Personally, I hope I never see any of those!!

On a slightly less anatomical note, I recently posted a very similar question on my Ural owners forum, as I had read that dual-plugging on these venerable B;W analogues could be helpful for torque, power, starting, smoothness and fuel economy (by goodness, Urals need all the help they can get).

The only firm advocate was a guy who was also a pilot and drew parallels with the extensive use of D/Ping in aircraft engines. Personally, I can't see how it would nopt be beneficial once set-up properly. Perhaps one difference is that in the Ural, the two plugs are both located in the cylinder head in opposite positions and I seem to recall that with some BMs the second plug was not a mirror image of the first but in a slightly different position meaning you would need to get the spark just right so the flame fronts work together rather than against.

However, I may be wrong on this count: it is a vague recollection and therefore even more prone to inaccuracy!!

Dual plugging has its advantages, and disadvantages...

What would have a potent effect on the Ural 750cc are two other things to beging with:
- larger inlet valves
- higher compression ratio
...or/and put some more cc there... -;)

Dual plugging will aid to get a bit more of of the energy in the petrol, and with gas prices as the once we have today even a small improvement makes quite a difference in the wallet in the longer run.

Do not spend hundres of pounds ripping the engine apart to save a few pennies on petrol! Plan modifications to be done at the normal major overhaul intervalls, or if the engine needed to be opened by some other reason (leaking pushrod tube e.g.) - then the extra costs are quite moderate -:)

Ural have small bore and low compression so I wouldn’t bothered to dual-plug it unless it is heavy modified.
I believe all 750s have the Ducati-ignition and it’s impossible to alter the ignition-curve without changing the black-box.

Doesn't Ural have "stock" ca 82mm BMW barrels?
BMW 800 have ca 84mm.
BMW 1000 have ca 94mm.
ca 71mm stroke.
Compression ratio varies on BMW from 8.2-9.5 with the exception of the Egyptian Police special edition which -I guess- had about 7.0:1.

If so - he should expect just about what I got on my 800cc, right?

Doesn't Ural have the old BMW brakerpoint system?
Altering such a system is very well described in Oak Okleshen article 13 pages "Dual Spark Plug Ignition, Part 1" (last revised in 2002 as far as I know):
Airheads Beemer Club - Oak's Tech Articles
First published by BMW Owners of America “BMW News” November 1980.
Then there are:
Tom Cutter's article Tom Cutter's book on Dual-Plugging Airheads- Available now! - - Airhead Tech Archive - - Airtech BMW Archives - The Airhead Museum - Message Board - Yuku
http://www.nwlink.com/~paulcl/at/tc/pointsplate.gif
and
Scot Marburger Airheads Beemer Club - Dual Plugging The R100GS

There are -very- few ho have tested dual-plugging on airheads on less cc than 1000cc... and even fewer who have tested it on the old 750cc and 600cc... less one have personal experience of the dual-plugging on less than 1000cc one should avoid repeating opinions on wether or not these will benefit from dual plugging. I know for a personal fact that my 800cc, with 8.2:1 => 9.2:1 => 10.3:1 did benefit very well; and then 750cc with 9.0:1 should be expected to do it too -;)
Wether or not the old 750cc that Ural users also does it... I do not know, and since I have no engine data on them I can not make an informed guess either - but what I can say is that I would expect it to have -an- effect and -am- looking forward to hear from someone who have tested dual-plugging the Ural engine -:)

A very good point though is that if the compression ratio is too low... I guess dual plugging may cause more headache...

As for the part of where to place the plug... well, it will not work -against- the original plug, but it may aid it well or less well. As for the beemer heads... there is one (1) possible position for the second plug... the tricky part is not the position, but the making of the plug hole and threads. Look at Scots pics - then you see what I try to say.

It has 78 mm bore (square engine).

The Ural has 8.6:1 and a smaller bore then your R80 so I would think less effect then you got. There will be some effect, but as long as the bore is small and compression is low I wouldn’t expected much.
Personally I think a boost in compression and some tweaking of the heads will be better. It’s fun to drive a tuned Ural and the engine is smooth.


Ignition is full-electronic, not like BMW. It’s a nice system (Ducati) but it’s impossible to alter the ignition-curve.


But I agree that no-one can tell for sure unless they have tested it and it would have been fun if someone did! :thumbup1:

Spending pennies again - Next two improvements to come along on the bike will be carried out soon. Having already ran an endurolast 450 charging system I have bought an electronic ignition system with a selectable ignition curve for both single and twin plugged bikes - bit like silent hectic stuff but cheaper and works with the enduralast alternator. I have also bought a siebenrock sb2s exhaust sytem. I was going to fit a assymetric cam but siebenrock state this wont work as it was designed for the r100gs would need r100gs carbs and ideally cylinder head so thats a no go. (mine is an r80gs with siebenrock 1000 conversion) will update once i get into the garage and get it all done.

I haven't tested the asymmetric cam but I use a 296° cam (with the same Siebenrock-kit as you, standard carbs and slightly modified heads). The 296° cam gives a lot of torque at low RPMs and a bit less at high rpm (above 5500RPM).
This setup works rather nice!

