The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: octane on 17.07. 2008 18:23

Title: Side cover "circular plate" question
Post by: octane on 17.07. 2008 18:23
Hi !

According to my Haynes manual there's supposed to be a 'circular plate'
behind the left-side side-cover:


Mmmmmm: mine doesn't have one.
So I checked my part-lists
 (I have a couple, as the parts in the engine comes from different models/years)


The one for 1954-57 doesn't list such a thing (left side of pic)
where as the 1960-62 does. (Blue arrow) listed as: 'washer'

Looking at the two diagrams there seams to be a distinct difference
between the size of the big hole in the two covers (Red arrows)

Now here's the thing that confuse me:
Mine DOES have the big hole (left diagram), so suposedly I don't need the 'circular plate'
the pics in Haynes show a cover like mine (big hole) AND the 'circular plate'

Clearly I DO NEED this to keep the covers further from the crank-case
as one can seee from this pic
showing how the sleve nut have been grinding deeply into the outer cover.


Can anyone explain this
or should I just put it down to the fact that my bike
is a highly un-original come-together of parts from different bikes ?


Title: Re: Side cover "circular plate" question
Post by: bsa-bill on 17.07. 2008 18:56
Yep like many of us I think
The washer would be better desrcibed as a "spacer"
The damage to your chaincase is fairly common, the cush drive nut comes undone, spins out and wears a groove in the case.
SRM do a cush drive nut with a nut shape in it's centre this allows you to torque it up with a torque wrench to it's poundage (65), something that is difficult to gauge with a chisel which is the time honoured method of screwing it up.

All the best - Bill
Title: Re: Side cover "circular plate" question
Post by: RichardL on 17.07. 2008 19:14
If I recall correctly, in addition to keeping the cush drive off the primary cover, the spacer is necessary to place the entire primary chain case in position for bolting to the frame.

Title: Re: Side cover "circular plate" question
Post by: Beezageezauk on 17.07. 2008 19:19
Hi Octane,

I'm sure the item in question is number 39 in the left diagram.


Title: Re: Side cover "circular plate" question
Post by: octane on 17.07. 2008 19:54
Thanks Bill and Richard!

allows you to torque it up with a torque wrench to it's poundage (65),
For that I guess I could use this thing I made up to adjust the torque
on the steering stem on my Honda CBX1000. (Just needs to be filed down a bit)
Just a socket with a couple of 'ears' welded on.
The socket will accept the torque-wrench


Hi Octane,

I'm sure the item in question is number 39 in the left diagram.


Thanks BZ; I was wrong, you're right !
I can see it now.

Well, well, I've learned something today....that's good!

Better go hunting for one of them 'spacer-thingies'
or maybe make one myself from some of that thick cork-gasket material I have.

Thanks y'all!
Title: Re: Side cover "circular plate" question
Post by: octane on 17.07. 2008 21:30
Made a couple of cork-things


Put together they're a little less than 3mm  /  1/8"
Does that sound about the right size?

Title: Re: Side cover "circular plate" question
Post by: trevinoz on 18.07. 2008 05:43
Octane, the picture above with the small hole is the inner off a single, not a twin. The spacer in question has the following dimensions :-  O.D.  6.75"     I.D.  3.8" approximately, size to suit crankcase.  Thickness - 0.095".   Material - steel!
I would make one out of metal. It has a paper gasket either side of it.
When you fit the cush drive nut, make sure you fit a tab washer, it may prevent the nut coming loose in the future. I also fit a split pin through the crankshaft in the hole provided. A bit difficult but worth the effort.
Title: Re: Side cover "circular plate" question
Post by: groily on 18.07. 2008 06:24
trevinoz beat me to it re the pic.
Having just this week  reassembled a single the differences were fresh in my head.
The spacer really ought to be steel with paper gaskets, but can't see why a cork thingy couldn't work to get the alignment. Not sure if the original isn't made of steel to add rigidity though?
On this general subject, I find with my inner case that I have to put a small spacer between it and the rear mounting lug at the clutch end. If I don't the clutch kisses the heads of the bolts that hold the plate (part 25 in the pictue) round the gearbox mainshaft entry hole.
The only other thing I'd say re the big spacer, is be careful to ensure that the holes correctly align with the threaded holes in the crankcase . . . the first time I put mine together, I didn't look carefully enough and then found, having reassembled clutch and all, that one or more of the 3 mounting screws wouldn't pass the spacer. Mine only goes together one way. Eejit. Oh, and Yes to split pin, every time.
There's a pic here somewhere of the alternative shock absorber nut from SRM with the hex on it - courtesy if I recall of Richard, aka Manosound. Excellent for getting the torque correct. But your Honda steering head thingy will probably do just as well! I use more primitive methods for shock absorber nuts - mega slip joint pliers about 2 feet long with which you could pull the teeth out of Tyrannosaurus Rex.
Title: Re: Side cover "circular plate" question
Post by: octane on 18.07. 2008 10:35
Thanks Trev and groily.

