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Where is it coming from?
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Isbfan
Mickleover, Derby
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April 24, 2020 - 6:16 pm
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Only had my Bantam a few weeks, but enjoy getting my hands dirty (just as well) tinkering. Whenever I start the engine I get really black oil leaking from both the back end of the silencer and where the exhaust joins the barrel (despite tightening the clamp ring). I've removed the sump plug and drained the crankcase but still the oil keeps appearing. Could it be seeping through the crankcase from the gearbox? Any other suggestions?

 

Thanks in advance

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Blue Heeler
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April 24, 2020 - 6:53 pm
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If gearbox oil was leaking into the engine, you`d have a smokey silencer and your spark plug would have black carbon build-up on the earth electrode and you`d notice starting and performance issues.

Could be any of the following:-

Pattern front pipes often have poor flange lip angle/finish.

Gasket, made of composite material encased in a copper ring, could be squashed past its best.

Threads on barrel may need cleaning up. Sometimes it appears you`ve leaned on the C spanner enough, but if the threads are corroded, what may have seemed like sufficient purchase may not have been enough. I`ve found that by removing the front pipe and tightening the collar without it, that it can bottom out on the threads before it`s screwed on enough to be able to tighten the pipe flange. Cleaning those threads with a thread file or jnr hacksaw blade, then screwing the collar on & off minus pipe until it tightens all the way, often does the trick. After cleaning oil out of exhaust port and off the gasket with thinners, a touch of exhaust sealant can help if you don`t have a new ring at hand.

Blue.

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Peterg
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April 24, 2020 - 7:07 pm
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Quite normal.

Oil transfers onto surfaces by pressure and heat. When you start up the motor the heat element is missing. Excess oil will pass into the combustion chamber and out into the exhaust as carbony sludge which will collect in the exhaust pipe and silencer where it will remain until it drips out of joints and the end of the silencer until they heat up enough to burn off this residue.

The more residue you collect, the more dripping and smoke you will get (also cokes up the silencer).

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Isbfan
Mickleover, Derby
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April 24, 2020 - 7:17 pm
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Thanks guys, I'll follow your suggestions forthwith - or maybe tomorrow 😉

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mikef
Chatham Kent
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April 24, 2020 - 7:25 pm
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Hi.
    Well it suggests that you have a leak from the cylinder barrel to exhaust down pipe, that's not unusual. A new copper washer should sort that.
It is also possible that the down pipe is an after market part that was not correctly fitting, you need to check that the flange sits square on the barrel.
If oil continues to appear from the crank case drain bolt then it could be caused by leaking crank oil seals. Another possibility is a leaking fuel tap.
After a period of non use fuel leaks past the tap cork and eventually it gets through the float valve needle in the carburetor and ends up filling the crank case with petroil. The petrol evaporates and just leaves oil in there. This make the bike hard to start and smokey when it does.
If you have only had the bike for a few weeks then it could be possible that the petroil mixture is wrong. A fresh mix of 25:1 would be a good starting point.
Normally I would suggest a good ride to warm it up completely, unfortunately not possible just now.
Some ideas.
         Mike.

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Sponge
Lancashire (A chip shop somewhere near Preston)
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April 24, 2020 - 7:47 pm
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I had exactly the same problem on a B175 that I had just purchased in early 1990s.  It was assured as a good runner which had been 'built' by a bloke who really knew what he was doing......!!!   So I took it on trust and decided to use it.   Normally I would strip a new bike down to discover its secrets !!!

 Anyway - getting back to the point - it had the same problem as yours - lots of black oily stuff spitting out of the silencer and getting all over the back wheel etc  Black oily stuff seeping out of the whole exhaust system and also filling up the crankcases.  Very heavy running and a lumpy feel to it was my clue - I removed the carb (concentric 626) and stripped it down. It had a shorter needle ( from where I do not know), and a 250 main jet - other bits were missing and the inside of the float bowl was a mess (some people will do anything to save 50p on a float needle) - it was a complete lash up.   Turns out it was over-fuelling because the carb was all wrong.  Result an over-rich mixture. The black oily stuff was actually unburnt petrol spewing out all over the place. 

I put the known good carb onto it from my Bushman and it ran as sweet as any B175 I had ever ridden before.  Didn't last long as there were other problems with the engine ........another story but my advise would be to never buy a bike as a good runner, from a bloke who knows what he is doing unless the vendor is prepared to ride it to an RV with you at least 100 miles from your house and then to ride it those 100 miles to your gaff whilst you follow in a car or your other bike.  In this way you will know if it is genuine or not.  Most hacks and painted ladies will break inside of 100 miles if there is anything wrong.  Otherwise, no matter how great it looks,  buy it as a non runner and take it to pieces as soon as you get it home,  build it up properly and then have some peace of mind when you go for a long day out on your pride and joy and have no mechanical issues that you did not expect.    

Something to check I think, easy enough to do. Hope this helps, hope you get it sorted - don't worry you will get there in the end and it will be worth it.   

Sponge

   

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Isbfan
Mickleover, Derby
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April 25, 2020 - 9:22 am
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So much helpful info, thanks again

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Number6
Lincolnshire
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April 25, 2020 - 7:50 pm
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http://livinginthepast-audioweb.co.uk/imagex/misc/like-button2.jpg

painted ladies will break inside of 100 miles if there is anything wrong.

That's what I got! Runner? No! Not a chance

take it to pieces as soon as you get it home, build it up properly

Yep! Was definitely for looking at not using laugh

Mike H --

Murphy's 4th law of motion states that any small object that is accidentally dropped will immediately hide itself under a larger object.

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Sponge
Lancashire (A chip shop somewhere near Preston)
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April 26, 2020 - 9:37 am
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Hi 6, 

Definately - its a sad fact that there are people out there who build bikes to look at (as you say). Some of these builds are beautiful but hide the most dissapointing secrets.   I have no problem with people who build bikes to look at but when they sell those bikes on as 'fully restored', to a punter who actually wants to ride them we get sad misunderstandings.   

I would not consider a bike to be 'restored' unless it was mechanically correct as well as cosmetically - hence the 100 mile test. 

This is why I recommend new purchasers to take an experienced club member with them if they want to buy a Bantam - there's a lot of pitfalls and a lot of tricks.   

Of course there are genuine bikes and genuine sellers out there and I mean no insult to them. 

If you intend to take it to pieces before you use it then buy it at the right price on sight and spanner down.  If you want to use it straight out of the sale then insist on the 100 mile test or walk away if the vendor is not prepared to oblige.    

I could say a lot more but wil probably get into trouble. 

Sponge 

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sunny
Norfolk
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April 26, 2020 - 10:04 am
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   post   number   9   spot  no  Les      as   with  all   your  post         sunny   

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nickjaxe
Runcorn Cheshire UK
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April 27, 2020 - 6:09 pm
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When I had a poor fitting pater front pipe once...I fitted 2 copper sealing rings...that sorted it.

My Bantam video              https://www.you.....jpOFmzRZRI

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Isbfan
Mickleover, Derby
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May 15, 2020 - 5:50 pm
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Pleased to report the bike is now running.😄

changed the exhaust gasket, did a full carb strip down and clean, fresh fuel and there we are. 

perseverance pays

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Sponge
Lancashire (A chip shop somewhere near Preston)
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May 15, 2020 - 7:20 pm
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Well done

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