (Is an O ring novel ?).

I have never tried to use them as I have some concerns about their design.

The 'expansion' nuts used to be made from an Aluminium Alloy and I am not sure if enough compressive force can be applied to fully expand the shaft ends.

If you do tighten them fully will the O ring shear between the shaft end and the expansion nut?

If you look at the photograph (I haven't copied this because of copyright) of the nuts then one end does not have any feature to enable it to be gripped and I think that this raises two questions.

1. Will the O ring give enough grip to allow the bolt to be fully tightened and not come loose due to vibration. I guess you could use Locitite but then .....

2. What if the nut spins rather than allowing the bolt to undo? It would then be difficult to remove the shaft.

Old 11-14-2013, 07:48 AM
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