One thing:
Octane, the picture above with the small hole is the inner off a single, not a twin.

That's kind'a strange
as the diagram is straigth out of this catalouge:



Title: Re: Side cover "circular plate" question
Post by: RichardL on 18.07. 2008 13:17
Hello Octane,

Yes, I did post the picture of the SRM nut. I really like the tool you made and think it should be added to our "Home Made Tools" topic. However, I wonder if the height of the socket off the nut will make it difficult to put 60 ft. lbs. of torque on it, due to stability. Hard to know, until you try. Regarding pinning the standard cush nut after tightening, I should share with you that SRM does not recommend it. It turns out that if the nut loosens and contacts the inside of the primary cover, it alerts you to the loose condition and the worst thing that happens is, probabaly, marring the inside of the cover. On the other hand, if the nut loosens and you don't know it,  the cush drive slips and slams the crank back and forth with the result of bottom-end problems, as in, destruction of shims or bearings, leading to other  problems. This point about destroying shims will, likely, raise some debate, but I am just repeating what I was told by SRM. If you contact them directly, by email or phone, I am certain they will be happy to clarify or expand.

About the big disk spacer, I would definitely use steel. I believe anything soft will self-destruct leaving the primary case to flex on the frame mount, clearly, not what the BSA engineers (perhaps, Roland Pike) envisioned. I believe you would have no problem buying a reproduction spacer from SRM, or others, at a reasonable price.

Title: Re: Side cover "circular plate" question
Post by: groily on 18.07. 2008 16:36
Ah, but Richard, with the pin in there it shouldn't/couldn't loosen should it? Unless it's a flimsy and edible pin. I've always assumed that roughly the correct torque is obtained when the nut clears the holes for the pin and said pin can be inserted. Whether that's 65 ft lbs or not I've no idea, but on my beast it's pretty darn tight.
If the face cams on the cush drive jumped, which I agree would be bad in terms of stressing everything if it went on for long, it would be accompanied by a jerk and probably a noise sufficient to make even the most idle of us investigate asap wouldn't it? Long before it could transmit enough stress along the mainshaft to destroy anything on the other side of the case?
Not having the pin in there leaves the risk of the nut coming right off and smashing the primary case or at least grinding (like Octane's has started to) a hole all the way through it. The good man at BSA (perhaps Roland Pike?) clearly intended a pin to be inserted, otherwise he wouldn't have made another good man at BSA cross-drill the shaft. I'm sure he cross-drilled it far enough towards the crankcase to be sure the nut would be done up enough provided all the bits were there and the spring was in good shape.  I'm pretty confident (famous last words maybe but I hope not!!) that my own Big Nut can't come undone, and I'm definitely leaving my pin where it is! I'll eat the humblest of humble pie and wear sackcloth for ever if disaster strikes in this department.
When I was a callow and even more ignorant youth than I am now I indeed had a nut come off an A10 (very suddenly on closing the throttle from high revs). . . for . . .  the want of a pin - and probably tired threads too. It was messy.

Title: Re: Side cover "circular plate" question
Post by: RichardL on 18.07. 2008 16:55

It's always great to hear your well-experienced take, as you know, most of my A10 experience is in owning a wreck waiting for restoration. I apologize for taking the part of the parrot here, but I was trying relate the points as told me by SRM when I reported shards of metal (i.e., shim) in the bottom of my crankcase. Below, are their verbatim comments. I trust they won't mind me posting them. (I misquoted the torque. They say 65 not 60.)

