My 1966 BSA Bantam D7 Super Restoration



Restoration Tips

Firstly, don't think that you can restore a Bantam to make money.  I think in most examples the cost of the restoration will exceed the commercial value of the bike when completed.  Do it for the fun of it and the challenge, not the money, you will probably be dissapointed if you do.

Don't give up!  Press on, persistence and determination are omnipotent!

Before you dismantle your Bantam for restoration, and during the dismantling process take lots of photos.  When you have taken all that you need to, multiply this by 1.5 and this is how many photos you really need to take.

When you strip down your Bantam use a BSA spares list with exploded views and number all of the parts with the BSA part number.  Then when you reassemble you can use the exploded view and part number to identify each part.

Do not throw anything away, keep all the old bits and pieces as you progress, its amazing how many you need to re-use, as a pattern for new, as a reference point and how many bits are not readily available.

Always use the correct tool to remove the fly wheel generator rotor.  Resist the temptation to try anything else as this will without doubt result in a bent shaft.  I obtained my removal tool from e-bay.

The piston has "front" stamped on its crown and this is important for the following reason.  When the piston is positioned correctly, i.e. with "front" at the front it is important to ensure that the piston rings are located such that the gap in the ring lines up with the piston ring "pegs", this ensures that the piston rings do not foul the apertures in the cylinder head.  If you get this wrong it could cause untold damage to the pistin, rings and cylinder head. 

Always check the swinging arm bushes as they apparently wear at relatively low mileages and replace if necessary.

The baffles can be removed from the exhaust silencer in some examples, but they can be cleaned "in position" with a Caustic Soda solution by removing the silencer and sealing one end.  You need to take precautions such as wearing Person Protective Equipment e.g. gloves, face mask and following the manufacturers instructions.  Caustic Soda reacts violently with aluminium so ensure the end cap is removed from the silencer prior to cleaning.  Chrome surfaces should also be protected and I suggest you search the web for additional advice prior to undertaking this task.  NB The Caustic Soda solution gets hot in use.

          This is a potentially dangerous substance so visit,


          and research the product and its use and the Health and Safety

          implications prior to use.

The Haynes BSA Bantam manual is a usefull book to have, but it is not conclusive by any means.  Join the BSA Bantam forums on Yahoo, the members are very helpfull and can and do provide excellent advice.  See the usefull links page.

When you remove the fly wheel generator rotor and the stator coil assembly, store them as they are installed or the electrical characteristics may be affected by the magnetic properties of the fly wheel not being retained.

To remove the Amal carburetor without dismantling the tool box covers etc, try tightening two nuts onto the end of the fixing studs and use the nut nearest the carburetor to undo the stud.  Alternatively, replace the studs with bolts and this makes the removal of the carburettor much easier, the bolts should be 5/16th British Standard Whitworth (BSW) thread which is the thread size in the engine casing.  Make sure you fit spring washers as the BSW thread is "course" and could become loose otherwise.  Maybe this is something to do with the original studs have two threads, a "course" thread into the engine casing and a fine thread for the nut to tighten onto.  

When I had to replace the con rod small end bearing I removed the old one by positioning a 1/2" drive socket the same size as the small end bearnig on one side of the con rod and an oversized 1/2" drive socket on the other.  Through the complete assembly I passed some threaded rod with nuts and washes at either end.  Then by tightening the oversized socket end of the assembly, the same sized socket pushed the small end bearing out and into the oversized socket.  Simple, a bit "fiddly" but effective!  Use the same concept but with thick "penny" washers to push the new bearing into position.

You can buy a clutch compression tool for the Bantam but I did the following instead.  I already had a three legged fly wheel puller so I made a rectangular steel plate that sits in between four of the spring cups with a hole in the centre to locate the puller.  With the steel plate in place between the four spring cups, locate the three "legs"and tighted the puller, it works!  The steel plate I made was about 5mm thick.

The front mud guard stays are "handed" i.e. one is for the right hand side and one for the left.

When I fitted the piston rings and tried to fit the cylinder head I was having trouble compressing the rings and keeping them in their correct position.  I tried the following and it worked well.  Get someone to hold the cylinder head just above the first ring, having alrady oiled the cylinder and piston etc lightly compress the first ring with a length of string and carefully lower the cylinder head to just above the second ring position.  Repeat the process for the second and third rings.

Get a copy of "Pitmans Book of the BSA Bantam", lots of information regarding the service and maintenance of the BSA Bantam.

Use grease to hold the head stock bearings in place during their installation.

I am refurbishing the original seat and I have purchased some "dense" foam to replace the original.  You will not believe this but it is true the best implement to cut and shape it with electric knife!  Yes, the sort you get from the kitchen without the wife knowing.  No really its true, works better than any thing else I tried.

The original Champion L7 spark plug can be replaced directly with the modern day equivalent a Champion L82C or an NGK B7HS or a Bosch W6BC,W5BC. 

