The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: bsa-bill on 09.06. 2010 16:35
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Can I tap into the Forums combined wisdom.
How tight do you pull up the camshaft nut, I recall when fitting it up that if I pulled it up tight then it being on a keyed parallel shaft it just moved the gear in until it locked up the camshaft.
I slackened it off until the shaft turned and used the tab washer to keep it in it's bit, having just revisited the timing side I find that I can turn the nut slightly, maybe I need to tap the lock washer down a tad tighter.
Maybe some locktite might be a good idea or have I missed something fundamental here
Cheers _ Bill
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The nut needs to be tight. The camshaft gear pulls up to a shoulder on the camshaft so it cant move too far, if that's binding your camshaft up, check the bushes as it shouldn't do that. Having the nut semi loose even with a lock washer is a bad idea. Yes, I always use loctite on the threads too.
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Hi Bill
*eek* *eek* *eek* *eek*
The camshaft nut should be fully tightened!!
It sounds like the key has not been seated correctly and is being pushed back up against the cam bush???
The cam position is governed by the shoulder on the cam inside the trough (crankcase) and the gear being fully pulled onto the cam, up to the outside bush.
As the gear is being fitted keep a close watch on the key to make sure it stays fully seated in its keyway!
If the cylinders have already been fitted, DO NOT TAP THE GEAR ON!!
This will drive the cam inwards and the key will damage the bush, If the cylinders are off you can put a piece of alloy or soft copper between the leftmost cam and the case while you fit (hit *eek*) the gear
I know there are special tools to fit Truimph cam gears so as to avoid the same damage issues to the cam bushes
but I have not seen a BSA version????
I have always fitted the gear when the cylinders were not yet fitted!!
HTH
John o R
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Have to agree here, the nut should definitely be tight.
It is either the woodruff key that causes your problem or the camshaft bush could be too long (pattern part maybe?)
Btw, there are camshaft shims available that go between the shoulder on the camshaft and the bush, so that axial play can be minimized.
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I'll put my $ on the key. It has caused me trouble on more than one occasion.
MG, those shims would have to go between the bush and crankcase, otherwise it would be between moving parts, not advisable.
Cheers
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Surely if the woodruff key had been pushed out into the bush, that would be very obvious during assembly?? [quite likely though]
Bill, when it locked up did you remove the gear again to see what was happening?
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Hi guys - thanks for the replies I'm investigating at it the minute, just popped in for a cuppa..
The key might be at fault but I can't see that the nut would have went on as far as it did if the key had moved and it was firmly where it should be when I drew the gear off.
Now the shoulder on the cam is very slightly below the shoulder on the bush, so I'm thinking this is where the problem could be possible the bush /bushes are not right in, it's only a few thou so at present I'm looking for a spacer /washers to cover the camshaft and butt up against the bush shoulder, then If I screw them up tight they should draw the camshaft through and squeeze the bushes together.
If this does not bring the camshaft shoulder through enough then I'm thinking of relieving the bush shoulder somehow, somehow means keeping it square to the shaft.
first though I have to find where on earth I put the key ???? or find where I have the spare ones ??? both have to be in the shed and it's not that big!!!
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MG, those shims would have to go between the bush and crankcase, otherwise it would be between moving parts, not advisable.
Yep, you are absolutely right muskrat. Looks like I hadn't been completely awake yet when I wrote the post this morning. *sleepy* *smile*
Wouldn't work that way anyhow as the inner diameter of the shim is much larger than the camshaft.
Cheers
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looks like I was dreaming a bit this morning too, can't find the key anywhere , must of kicked it into some far corner of the shed, anyway I've got two ordered as my spares seem to have fallen foul of one of my shed cleanups.
Looking now for something to sleeve over the camshaft where the gear sits to ensure washers I have clear the shoulder of the camshaft, it's such a small amount I need to draw it through, another way would be a shim to sit up to the shoulder, might end up with this solution
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Sounds like me and my shed.
Looks like you found the cause, now for the reason it is like that. Which bush has moved ? Your method of drawing the bushes together is sound. Be gentle on the cam shaft thread and nut, pack it so the nut is all but 2 threads home. Might be difficult to stop the shaft from turning. Do it all with the pistons at BDC as if the shaft turns you don;t want to bend a valve !
Good luck.
Cheers
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Well I reckon it's not a case of a bush moving, either the bush faces are too thick or the camshaft shoulder in the trough is to thick.
It is only a few thou but enough to lock the shaft up when the nut is tightened, I did have some luck squeezing the bushes together but not enough to bring the camshaft shoulder proud of the bush face although as already stated it is mere thous.
My thoughts were to pull it up till it locks and then kick it over until it wears in but then controlling all the bits of phosphor bronze dropping about plus my poor leg, and I decided it was not in keeping with Forum standards
Another option was a complete stripdown and adjust the camshaft or bush faces - it's taken five years so far , this would be a last resort also I know I did measure and compare the camshaft with the old one so don't think there is an issue with it.
Third option was to shim the camshaft shoulder that the gear butts up to, not easy to get a shim washer the right size (ID 16mm OD 19mm)
looked at several things and finally found a circlip that was just short of 19mm, I had to grind off the lugs leaving just enough hole for the circlip pliers to grip so it should rotate with the shaft without fouling the bush ( or at worst not much and not for long)
Fitted the gear,tightened the nut fully and it turns ok, also took the time to mark the magneto pinion and the Camshaft pinion so wont need to retime the ignition ( although I think I might just check to be sure)
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That's a dodge i would have done. Stuff pulling the motor apart again, nothing worse!
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G'day Bill,
good work, I would have done same as well. Shame you didn't notice it before joining the cases. Just put a note in your manual to rectify on next strip down. Just another issue with patten parts I guess.
If the mag pinion wasn't touched the timing will be OK.
Cheers
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You've got to love the search function on the forum. I've got exactly the same problem as bsa-bill and was wracking my brains trying to work out how to fix it without splitting the cases again - I'm off to find a suitable circlip! *smile*