A10/RGS engine screws/gearbox

[sprint]

Without having to removing and measuring every screw can anybody advise what the various lengths are for the A10/RGS timing cover, chaincase and gearbox covers are?

Should they be cheesehead or raised (fillisler) head? I take it that either UNC or BSW threaded screws can be used as a direct replacement for the original BSW despite the slight difference in the thread angles?

What is the thread used for the two g/box inspection cover, 24-7178?

[Billybream]

Hi.
Screws are cheese head as standard, but many people have changed to allen head, as the original cheese head get,s abused easily, a word of caution when using allen head as damage to casing,s through over tightening can occur. My choice would be s/steel cheese head from Barleycorn.
This link should give you screw thread sizes and length : http://stainlessbits.com/link12.html

[bsa-bill]

Should they be cheesehead or raised (fillisler) head?

I think the correct ones are fillister, Cheesehead are too square but fitted by many including myself as they are probably easier to get


 

[trevinoz]

Gearbox inspection cover screws are 1/4 x 26 tpi.

[sprint]

Thanks to all for the replies.

Andy

[sprint]

Hi.
Screws are cheese head as standard, but many people have changed to allen head, as the original cheese head get,s abused easily, a word of caution when using allen head as damage to casing,s through over tightening can occur. My choice would be s/steel cheese head from Barleycorn.
This link should give you screw thread sizes and length : http://stainlessbits.com/link12.html

Thanks for the link.

Looking at some of the numbers there is some confusion?

67-1706 - 1/4" x 1-5/8" x 20
67-1711 - 1/4" x 1-5/8" x 20

Both listed as being the same, so why separate part No's? Is there some other difference between the two?

42-7517 - 1/4" x 15/16" x 18? Is that a typo error as BSW is normally 20 not 18 tpi?

[BSA_54A10]

Go to http://stainlessbits.com/link12.html this site , download the list & then print out a copy & keep it in the workshop.

As for different part numbers for the same bolt, many of them have different thread lengths which will naturally give them a different part number.
Polishing the head will also mean they have a different part number.

As for using Allen headed cap screws you should always use at least 1 if not 2 washers under them.
Otherwise you will eventually destroy your covers.
BSA used fillister heads particularly because they are the largest standard head.
This was to spread the clamping force over a large area under the heads so the heads did not either collapse the clamping zone back into the hole or dig a deep ditich and distort the bottom of the hole.
I have seen some covers where the DPO has actually managed to drive the heads totally through the cover.
An Allen head has 1/3 the area under it as a Fillister head.

[sprint]

Go to http://stainlessbits.com/link12.html this site , download the list & then print out a copy & keep it in the workshop.

As for different part numbers for the same bolt, many of them have different thread lengths which will naturally give them a different part number.
Polishing the head will also mean they have a different part number.

As for using Allen headed cap screws you should always use at least 1 if not 2 washers under them.
Otherwise you will eventually destroy your covers.
BSA used fillister heads particularly because they are the largest standard head.
This was to spread the clamping force over a large area under the heads so the heads did not either collapse the clamping zone back into the hole or dig a deep ditich and distort the bottom of the hole.
I have seen some covers where the DPO has actually managed to drive the heads totally through the cover.
An Allen head has 1/3 the area under it as a Fillister head.

Thanks for the reply and link.

However, the confusion has been caused from the info given from that link, namely as previously indicated:

The following two outer chaincase cover screws have the same dimensions but a different part No and I would like to know what the physical difference is between them or can I just simply use the same screw in both places? In the case of 42-7517 it lists it has a 1/4" BSW screw but with 18 tpi and not 20 tpi? Is that just a typo error or is there actually a 1/4" BSW screw with 18 tpi?

67-1706 - 1/4" x 1-5/8" x 20
67-1711 - 1/4" x 1-5/8" x 20

Both listed as being the same, so why separate part No's? Is there some other difference between the two?

42-7517 - 1/4" x 15/16" x 18? Is that a typo error as BSW is normally 20 not 18 tpi?

[BVSR]

Sprint, take a closer look at list. 42-7517 is 5/16" - 18 x 1 5/16" not 1/4" x 15/16" x 18.

Regards Markku

[BSA_54A10]

67-1706 are 1/4 BSW 20  x 1 & 5/8 " long these the oil level & drain screws and are threaded their full length and when new had a dob of red paint on their heads.
67-1711 are the same size but threaded to the standard length for their size about 1/3 their length.

I might be wrong but I seem to remember saying this in a previous post.
Please get yourself a parts book.
I am fairly sure you wll see that on n umber is drawn as fully threaded and the other is drawn partially threaded.
If you printed out the copy of the stainless bits book as suggested you might like to ammend your copy thus wise to aid in further repairs.

As to substitution of thread forms, you can get away with it but the screw will eventually stuff the hole and tear out the thread out of your cases as it is only in contact for about 10% of the surface area as it should be.
Get 2 pieces of paper about 3" to 4" and cut a V in each one @ 60 deg ( UNC ) & one at 55 deg ( BSW )
The bit you cut out represents the steel screw while the V in the paper is your soft aluminium hole.
Put one inside the other and it will be clear why it is not a good idea to ever use the wrong thread form