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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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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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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.

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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

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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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Originally Posted by aiden65
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?
Unfortunately, the cases have to be split to shim the crankshaft end float. The .0015" - 003" figure is for initial assembly. From (unreliable) memory, the workshop manual lists.005" as the upper limit, so .006" is probably sort of alright. The bigger concern is whether the sludge trap was cleaned out. Many of the failures attributed to a worn timing side bush were more likely to have been caused by a blocked sludge trap.

Those engines are pretty tough, and will tolerate all sorts of things out of spec if they aren't thrashed or lugged.

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Thanks Shane,
I think since it isn’t making any noise I may see what happens unless you think that’s just foolish. I just would like to take it for at least one decent ride.
It is not going to be thrashed on, I have a Ducati for that. Mostly to work and back and some weekend rides.

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Pulling the stator (or rotor) and shimming behind the rotor will only effect the primary chain alignment. You’d have to remove the bearing and split the cases the change the end float.

I agree with Shane, I’ve seen a good bike with more than 0.006” end float and my biggest concern would be the sludge trap, unless you know it’s history.


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.006" end float is in the "keep am eye on it" category.
We took a 1970 Lightning with .006" end float down to the BSA International at Halls Gap in 2018. It was ridden about half of the 3-day ride to the rally, then did most of the runs at the rally. Most of that was on quiet country roads, so sitting around the 100 km/h (just over 60 mph) speed limit It's since moved to Queensland, and was still going strong last I heard.

How did you measure the end float? I remove the chain case and the inner and outer timing covers and use a dial gauge on an arm connected to a "post" screwed into one of the tapped holes in the crankcase. That also allows checking of vertical play in the timing side bush.
It's fiddly and time consuming, so really only worthwhile when you're putting the engine together in the first place or you want to be really, really careful.

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To measure the end float I used a dial indicator with a magnetic base, tapped the crank to the right with a rubber mallet, zeroed the indicator then pulled the sump cover and levered to the left on the flywheel. I repeated this a few times with consistent results.
Can’t say about the sludge trap, tried to call the previous owner with no response. I don’t suppose there is any way to know without splitting the case.

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Originally Posted by aiden65
To measure the end float I used a dial indicator with a magnetic base, tapped the crank to the right with a rubber mallet, zeroed the indicator then pulled the sump cover and levered to the left on the flywheel. I repeated this a few times with consistent results.
That's less hassle than taking the timing covers off.

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In thinking about some of your comments and given that half of the attachments have already been removed in getting the cylinder head off I am thinking maybe it is time to split the cases to remove the unknowns.
My question is whether you would reuse the bearings that the previous owner put on (only as evidenced by having the old shells in the parts box)?
Would still remove to evaluate the journals, plastigage, etc. Not trying to cheap out after getting to that point, but don’t want to replace new parts if there is no harm.
Thank you,
Aiden

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If everything is in spec and the surfaces appear to have little wear, I don't see what not.

Replace the big-end nuts as a matter of course, and be prepared to replace the bolts as well if they are showing their age. It's always a juggling act as to which components can be safely re-used and which should be replaced.

When we were younger and put in lots of miles rather less sedately, we used to re-use as many of the existing parts as possible. As we have become older and more "responsible", we tend to replace more bits even though our riding styles have mellowed smile

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Got the cases split and by the looks of the plug for the sludge trap the previous owner tried but was unsuccessful in getting it out. The trap was pretty much empty though. Bearings and journals, gearbox gears, etc. were in good shape too. Well, at least now I know.
Any suggestions for other things to make sure of before I reassemble?

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Make sure the gearbox layshaft endfloat is no more than 0.003", keeping this correct really helps the gearchange.


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well the gearbox isnt going to creat popping and backfiring.

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Thanks Gavin, I am going through your previous posts for the procedure.
Hacksaw, I think Slipping the pushrod from the valve sticking was the primary problem, but based on the recommendation of others to check the sludge trap I disassembled. Just want to do whatever I can while it is apart so I don’t have to do it again anytime soon.
Thanks,
Aiden

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Another dumb question regarding crank end float. When I took the roller bearing off there were 3 shims at 0.010” each outside of the roller bearing and none in the shim cup. Are these for final drive alignment? Since I need to make up 0.003, can I have just one 3 thou shim in the cup?

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There are two sets of shims, one for the crank endfloat (in the shim cup), the other for aligning the engine and clutch sprockets (between the engine sprocket and distance piece).

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Got it, thanks.
As for layshaft end float, I have 0.010”, and my thrust washer is .123. Max available is .125. Anything special about that washer or can I just try to get something from the hardware store to make work?

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So long as the lay shaft thrust shim/ washer is flat and made of steel pretty much anything is better than excess end float, something with the correct ID and OD can be lapped down on an oil stone if it is over thick.
While you are in there stone flat all gears with female dogs. Bitch holes? Polish the cam plate around the plunger track and selector fork areas , and cut 2 turns of the index plunger spring.

Check the primary drive side is aligned properly ( a steel rule held against the primary offered to the clutch chainwheel with no chain will tell the truth, get it within 5 thou), check all steel clutch plates are truly flat, reject any that will pass a 3 thou feeler blade.
look really closely at the clutch hub cush drive, its often passed over, wear internally gives a lot of bother.


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Thanks for the good info. Will do what you recommend. With regards to the “bitch holes,” (nice) do you mean to lap the flat face of the gear with the series of drilled holes that articulate with the adjacent gear on the same shaft? I don’t have the terminology, sorry.

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I look /feel for burrs where the male dogs engage in the female receptacles ( bitch holes), dress these flat with an oil stone, low tech.
There are two sliding gears in the box , each sliding gear has male dogs, I am specifically referring to the mating gears that the sliding gears engage with, if the clutch has been badly adjusted or / and the user is heavy footed , these take a beating, burrs on these faces prevent clean shifts.

Last edited by gavin eisler; 01/13/21 4:10 am.

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