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#834833 12/29/20 9:23 pm
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Hello,
I am new to posting to the forum but reading old posts has helped me a lot, thank you all.
I have a 70 A65 L that I recently acquired as a project. This is my first BSA. The engine was supposedly refreshed by the previous owner. Not sure exactly what that involved or what his level of expertise and attention to detail were, but I have the old bearings, valves, springs, rings in spare parts box so I am assuming at least that much. Has AMAL 930s and I just installed a Boyer mk 4 setup. New battery and wiring harness.
I had it running really well, but had only ridden it half a block at a time while I was working out brakes, clutch, timing and carb adjustments. The other day I decided to take it out for a little longer ride (a few miles, at around 45mph), and it was running great out and back until I got to my driveway, at which point there was a terrible metallic ping followed by what sounded like metallic grinding sound in proportion to engine speed. For the short trip up the driveway it was popping and backfiring on what sounded like every other cylinder, and I shut it down immediately.
I am concerned about a spun bearing based on the awful sound of it. However after reading some posts and checking some things, the following is what I found:
When I lever on the crank end at the stator nut using the footpeg for leverage, I get no appreciable movement on any of the 6 faces.
When I put a stick into the spark plug hole and push on the piston as I spin the engine, there is no binding, catching or dropping on either cylinder.
The crank rotates by hand smoothly and without making the terrible grinding noise I heard at the end of the previous ride.
I drained the oil at the sump plate and there are no metal flakes in it., or on the magnetic plug. It was new oil and I could see clearly through it with no glitter.
When I used the kickstart lever to rotate the engine, it has a point maybe every 180 degrees that feels very stiff, as with very high compression all of a sudden.
Of course after just having gotten it into rideable condition I am not really excited to do a complete teardown, but if it is a bearing or the like I would prefer not to completely grenade the engine. I suppose it was lucky that at least it happened in my driveway and not on the main road.
I would appreciate any further investigation you would suggest before I start disassembly.
Thanks for your time.

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With the engine turning and no crud in the sump, I would rule out the engine at this point. Remove the rocker cover and make sure a pushrod didn’t pop out due to poor installation. Drain the trans and primary to rule out issues there.

Some of the other symptoms may be related to low voltage or timing change.

You may also need to take the small round cover off the rotor to see if the nut is tight on the crank.

I am certain you will get ideas on other things to check


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Hi aiden,
Have a read through recent posts on the problems of incorrect spec valve springs being fitted ant the consequent troubles

John

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aiden65 Offline OP
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Rich,
Thanks, that is what I was hoping someone would say, even if they were only saying it to be nice.
I will pull the rocker cover and drain the primary and transmission oils. I am hoping not tranny. Forgot to mention that the clutch lever was pulled in when the noise happened.
Thanks again

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aiden65 Offline OP
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John,
Will do. Anything could be possible as I did not do the work.

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Originally Posted by aiden65
When I lever on the crank end at the stator nut using the footpeg for leverage, I get no appreciable movement on any of the 6 faces.
That covers vertical movement at the drive side main bearing. How about end play?

Originally Posted by aiden65
When I put a stick into the spark plug hole and push on the piston as I spin the engine, there is no binding, catching or dropping on either cylinder.
The crank rotates by hand smoothly and without making the terrible grinding noise I heard at the end of the previous ride.
I drained the oil at the sump plate and there are no metal flakes in it., or on the magnetic plug. It was new oil and I could see clearly through it with no glitter.
When I used the kickstart lever to rotate the engine, it has a point maybe every 180 degrees that feels very stiff, as with very high compression all of a sudden.
If everything feels alright turning the crankshaft, the next thing to check is the primary drive and gearbox.

Could it be a tight spot on the primary chain? How is the primary chain tension?
Does it show a similar symptom if you put it in gear and turn the rear wheel?
What does the kickstart feel like if you pull the clutch lever in and push the kickstart through by hand?

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aiden65 Offline OP
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Rich,
Good call! Pushrod had skipped out of the rocker. Looks like the valve spring is not pushing the valve up enough to keep the pushrod in position.

Last edited by aiden65; 12/29/20 11:09 pm.
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aiden65 Offline OP
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Shane,
Thanks for your suggestions. I will check on the primary tension and end play. Same resistance when spinning the wheel while in gear, and no resistance at all in kickstart with clutch held in.

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Originally Posted by aiden65
Rich,
Good call! Pushrod had skipped out of the rocker. Looks like the valve spring is not pushing the valve up enough to keep the pushrod in position.

If the valve was not coming all the way up, you would not feel compression as you describe. It is possible the pushrod was not correctly installed when the engine was rebuilt.

Make sure the pushrod and rocker are not damaged. If no damage, crank the engine so offending pushrod is at the low point on the cam. You can use a screw driver to raise the rocker arm to allow the pushrod into place. Make sure the socket seats in the cup of the pushrod. Then check the other 3. Then set the valves.


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aiden65 Offline OP
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Done, and interestingly as I was rotating the engine the valve did come up. Got the tappets adjusted and now the compression seems normal again??
Maybe the hamsters were tired.

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It seems Rich nailed it.
A65s are fairly good, but with some other engines it's quite easy to mislocate the pushrod on the cam follower. Everything seems alright when setting the valve clearance, apart from the adjusters having to be screwed out a long way. After the engine has run for a while, the pushrod finds its proper place in/on the follower, and suddenly there is very excessive clearance at the valve and the engine runs like a hairy goat. If you're unlucky, the pushrod will jump off the ball on the rocker arm, and if you're really unlucky it will bend.

