Author Topic: Later type iron heads  (Read 1065 times)

Offline beezermacc

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Later type iron heads
« on: 14.10. 2015 08:49 »
I'm just trying to get my head (pun) around an issue to do with the later carbs and iron heads. I noticed that BSA fitted a 389 carb from 1960 and at the same time the cylinder head part number changed from 67-1065 to 42-0180. I've got quite few (daren't say how many!) cylinder heads that I might use if I live to be 160 but they all have a part number 67-1066 cast in which is the earlier head, BSA part numbers are often one removed from the number in the book due to assemblies etc. I have never seen a cylinder head with part number 42-0180/1 so, is there such a thing? The 389 used in 1960 has a bore of 1 1/8 whereas the previous 376 has a bore of 1 1/16 so, presumably, the inlet tract on the later head is enlarged slightly. I'm also aware of a change in part number for valves which in 1960 became 67-0742/3, yet Alpha in Dudley (the gurus of valve engineering) list the same valve for both heads. Associated with this question is whether or not you can retro fit a 389 to any of the 67-1066 heads as I've just fitted a new 389 to my '59 Golden Flash and had a few issues which I'll put in another thread. It may be however, that the issues are related but if you read the 'spitting back' thread you'll see are primarily to do with carb rather than fitment. So, can anybody fill in my knowledge gap about what happened to the cylinder heads in 1960......?
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Offline beezermacc

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Re: Later type iron heads
« Reply #1 on: 15.10. 2015 08:19 »
Just wondering if anybody has had a look at this one yet?
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Online muskrat

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Re: Later type iron heads
« Reply #2 on: 15.10. 2015 08:53 »
68 have read it so far. Sorry I can't help but give it time, someone must know.
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Online groily

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Re: Later type iron heads
« Reply #3 on: 15.10. 2015 09:28 »
Is the part no stamped somewhere I can read it easily Andrew without having to take too many bits off? My iron head is inch ' n 'n eighth on the inlet tract and (now) has a correct bore 389, but what the part no is I dunno. Happy to try and find it though  . . . (It's not what should be on the bike, which is supposed to have been an SR originally, but hell, it's a Mixabitsa anyway).
As for comments elsewhere about the hassles of getting new carbs to run right - couldn't agree more. Only ever had one (of maybe half a dozen in recent years) that ran right out of the box and that was a recon (so not new then) 276 from Surrey Cycles. (Still leaked from the banjo now and then,, as they often do.) The others (from Amal) needed playing with. Spitting and farting a speciality, needle/ needle jet probs, etc. I don't enjoy playing with them, because it's hard to know what to do next when you think you've got things set up right and there are still things not quite right.
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Re: Later type iron heads
« Reply #4 on: 15.10. 2015 12:41 »
Thought I would have a look.
Found the part number is underneath the head (at least on 2 ebay listings I found, both 67-1066, one did day it was a later big fin head)
Afraid I am not taking the head of the 1960 A10 to look. It does have a 389/45 carb though.
1961 A7 since 1976
1960 A10 Gold Flash Super Profile Bike
1958 Matchless G80 Project
1952 Norton Model 7 Plunger
1950 T100

Offline beezermacc

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Re: Later type iron heads
« Reply #5 on: 15.10. 2015 23:43 »
Hi Groily, Thanks for the info. As Angus says, the part number is in the middle of the bottom fin facing downwards so it is impossible to see whilst connected to the barrels. I'm beginning to think that the 42-0180 was never stamped as such but it may be a 1066 with a slightly overbored inlet tract. I'll get the calipers out tomorrow and see if there is any difference between various heads I have.
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Online groily

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Re: Later type iron heads
« Reply #6 on: 16.10. 2015 08:04 »
Had a look - but nowt visible, and Angus and you explain why not.
Before I put the correct new  Amal/Burlen 389 on, the thing was running with a rather tired I" 376 (which I had reamed out to inch 'n a 1/16th). It ran pretty well for tens of thousdands of miles, but having the right bore made a decent difference, as you'd expect. I also tried a new 928 concentric - but couldn't seem to get on with that, whatever I did to it.
In my shed, it's the beasts with original carbs on that seem to run best on 'book' settings, for some reason or another (might be just me, but there's a distinct pattern  . . .)
Bill

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Re: Later type iron heads
« Reply #7 on: 16.10. 2015 09:30 »
My machine has its original pre concentric carb, with an air filter. When restoring the machine I only bought a new air slide and needle. I've been very happy with this set up: the engine starts first kick after priming and proceeds smoothly through its rev range. Of course, I have to state that the bike was off the road for nearly 40 years so not as worn out as most others.
I can't help but wonder if running without an air filter is the source of many peoples carb problems.

Offline beezermacc

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Re: Later type iron heads
« Reply #8 on: 16.10. 2015 10:35 »
I've just spent a couple of hours of unbridled excitement (?) measuring inlet tracts on 67-1066 cylinder heads. What I've found seems to confirm what I suspected. 1) all square type iron heads, as used on sw. arm models and the last of the plungers, are marked 67-1066 though some markings are difficult to read. 2) These things were mass produced, rough cast, then finished off on some fairly inaccurate tooling so there are some variations but the heads fall into two distinct categories a) inlet tracts measuring somewhere between 26.5 and 27 mm and b) inlet tracts measuring in excess of 28 mm, typically about 28.3 or 28.4 mm. There are variations in the castings and shape and profile of the inlet tracts but nothing consistent which suggests, unsurprisingly, that there were a number of moulds and processes used at the same time and/or over a period of time. I have only come across one rogue head which seems to fall between the two categories; I suppose this may have been modified by a P.O. or it could be one of BSA's Friday afternoon jobs. The general difference between the sizes is about 1.5mm which is equivalent to 1/16". This could account for a number of fine tuning issues which have been attributed to carburettors when the actual problem is a slight mismatch of inlet tract to carb. The valves are all the same. Problems with cylinder heads and carbs were often resolved, back in the day when these bikes were worth nowt, by simply swapping items from the spares box under the bench. I suspect many of the lads fixing their bikes in the coal shed back in the sixties might not have measured inlet tracts assuming all the heads were the same, or even if they had spotted a slight variation would have attributed it to sloppy machining.
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Re: Later type iron heads
« Reply #9 on: 16.10. 2015 11:32 »
I suspect many of the lads fixing their bikes in the coal shed back in the sixties might not have measured inlet tracts assuming all the heads were the same, or even if they had spotted a slight variation would have attributed it to sloppy machining.

And if they (we?) were driving a lot harder back then, quite possibly less sensitive to carburetion glitches at part throttle settings?

Good thread this one though - appreciated.
Various, including ...
'58 Iron Head Flash Bitza