The BSA A7-A10 Forum

Technical (Descriptive Topic Titles - Stay on Topic) => A7 1946-1950 => Topic started by: Brandis on 18.05. 2023 20:59

Title: valve setting with tight cam followers
Post by: Brandis on 18.05. 2023 20:59
Clearly, I should have paid more attention to ensuring that all the cam followers moved freely before proceeding.  One exhaust is stiff and it's hard to set the clearance.  I' ll just set it wide and get back when the engine has run a bit.

Still, remembering when you guys were talking me through crankshaft issues, the good news is that I'm setting valves.
And, for the record,  I followed the old Forum advice to cut the too long exhaust push rods to 205mm.  That works.  And the intakes are 180mm.

Soon, off to the DMV with dodgy paperwork to get a title and plate.   I did check at the beginning that it had never been reported missing or stolen and discovered that it had first and only once been registered in 1948. 
Title: Re: valve setting with tight cam followers
Post by: muskrat on 18.05. 2023 21:08
G'day Brandis.
Good to hear (pics would be better) it's moving along. Dump a cup full of oil down on the lifters before you try to start her.
Cheers
Title: Re: valve setting with tight cam followers
Post by: Brandis on 19.05. 2023 00:24
Got it as a heap of junk with 1/3 the parts missing.  I had never seen a complete A7.
Title: Re: valve setting with tight cam followers
Post by: muskrat on 19.05. 2023 01:44
G'day Brandis.
Well done mate. For a rare one with bugger all info  *yeah*
Keep us posted.
Cheers
Title: Re: valve setting with tight cam followers
Post by: Brandis on 30.05. 2023 02:53
I'm going back into the engine.  The exhaust cam follower didn't loosen up and there's no compression on that side.

Swarfy and Muskie are nodding wisely. 

It shouldn't take that long now that I have all the parts and know what not to do.

Off subject;     I've used the new Amal replacement carbs for 500 thumpers.  I didn't on this one 'cause I'm trying to stay original.   Opinions??
Title: Re: valve setting with tight cam followers
Post by: Swarfcut on 30.05. 2023 08:28
 Are you sure the valve and rocker arm are both free to move? A binding exhaust follower could be an easy fix....simple lubrication. But if the binding is due to corrosion, or some other cause eg bowed follower stem or tappet guide problem, you know that it's maybe back to the start.....the motor is assembled around that central tappet guide, and  this is unlikely to come out without splitting the cases. If the binding is there, lift the barrel and try lubrication and heat as a first try...could save a lot of work.

 Strange to hear of this malady, I thought it was a complete teardown and a tappet problem like this would have been seen before the barrel went on. Those followers are usually  very free in the guide.

 As for carb choice, anything that gets a runner for now is fine. Final choice depends on the degree of authenticiy versus reliability required.

 Swarfy.
Title: Re: valve setting with tight cam followers
Post by: Brandis on 30.05. 2023 12:38
I have been pouring oil on the springs and push rods and cranking it over on the assumption that it would loosen up.  No deal.  It's definitely not corrosion.  It was a bit tight on assembly. 
The rocker moves when I turn the motor but there isa perioding loud 'sproing' noise as something that's jammed releases and the the spring jumps.   And no compression. 
Title: Re: valve setting with tight cam followers
Post by: Brandis on 30.05. 2023 13:26
PS:  With the rocker assembly off, the push rod will rise when the engine turns but you need to tap it with a hammer to set it back down.  So it's not valve stem issue.
Title: Re: valve setting with tight cam followers
Post by: chaterlea25 on 30.05. 2023 13:41
Hi Brandis,
If the follower is damaged when you get in there, I have a full set of new original BSA followers available

John
Title: Re: valve setting with tight cam followers
Post by: RichardL on 30.05. 2023 14:37
I wonder if it's possible for the tappet locating pin to be installed or distorted in such a way as to interfere with one of the exhaust tappets.

Richard L.
Title: Re: valve setting with tight cam followers
Post by: Brandis on 31.05. 2023 02:41
What is the 'tappet locating pin' .  I assume I have 4 but maybe I know them by a different name?
Title: Re: valve setting with tight cam followers
Post by: RichardL on 31.05. 2023 03:24
In the center at the back of the tappet tunnel. Goes between the cutouts in the exhaust tappets to keep them in the tunnel.

Richard L.
Title: Re: valve setting with tight cam followers
Post by: muskrat on 31.05. 2023 07:31
G'day Richard.
That's for a short stroke A7 and A10. Brandis has a long stroke.
Cheers
Title: Re: valve setting with tight cam followers
Post by: Swarfcut on 31.05. 2023 07:48
 Brandis. RichardL is correct about the position of the locating pin.....but that is only used on the later engine where the tappets are fitted into the cylinder base.

 Rest easy. Your Longstroke does not have this feature.

 There are two oilways on your centre tappet carrier, The larger horizontal drilling feeds the two guide tubes. A smaller drilling at the rear feeds down to the tappet blocks and then oil passes to the cam lobes. These may be obstructed after the years standing idle.

