Number 1 exhaust rocker shaft keeps backing out.

[Mark Henry]

3.0 SC engine, web 120/104 cams, elbach sport springs, rebushed rockers, RSR seals, within spec shafts. I know I inspected the cam carriers when I built the engine.
I've tried dry fitment, lubed, different shafts... same #1 ex. shaft every time.
Could the carrier shaft hole be damaged?

Any ideas?

[Classic 911]

Following


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[OSC911]

New bolts each time?

[gsxrken]

The bolts are a stretch bolt and some say aren’t reusable. Experience says otherwise but maybe not for this one. Housing could be out of spec, too.
Turbokraft makes locks you might want to look into.

[Mark Henry]

Originally Posted by OSC911

New bolts each time?

Originally Posted by gsxrken

The bolts are a stretch bolt and some say aren’t reusable. Experience says otherwise but maybe not for this one. Housing could be out of spec, too.
Turbokraft makes locks you might want to look into.

No, I'll try new bolts. but the rest are staying put, just this one shaft has the issue.
gsxrken do you have a link to the turbocraft locks?

Edit found them...sold out.

[john walker's workshop]

What is your torque spec? Cam towers are probably the most abused part in these engines.

[Henry Schmidt]

Originally Posted by Mark Henry

3.0 SC engine, web 120/104 cams, elbach sport springs, rebushed rockers, RSR seals, within spec shafts. I know I inspected the cam carriers when I built the engine.
I've tried dry fitment, lubed, different shafts... same #1 ex. shaft every time.
Could the carrier shaft hole be damaged?

Any ideas?

Damage is certainly possible. Over the years it's possible that a previous machanic over tightened the shaft in an attempt to cure a leak.
Chris at Turbo Kraft has a system of indexing rocker shafts that work pretty cool.
Check it out.




https://parts.turbokraft.com/collections/engine/products/rocker-shaft-lock-set?variant=18360163393

[Neil Harvey]

In the past we have seen where the rockers bore was not 90° to the arc of the rocker arm. This resulted in a slide hammer effect on the shaft. Not saying this is your problem, but the cause is there to been seen. When installed correctly and all parts are to spec, they do not come loose.

Things to check are; housing bore diameter, condition and alignment. Pin OD size. Torque the bolt in the pin outside of the housing and measure the end diameters. Then compare with what you measured the housing bores. You should show some interference. Compare to one of the valve positions that hold.
Check the cam lobe for taper across its face. Do the same on the rocker pad. You should be able to see odd contact surfaces if there is any.

After all is done, re install a different rocker arm shaft into #1 and move #1 shaft to another housing bore, See if the problem moves with the shaft.

Hope this helps.

[AJKelly]

Struck this problem with an inherited engine that we were running at an historic meet in Europe once.
No time for tear downs and complete rectification so drilled and taped a small thread into the cam housing that lined up with groove in the rocker shaft and lock tighted a grub screw in that partially went into the groove. Rocker shaft never moved again.
In the end during the next scheduled tear down the mod was made to all the rocker shafts, as it was deemed another level of protection for an old but very valuable old race car.
Car did a few more seasons under our care before being moved on and never had another problem. In that area anyway.

[Classic 911]

Originally Posted by AJKelly

Struck this problem with an inherited engine that we were running at an historic meet in Europe once.
No time for tear downs and complete rectification so drilled and taped a small thread into the cam housing that lined up with groove in the rocker shaft and lock tighted a grub screw in that partially went into the groove. Rocker shaft never moved again.
In the end during the next scheduled tear down the mod was made to all the rocker shafts, as it was deemed another level of protection for an old but very valuable old race car.
Car did a few more seasons under our care before being moved on and never had another problem. In that area anyway.

Sounds like a great mod. Do you have pics?


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[Mark Henry]

Originally Posted by Henry Schmidt

Damage is certainly possible. Over the years it's possible that a previous machanic over tightened the shaft in an attempt to cure a leak.
Chris at Turbo Kraft has a system of indexing rocker shafts that work pretty cool.
Check it out.




https://parts.turbokraft.com/collections/engine/products/rocker-shaft-lock-set?variant=18360163393

I'd do this but they're sold out.
If anyone has a set they want to sell message me.

