A10'1956 (modifying compression ratio)

[RichardL]

Hello A101960,

Thanks for the great history lesson, I appreciate it (as I am sure athers do).

One thing not clear to me is how far back the Eddie Dowe customizations went. My bike is a '55 swinging arm. I don't think there is much qustion as to the year, as it was titled when I got it in '73 and I can't imagine the year of manufacture would have gotten confused that early on. To the best of my recollection, the original frame was a CA7, which would have been matching numbers for my '55 engine number. Accordingly, the frame was made for the left-sde rear brake rod. Unfortunately, in the single most regreattable act of the restoration, which began in '03, I no longer have the original frame. When I started the restoration I had no sense for the importance of matching numbers nor did I know that the very next year model changed the frame for the right-hand cable-pull rear brake. I aslo had no idea how good or bad the engine was after it sat outside for 10 years (granted, often, but not always, under a tarp) with the barrels off. With me living in Illinois and the bike sitting in California, I could not bring myself to cough up the frame straightening expense. So, (are you sitting down?) I cut up the frame and discarded it rather than pay for shipping it back to Illinois, considering its unknown (to me) usefulness. (Do I hear people screaming, "Let's get 'm boys!". Maybe this is a good reason for anonymity. I wouldn't be surprised if I was now shunned by the entire A10 community for sacrilege.)  I proceded to purchase a frame on eBay and only discovered it was a later vintage for right hand rear brake about a year later when I got around to some assembly. The labor and costs associated with converting the frame for the left-side brake would have so easily offset the cost of straightening the frame it makes me sick to think about, but it's in the past now.

Well, I got off an a tangent that has little to do with Eddie Dowe, RGSs or modifying compressions. I assume you could confirm that the thick flange barrels were available in '55 and, also, that that flange thickness is close to 7/16". Would you mind chiming in on this?

Now, for something entirely different, I have language issue to discuss. Until about two weeks ago I had never heard the word "anorak" until I read it in a Ken Follett novel based in Scotland. Now, suddenly, it pops up again on the A10 forum. Are you, by chance, in Scotland, and are you referring to a parka coat? My uuse of the language may not be the best, but you have raised my semantic curiosity. 

Regards,

Richard

[a10 gf]

a101960 wrote

you have opened a whole can of worms here!

... a can of words,  , and an very interesting can.

[bsa-bill]

A101960 comments about the use of Goldie frames and parts reminds me that I have always wondered just how much difference these would make to the handling of the bike.
In fact apart from the bulge for the oil pump just how much does the Goldie frame differ from the A series frame, I do know there is some difference about the headstock ( taper bearings for a Goldie differ slightly from those for a Flash/Rocket ), and of course the rear brake is on the other side but is it a better brake ( possibly rod is better than cable )

All the best - Bill

[a101960]

Manosound the word "Anorak" is a very English thing. You are indeed correct in assuming that anorak is the same as "Parka" so for the sake of clarity I will give a brief explanation of the context in which I used the word "Anorak". I do not know if you have train spotters in the U.S. but here in England there are many people that spend all of their spare time visiting railways (railroads to you) all over the U.K. in order to log locomotive numbers. There are also people that do the same thing with aircraft. Another term that is used to describe these people is rivet counters. Anyway, I digress. Collectively these people are known in England as Anoraks because that is the type of clothing that they wear to protect themselves from the weather while they are out pursuing their chosen hobby. The term rivet counter arises because their alleged knowledge will lead to arguments among themselves about how authentic something is: e.g. wrong shade of paint or something similar. What they all have in common is the fact that they wear Anoraks (Parkas). Now to return to the subject of A10 cylinder blocks. According to the information sources that I have, the A10 was fitted with cylinder block 67-253 from 1950 until 1954. In 1954 the fin area was increased. The A10 Road Rocket was introduced in 1954 and was fitted with a new block 67-1210 this was the so called thick flanged block. The flange was thickened by 1/8" to give a thickness of 1/2". The standard A10 used part number 67-1074 until 1958 when the Road Rocket block was then fitted until the end of A10 production. It has been said that BSA only produced the RGS in order to use up parts that were left in the bin due to the unit models being introduced. Who knows? It is not implausible, but I doubt if we will ever know one way or the other. Now, in a direct answer to your question according to the BSA model catalogue thick flange blocks were not fitted to the A10 until 1958, but I am going to sit on the fence, because export models did not always conform to U.K. catalogue specifications. However if you do have a thick flanged barrel then I would think that the most likely explanation would be that another block has been fitted at some time in the past. What ever the explanation is, it does not detract from the fact that it is a BSA A10, and apart from the "Anoraks" and you, who is going to know. Incidentally the thick flanged block was introduced to allow higher compression ratios.

