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#831159 11/27/20 2:01 am
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Mark Z Offline OP
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This is the engine discussed in my "A65 forensics" thread. It's a fresh engine, torn down because it was making a funny clicking noise, which I suspected was detonation. We didn't find anything clearly wrong, except that the head gasket bore holes were a tad smaller than the bores. We also noticed some staining on the head mating surface, and a lot of soot on the exhaust side of the head.

Now I'm attempting to resurface the head on sandpaper. I've scrubbed quite a bit, but I haven't yet reached the center between the combustion chambers. I'm getting closer though, so I'll keep going. I believe now the discoloration is from over-rich exhaust gases.

Question: I noticed that the mating surface toward the front of the cylinder head is damn near flush with the bottom cooling fin, whereas in the back the mating surface is raised a good 1/16" from the cooling fin. Is this normal? To my knowledge, this head has never been skimmed (as by machine).

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Quite normal, i've seen a few with virtually no step.

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Very possible the sound was a head gasket leak

As Nick stated, the gasket surface with no step is common

I have seen some Triumph heads where its almost flush with the fins

Keep lapping the head, remove any sharp burs in the chamber and piston

Don't forget anneal the head gasket


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Originally Posted by NickL
Quite normal, i've seen a few with virtually no step.

I have a couple of heads where the bottom fin looks like its part of the gasket surface at the exhaust end, its been skimmed that much.


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Mark Z Offline OP
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Thanks all for the votes of confidence! On annealing the head gasket:

With my rather small rosebud torch tip, the most I've been able to do is chase purple shadows, no matter how long I hold the torch in one spot. Note this gasket is significantly thicker (.050") than the last couple I annealed, but I think I should still get it to turn red or at least orange. I'm thinking of taking the gasket to work, where we have some bigger torch tips.


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Use a depth gauge in the front/rear bolt and left/right holes to see if you are wearing down the surface unevenly.

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don't you have a bar
Originally Posted by Mark Z
Thanks all for the votes of confidence! On annealing the head gasket:

With my rather small rosebud torch tip, the most I've been able to do is chase purple shadows, no matter how long I hold the torch in one spot. Note this gasket is significantly thicker (.050") than the last couple I annealed, but I think I should still get it to turn red or at least orange. I'm thinking of taking the gasket to work, where we have some bigger torch tips.

use your bar b que.

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Originally Posted by NickL
don't you have a bar
Originally Posted by Mark Z
Thanks all for the votes of confidence! On annealing the head gasket:

With my rather small rosebud torch tip, the most I've been able to do is chase purple shadows, no matter how long I hold the torch in one spot. Note this gasket is significantly thicker (.050") than the last couple I annealed, but I think I should still get it to turn red or at least orange. I'm thinking of taking the gasket to work, where we have some bigger torch tips.

use your bar b que.

I'll consider that when I get around to my engine. For now, the bigger torch at work did the trick.


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Ticking... sometimes cause by a rotor center getting old.
just thought.

Todd

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Originally Posted by mxman1
Ticking... sometimes cause by a rotor center getting old.
just thought.

Todd

You mean the alternator rotor, right? Good thought, but the click or tick sounded like it was coming out the exhaust, and it was on the right side.


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Correct. It's caused many a total rebuild:)

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Mark Z Offline OP
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Originally Posted by mxman1
Correct. It's caused many a total rebuild:)

Are you referring to a bad rotor center?


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Last edited by mxman1; 12/04/20 12:53 am.
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Mark Z Offline OP
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Ok, but this is more of a "click" or a "snap" than a knock, and it seems to be emanating from the right side silencer. It happens when the engine is idling, and it occurs every few seconds, not on every cycle.

I'm putting the engine back together now. The closest thing I found to a "smoking gun" was some staining on the cylinder head between the two cylinders. Also, the holes in the head gasket were a tad small for the +.060" bores. Everything else looks normal, and I did remove the cyl. barrel to confirm there were no broken rings.


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Originally Posted by Mark Z
Ok, but this is more of a "click" or a "snap" than a knock, and it seems to be emanating from the right side silencer. It happens when the engine is idling, and it occurs every few seconds, not on every cycle. .
Do you have a muffler baffle coming loose? Those type of noises are often somewhat random. Take that thing off, shake it around and listen for noises and look into each end with a strong light.

