Rocker box- is this right?

[Duncan R]

Persistent problem with a top end leak and still leaking but less after replacing gasket. One of the rear studs pulled its thread, I have just helicoiled  it and decided to do a test fit (no pushrods) just to make sure I had done it straight. What appears alarming is the 2 faces don't seem to meet that well and the box does not sit flat and it appears to pivot somewhere in the centre - this can't be right surely? Do I need to get the gasket faces skimmed?

[muskrat]

G'day Duncan.
Yes it will need facing. Also check the four bolt holes in the head are flat (the edge of the hole can sometimes be pulled up through over tightening of the bolts).
Cheers

[Duncan R]

Hi Musky,

Thanks, thought that might be the case. Thread inserts all ok ,I did dress them with a file sometime ago. Do you think head needs facing as well ?

[duTch]

 

......... Do you think head needs facing as well ?....

 It's well worth checking, especially where the rocking area is.... probably less likely the culprit
   I use the wide end of a metal wood square as a straight/flat edge, and then carefully filed them flat  (along the face as well as across using the opposite side as a guide) took some time but no other easy option seems to have worked reasonably well 

 If you haven't seen another  similar thread on the go,I think this is it;
 https://www.a7a10.net/forum/index.php?topic=14429.0

[Duncan R]

Thanks Dutch

[Swarfcut]

duTch is right, the head top face is unlikely to be the problem. To remedy any deviation  properly on a fly cutter would need the valve guides to be removed, so is best left alone unless you can see major damage or deep scoring to the mating face. Otherwise it would entail milling along the faces, labour intensive, more expensive.

  To see if the fault is head or box, remove the studs from the rocker box and place it on a sheet of glass...glass topped table, window glass etc, If it sits with no gaps or rock, the fault is in the head face. More likely  the rocker box is the problem and the high spots will show themselves. A little bit of attention to carefully flatten them out should effect a cure for the leaks. If it proves too badly warped, a trip to your local engine reconditioner and a couple of minutes on a fly cutter will restore the faces. If this is required, only remove the minimum amount of material, its a bit crowded inside that rocker box. As musky says, make sure the corner stud threads are not raised, and aim for no rock when placed on the sheet of glass.

 Swarfy.

[duTch]

 

.... As musky says, make sure the corner stud threads are not raised..

 To be specific- primarily the main long ones with the brass thread inserts...plus the others

[Duncan R]

Thanks Guys - I will check it out

[Duncan R]

Just checked - it appears to be the rockerbox. I will get it looked at  the local machine shop/

Thanks again

[RDfella]

As a DIY (presuming you have access to a surface plate or other really flat surface  - such as the bed of a bandsaw etc) then put down a sheet of 100 grit sandpaper and work the offending item across it. Be careful not to rock it when pushing it over the paper.

[Duncan R]

Thanks might give that a go . Ordered some engineers blue to try and see how bad it is.

[RoyC]

As a DIY (presuming you have access to a surface plate or other really flat surface  - such as the bed of a bandsaw etc) then put down a sheet of 100 grit sandpaper and work the offending item across it. Be careful not to rock it when pushing it over the paper.

I used a plate of glass and stuck the wet & dry on with water suction.

[coater87]

As a DIY (presuming you have access to a surface plate or other really flat surface  - such as the bed of a bandsaw etc) then put down a sheet of 100 grit sandpaper and work the offending item across it. Be careful not to rock it when pushing it over the paper.

 Thats how i would do it, no blueing needed- the color of the aluminum will show you whats low. Use a black sharpie when in doubt, quicker and cleaner than blueing.

 Also rotate your part 90 degrees each push on the sandpaper - helps keep/make the surface really flat.

 This goes faster than it sounds.

 Lee

[Bsalloyd]

When working with aluminum it is a good idea to champher the hole to the depth of one thread. When you tighten the bolt the force is on the first couple of threads and that causes the metal to be pulled outward. The first thread is deformed and stands proud of the surface. I usually do this with any threaded holes in aluminum or brass. If this causes you to eliminate the gasket surface required to seal the item, don't do it.

[Butch (cb)]

As an aside to this discussion, a question or two if I may;

I have lapped surfaces before, but this was on a proper plate. So this was of a known flatness, and I thought purposely soft enough that the lapping paste stuck to it such that the surface you were moving across it took all of the abrasion.

A glass plate is to some extent flexible and so will take the form of whatever you’ve sat it on, and hard – so the paste won’t stick to it.

But a lot of folks use glass and I presume very successfully. Why am I wrong?