Thunderbolt help please.

[A10 JWO]

I am waiting for the moderator to approve my membership for another forum so I am ask my old mates on here.
New acquisition today 1972 A65 Thunderbolt. Frame & Engine both A65T HE 11587.
Looking at the pistons I cannot see any plus signs to indicate a rebore, this bike that has done 43,000 miles.
Nearside piston markings 68/907 BSA
46/6171H

Offside piston markings
68/907 BSA
46/6171M

Surely these are not standard pistons.

Thanks lads.

[JulianS]

68 907 is the casting number of a standard piston, 68 906 being the number for a complete piston.

HE decodes as H =July  E=1971, so the bikes is 1971 season. 1972 bikes would have G as second letter. They did not always sell very fast. production finished in April 1972 but some bikes did not leave the factory until 1973.

[A10 JWO]

Thanks Julian. It was registered May 1972. My wife put her head in the garage and swore when she saw it. It will need a full restoration ( said with a heavy heart ). Dragonfly list all the parts but I will have to watch the pennies. Will need two wheels rebuilt and tyres, mudguards , Head light, frame painted and all other paint. New wiring and controls etc etc. Need a sand blaster in Essex. Have not found the rocker assembly yet, hope it's there in one of the boxes. 

[JulianS]

Consider very carefully before sand blasting or any solid medium blasting of an oil bearing frame. Get any in the frame it is extremely difficult to be sure that you have got it out. Does not mix well with bearings and bores.

[Butch (cb)]

I use;

http://www.ctc-powder-coating.co.uk/

[A10 JWO]

Hi Julian. I am going to leave the sump on and filler cap. I will block the feed pipes up as well. Good advice thanks. I will pull the sump off when I get it back and rinse it all through. Thanks for replies lads. I found a company near Rayleigh who will do it for £150 which seems fair.

[morris]

SRM have some nice goodies for the A65. Yummy...
http://www.shop.srmclassicbikes.com/product-category/bsa-a65-big-bore-kits
Don't tell the wife though... 

[Sluggo]

Mods......While Brit bike dot com has its uses, I for one would approve perhaps a sub-genre of Preunit singles and Unit twins of the BSA parentage as being useful and seeing as they are ALL the same breed it would make sense to my self absorbed thinking.   
I joined here to learn and ask for help on these early bikes but there is a lot on the early singles I need help with as well.   
I have much more experience on the Unit twins, but even then dont know everything.

That being said..I have a LOT of unit twins, and downsizing the volume. I am keeping only 2 but happy to offer my help on these.  I would STRONGLY STRONGLY and FORCEFULLY encourage this poster to NOT use ANY abrasive media around that Oil bearing frame aka OIF.  BAD IDEA sparky!   You cannot totally cap it off or seal it. Worst idea ever.  Grit has its magical abilities to migrate into where you dont want it. Even one shard of media will ruin your whole day, week and month.

I have a bunch of OIF Triumphs and BSA and while I am only keeping one of them (A custom T140D cafe) they are quite popular now as Street trackers modified to resemble Trackmaster frames. (Also relocate the oil filler cap where originally intended).
In the past, I have always painted frames,  Powder coat has its uses (Brackets, center & side stands etc) Its bad form to use on a frame.  If you ever scratch or damage it, its easy enough for a competent painter to touch up and repair the finish and also possible to mask off the bike and does not require a full strip down.  You CANNOT do so with a powder coat.  It is also extremely hard to find a shop who can strip powdercoating.  Cant speak for your area, but I had a friend who crashed his Norton after a 2 year build and we had at that time just under 30 shops in the extended area that do powder coat.  Only one shop could strip the material. And it was not cheap.  Being a stubborn sort and slow learner he DID re-powdercoat his frame again.
(Some people you just cant reach, just like we had here today! -Apologies to slow hand Luke)

While not appealing, you can strip with chem stripper and scrub and clean it yourself. (then paint)  But I have used a chemical stripping shop.  There is one in a nearby city and they have tanks large enough to drop entire car and pickup bodies into. (Parts must be degreased before arrival)  But they happily did multiple frames for me and cost was reasonable.  First tank removes all paint, bondo and stickers and leaves it bare metal. Second tank is a treatment for corrosion so your parts dont flash corrode on you.

Congrats on the OIF bike, they are the pinnacle of BSA twin engineering. Not the most stylish at times. (Does yours have the bread box tank or the Triumph variant tank as they interchange?)
But the motors had some very important upgrades and improvements. (Especially that cast Iron pump).   I have a basket case version sitting here I am planning on selling, Perhaps your wifes fears will be assuaged if you promise a His & hers?  I have a friend from the UK arriving here next month to ship a container load back to Blighty so perhaps I can send it to you?

[morris]

Sluggo has a point there. I also turned away from powder coating. When I had the plunger's frame powder coated, in spite of having all the holes blanked off carefully with bolts and purpose made blanking plates, I still found the frame full of blasting media. Took me ages to get the most of it out, but never got all of it.
A good quality modern paint, laid on by a professional sprayer, will last as good as any powder coating on a motorcycle frame.