Originally Posted by AJKelly

Struck this problem with an inherited engine that we were running at an historic meet in Europe once.
No time for tear downs and complete rectification so drilled and taped a small thread into the cam housing that lined up with groove in the rocker shaft and lock tighted a grub screw in that partially went into the groove. Rocker shaft never moved again.
In the end during the next scheduled tear down the mod was made to all the rocker shafts, as it was deemed another level of protection for an old but very valuable old race car.
Car did a few more seasons under our care before being moved on and never had another problem. In that area anyway.

I'll keep this open as option #2

[Mark Henry]

Originally Posted by Neil Harvey

In the past we have seen where the rockers bore was not 90° to the arc of the rocker arm. This resulted in a slide hammer effect on the shaft. Not saying this is your problem, but the cause is there to been seen. When installed correctly and all parts are to spec, they do not come loose.

Things to check are; housing bore diameter, condition and alignment. Pin OD size. Torque the bolt in the pin outside of the housing and measure the end diameters. Then compare with what you measured the housing bores. You should show some interference. Compare to one of the valve positions that hold.
Check the cam lobe for taper across its face. Do the same on the rocker pad. You should be able to see odd contact surfaces if there is any.

After all is done, re install a different rocker arm shaft into #1 and move #1 shaft to another housing bore, See if the problem moves with the shaft.

Hope this helps.

I've done most of this list already, I just have to try a new bolt as suggested by OSC911 and gsxrken. I swapped out the shaft, but I didn't move them around I just used a different shaft, same result.

[gled49]

I’m sure you’ve checked but confirm washer end under the Allen bolt head hasn’t fractured.

[356911930]

Have you tried changing out the rocker arm? May have the bushing miss aligned.

Rahl

[trond]

what torque are you using ?

[Mark Henry]

Originally Posted by trond

what torque are you using ?

Pretty hard to get a torque wrench in there for one shaft, for me (914) it would be easier to drop the engine to remove all the shafts, more work than I really wanted to do.

I did a test with my inch pound torque wrench and found 18-19 lbs using stubby Allan keys was about the repeatable limit. IIRC that figure was John Walker's suggested torque for used bolts.

Yes I tried different shafts I have, and the washer (bolt end) is good, new rocker bushings, etc...

[AVI_8]

Originally Posted by Mark Henry

I'd do this but they're sold out.
If anyone has a set they want to sell message me.



I'll keep this open as option #2

I emailed Turbo Kraft regarding these rocker keepers a few weeks ago, they replied that they’d be back in stock in a couple of weeks, might be worth a call or email.

[Walt Fricke]

Which way does it move?

Short term if to rear, cut a piece of hex stock so when in place in the hex it rests on the back of the housing. Install the piece by maneuvering the shaft, and tighten everything up. Shaft now mechanically prevented from moving that way.

If not twin plug, could use similar scheme if it always moves toward front.

I did this at track for a rearward moving #4 intake.

The grub screw fix is a great idea - I'll remember that.

[bmwphatpat]

Turbokraft has limited stock again, I just bought a set, seems like cheap insurance against a shaft walking out and causing mayhem. Plus they seem to locate the rocker shaft correctly side to side which from what I've read can be challenging. Am doing an engine out reseal with typical scope creep (RSR seals, new rocker shaft bolts, bunch of CIS refresh stuff) etc etc...

[Walt Fricke]

These are a nice item, but hardly essential.

Locating the shaft in the proper place is dead nuts easy. Porsche, with its feeler gauge procedure, makes it far harder than it is. If these do this automatically, that isn't bad, but hardly worth spending any money on. No challenge there. Line it up on the short side of the carrier, and you are good to go. I think people vary a bit on what constitutes lining up, but there is enough leeway that you have to work at it to screw things up. Of course, if you do get the shaft in too deep, when you tighten things you will lock the rocker, which you should recognize well before it is a PITA to fix.