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aiden65 Offline OP
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Yes I have to say that was some serious mechanical voodoo on the part of Rich to turn a total rebuild, 3 months of my time and several hundred dollars into a valve adjustment.
Luckily the rod was not bent, and it is running great again.
Thanks so much, you guys are awesome.
Aiden

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Sometimes a blind squirrel finds a nut! laughing

As much as I hate to admit it, happened to me once, and have “fixed” a few that other people did.


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Took John’s advice and in reading about valve spring coil binding, it sounds like it is generally preventing compression and causing damage to pushrods or cam. Could they also bind in compression and that be why the valve was not closing fully? I am wondering if I should be swapping the springs or this might just continue to happen, possibly with a worse outcome.
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So Aiden65 you said

I had it running really well, but had only ridden it half a block at a time while I was working out brakes, clutch, timing and carb adjustments. The other day I decided to take it out for a little longer ride (a few miles, at around 45mph"

So the question i ask is how could it be a problem with coil binding of the springs , surely that problem would have been obvious immediately? Perhaps the valves were just sticking in the guides due to lack of use ...don't know

but since it is pretty easy to do i would go over the primary drive first , if you loose the little cushioner (around 10mm diameter) on the top of the slipper adjuster bolt that can make a terrible noise similar to what you described.

Besides you need to go over the primary drive at some point anyhow


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aiden65 Offline OP
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Gotcha, I didn’t know if it could be intermittent binding but it sounds like not. I will check the primary. The tensioner was there when I had the cover off but I haven’t properly gone through the process yet.

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Reading through this thread it seems that you have identified the noise but I am not certain if you have eliminated the problem?

Valve springs have been mentioned and are a good call.

One thing that has happened to me ones was a valve that occasionally, partially, siezed in the guide. It was due to someone else work not mine, but it manifested itself as a valve that didn't close fully. It might be a long shot but worth noting if your valve springs are OK.

John

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Originally Posted by aiden65
Gotcha, I didn’t know if it could be intermittent binding but it sounds like not. I will check the primary. The tensioner was there when I had the cover off but I haven’t properly gone through the process yet.

back the adjuster bolt right back as far as you can and make sure that little cushion block(some kind of fancy plastic, a small disc) is sitting on the end of it where it bears on underside of the slipper plate ...if those disintegrate there MIGHT be bits of it left in the case so it will be obvious if you have had steel on steel contact . That really can make a terrible noise if it lets go ....not saying that is the problem but it sure is one easy thing to eliminate I had that happen on my 70 a while back and was sure i had *ucked the engine!

keep us informed


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aiden65 Offline OP
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John, that was my concern too. I rotated the engine through numerous revolutions after adjusting the valves and did not note any catching or sticking. Not sure unless I tear the head apart how else to determine whether the valve is sticking.
Ignoramus, thanks for the info. I will pull the cover this weekend and report back.

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If the valve is picking up intermittently in the guide it will probably only be doing it when the engine is hot.
Maybe that it is why it did it only after a longer ride?
HTH

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Hi Aiden,

Quote
If the valve is picking up intermittently in the guide it will probably only be doing it when the engine is hot.
Maybe that it is why it did it only after a longer ride?

I think this is most likely what has happened

John

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Originally Posted by Tridentman
If the valve is picking up intermittently in the guide it will probably only be doing it when the engine is hot.
Good call.
If the exhaust guides were not sized for correct clearance after installation, whether by honing or reaming, sticking valves can happen.

But also, have you checked for return oil flow at the oil tank? That return oil also provides lubrication for the valve gear. No return oil can mean no oil for the valves and rockers. BUT, it also means other serious oil system issues that need looking into. It could be as simple as incorrectly connected oil lines or as serious as a faulty oil pump. HOWEVER, either scenario can badly damage your engine.

Please be sure of this before going any further if at all possible.

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aiden65 Offline OP
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Thanks everyone,
That makes sense that as the valve expanded it could bind. I guess I won’t know until I get it apart whether honing would be sufficient or whether I need new guides? Probably safe to say I shouldn’t run it until I do that.
I do have a steady flow from the return tube in the tank, and have a very slow trickle from the metal feed tube at the head, which I read is all that should be expected?

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Originally Posted by aiden65
I do have a steady flow from the return tube in the tank, and have a very slow trickle from the metal feed tube at the head, which I read is all that should be expected?
Excellent. That's reassuring news on your return flow. You have oil circulating through the engine so if a valve was sticking it probably was not from insufficient lubrication. As an aside, consider putting an oil pressure gauge on your engine once it is up and running again to monitor that vital sign. But for now, the wise option would probably be to pull the head and verify your valve stem to guide clearance.
It's likely the guides are ok and just need to be sized by a machine shop.

Have we got you running in enough different directions yet? Hope not.

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Update:
Thanks for the suggestions above. My primary was loose, perhaps 3/8” on the top run so tightened to get to 1/8”. As for crankshaft end play I have 0.006”. I understand the specs are 0.0015 to 0.003 on a fresh rebuild but have read accounts of not hearing knocking until 0.015 or more. What would be your suggestion? Pull the stator and shim or just monitor for now?
I have the head in the shop for valve guide reaming currently.
Thanks,
Aiden

Last edited by aiden65; 01/03/21 8:45 pm.
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