The metal is more than likely shim material, common problem caused by the non tightening of the cush drive nut in the clutch side, clanking is cush drive assembly loose on the crankspline, and possibly loose crank bearing on the crankshaft .
The cush drive nut is critical, must be 65 foot lbs torque tightened, this holds the cush drive assenbly tight against the oil seal spacer, which in turn holds the crank bearing , which in turn hold the shims against the crankshaft; if this is all loose , crank splines wear badly, crank bearing wears crankshaft so it is loose fit on shaft , and shims break up and fall inside engine. Usually if the split pin has been fitted above the cush drive nut , when nut comes loose, it goes against pin, and you dont know it loose, happily riding and causing engine damage, best to leave this pin out, so nut touches primary cover and makes a noise , so it is investigated before the serious damage is done. But this is not the casue of the engine noise !
(meaning, the noise in my engine that I posed on YouTube for SRM to hear).

Title: Re: Side cover "circular plate" question -
Post by: RichardL on 18.07. 2008 17:40
OK, I'm obsessing now. Looking at the damage in Lars' primary cover, it looks like the loose nut made the "C"-shaped damage, then, came all the way off, allowing the spring to make the smaller diameter circular damage. Groily, is this what you meant?

I think SRM's point is that you make the thing so incredibly tight that there is no chance of slacking off.

Title: Re: Side cover "circular plate" question
Post by: groily on 18.07. 2008 21:17
It is , it is, Richard! Exactly so. Mine, all those years ago (more than 30), made a hole. Not a nice mendable hole which could be passed off as a factory hole, but a jagged ragged messy embarrassing hole!
But I think we and SRM agree - this darn nut has to be done up well and truly so it does not and can not come off! I'm loath to disagree with SRM because I have huge respect and they know far more than I . . .  and I don't really d(isa)gree, it's just a matter of d(e)gree. My tekkie points would be that the splines on the mainshaft do not allow the crankshaft sprocket to bear on the main bearing directly; and in no way does the s/absorber assembly control c/shaft end float contrary to occasional misinformed opinion. Therefore, although shocks on the mainshaft caused by a loose sprocket whacking the inner end of the splines on which it sits are A Bad Thing, they do not directly affect the end float of the crank nor do they directly cause a problem for the shims. The crank is positively located within the cases and the cush drive is positively and independently located between the sprocket and the Big Nut. Were it otherwise, think of the life the worm gear on the oil pump would have at the other end of the crank!
Now, the bit I agree completely on -  a constant whacking caused by a loose sprocket and/or jumping cams if such is possible will obviously be transmitted through to the bottom end . . . but to wreck it the Big Nut would have to be very loose, the cush drive spring broken, a face cam shattered - or a bit missing altogether - and it would have to have been like that, and ignored, for a while. It's likely that the primary chain and the clutch drum's rollers would be knackered by mis-alignment woes before the crankshaft made a fuss, although anything is possible. If - I think - the nut were loose enough to cause all these bad things, it would probably also be touching the inner side of the outer primary case.
Ergo, in my view, a split pin in one of the holes so kindly provided by the nice man at Small Heath must be better than no split pin, as even if the thing isn't placed to give the 60/65 ft lbs required, it's far enough up the mainshaft to stop the nut coming too far undone. I don't believe the Nut could consume entirely a split pin of the dimensions we're talking about and so I do not believe it could ever back off far enough to let the face cams override one another - or to hit the primary case for that matter.  One can see how hard it is to make the cams jump by doing the Big Nut up until it forces the cams to do just that. It can be done - with a T Rex tooth puller or otherwise - but it takes more leverage than the clutch and/ or the rear brake can comfortably stand. I do my Big Nut up with the bike in gear and the rear brake well applied. When it is so well done up that the brake can't hold it - or the clutch slips - I stop and call it a day. It's there or thereabouts that the split pin can be inserted outboard of the Nut. Short of doing the nut up on the bench with something wedging the pistons or rods to stop the crank turning, or a heavy clamp on the primary chain (which will stress the clutch rollers let alone the chain itself), there's no way I can think of to get it any tighter. Which one shouldn't want to do anyway - or it will be impossible to get the thing undone for routine maintenance, like sprocket renewal, gearbox work, etc. In my other, AMC, world, I am constantly amazed at how darn hard it is to get the crankshaft shock absorber assemblies off - often takes more torque than clutch and brake can stand and requires 2 pairs of T Rex tooth pullers. But they don't have a split pin (although they do have hexes) and their sprockets do abut the main bearing - so slack is a capital letter NO-NO - and I do 'em up REALLY tight!
Title: Re: Side cover "circular plate" question
Post by: RichardL on 18.07. 2008 23:28

