Why does the lower rear (allen) screw holding the Sprint rocker, and only that one, come lose all the time?

[GrahamFountain]

I'm a bit leery of overtightening it, but I get it at least as tight as all the others. However, every few thousand miles, that one and only that one, comes loose, and oil drips onto the manifold and smells.

Graham

[cleverusername]

There thread is probably on its way out, it is very easy to damage the thread on the alloy heads. The solution is to use a helicoil and repair the thread.

[GrahamFountain]

It may be worn, though it doesn't feel like that, and takes a good tighten with a standard Allan key. My experience is that if a thread into aluminium is that worn that it won't stay tight, it wouldn't tighten in the first place and would just keep on turning.

I think it must creep from hot-cold cycling - they are stainless in to allou -, but I can't see why this one is so much more susceptible than the others on the bottom row. Maybe a shake-tight or a spring washer is needed.

Graham

[xvivalve]

You should be using a spring washer anyway.

The allen key bolts allow you to get purchase on this particular one that the original cross head screw didn't and they normally solve the problem on their own, but I also torque down the rocker cover incrementally in a similar manner to the head so it is pulled down to the head evenly. I've also known the thin paper gaskets to tear radially around the hole when tightening these screws....

[cleverusername]

You should be using a spring washer anyway.

The allen key bolts allow you to get purchase on this particular one that the original cross head screw didn't and they normally solve the problem on their own, but I also torque down the rocker cover incrementally in a similar manner to the head so it is pulled down to the head evenly. I've also known the thin paper gaskets to tear radially around the hole when tightening these screws....

Which is why I replaced it with a thicker rubber one. No more leaks and I can take the cover off without having to worry about damaging it.

[Bish]

Quick question on these Allen key bolts if I may Gents - what size Allen key are they?

I bought a set from the club a while back, but couldn’t find an Allen key in my box that would fit! To be honest, I threw them in one of my spares boxes and had forgotten about them until seeing this thread.

Cheers, Bish.

[Carledo]

Quick question on these Allen key bolts if I may Gents - what size Allen key are they?

I bought a set from the club a while back, but couldn’t find an Allen key in my box that would fit! To be honest, I threw them in one of my spares boxes and had forgotten about them until seeing this thread.

Cheers, Bish.

Think it's something like 3/16" (4.75mm) A 5mm hex key is too big and a 4mm too small!

I keep imperial Allen keys but seem to have lost that one, I eventually found a Torx that would do it!

Steve

[GrahamFountain]

You should be using a spring washer anyway.

The allen key bolts allow you to get purchase on this particular one that the original cross head screw didn't and they normally solve the problem on their own, but I also torque down the rocker cover incrementally in a similar manner to the head so it is pulled down to the head evenly. I've also known the thin paper gaskets to tear radially around the hole when tightening these screws....

I checked and there is a spring washer on all these screws. So I'm still not sure why it's just this one that works loose every few thousand miles. Maybe a shake-tight would work better than a spring. But that'd need replacing every few times the cover's off. Still not every few thou though.

Graham

[DOLOMITE 135]

It could perhaps be that the screw on the lower rear of the head is subjected to higher temperatures than the other rocker screws, you do not state what your Allen screws are made of, but I assume that they are Steel or Stainless steel.
The coefficient of expansion of Aluminium is greater than that of Steel or Stainless steel (it can be more than double that of Steel or Stainless steel depending on the grade of Steel or Stainless used). A larger differential expansion resulting from a higher temperature, in turn resulting in a greater reduction of the screw holding torque, combined with the usual vibrations from the car could result in the screw shaking loose over time.

[GrahamFountain]

It's possible. That screw is at the back of the engine bay and probably getting least cooling from airflow.
I suppose the solution is a dab of Loctite, almost whatever the cause may be. I'm just not a great fan (though I have been accused of blowing a lot of hot air).

Graham

[GrahamFountain]

It's possible. That screw is at the back of the engine bay and probably getting least cooling from airflow.
I suppose the solution is a dab of Loctite, almost whatever the cause may be. I'm just not a great fan (though I have been accused of blowing a lot of hot air).

Graham

[Bish]

Quick question on these Allen key bolts if I may Gents - what size Allen key are they?

I bought a set from the club a while back, but couldn’t find an Allen key in my box that would fit! To be honest, I threw them in one of my spares boxes and had forgotten about them until seeing this thread.

Cheers, Bish.

Think it's something like 3/16" (4.75mm) A 5mm hex key is too big and a 4mm too small!

I keep imperial Allen keys but seem to have lost that one, I eventually found a Torx that would do it!

Steve

Thanks Steve, appreciated.

[xvivalve]

It is 3/16"

You think I'd buy in metric ones????

[new to this]

Have you tried swapping that allen screw for one of the others,that way your tell if its the thread of the screw faulty or the thread in the head

[GrahamFountain]

Have you tried swapping that allen screw for one of the others,that way your tell if its the thread of the screw faulty or the thread in the head

No, but it's an interesting idea. and I'll give it a try.

Graham