As far as I am aware the only real difference between the A10 frame and the "B" series frame is as someone has already stated: The kink in the bottom rail to allow for the "B" series engine oil pump clearance. There are many old wives tales associated with the the Gold Star, but the sad truth is that the the Gold Star cycle parts were shared with the rest of the "B" series range. There were cosmetic changes (rear set foot rests on some models for instance) and various other options, but a Gold Star could be ordered in several different trims, I.E. Clubmans, tourer and scrambler. It does not pay to be to pendantic about these things. If you enjoy your bike that is all that really matters.

[RichardL]

a101960,

So, as you said, the thick flanged 67-1210 was fitted as early as '54, and that is what I have on my '55, including the "HHC" on the crankcase. This makes me beleive the barrels are original. I have 9:1 to pistons but, I reckon, the original had 8:1 "high compression."

Also, thanks for the explanation of "Anorak." I never would have guessed that was how you were using the word and, now, it makes perfect sense. So, if I went back and watched the movie "Train Spotters" would I find that the characters are wearing Anoraks?

Again, thanks for your comments and the information.

Richard

[a101960]

Richard, It seems to me that you have a Road Rocket. You say that your case is stamped HCC. In which case the engine number should start with CA10R if this is so then it is a Road Rocket and it should have an aluminium cylinder head. If the engine number starts with CA10 then it is an A10 and should have an iron head. After all this time though, it is anybody's guess, as to what combination of parts have been fitted in the past! To confuse matters even more, some Rockets had a tacho drive located on the timing cover driven by the magneto. On later models the tacho was driven by the oil pump as on the RGS. Not all Rockets had a tacho though. Rockets were also fitted with a manual advance magneto, but it is quite common to find auto advance on Rockets although as far as I am aware this was never a factory option. For your year pistons could be 8.5.1 or 9.1

John

[LJ.]

Superb thread.... must add my tuppence worth!

the Gold Star cycle parts were shared with the rest of the "B" series range.

Indeed they were, and with the "M" series too!

and of course the rear brake is on the other side but is it a better brake ( possibly rod is better than cable )

My M21 rear brake that has a rod rather than cable... It is a far better brake, easily locking up the back wheel. Yet my A10 rear brake (on both A10s) is very poor, maybe because the "A" seris bikes are so much heavier?

[RichardL]

a101960,

It really is sounding to me like BSA built a Road Rocket and didn't bother to give it an "R" following the "CA10" engine number. I envision an internal BSA conversation going something like, "Lads, the case is already stamped in the Golden Flash series, but the bloody Yanks are power crazy, so we'd best give it to them, what?" (No offense intended in my British characterization.)
I guess a pre-'73 owner might have scavenged a Road Rocket to modify this bike, but I will never know.

Richard

[RichardL]

a101960,

I forgot to mention, I have the magneto-driven tach drive opening in my timing cover, but no tach. Also, I have auto advance.
With as much time as goes into the motorcycle, it's fun and easy to talk about it at length. Thanks for your help and interest.