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Yep.
If you have an old one, strip the magnets off then fit the center and see if the noise goes away.
If you don't cut a legth of gal water pipe to make up the space on the crankshaft .


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Originally Posted by Stuart Kirk
Originally Posted by Mark Z
Ok, but this is more of a "click" or a "snap" than a knock, and it seems to be emanating from the right side silencer. It happens when the engine is idling, and it occurs every few seconds, not on every cycle. .
Do you have a muffler baffle coming loose? Those type of noises are often somewhat random. Take that thing off, shake it around and listen for noises and look into each end with a strong light.

The silencers are brand new (Emgos, too loud if you ask me), but I'll check them out, and all the mounts as well.

Originally Posted by BSA_WM20
Yep.
If you have an old one, strip the magnets off then fit the center and see if the noise goes away.
If you don't cut a legth of gal water pipe to make up the space on the crankshaft .

Trevor, I'll keep this in mind if the noise is still there when I get the engine back together and running.


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So this engine was "fresh", that means it was freshly rebuilt, then had a problem with a noise, then it was torn down again to fix problems?

Who did the "freshening" where they assembled the engine with a warped head and a head gasket hanging in the bores? That makes it sound like a lawn-mower mechanic worked on it.

Usually pre-ignition or detonation will sound like it is coming right from the engine. I agree the engine may have been running really rich if the soot was washed off the intake side but baked onto the exhaust side. If the problem was a head-gasket leak, the that is further evidence that someone did not know what they were doing as they may not have re-torqued the cylinder head bolts after the engines first very gentle run/heat cycle.

Detonation could also be cause of coarse by too much ignition timing, which would be another thing the lawn-mower mechanic got wrong besides the jetting, warped head and it's gasket.

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We all fumble along the best we can. The lower end, cylinder, and head work were assigned to a pro; the rest was left to the owner (my son). I stepped in for initial startup and tuning. The carbs are brand new AMAL Premiers, and apparently, they do not conform to "the book" for OE Concentrics. Primarily concerned with breaking in the engine, we did not get as far as dialing in the jetting. I can vouch for the ignition timing though.

As long as I've been doing this, I must admit it wouldn't have occurred to me that a head gasket must be custom tailored for an oversized bore. And the "overhang" is subtle, not something that would jump right out at you.

I know that the head was not re-torqued right after the first heat cycle. I've gotten away with this on my A65 a few times. I will say they're not as finicky as Triumphs in this regard, due to the cast-in rocker stanchions and much higher torque specs (31-33 ft. lbs. vs. 12-18 on a Triumph). Nevertheless it WILL be retorqued after the first heat cycle this time around.

So yes, we know that mistakes were made. The important thing is that we learn from them and do it better the next time.


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Which book didn’t the carbs confirm to? The spares manual/workshop manual or the AMAL catalogue?


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Why the obsession with re torquing the head after one heat cycle?
I'm absolutely certain BSA or any other manufacturer did it, there MAY have been a torque wrench put on the head bolts at the first service. I would say checking the tightness of the cylinder base studs to be more important as the paper gasket will "settle"


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Well. I had to remove the head on my rebuilt A65 to address valve spring issues. I annealed the copper gasket and assembled. I don't know about one heat cycle, I took a few tuning rides and noticed oil seeping around the push rod tunnel. I backed off all the bolts/nuts and retorqued. Oil don't weep no more. At least after yesterdays nice test ride. While I was there I installed mushroom head tappet adjusters. They seem to run quieter and are easier to set.

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Originally Posted by Allan G
Which book didn’t the carbs confirm to? The spares manual/workshop manual or the Amal catalogue?

Well for one thing, as you know Allan, the pilot jet is a whole different setup. In all fairness, I haven't yet assessed the other circuits.

...which brings me to the same old question to which I've forgotten the answer: When the book says needle "position 1", does that mean the clip in the top groove? Right now the needles are in the center groove, and I suspect that may be part of the problem.


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It was a 'first service' job. I tend to do it after around 500 miles.
Beezers aren't that finicky, but it's a good idea to do it as a matter of course.

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needle clip 1 is the top groove, or leanest setting.


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