[heloego]

The exhaust seal was definitely leaking, too.Maybe if you let it warm up and see if the smoke decreases. That would definitely indicate a leaking valve stem seal.

[grumbern]

Checked the plug and that's how it looks:




I don't know if you can see it, but it is oily and with fresh oil. That can only mean its coming from the inlet or by the piston. There's oil in the exhaust naturally that is black, but it doesn't mean it can't come from there, too. I will have to check the inlet and if it's not oily, it will most probably only leave the piston rings.

Can a bad head gasket result in this, without any signs of oil in the sealing area? Who knows, it has to come from somewhere...
So long,
Andreas

[Adrian II]

If we were talking about a Bullet rather than a 700 twin, my first response to that oil smoke would be "that's a classic case of wet-sumping", i.e. oil escaping from the timing chest into the bottom of the crankcase past whatever sealing mechanisms are supposed to stop this from happening. There is enough oil to overwhelm the rings and oil pump temporarily, but the scavenge pump usually catches up after a few minutes.

My AVL hybrid does something very similar on occasion. Bullet Whisperer and I tried all sorts of solutions. Unlike classic wet-sumping however, this will also happen when the scavenge drain plug has been left out overnight with virtually no oil collected underneath, only for the smoke to happen as soon as the drain plug is replaced and the engine re-started, i.e with a peviously empty sump. This usually clears after I have ridden the bike a kilometer or two. From talking to B.W. a bit further the likely cause might be poor oil control rings on the piston, whose rings are you using and what sort did you fit?

I will look out your address for the old rectifier, I think I still have it from the Abfangjäger light switch - any news of this bike?

A.

[grumbern]

Hi Adrian,
the odd thing is: The left cylinder runs perfectly "dry" and they both share a crank case. It still might be a piston ring though. I bought both pistons and rings from HMC and the cylinders were bored and honed to ~10/100mm. Another thing that was mentioned was a second ring that could be mounted upside down to cause such heavy oil burning. We'll see.

The Interceptor is still on pause. I have plenty to do with the Chief and also have a friend's Bullet here that we converted to 535cc, and did some cosmetic surgery. It has Boyer ignition, big valves and ports as well as a Mikuni carb and Alpha crank shaft. Pulls like a tractor

Yet I am always hunting for treasure, or parts if you will, so I can start with the interceptor as soon as the Chief is done.

Andreas

[Adrian II]

Another thing that was mentioned was a second ring that could be mounted upside down to cause such heavy oil burning. We'll see.

Yes, been there, done that! 

A.

[ERC]

They made a few of the later models that didn't have the cam tunnel drain holes drilled, there is a service bulletin on this. Also a broken ring would do this. If you pull it apart and the rings are ok the tunnel drilling could be your problem.  ERC

[ERC]

Here's the bulletin

[ERC]

Here's the other

[grumbern]

Well, that is some interesting piece of information. In Fact my engine case does no have these holes, but two a bit higher near the tappets. On the inlet side it comes close to the upper hole of the ones recommended, on the exhaust it is quite a bit higher, as you can see here:




I guess they recommended two holes, one above and one below the shafts, to use the upper ones for air to exchange and increase oil drainage from the lower ones?!
Is there still enough oil for the cylinders and cam shafts, if you drill that low?
Regards,
Andreas

[grumbern]

As I found that former post quite interesting, I did some research and compared all the 700 and 750 twin crank cases for sale at HMC and it seems that this named modification only relates to very early 700 twins as the Trailblazer, with the Meteor engine. These do sometimes not have any drainage bores, some have a small ones in the bottom and some have both bottom and top. Later cases however, as the Super Meteor, late Trailblazer, Constellation and Chief use the two bigger (~5/16) bores as shown above. This can also still be seen on VAX and early MK1 Interceptors, while later ones and the MK1A do not have them at all!

I think there was a lot of back and forth experimenting done somewhere around the mid-50s and it seems they where ok with that configuration, as they used it for all the bigger twins from around 1958 onwards.
I might check on my Interceptor if it's the same, but keep the Chief as it is for now. If there still is any problem after revision of the top end, the two drainage bores might yet be an option, but would require to remove all the timing gears.
So long,
Andreas

[ERC]

This may be stupid but were your cylinders drilled with the holes drilled in them on both sides? If they weren't the oil will build up in the cam tunnels.

[grumbern]

Hi ERC,
interestingly, only the rear of the barrels is bored, not the front (exhaust side). Why, I don't know.

But I found out, what was causing the oil burning. First was an upside down second ring - what a stupid mistake!

Second, and that is far worse I found when I checked the ring gap. A whole 0.6mm for the first and unbelievable 1.1mm for the second ring! That made me curious and I quickly measured the cylinder bore and the piston diametre. Cylinder is ~70.30mm and piston only ~70.00mm! What a shock! I absolutely did not check after I received them from the machine shop, now that really seems naive.

I guess +.020 pistons wouldn't fit? Unfortunately HMC also are currently out of stock and I did not find an exact table of how big the bores would have to be.

What a bummer...

Here's the pictures by the way.

A lot of oil on the piston:




And even on the left hand head gasket:




Definitely enough oil:




Speaks for itself:








That's it for today:






So long,
Andreas

[Adrian II]

+ 0.040" pistons any use, Andreas?

http://www.pricepartmotorcycles.co.uk/ourshop/prod_1097717-110085-JP-040.html

Henry Price also has + 0.020" items

http://www.pricepartmotorcycles.co.uk/ourshop/prod_1097715-110085-JP-020.html

A.

[grumbern]

Hi Adrian,
+.040 would be too big and I'd have to rebore the cylinders even more. With the +.020  a re-honing might be enough and safe some money and cylinder wall

Priceparts do take that "price" seriously, do they? HMC takes half the price, if these aren't forged or anything special
I'll call an Enfield dealer near me if he has some stock left.
So long,
Andreas

[ERC]

That's interesting all the cylinders I have or have used have the cylinders drilled on both sides. The holes help get rid of excess oil in the top end.