Richard

[a101960]

Richard, You say that you have a timing cover with provision for a tacho drive. There is one snag here if you have an auto advance magneto. In order to fit a tacho if you so wished you either have to source a manual advance magneto or convert yours to manual because the drive is taken off of the magneto pinion retaining nut. It is quite easy to do the conversion and you should have no problem getting hold of the relevant parts if you wanted to go down that road. Incidentally what tin ware was on your forks? because that varied from year to year. In 1955 the A10 would would have had a separate cover over the top of the forks and headlamp. The light switch and the ammeter would have been fitted to that cover. The light switch to the left and the ammeter to the right, with the speedometer in the middle. The rocket would have had a separate headlamp shell with the ammeter and light switch mounted on the centre of the shell. The speedometer and tacho would have been mounted on brackets on top of the forks.

My M21 rear brake that has a rod rather than cable... It is a far better brake, easily locking up the back wheel. Yet my A10 rear brake (on both A10s) is very poor, maybe because the "A" seris bikes are so much heavier?

LJ you are quite right with that observation. My rod brake feels very wooden and does not seem to work very well, but much to my surprise the M.O.T. tester commented on how good my brakes were! odd that isn't it?

[RichardL]

a101960,

I'm not being real agressive about adding a tach, but I generally take a look at drives that come up for sale. However, I did not realize that the tach drive required manual advance. I'm glad you cleared that up becuase I might have marched merrily ahead. I think I prefer automatic advance over having a tach. Maybe some day I make it even at the "Elephant and Castle" or the like.

As for the tinware, that is a whole other issue that can be seen in the Bike Pictures area of the forum as "Richard's 55 A10". You will see there that I have a Rocket headlamp supported by ears, no cowl. (The pictures were taken before I aimed the headlight, so it kind'a points up.) The fender could easily be off an A50, because the top tree also appears to be, with the fork yokes dropped down about an inch versus the straight across form of conventional A10 top trees. The headlamp ears follow suit, being about an inch shorter than those for an A10. All of this is as it was when I bought the bike in '73. I only discovered the top tree issue because I had bought a new one (for an A10) on eBay to replace the one that was bent in my accident of '79. Imagine my surprise when the headlamp ears I had just paid dearly to have rechromed fell short of reaching the underside of the tree. Another funny thing you might notice in the photos is the front fender stay arrangement. Again, the '73 version was similar, with flat stays instead of round. The fender I have wants a yoke and screw holes on the insides of the fork legs, but I have neither. Though it may not seem so, I did not set out to build a bobber and I hope it doesn't seem like one, but if it does, I say "too bad" to the "Anoraks."

Richard

[trevinoz]

According to my parts book, the RR engine in 1954 - 55 was as standard A10 except for listed differences. The crank and barrels were not mentioned. This leads me to suspect the beefed up items were not available until '56. Certainly the '56 had the billet crank, much heavier than the bolted type. Also, all early Rockets I have seen have CA10RR prefixes.
Confusion reigns.

[muskrat]

G'day Colin.
7.25 will be fine. Higher compression increases heat. Small fin barrels can't get rid of too much heat.
By the way this thread is 14 years old!
Cheers

[bikerboy]

As far as I am aware the only real difference between the A10 frame and the "B" series frame is as someone has already stated: The kink in the bottom rail to allow for the "B" series engine oil pump clearance.
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The head steady bracket is also slightly different on the A10 its a tube welded across the main frame tube on the others its  flat piece of metal welded in line with the main frame tube.

By the way I am not an "anorak" I just happen to have an A10 motor in one of those frames 

[edboy]

this thread may be 14 years old but highly controversial to crankcase number studying anaracks like myself [blue quilted with hood option ]. i would like to add that bsa supplied rockets with 8.25 /1 as H.C.  these are flat topped not domed like 9/1 s. a lovely piston that was always unavailable and for some reason the domed 9/1 was sold on mass as aftermarket H.C. i have never seen a 9/1 with a bsa part number and were a pinking nuisance if like me your maggie camring was worn down on one lobe.