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#858896 09/20/21 3:23 am
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Hi all, now that I am up and running a couple of issues have presented themselves. One is that there is a loud knock occasionally coming from drive side/clutch. This seems to happen under load such when I accidentally shifted into fourth at a stop thinking I was in first (too much Triumph riding). Also happens occasionally when pulling from first. When reassembling the clutch I noticed the key in the mainshaft looking a bit beat up. I put things together just to get her up and running. Obviously need to change out mainshaft anyway but has anyone experienced a similar loud knock due to a lose key and slot on the mainshaft? Anything else I should consider as the culprit? Gearbox is ScT2. Mainshaft 67-3330? I should add that an SRM 4 spring clutch is fitted.

Last edited by AlexVoc; 09/20/21 3:29 am. Reason: Clarity
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A single knock (e.g. when you accidentally put it in 4th), or a regular knock that increases in rate as the engine speeds up?

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Hi MM, thanks for reply. More of a quick "rapping", a few quick knocks in succession, then disappears when I clutch, let go of throttle, and slowly rebuild speed. Only happens when taking off from stop. I had bike up on a stand and put bike into gear. I put my hand on primary cover and don't think I felt a knock against the cover specifically but seemed obvious the knocking was coming from clutch area.

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Your cush drive nut could be loose causing the face cam to go over the crest. If the nut is loose it will quickly wear a hole in the case


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Thanks Andy. Yes, worth double checking once I pull cover off. The previous stock cush drive nut was in fact grinding against the cover. I switched it out for the SRM unit with the socket drive. Locking the cush drive and getting nut torqued right was a challenge so worth double checking. Would be nice if that's all there is to it.

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Alex,
It is well worthwhile to get a clutch locking tool as an aid to tightening the crank nut
two old clutch plates can be bolted together, add a length of 1" x 1/4 steel to two of the bolts at one side of the plates ant this can rest on the bench or floor while you tighten the nut
This can have a side affect in that it can pull the gearbox sideways loosening the primary chain
Alternatively use an impact wrench with caution

John

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Hi John, locking the primary was not the challenge. My challenge was locking the cush drive sleeve against the engine sprocket. With the primary locked, when I tried to tighten the cush drive nut, the cush sleeve would simply turn over the lobes on the engine sprocket. I had to wedge a piece of wood between two lobes to get it to stop moving. Hope that makes sense. I am starting to think there is a problem here and perhaps the source of the noise I am talking about.

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Originally Posted by AlexVoc
.... My challenge was locking the cush drive sleeve against the engine sprocket. With the primary locked, when I tried to tighten the cush drive nut, the cush sleeve would simply turn over the lobes on the engine sprocket. ......
Did you try threading that new SRM nut onto the crankshaft without the spring to make sure the threads were OK with each other?

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Originally Posted by AlexVoc
the cush sleeve would simply turn over the lobes on the engine sprocket. I had to wedge a piece of wood between two lobes to get it to stop moving.

From preunit Triumph experience, I'm wondering if maybe the engine sprocket cush spring could have settled (lost it's springiness)? I can see how this spring being weak could cause a rattle under load as the lobes are not kept tightly pressed against each other, slipping to the next lobe and clunking until the load on the spring of moving the bike is gradually reduced as speed up begins.

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Hi Alex,
I believe you have some incompatible parts ?
It should NOT be possible for the cams to ride over even without a spring fitted
Unfortunately there are multiple BSA cush drive components and its extremely difficult to place part numbers on a particular part by sight
There have been some long threads on the A10 forum recently where guys are finding extreme difficulty getting an assembly that will work properly,
If your primary chain line is correct the problem could be the sliding cam? I found some with different length "sleeves"
The sliding cam should butt up against the nut before the cams can ride over
If the cush drive rides over in service it can cause devastating damage to the crank

John

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AlexVoc Offline OP
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Well, now I'm more confused. The lobes skipping-over seems to be the most likely culprit for the noise. Pulled cover off. I have:
15-1560 21T engine sprocket
15-1555 4 lobe cush drive sleeve
67-1135 SHORT cush drive spring
I have 3 different manuals, none of which have this combination.
So what is stock? Does the '54 GS have a stock 2 or 4 lobe sleeve? At least 2 of my manuals have conflicting info.
I purchased the taller 66-1706 spring thinking this was the answer but no way can I compress spring enough to thread on the nut.