 The tappet blocks have a straight and a curved side. On the inlet tappet guides there is room for them to go in either way, but on that central exhaust tappet guide there is a greater clearance between the opposing faces of the blocks if the curved faces are fitted to the outside, matching the curved periphery of the carrier. Bit late now to check, but with that centre carrier removed somehow, all will become clear.

 Swarfy.
Title: Re: valve setting with tight cam followers
Post by: RichardL on 31.05. 2023 12:46
Ah! OK, I'll stop "wondering."

Musky and Swarfy, thanks for the illumination. Brandis, sorry if I spawned consternation.

Richard L.


Title: Re: valve setting with tight cam followers
Post by: Brandis on 31.05. 2023 16:25
It's all good.   Onward and upward.   I'll get back to you when I sort it out.

And thank you Chatterlea for the kind offer.    I'm hoping a dab of fine grinding compound and some gentle spinning will do it.
My own damn fault for being dumbass when it was there on the bench.
Title: Re: valve setting with tight cam followers
Post by: Swarfcut on 31.05. 2023 17:20
 Dunno which bit yo' gonna spin.....Not these bits, if they are still in place. Off the engine, that's an altogether different ball game.

 Pictures show A7 Longstroke Exhaust centre tappet guide, along with well worn followers, and shown in situ.

 Swarfy.
Title: Re: valve setting with tight cam followers
Post by: Brandis on 31.05. 2023 17:32
I thought I'd push them in upside down and spin. I think the entire machined surface can be polished. Not ideal but it will be easy to see if it works.  If the issue is in the flat surfaces, that's pretty easy to deal with.

But first, I have 2 other cam follower guide blocks. I'll see if they solve the problem.  And if anyone needs one . . .
Title: Re: valve setting with tight cam followers
Post by: Brandis on 02.06. 2023 20:58
Hmmmmm . . . . .
So I took the engine down to the cam followers.  3 worked perfectly, one exhaust was a bit stiff.  I had hoped to loosen the adjacent nuts and ease the whole guide block out but that was not to be.  So I spent half an hour lubing and moving it up and down by hand until a firm thumb push moved it back down.  Much less force than 2 springs. Back together again.
Now, when I turn the crank with the plugs out, I get a loud 'sprong' sound when the valve springs in question relax.
Sticky valve, I thought.  It seemed unlikely because they were all new and had been well lapped in, so the stem had spun easily in the guide.  So, off comes the head and springs and the valve moves perfectly.  I had examined the springs to see if they were somehow askew, but things looked normal. No solution there.
So, It appears that something in the valve train is interfering with the closing motion until that something releases and it moves suddenly to catch up.  That delay in motion is major enough that sometimes, even at low speed the pushrod comes totally clear and disconnects from the rocker arm before the motion resumes.
Those are the push rods that I cut down from longer rods and they may be a bit shorter. So the valve adjuster shows perhaps 4 threads more in the exhaust side than on the intake side. But the other exhaust valve is the same and has no issues.  There's room for it to move at both ends of the rocking and I set the lash before spinning the crank.
The rocker arm moves freely.  I've switched push rods left to right with no effect.   
Someone in the Forum has been down this road and hasbeen smart enough to figure it out themselves.  Not me, unfortunately.
Title: Re: valve setting with tight cam followers
Post by: Brandis on 03.06. 2023 00:33
Aha !!!

You will recall I said the exhaust push rods were from another BSA,  considering the length, probably a 500 single?  Well,  a close examination of the bottom, socket end revealed that the OD of the socket was a tiny bit larger than the OD of the proper A7 intake push rods.   Since they are so close together, it appears that they interfered with each other's motion, one popping past the other when the other moved enough to get out of the way.  That caused the spring to sprong every time.  It was the every time identical that got me thinking. A tight spot on the slide would be more variable? 
A quick grind to thin them up and all is well.
Sorry about all this hand wringing.   Hopefully this is the end of my travails, at least until the next one. 
Title: Re: valve setting with tight cam followers
Post by: fido on 20.06. 2023 14:52
Apologies for adding to your post rather than create a new one but I have a question about cam follower orientation. It is obvious for the 2 centre followers but I don't know which way round the outer followers go. Does the convex side face inwards or outwards? My followers are a bit worn and there is an unworn bit at the edge, where the cam lobe didn't reach.
Title: Re: valve setting with tight cam followers
Post by: Swarfcut on 20.06. 2023 16:34
 My thought would be for the curved sides to face outwards. No particular reason, just to keep things so-so and as the two inlet guides are symmetrical....  in the grand scheme of things, I doubt it matters.

 The two centre followers look happiest flat faces together, but on parts to hand, they will actually fit in the centre block curve to curve without fouling.

 The majority of used followers I have seen all exhibit the same wear pattern pictured above, it is obvious the cam has missed some of the follower face. Whether this is down to followers the wrong way round, camshaft end float or just the was it is, who knows. You can bet back in the day they were nailed together without too much thought to the finer detail we consider now.

 When I get a new cam cheap in the fire sale, I will take great care to get lobes and followers aligned as best I can, my guess is that the alignment can be seen via the sump plate aperture, before fitting the crank and by trial and error getting the best match. Then again,....Is it actually possible without moving bush positions or facings?

 Swarfy.