The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: AdrianJ on 02.03. 2019 16:41
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I've just bought a set of stainless Allen screws for the chaincase, but I've lost the piece of paper with my notes of which go where.
I appear to have two long, 7 medium and three short screws.
One of the long ones fits the extreme rear hole, but i am reluctant to wind the others in in case I do some damage.
Can anyone enlighten me about the screw positions please? The plunger case seems quite different to the SA.
I've searched the forum and found the lengths of the screws but not the positions.
Thanks in advance,
Adrian
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Usually best to check while the cover is off, but if replacing the screws while in service, fairly much the three short ones go to front, medium ones behind those and the long ones rear and above or below the centre line . You should be able to gauge it with a bit of wire for a depth gauge.
I didn't think all the ones in the set were long enough so customized my own anyway...
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Ta, That really helps, I'm not sure my new ones are all the right length. I'll use wire to make sure I don't destroy anything. I seem to have too many long screws, may have to shorten some.
Adrian
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Adrian...It is a good idea to make sure there is no crap and old jointing compound at the bottom of the blind holes. Smaller drill or a woodscrew, both hand held, will clean them out. As long as they do not bottom, it is a case of check and shorten to use the maximum thread depth. The bolts should be 1/4 Whitworth Thread, same thread as sump plate studs or rocker cover studs, into the aluminium castings.
Swarfy.
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Thanks very much Swarfy.
Adrian
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The bolts have different part numbers
The bolt lengths & threads are listed in the stainless fasteners BSA/Triumph fastener list
So parts book then list to check the screws.
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Hi Trevor,
I have the lengths sorted, it's just which go where that isn't clear (the parts book doesn't help with the positions) but I'll sort that with a piece of wire.
Adrian
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I run a 1/4" Whitworth tap down the holes. It's amazing how much crud can come out with the tap. Be careful not to over-tighten the cap screws - one reason I stick with the original cheese-headed screws.
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Thanks very much everybody.
Sorted now, not too tight but hopefully oil tight.
Stacks of crud in the holes.
Adrian
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... I stick with the original cheese-headed screws.
Fillister *smile*
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So some one who used cap heads would be a fillis-tine Boom Tish.
The thing you have to be careful with when using cap is the head on them is about 1/2 the surface area of the correct Fillister heads.
So when done up a little too tight they mutilate the clamping face under the head and cause the alloy to collapse into the hole.
You should always use flat washers under allan headed caps to spread the load.
Allan headed caps were designed for use on machines that were steel not alloy so the head is the appropriate size for clamping down onto steel not alloy.
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Fillister - that's the word! *smile*
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Diagram of Timing cover screws attached
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Anyone looking for the "original Look" screw, we have them in 1 3/4" lengths for various applications. Sold in lots of 10
https://mikesclassiccyclespares.com/product/new-bsa-triumph-timing-primary-gearbox-cover-cheese-head-screws-1-4-unc/
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Fillister
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The Allen screws I have just got for the chaicase appear to be the same head diameter as the mangled Fillister screws I removed. Is this likely and would it remedy the above mentioned problems with socket head screws?
Adrian.
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Adrian...As long as they go into the primary case and are a good match for the diameter of the original screws, you will have no problem. The secret to an oiltight case is a good quality gasket and smooth mating surfaces. My favourite jointing is Hylomar, purists will use Red Hermatite. Silicone bathroom sealer if that's all you have.
One of the screws acts as a level plug, one as a drain, so these will need a fibre washer under their heads to act as a seal. The oil level is quite critical. I run the oiled chain "dry" and add oil until a nice stream of drops passes the filler hole as the motor ticks over.
This means that now the chain is running in oil, but the oil is not deep enough to get into the clutch.
The screws you have will be fine, they may actually be made for the job, rather than some generic fastener. They only need a firm tighten, not the extremely murder tightness that results in knackered screws when you try to get them off.
Swarfy.
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Thanks Swarfy,
I'm short of the fibre washers but I'll find some.
I believe that these screws were specially made.
I used to use Red Hermatite , mucky stuff, didn't know you could still get it. I'm using Hylomar now.
Adrian.
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I don't actually use anything on my chaincase gaskets except a smear of grease. Seem to work. Nothing worse than trying to get red hermetite out of the bottom of threaded holes in the chaincase. There was a time when it seemed compulsory. Actually, thinking back, people did use red hermetite on threads as a primitive version of loctite.
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Fillister
Starts looking like filibuster GB! *smile*