My response will be pathetic, by comparative length. First, thanks for the good read. Assuming SRM is wrong, it makes me wonder how they came to have such a definite opinion, considering the number of engines and bikes that must pass through there. Anyway, the upshot, for me (hey, I thought this was supposed to be about Lars!) is that I will put in a cotter key behind my SRM nut done up to 65 ft. lb.. I believe the expression is "belt and suspenders."

Title: Re: Side cover "circular plate" question
Post by: Brian on 19.07. 2008 00:55
Its a bit difficult to explain but I will try. SRM are correct with their explanation. Imagine you have the crank sitting on the bench in front of you. First you would put the shims on, then the bearing, then the steel spacer [the one the seal runs on] then the splined sleeve and finally the nut. Once the nut is done up all these parts are trapped between the crank and the nut. This is why the nut must be done up tight to stop any of these parts being able to move. With a roller main bearing the end float is critical as even with the nut done up tight the whole crank assembly can move sideways. The early [plunger] engines had a ball bearing main and provided the outer of the bearing is tight in the crankcase the crank is held in position by the bearing. Some people use ball a bearing main in the later motors that originally had roller main and there are arguments both ways on this subject. Anyway, back to the cush drive. The sprocket and lobed piece and spring are independant of all the parts on the crank. Even when the spring is fully compressed the lobed part can not ride up and over the other lobed part. The idea of this is that as the two lobed parts work against each other, when you accelerate the lobed parts climbs up its opposing lobe and when you are running on a constant throttle it settles back to its normal position. I should also mention that sometimes when you dismantle these things you will find shims between the steel spacer [the one the seal runs on] and the splined sleeve. These are to align the sprocket to the clutch. If you have a six spring [plunger type] or a four spring type clutch it does pay to check the alignment of the sprockets and use shims if necessary. If you have the other six spring clutch [external springs with nuts on them] it doesnt really matter as the chainwheel moves anyway. I have that type of clutch in some of my bikes and have got them to work well but I dont like them, poor design I reckon. Well I am not sure if this will help or just make it all more confusing.      Brian.
Title: Re: Side cover "circular plate" question
Post by: groily on 19.07. 2008 06:53
Illumination! So in fact what I call the AMC factor does apply Brian - in that the spline/sprocket etc DOES abut the bearing effectively and I was wrong to have said the crank and its end float, shims etc are independent and unrelated. I thought the sleeve was held just proud of the spacer (and therefore of the bearing) against a non-existent inner end of the mainshaft spline and that therefore the sleeve could not whack same. Humble pie with extra worms on order . . .  But I'm keeping my split pin all the same! And the tooth puller.  I shall look at it all a bit more carefully the next time (it'll be the first time for this engine) the crank is on the bench. Hope it's not any time soon as it runs so sweetly it'll be a shame to disturb it. Looks like it's in for a very wet and miserable couple of hundred kilometres today . . . where is Summer (for those of us who ought to be having one by reason of our northerly orientation)? Nothing worse than wearing wet-proof gear on warm and  heavy days . . .
Title: Re: Side cover "circular plate" question
Post by: octane on 19.07. 2008 15:01
Oi ! Lot's of interesting stuff here Gentlemen

But one thing totally beats me:
WHY that seperate 'circular plate' ????
Why isn't it just a 'build-in' part of the crank-case.
Why doesn't it just have that extra 2.4 mm / 0.095" , where the plate is put on?

..or why isn't this flange just 0.095" further 'out'


It's a bit weird.
Title: Re: Side cover "circular plate" question
Post by: groily on 19.07. 2008 18:05
Probably because the drawing office made a ****s of it; or because of the problems of making one semi-standard design of frame and transmission cope with all sorts of engines! It all adds to the mystery of it . . . some of which I am exploring with the addition of a gentle and charming single to the shed  (with attendant hassles, as ever . . .)