[Sluggo]

I cant speak of what products are available outside the US, although I am a big fan of RM-BASF based products and those tend to be universal.  But I have spoke to countless powder coating and ceramic coating shops and staff.
Aint no such thing as a one size fits all powder coating!  I have perused catalogs at several shops of their offerings and what they can order.  People tend to view powdercoat as one entity and its not.  Some of it is soft, some of it super hard and durable, some of it glossy, some of it not.
Many motorcycle enthusiasts tend to want a hard and shiny finish and most shops pick a product that checks off most of those box's,,But the range of products available is actually quite diverse depending on what you want to do, price and certain application issues.

Now, Paint is just as diverse, Originally MOST of these frames and ancillary bracketry were dipped into large vats of lacquer paints, many of the applicators did not wear PPE and horrendous working conditions.  I have several articles and have seen some period films of people doing this work and its appalling. (Talk about a version of "Black lung", plus ciggies on top of that!).

I used to do, and still do on occasion body and paint work,. I dont want to do it as a full time job but I enjoy paint work as an artisanal pursuit.  (I painted my Father in laws MGB a while back and recruited to be painting his 51 MG TD soon)  But while body work and and tanks, fenders etc is where it is really fun, I dont mind doing a frame, its the brackets that is a pain and will farm out to powdercoat.  Frames can be a bit challenging as there is overspray issues and getting a good uniform finish with the best parts focused in where its visible. 

You cannot simply beat a quality Polyurethane and if you want extra gloss I can easily cocktail in some clear coat in the final coats.  This is good as well if there are transfers, decals or stickers as well because they can be sealed under clear.

In the area here I have 2 product lines I will use on frames and such parts...

Diamont/RM (BASF) I use DE15 etch primer (Excellent bonding and corrosion control properties)
followed by single stage Black Poly, and final coats cocktail in a little clear coats for extra gloss

Valspar (Oldest US manufacturer, George Washington's house was painted with Valspar house paint when built back in the 1700s)  I use VP-50 and thinned out to a etch coat formula (again great etch bonding and corrosion control properties) followed by Valspar single stage Poly Black, and again, some of their clearcoat in the final coats.

The beauty of both of these product lines is the reducers is cross compatible for all the products and I can cocktail in other stuff. For example I can color tint the primers.  Or mix a clear coat with a single stage Poly.   But... if you scratch the finish (Which when fully cured is VERY durable and resistant to fuel, oil and clumsy mechanics with butter fingers)  I can then, EASILY go back in and do a repair, touch it up or even respray an entire area and then melt it in (Blend) so that it is entirely undetectable.  In some cases I can blend with a solvent and when dried it all melts together into one finish, in some cases a little polishing compound or sanding and then polish-wax and Bobs a close relative.

I have some paint work coming up in late August and September (multiple projects) so would be happy to do a tutorial-paint topic.

[coater87]

Like said, powder coat is easy enough to remove. About 50 bucks in aircraft stripper, half a pound of burnt flesh, and time. Job done.

 Look at your frame number stamping. If they are not deep or well defined, either skip the powder or go to a smaller non-production shop. The big places are going to use the nastiest abrasive they can find, with enough pressure to blow a small house down to blast everything for maximum production.

 If your numbers are faint, they may be gone when you get it back.

 Most times you can block sand over the number area and still pick them up, but the job is ruined. If they blasted long and hard enough, a letter or two could literally be erased.

 With small batch shops you have a better chance of them actually listening and being particularly careful around the neck area.

[Sluggo]

Depends on the powder coating, I can personally attest to one frame that had no numbers, the owner could not get the DMV to issue a title, so it was a legit deal so I stamped them for him. The powder coating was so soft, 400 grit sandpaper removed it.

 But I can also personally state that I have seen powdercoating that NO paint stripper would touch, nor sandblast (Only slightly dulled it) or any number of other attempts.  I would have to research what the shop we paid used, but my friend spent a lot of time trying to remove the powdercoat on his frame to no avail.  When he built the bike originally he used a special spot face carbide tool to clear off the powdercoat on the bolt holes because if you dont, fasteners mysteriously come loose.  But thats carbide machine shop tooling thats razor sharp. 
When he finally had to resort to taking it to a specialist to remove the damaged powder coat it was VERY expensive but his only option.

If someone can easily removed powdercoat with chem strip, then it was not that durable to begin with but as I said, theres multitudes of coatings out there all with different properties. But the original issue is avoid media blasting a oil vessel.

[BSA_54A10]

If you are going to blast the frame back to bare metal if you do not give the frame a POR 15 treatment then you are insane.
POR 15 do a black base coat, it will get into every nook & cranny and once fully cured it can not be removed apart from agressive mechanical means, sand blasting bounces right off.
Do not leave it in the sun as it is not UV stable ( well it is Chassis paint ).
A week after you have applied the  POR 15 take the bits to any company who dips bull / crash bars & get the frame dipped.
Dipping is how BSA painted their frames

[scotty]

Ditto on the POR 15 chassis paint

Sticks like s#*t to the proverbial blanket, flows out nicely when applied.
it's a tough coating and looks good

I use it on all my frames

S