The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Duncan R on 24.07. 2019 20:06

Title: Rocker box- is this right?
Post by: Duncan R on 24.07. 2019 20:06
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?
Title: Re: Rocker box- is this right?
Post by: muskrat on 24.07. 2019 20:59
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
Title: Re: Rocker box- is this right?
Post by: Duncan R on 24.07. 2019 22:27
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 ?
Title: Re: Rocker box- is this right?
Post by: duTch on 24.07. 2019 22:59

 
Quote
......... 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  *work* (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  *beer*

 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 (https://www.a7a10.net/forum/index.php?topic=14429.0)
Title: Re: Rocker box- is this right?
Post by: Duncan R on 25.07. 2019 08:22
Thanks Dutch
Title: Re: Rocker box- is this right?
Post by: Swarfcut on 25.07. 2019 08:29
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.
Title: Re: Rocker box- is this right?
Post by: duTch on 25.07. 2019 08:57

 
Quote
.... 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
Title: Re: Rocker box- is this right?
Post by: Duncan R on 25.07. 2019 12:46
Thanks Guys - I will check it out
Title: Re: Rocker box- is this right?
Post by: Duncan R on 25.07. 2019 12:54
Just checked - it appears to be the rockerbox. I will get it looked at  the local machine shop/

Thanks again
Title: Re: Rocker box- is this right?
Post by: RDfella on 25.07. 2019 20:45
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.
Title: Re: Rocker box- is this right?
Post by: Duncan R on 26.07. 2019 18:47
Thanks might give that a go . Ordered some engineers blue to try and see how bad it is.
Title: Re: Rocker box- is this right?
Post by: RoyC on 26.07. 2019 19:20
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.
Title: Re: Rocker box- is this right?
Post by: coater87 on 26.07. 2019 20:07
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
Title: Re: Rocker box- is this right?
Post by: Bsalloyd on 28.07. 2019 15:31
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.
Title: Re: Rocker box- is this right?
Post by: cyclobutch on 29.07. 2019 17:23
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?
Title: Re: Rocker box- is this right?
Post by: muskrat on 29.07. 2019 20:35
G'day butch.
A sheet of 1/4" glass on a flat surface like the kitchen bench top (wait till the wife's away) is well good enough. A little moisture (water or oil) on the glass will hold a sheet of wet & dry paper flat and still. I've done many this way and get them to within a thou".
Cheers
Title: Re: Rocker box- is this right?
Post by: Duncan R on 30.07. 2019 13:20
Hi All - many thanks for the tips
Title: Re: Rocker box- is this right?
Post by: Peter Gee on 01.08. 2019 21:27
I would certainly say the culprit is the RockerBox faces...I found .0002+ clearance with my head, which is a very good one even on a NOS rockerbox I had in tock. Have the Rocker Box milled dead flat on the surfaces, which those machinists with cylinder head refinishing grinding wheels ( huge vertically mounted things) will have.
Title: Re: Rocker box- is this right?
Post by: cyclobutch on 02.08. 2019 08:48
G'day butch.
A sheet of 1/4" glass on a flat surface like the kitchen bench top (wait till the wife's away) is well good enough. A little moisture (water or oil) on the glass will hold a sheet of wet & dry paper flat and still. I've done many this way and get them to within a thou".
Cheers

Of course, paper not paste. Duh. Thanks.
Title: Re: Rocker box- is this right?
Post by: Peter Gee on 05.08. 2019 16:05
Had this prob too. After checking a NOS box I have to hand, never used..it too had about  2 thou " warp. Seems they made  them like that. I got it down to a thou with plate glass and emery No 800 and will leave it and hope three bond does the rest!
Title: Re: Rocker box- is this right?
Post by: Greybeard on 05.08. 2019 16:41
My feeling is that a rocker box should easily flex to mate the cylinder head.
Title: Re: Rocker box- is this right?
Post by: ironhead on 06.08. 2019 04:59
My feeling is that a rocker box should easily flex to mate the cylinder head.

Sorry GB that's a bad feeling, They've both got to be flat.
Title: Re: Rocker box- is this right?
Post by: JulianS on 06.08. 2019 09:34
The cylinder face also needs to be flat or the head will flex..........
Title: Re: Rocker box- is this right?
Post by: Greybeard on 06.08. 2019 10:18
My feeling is that a rocker box should easily flex to mate the cylinder head.

Sorry GB that's a bad feeling, They've both got to be flat.
I wasn't thinking huge distortion; just a few thou.
Title: Re: Rocker box- is this right? UPDATE
Post by: Duncan R on 13.08. 2019 14:58
Rocker box was tidied up with the wet n dry and plate glass method - came out pretty well, placed it back on the head- shockingly bad and still pivoting on a high point on the head and could get a 25 thou feeler gauge in the gap! Also discovered a high point on the head, appears to be on the face that separates the cylinders. The whole lot has gone of for refacing to a local engineer, had to knock the guides out which will need replacing. So with all those issues not a chance in hell of getting it oil tight.

Hopefully this will sort it once and for all- will keep you posted.
Title: Re: Rocker box- is this right?
Post by: bikerboy on 15.09. 2019 13:15
SRM are doing a one piece rocker box gasket for A10's. I used one for the first time on a recent build and must admit its a nice gasket and does make it a bit easier to fit the rocker box
Title: Re: Rocker box- is this right?
Post by: Duncan R on 18.09. 2019 12:51
Hi Bikerboy,

I also used the SRM gasket and found it stayed in place whilst fiddling around with the pushrods - would definitely use again.

Update on my oil leak issues- my mate who  resurfaced the gasket faces had to take 1mm off the cylinder head to rockerbox  gasket face to true it up ! so seriously warped. Only 5thou off the cylinder to head face. Almost oil tight got a very slight weep which is still being investigated.