The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: NickSR on 13.03. 2009 18:42

Title: Stainless Steel Change Over
Post by: NickSR on 13.03. 2009 18:42
Hi Everyone
I have purchased some stainless steel Allen Screws for the timing and primary covers, I would like opinions on if its possible to change over by taking out the existing screws one at a time, bearing in mind both cases are oil tight.


1962 Super Rocket
1954 C11G
Title: Re: Stainless Steel Change Over
Post by: bsa-bill on 13.03. 2009 19:54
Should'nt be a problem, make sure you have the same legth as you took out and check that the hole it goes into is clean to it's full depth, it is possible to screw a screw nto a hole with muck in it (red hermatite) and burst the case.

All the best - Bill
Title: Re: Stainless Steel Change Over
Post by: BSA_54A10 on 14.03. 2009 08:53
Exceptionally , extremely important,
Put the biggest flat washer you can find under the head of the allen bolts or your nice oil tight cases will not stay that way for very long.
The heads of the allen screws are a lot smaller ( around 50 % if you care to measure ) so you put enough force on the surrounding alloy to cause it to collapse, thus loosing clamping pressure , thus starting to weep from the  joint , thus causing you to do them up tighter , thus causing more metal to collapse from under the head, thus causing it to loose clamping pressure , thus causing it to start to weep from the joint, thus causing you to nip them up tighter , thus,thus,thus,,,,,,,,,,,,, .
You used to be able to get thick washers to fit under them but they do not seem to be stamping thick washers in these small sizes any more so I generally use 2 thin  mudguard washers.
I clamp a dozen or so on a bolt, mount them in the drill and "file" them down to be close fit in the hole as standard washers in this size are too thin both radially and axially .
Prior to this I used oversized pop rivet washers ( for pop riveting soft materials , but even these seem to be unobtanium now days.
Bike Beesa
Title: Re: Stainless Steel Change Over
Post by: NickSR on 14.03. 2009 14:29
Bill & Trevor

Thank you both for your help, would not given the head size a thought.

Again thank you.

Regards Nick

1962 Super Rocket
1954 C11G
Title: Re: Stainless Steel Change Over
Post by: RichardL on 14.03. 2009 14:30

Thank you, excellent point. Distributing the force over the maximum area when fastening-down valuable and potentially fragile parts is the best way to go.  I believe I will take your advice and find or fashion some washers. However, I did "care to measure" and you may be surprised by the results. By my measurements, the counterbores were made with a 13/32" (0.406") tool (on the assumption that they would choose a standard size available.) I believe this would dictate using a 3/8" O.D. washer. The clearance holes are 17/64" (0.266", or very close). The screw-head diameter I measured was 0.362". Without boringly walking through the arithmetic, the result was that the Allen head's clamping area was 86.4% of the available landing for a 3/8" (O.D) washer or 64.2% of the availble landing if you could fit a 13/32" (O.D.) washer.  Does this sound right? Regardless of suggesting this adjustement in your estimate of area, it is still a great point and, as usual, your knowledgeble advice is invaluable.

Richard L.
Title: Re: Stainless Steel Change Over
Post by: RichardL on 15.03. 2009 01:22
...and before you know it, a complete set of bespoke "Trevor Washers". In one photo, lined up on a drill bit for reduction of about 1/32" radius (also served as a nice wheel dresser). In the other, measured and dipped in some Rustoleum primer to cut down on rusting due to grinding away the plating. So, for the finished diameter of the new washers, a 48% increase in contact area.

As I said, Trevor, good advice, thanks again.

Richard L.
Title: Re: Stainless Steel Change Over
Post by: NickSR on 15.03. 2009 22:16
Hi Bill, Trevor & Richard

With all the good advice given I proceed today to take one of the the steel allen screws which I guess had been in from the late 60s no later than 1971 ( I have been in contact with the second owner) who purchased in 1972/73 and knew the bike from new).

The heads of the old screw completly fill the hole recess, now for the problem when I examined the new stainless steel allen screws I notice that they are poorley machine on the under side of the head ie not 90 deg to the thread.

From your comments I now can see why there are problems exterting pressure, washers or no washers.

Plan for the moment is to leave things alone and source some high quailty allen screws.

Regards Nick

Title: Re: Stainless Steel Change Over
Post by: Brian on 15.03. 2009 22:28
Not wanting to pour cold water on your idea but why change them?. The allen screws will not do the job as well as the original screws and will potentially cause more problems in the future. Original slotted screws are readily available and if you have a decent screwdriver will not cause any problems. Plus I reckon allen screws look lousy on a old bike.
Title: Re: Stainless Steel Change Over
Post by: RichardL on 16.03. 2009 03:46
No arguement on the appearance question, but, from a mechanical point of view, I have to believe the Allen screws are likely to perform equally to cheeseheads at the same torque, assuming equal clamping area when using washers with the Allens. Additionally, the Allen screws will get to the desired torque more easily than using a flat blade in the cheeseheads. There may be a drawback to the Allens in that they might invite overtightening, but I have no experience with cheeseheads to know if they readily get tight enouph to preclude leaking or if they take an heroic effort with the flat blade.

But then again, there is the appearance issue.

Richard L.
Title: Re: Stainless Steel Change Over
Post by: BSA_54A10 on 16.03. 2009 05:48
I personally love the look of allen heads and find them much easier to use particularly in the dark on an oily cover ( there is usually a good reason to remove the cover on the side of the road & it aint to admire the clutch) .
Secondly once these are replaced there is no need to cary a large screwdriver.
My tool kit fits into an old Kanebo chamois tube which will comfortably fit into the bell staff side pocket.

As for the differences in clamping area, I did mine on the A10 timing cover bolts a long time ago and am fairly sure that it was around 50% remembering that you are comparing the area of two rings ( the shaft must be deleted from both before the comparission ) and that the stainless allen bolts that I use down here have a knurl on the sides which makes the apparent diamenter a fair bit bigger than the actual one.

I also have a sneaky feeling that the heads on the OEM bolts have been getting a bit smaller over the years.
I think that the original BSA bolts had a larger head than standard size and have been replaced with standard bolts which have a smaller head.
Now the memory is getting real thin here but original bolts were phillister heads while the latter replacements are pan headded.
Pan heads are taller with a smaller diameter than phillister and of course have square edges against the phillisters shoulder.
The again the medication might be letting me down to ( trevie, time for you pillie poos )
We used to replace the phillister ones with pan heads because the screwdriver was less liable to slip & gouge the cases in the deeper slot.