Smoking Rear Cylinders

[Alan Cun]

Hello All, An interesting think happened on the morning tea stop during the Sunday run at the Burnett Douglas Get Together. The 3  E29s arrived only minutes apart and were lined up for the photo that is elsewhere  on the forum. With all the spectators looking on a remark was made look at the smoke coming off the rear cylinders on all three machines. I can only again say how much hotter the rear cylinder gets and the importance of the correct plug range, premium unleaded with addative. A very good oil and as previously mentioned and maybe a little more rear piston clearance. I heard one operator of a direct drive Triumph say that only uses two stroke racing oil. I still use Castrol R only because I have a fair quantity left over my days of Historic Racing and I love intoxicating the following riders.    regards Alan

[trevorp]

It is a good smell

[bazza]

Hello All, An interesting think happened on the morning tea stop during the Sunday run at the Burnett Douglas Get Together. The 3  E29s arrived only minutes apart and were lined up for the photo that is elsewhere  on the forum. With all the spectators looking on a remark was made look at the smoke coming off the rear cylinders on all three machines. I can only again say how much hotter the rear cylinder gets and the importance of the correct plug range, premium unleaded with addative. A very good oil and as previously mentioned and maybe a little more rear piston clearance. I heard one operator of a direct drive Triumph say that only uses two stroke racing oil. I still use Castrol R only because I have a fair quantity left over my days of Historic Racing and I love intoxicating the following riders.    regards Alan

Hi Alan,I just had a thought re this problem of rear cylinders overheating etc with the EW it has a non return valve on the front cylinder which one can manually feed the front cylinder with oil.Would it be feasable to put one on the rear cylinder and connect up to the oil lines or is this a silly idea,and can the E29's benefit from this.
All the best Bazza

[Boxer]

Hi,
I think we had first to differ what smoke we have. As I understood Alan said there is a steaming smoke outside the cylinder from overheating.

Another form is smoking out of the exhaust of rear cylinder. This form is a technical item of having a revolution of the crank which is throwing oil to the back cylinder. So here has the cylinder too much oil! There is a advise to lower the oil level in the engine. This is also the reason that only the front cylinder has an oil tube.

For the first case we only can do the technical advise (as Alan said) to have more play for the piston and an exact tuning of the engine.
Rudolf

[Alan Cun]

Hello All, The smoke I referred to is the heat rising from the rear barrel, which if everthing is correct is not a problem but just an indication that the passing breeze does not readily hit the rear cylinder. Extra oiling is not a requirement just a good quality oil to lubricate without breakdown of the lubricating qualities. Many years we talked about this problem of rear cylinder heat and the fitting of an air scoop but the Doug being so close to the ground and lack of room not really an option. I dont have a problem with the rear heating because with nearly 3000 miles since the last rebuild, the compression is still OK and it still has a top speed of around 70 mph with the mods I have done to the engine. I have fitted 70mm pistons from a Kawasaki 1100cc many years back the compression height was too high so it was necessary for 1/8 spacers under the barrels. This made it difficult for the intake manifold but have got it fitting. I discarded the piston rod  pin bushes and fitted piston pins with a tight fit into small end steel on steel. The pistons were then reamed out to a free fit for the new piston pins and fitted with Doug style bronze end pads. The Cylinders were bored on the lathe and polished to the desired effect and a little more clearance on the rear cylinder. The carby is standard B & B and the rear view mirror prevents the use of the air lever so it is just a matter of flood and kick. The magy is a BTH from a flat twin Army pump motor and is fixed timed at 40 degrees advance. The flywheel has about 1 and 1/2 inches reduced from the diameter. Out of all my bikes this is my preference to ride and like all Dougs with short suspension travel and its effect on rough roads, otherwise an enjoyable mount.   more later, regards Al

[Ian]

Interesting discussion - there seem to be two schools of thought about which cylinder runs hotter

1. The rear runs hotter due to the lack of air flow

2. The front runs hotter due to lack of oil.

I must admit that both my bikes run hotter on the front cylinder than the rear. In fact on the OC if it ever fouls a plug it is on the rear cylinder. The rear cylinder does get a lot more splash oil.

With regard to petrol, one of the issues apparently is the density of the modern fuels rather than the octane rating. I have been told by many people that the one not to use on an old bike is Shell Optimax as it is designed to suit modern engines. I sway between using premium and regular unleaded with additives. None of my machines of various makes seem to run any better on premium - in fact most of them seem to run cooler on regular !! I think the real trick is to change your ignition timing to suit whatever fuel you use. With the modern premium you should be able to advance more than the factory settings - none of the fuel used on these when they were new was high octane !!