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Put the bike against some thing solid
Remove the primary cover so you can see what is going on
Start the bike, engage 1st then let the clutch out slowly while watching the cush drive
If the lobes are skipping over each other it will be easy to see


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Originally Posted by AlexVoc
...... Does the '54 GS have a stock 2 or 4 lobe sleeve?.......
AFAIK, your Gold Star should have a 2 lobe cush drive. All the ones I've ever seen had a 2 lobe setup, that's '53 through '63.

Also, with the spring removed and the nut torqued back on, the lobes should not be able to slip past each other.

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Hi Alex,
The 54 CB parts book online from Baxters, https://www.baxtercycle.com/parts/parts-books-online/bsa/
shows a 4 lobe cush drive for the CB and the part numbers you quote are the same except for 66-1706 for the four lobe cush drive spring
You say you have a short spring ??? but I do not know if this is correct? what is the difference between short and long dimension wise?
I have not come across such a description before
The cush drive nut for the CB is part 65 -2520

But there are no part numbers on the bits so hard to know exactly what you have??
An incorrect cush drive nut like this one, https://www.ebay.co.uk/itm/114454684956 could allow the cush drive sleeve move outwards
more than the flat faced nut shown in the parts diagram ??

John

Last edited by chaterlea25; 09/25/21 10:52 pm.
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Hi all, thanks for the replies. I mentioned the "short" spring in my set up (67-1135?). By short I mean the spring stands about 1.5 inches tall with 3 coils. By comparison 66-1706 stands about 2.25 inches tall with 4 coils. Also, I have the SRM nut. Both springs are 2.24 inches wide. I removed the cover, made sure torque on nut was correct, then shifted thru various gears and pulled slowly away. There is a LOT of play in the spring but I didn't see the lobes skip over. Also, I could only get the knocking to occur once, again, noise is intermittent. But with the cover off seemed more like the noise was coming from engine, not sure top or bottom end. Time to pull the head and cylinder off to see what in there. I didn't assemble this engine so who knows what is going on in there. John, I am interested in your thoughts on the spring I mentioned. Will have to be replaced anyway but wonder if the sizes are what you have seen. Can the B34GS head and cylinder be pulled with the engine in the frame? Any tips or items to watch out for in the process would be helpful. Thanks all.

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Originally Posted by chaterlea25
Hi Alex,
The 54 CB parts book online from Baxters.........shows a 4 lobe cush drive for the CB......
John, thanks for this info. Both my BB and CB have two lobe cush drives because that is what came with them in their boxes of parts. But now I have looked at the link you provided and stand corrected. But it also explains why the threaded drive side stub on the CB isn't quite long enough to engage every last thread in the nut. But I'm going to stick with the 2 lobe setup anyway.

But, if the 4 lobe doesn't hold up as well, maybe Alex's have worn enough to let the peaks slip past each other.

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Hi All,
Alex, I do not have a 4 lobe setup to hand to check what type of spring is fitted
The 2 lobe springs I have for the A series twins have 3 1/4 turns
A new spring I bought from Auto Cycle intended for my GS replica build has 4 turns
I tried it on my A10 but it went coil bound before the nut was against the inner sleeve
I need to measure the length of inner sleeve for the GS but its 2 lobe

Stuart,
The inner sleeve (cush drive bearing) should be long enough to extend over part of the threaded end of the crank
The nut must tighten against the end of the sleeve in order to clamp the crankshaft to the outer ball main bearing, this locates the crank position within the cases. If it does not then its only spring pressure holding the crank. Not what BSA intended!!
On the A series twins the crank splines soon wear if the assembly is incorrect

John

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Originally Posted by chaterlea25
.......The inner sleeve (cush drive bearing) should be long enough to extend over part of the threaded end of the crank
The nut must tighten against the end of the sleeve in order to clamp the crankshaft to the outer ball main bearing.......
Hi John,
Thanks for bringing that up. Although I am well aware the sleeve is a part of the "stack" that must be held tight by the nut to avoid fretting wear and other worse things, it still, for the benefit of others bears repeating. It's vitally important that the cush drive nut be properly tight.

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HI Alex,
There is a 4 lobe cush drive on ebay, https://www.ebay.co.uk/itm/384414518051
It shows a spring with 4 + turns made from "square" section wire rather than the round wire used on the various 2 lobe units

John

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Alex.good that you are going to dismantle the engine. If you had been running with a loose cush drive nut, as you say the nut has sometime scuffed the inner primary case then there is a possibility tha the drive side spacer could have become worn because of sideways thrust on the main shaft, worst scenario. My Goldie had a tinkling knocking noise due to the mainshaft nut being loose and the side movement of the flywheels wore down the drive side engine distance collar and engine shaft shim


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