When checking and setting the ignition timing, rotate the engine slowly until top dead centre is achieved (TDC) and then turn the engine back (not forward) so that the piston decends 1/16th of an inch. 

The "closed" end of the spring link as fitted the the final drive chain should face the direction of travel when installed.

If you are going to fit the front number plate then do so prior to fitting the front wheel.

If you need a wiring diagram for your Bantam go to

If you have the engine and frame number for your Bantam and you want to date it go to

I wish I could take the credit for the following but I can't, the following was explained to be by Tony at 

I had the devils own job (which is code for !"%&*£$ annoying!) seperating the two halves of the crank case, hav'nt we all!  Well to get the process stated remove the cylinder head and in the aperture where the con rod is, insert some threaded rod, nuts , washers and sleeves as per the following sketch.  Carefully, turn the nuts to expand the aperture and "crack" the seal between the two crank case halves.  Obviously a hide mallet and lots of coaxing will still be required.  I hav'nt tried this but it makes perfect sense, Tony has and does and it works.  Tony also informed me that once the crank case "splits" the bits drop inside the crank case so then you have to continue with the task.  You could use one spacer, washer and nut of course instead of two and I suppose you could stuff the aperture with a cloth to catch the component parts if they do drop down. 

Remember, the headlight only operates when the engine is running.

The ratio of oil to petrol has changed since the time when these bikes were manufactured and mainly due to the advances in oil type and specification.  Clearly the ratios are a lot higher now than then and the concensus opinion appears to be that the ratio is something like 1 part oil to 40 or 50 parts petrol, i.e. 1:40 or 1:50.  Obviously research this issue yourself to determin what ratio you will use.  Its best to mix the the petol and oil (Petroil) in a seperate container prior to adding it to the fuel tank, to ensure the "mix", as opposed to adding petrol and oil to the tank seperately.  A ratio of 1:40 = 25ml of oil per Litre of petrol, and a ratio of 1:50 = 20ml of oil per 1 Litre of petrol.  

The "as installed" position for the Amal 375 carburettor throttle jet needle is groove number two, i.e. the second from the top according to the the BSA Bantam service sheets.  Raising the needle enrichens the mixture, and lowering it weakens the mixture.  This may need experimenting with and may of course be different in your example. 

If sparking occurs across the across the contacts of the contact breaker, accompanied by the burning of the contacts the condenser should be replaced as the condenser function is to prevent sparking across the contacts as they seperate.

Remember, when you re-install the existing, or install a new contact breaker set install the insuating "washer" as well.  If not the contact breaker points will always be "made". 

I needed a new battery for my Bantam and I have installed a Varta B49-6 which is 6 volt and 8Ah.  I purchased it from Manbat who were very helpful and have branches throughout the UK.  See for branch locations.

Remember the wiring on the Bantam D7 is a positive earth system as opposed to a negative earth system which you may be used to and familiar with.  Take care when connecting the battery and ensure that the polarity is correct.

Although my original wiring loom had no fuse installed I installed an in line fuse and holder when I re-wired the bike.

The cylinder head studs may be "weak" due to to their age and the number of times they have been removed and tightened up as mine were (one snapped in the engine casing).  They are low in terms of cost for new ones and it would be prudent to replace all four as a matter of course as opposed to having to remove a broken stud.

Take care when reassembling the Amal carburettor and in particular the needle seating, seating washer, filter gauze, banjo, washer and bolt (this is the assembly the fuel line connects to on the Amal carburettor) as a washer, or an additional washer fitted in the wrong place results in fuel entering the float chamber, the needle rising up as the float rises but the needle does not seat, and fuel continues to flow out of the tickler even when the float and needle have operated. 

The Wipac Magneto as fitted to my Bantam is,

Wipac No IG.1704

Generator output to AC Lights, trickle charge and ignition coil Model D7 Super (Two switches in headlamp model) Fitted from October 1963 to May 1966 

When you remove the drain plug to drain the oil from the engine, clean it before you reinstall it as "bits and pieces" gather in the drain plug because its "hollowed out".  Obviously a design point and quite a good one really.

Always replace the circlips that retain the piston pin in position.  Even though they may look OK if the "fail" the piston pin will "float" in the piston and produce "tram lines" on one or both sides of the cylinder bore, which may lead to loss of compression and so on.  Replacement is the best option when reconciling the cost of two circlips with the potential for failure and the consequences.

Having bought and installed a new exhaust silencer and installed it, I was a little worried that the kick starter would foul and scrape an arc into the silncer.  I have seen this example on lots of Bantams even though the silencer is installed correctly with the exhaust silencer bracket fitted to the "right" side of its supporting bracket that it bolts to, i.e. the bike side if this make sense.  So I removed the kick starter, clamped it in the vice, heated it up with the Turbo Torch on its "bend" and "straightened" it out a little.  I obviously got it hot enough as it was easy to bend, appears to be OK and I have increased the clearance between the kick starter and the silencer to an acceptable margin.  

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