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Jim Hultman
Jim Hultman
Minnesota, US
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Thread Like Summary
1971tr6, Allan G, JER.Hill, NickL
Total Likes: 5
Original Post (Thread Starter)
#831159 11/27/2020 2:01 AM
by Mark Z
Mark Z
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).

[Linked Image from]
Liked Replies
#832878 Dec 10th a 10:03 PM
by Mark Z
Mark Z
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.
1 member likes this
#832879 Dec 10th a 10:06 PM
by Allan G
Allan G
Which book didn’t the carbs confirm to? The spares manual/workshop manual or the Amal catalogue?
1 member likes this
#832927 Dec 11th a 10:21 AM
by Andy Higham
Andy Higham
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"
1 member likes this
#833005 Dec 12th a 01:44 AM
by NickL
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.
1 member likes this
#833020 Dec 12th a 08:45 AM
by gavin eisler
gavin eisler
needle clip 1 is the top groove, or leanest setting.
1 member likes this
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