Thanks for that ali I may pull he bottom end down later this year as it needs a new cam chain and a few seals are weeping a bit - so will maybe fit the 296 cam while I am on. have had to scrap the HPN frame idea it was booked in this month, but change of circumstances and the high Pound/euro rate make it too expensive at the moment. Tchus Jake.

Food for thought: Other models using dual spark are the latest 1150 boxers, the 2 valve Ducati 1000, the F650 GS single, the 1200 boxer and even my trusty DR650 has 2 spark plugs. I'm curious, doesn't pinging happen due to pre-ignition, before the spark plug fires? Are we talking about the same thing?

Yes we are talking about the same thing, you might wonder how twinplugging affects pre-ignition when pre-ignition happens before the spark?

There are mainly three things that leads to pre-ignition: Octane-rating, compression and heat in the combustion chamber.
If you run the highest octane-rating you reduce pre-ignition but high octane petrol is not always available and it might be expensive. You might lower the compression to decrease pre-ignition but you will reduce mileage and power.

Heat in the combustion-chamber is a bit more difficult. There are a lot of factors that makes it hot (or makes hot spots). This might be sharp edges, carbon-buildup, a hot plug, timing, mixture etc but we will focus on dual-plugging.

When the plug ignites the petrol the flame has to travel to all ends of the combustion-chamber. The bigger the bore is the longer the flame has to go. When the flame has to travel far the combustion will go slower and the temperature increases (which might lead to pre-ignition).
So basically big bore increases the chance of pre-ignition.

A DR650 has bigger bore then the R100. The new BMW S1000RR sportsbike has smaller bore then the R80.


If we look at the picture Adventure950 posted we will see that the original plughole (right) is not in the center of the head. The distance the flame has to travel is pretty "large". If we put in another plug (left) and fire both plugs at the same time the distance is reduced dramatically and the mixture will burn faster and cooler. This reduces pre-ignition.

http://www.horizonsunlimited.com/hub...w-p1010007.jpg



Because of the faster burn you should fire the plugs a bit later (esp on lower revs).
This is done in numerous ways and I think this is one of the reasons why people have different experiences with dual-plugging.
Timing is very important and if you fail you will not gain the improvements twin-plugging gives you. A lot of people bolt on their new parts twist the beancan a bit and ride, that's like buying a set of expensive running-shoes without tying the laces.

The faster burn will also lead to higher efficiency (esp on lower revs) and therefore reduced petrol consumption. It also reduces the levels of unburnt carbon and reduces the CO emissions at low rpm.
You can also run a twin-plugged engine leaner.

A given engine will normally have the best performance right before pre-ignition starts. That's why newer BMWs have a system that senses pre-ignition and it alters ignition (and mixture?)
to stay as close to pre-ignition as possible.

Thats a great explanation, thanx :thumbup1:. I never thought about the heat factor which puts everything into perspective.

Brilliant explanation AliBaba.

My wife has noticed a gas smell behind my R100 (especially when riding in countries on the left like the U.K. so that the exhaust pipe is pointed almost directly at her). I've leaned out the mixture as much as possible, just short of having it buck on low throttle and she still gets a whif every now and again. Perhaps twin plugging and then leaning out the mixture even more will reduce this smell. The trickiest part is exactly what you mention with getting the timing right.

I found as I mentioned earlier that I needed to change the heat range of the plugs as well as retarding the ignition 3 degrees the bike seems to run very well- this is still using the bean can - I am about to change this for an endurolast ignition with digital ignition curve (fits the enduralast charging system I have already fitted) - for twin plugged heads so should get a better response again. I have also decided to also stick in a 296 cam for more torque as well as a purpose built siebenrock sgs 2 exhaust system built for the set up I have (siebenrock 1000 upgrade with 80 gs carbs and lightly modified heads) so hopefully all these mods together should get my bike running as well as it possible can without going the 1070 cc route.
Its been a long time getting to this point a bit at a time but I decided to splash out this year on quite a bit of engine and gearbox work - as i am not travelling this year at all.

Just an update have put on the siebenrock sgs2 exhaust, really wonderful bit of kit, fits better than the original, no front balance pipe so each side can be removed independently most of the joints are tension spring connections so allow a bit of movement and the Y piece is in 4 pieces allowing it to fit and move enough to be easy to centre up and remove. there are no gaskets or stuff either. It sounds very deep but not noisy, torque delivery is very smooth top gear easy pulls cleanly fron 1500 revs straight through and will ride smoothly at these low revs in top gear, Pick up right through is cleaner and more positive - no huge jumps in power but noticable changes. Also weighs 5 kg lighter than standard system. Electronic ( euromotoelectrics) ignition system and 296 cam also lower first and higher top gear will be done in the next few weeks. :thumbup1:

ADV950 - Nice to see some feed back on the SGS2 exhaust. What style did you get - low, mid or high? I'm wondering about clearance to luggage etc. Look forward to hearing about your other modifications also.

I'm wondering about the benefit of dual plugging when travelling - i.e coping with bad or low octane fuel. Can anyone relate any experience to this?

I'm thinking about upping the compression on our US spec GS and dual plugging to suit, but my instinct is to leave it stock for a big overland trip.

Igor