A10 new restoration, ID engine & frame

[polly]

so it started after a few kicks..but smokes no pattern to it, it just smokes .oil level is good ,oil is clean .Sounds great.

So looking at the parts I got in a box I found an other set of barrels and two pistons ,I guess that was going to be fitted.So Im thinking I will send them out to a machine shop and see if they are any good then if they are replace them along with a cyld head overhaul and then try again.   

[polly]

The barrels only seem to have surface rust in the bores but even if it needs a rebore and new pistons thats ok ...

The pistons are very domed with big cutouts for the valves so Im thinking h/c but what I dont know what ratio .Also in the same box were studs so I looked at the ones on the bike and the flange seems thinner than the barrels in the box so I think the studs are longer to suit the barrels  in the box.

[KiwiGF]

Hi Polly, there are differences in A10 barrels, later bikes had "thick flange" barrels. I'm not sure of the change over year for the road rocket but my 56 golden flash should have thin flange barrels. The barrels are interchangeable though, with only the flange being different, apart from maybe needing to use longer studs.

There are reported problems with thin flange barrels failing, on highly tuned bikes anyway.

May I suggest you have a look at the state of the barrel on the bike before a rebore of the spare one? it may still be within rebore tolerance.

You never know you may have just a broken piston ring, or some other problem causing the smoking.

[polly]

Yes I was thinking that .....Im going to take the head off anyway to take to the machine shop with the barrels anyway so I will look closely at whats fitted.

But if what you say is right the [boxed] barrels maybe the best way to go.

I only want to do this once and im sure its not going to be cheap.

[KiwiGF]

That's good, you can check the head over as well, to make sure the guides are not the cause of smoking, as a rough guide, concave pistons are 6.5:1, flat tops 7.25:1, raised crown Pistons like you have are 8.5:1 or more.

There are a few other (less likely) causes of smoking other than worn barrels or guides of course.

Yes the thick flange barrel is better but if you were after originality you may want to check into what your bike had when it left the factory, before deciding which to fit, I would not be surprised if the road rockets had the thick flange barrel fitted as standard, before the standard A10 though.

[polly]

Yes exactly what this engine is, is hard to work out ....the frame for sure is 1958... but the engine numbers make no sense at all .

[RichardL]

Polly,

If your pistons are similar to these shown in the attached photo, then they are 9:1 (by name).  It's a bit hard to tell from your photo. If you could shoot at 640x480 the photos enlarge when clicked on.

Glad you were able to get it started and it seems like nothing horrible is wrong. The head rebuild should eliminate valve guides as the cause of smoke and the new head gasket should take care of any leaks from rocker-box oil return holes. I'm wondering how bad the bike is smoking. I think I'm going to be surprised if it's due to broken rings, but I could easily be wrong.

I think the reason you have a spare thin-flange barrel may be because a PO did not want to risk breaking at the flange while using  HC pistons if there was a barrel available that would avoid it.

Richard L.

[KiwiGF]

Well I'm partly responsible for mis matched cases and frames, in my youth (when I lived in West London) I would think nothing of nipping out to a bike breaker in Ladbroke Grove and buying a "short engine" for my 59 super rocket....me being still at school with limited income, and 10 pounds for a short engine was a lot cheaper than regrinding a crank......I regularly had problems with big ends failing and bought several short engines in a year 

I did not even care if the short engine had the correct engine number, beginning DA10R from memory....

Sacrilege nowadays but back then (mid seventies) British bikes were worth little and the bike breakers were piled high with unwanted bikes. You had to get to the short engines quickly before they got filled with water, as the breakers stored the bikes outside in the rain.

[polly]

Well didnt have much time today but loaded the thick flanged barrels and pistons in the car to take to the machine shop.

Looks like there H/C over 20size.

Looking for the frame number and was expecting an A7 number but it started with FB 31 ?..WHAT THE HELL HAVE I GOT HERE ,Also noticed a kink in the frame [looks factory] on the righthand side towards the bottom of the engine case where the downpipe runs.

[RichardL]

As I read the frame and engine number list (http://www.bsaownersclub.co.uk/Downloads/Engine%20and%20Frame%20Listing.pdf ), and trying to read the frame number, it looks like your frame is from a '58 B31 or B33 with an alternator. I was aware that Gold Stars used the same frame as A10's but with the added kink, but I didn't know it was similar for the other singles.

Richard L.

[Topdad]

Hi ,could be a 58 to 59 B31, cheers Bob

[Topdad]

Opps Richard beat me to it , Bob

[polly]

So its a good frame ?

[Topdad]

Yes, I've heard of people using b31 /b33 frames , they may have been a bit cheaper once . I don't know about the kink I thought standard B frames didn't have the kink which I believe was for the goldies but I could be way of ,which rear brake do you have ,if it's single sided then you could be on your way to a RGS replica , fingers crossed, Bob.

[polly]

Interesting you should say about the rear brake.

It is fitted with the cable but in the boxes of bits theres another rear hub that has the brake lever coming out of the same side that the foot pedal would be and a shortened foot pedal and rod