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I do remember going over the timing and advance issues with him over coffee in the cafeteria. Fact is, if the burn is incomplete, you are wasting gas...less power...less MPGs. And when you have a large diameter piston coupled with certain shaped combustion chambers, you will probably not get a complete burn. So you have two spark plugs to initiate two flame fronts. That speeds up the combustion process which is why you need to alter the idle timing and advance. Ever wonder why the RPM decreases by about 150 RPM in a piston engined aircraft when you switch the magnetos from BOTH to L or R during your pre-takeoff checks? |
IMHO the discussion shows again that this is a "nice to have" but not necessary in absolute terms.
The Dakar HPN Beemers in the '80s were not dual-plugged, had a higher compression and more cc (1040) compared to the standard Beemers and still performed excellent. IMO the main advantage is that the engine definitely runs smoother, resulting in longer engine life, less vibs - esp. at lower revs. I found the change in fuel consumption to be negligible. Power gain ????? Maybe, but from nominal 50 hp to maybe 52 - also negligible..... |
I think there are multiple reasons why people have various experiences with dual plugging. The technical differences can be:
When people change to dual-plugging they often change some of the other factors, maybe they “only” overhaul the carbs which often gives great improvement. Maybe some modifications where done to the bike prior to the rebuild, maybe the cleaning of the tops alone has changed the way the bike worked. It’s true that the old Paris Dakar bikes didn’t use dual plugging; the compression for some of the years was like this: 1980 9.3:1, 798cc, 55hp, HPN 1985 8.5:1, 980cc, 70hp, HPN 1987 9.0:1. 1050, 85hp, HPN But what type of petrol did they use? What other modifications were done to the engine? Today HPN recommends the use of dual-plugging, at least with high compression engines, but dual plugging is only one of the factors which are changed. These engines also have different camshafts, different pistons, rebuild heads and a completely different ignition-system and a few other changes. Personally I believe in dual-plugging, but I think that if you want a good result you have to change a lot of other factors. So I haven’t done it and there are a lot of things I would like to change with my engine before I do, it will probably never happen. |
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When looking at physics it is quite clear that there will be about a 40% faster burning, and hence slightly more efficient burning of the mixture. The slightly more efficient burning is what has been attributed to as the major factor of the better mileage - but I see no published testes confirming this statement. As for timing, it should be adjusted accordingly to the faster burn; 6' at idle should thus be set at 4' which would equate about 4mm on the flywheel if I recall correctly. Al "gurus" claim that timing is best at OT, which is about 12mm from the flywheels idle adjustment point. However, with a 32' max advance (is that figure correct? I have not been able to find it in any BMW litterature) a 40% change of the advance should result in about 19'; a difference of 13' and each degree is about 1.78mm which is about 23mm... To reset the timing with 23mm at idle is not possible... So... this pre-ignition by about 13' is probably what has caused the "overheating" of my engine since 1992 uptill this summer 2008 when I blocked the flyweights to about 19'. I have reset the idel to about 1' less, and that seems to be the best position on this very engine. There is one interesting thing that I have come across and that is that most (all?) that claim OT to be ok are riding brakerpointed engines... a friend of mine uses Boyer Bransden replacement kit for brakerpoints and claims that that is working perfectly. What about the 1981 and on engines ? Mine are not working well at all with the OT setting - but run well with the flyweight stops... any idea as to this difference ? Silent Hektik and Omega Ignitions would probably present the needed timing curves to get the dual plugging perfect. There are so many claims - and so scarse hard data; what are we to believe ? One indisputabel fact is that the 1200CC's have dual-plugging due to the hard California emission regulations - and those of us using dual-plugged 2-valves probably have the same comment on how the exhaust fumes smells with and without the second plug operating ? :scooter: |
I had my 83 R100RT dual plugged by Ray Peake (RJ's) in Australia. He has done many of these conversions on old boxers over here. I think it has definately helped with starting the bike, and stopped a lot of the pinging that I got when they stopped selling leaded petrol over here. I used to get around 320-350 a tank (24,litres) I now get 350-390, even up to 400 depending on the speed I ride at. It did not cost me a lot to get it done, ( I had to get the heads done anyway) so it was an easy choice for me, just do it! I definately think the old boxers benefit from it if the person who dose the conversion knows what they are doing.
Rob... |
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As my r80gs (60000 miles) is now used mainly for two up travelling I decided last year to upgrade to 1000cc for the extra torque and so fitted a siebenrock kit, the bike was fine but did pink a hell of a lot, I overhauled the carbs which helped as they were in need of a good pull through but the pinking remained a problem. In january I decided to rebuild the heads with new valves springs guides etc, while it was all apart i took the descision to twin plug the heads. I decided to get the second plug hole to be the same size as the standard fitment so this involved building up the outer face of the head where it was to be drilled with weld - to give enough depth (18mm) for the new plug. Holes were drilled, flame front cut into the plug seats on the inside of the head this guides the flame into the crown of the head for better burning,Guides were relined and Valve seats were reprofiled and cut to 45 degree inlet, 30 degree exhaust also the Tulip in the inlet port behind the valve head was cut back taking the step out of it where the valve stem comes through both the inlet and exhaust ports were lightly reshaped to improve flow. when I put it back together and after setting up the bike it runs excellent, Carbs were set with mixture screw 5/8ths turn out, timing retarded 3 degrees. There is no hint of pinking a notable increase in torque in the low to mid range and excellent acceleration and pick up. I have not done the fuel comparison for mileage yet as I need to do a few miles yet.
The Photo shows the head with the flame fronts cut into the spark plug holes, I cannot however get my other photos below 49kb to fit the limits on the site attachment manager. They show close ups of the cuttings and inlet tract work. |
Great thread
Thanks for the update Jake, let us know how it works out with the fuel economy when you've got some distance on it. Did you want to e-mail me the pictures and I'll see if I can upload them? I just use Flickr and haven't had a problem uploading.
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Ekke, ta for the ofer I have sent you three photos that I can not get to size thanks.
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Jake's Photos
Here are Jake's photos of the dual plugging on his R80GS (With Siebenrock kit)
http://farm4.static.flickr.com/3359/...0225194b_o.jpg http://farm4.static.flickr.com/3603/...b05d204c_o.jpg http://farm4.static.flickr.com/3352/...fc21aef8_o.jpg Jake, maybe you can comment on what each photo represents? Thanks! |
Ta Ekke, I did not take two many photos however the 1st in Ekkes comment above shows a close up of the new plug hole with a hollowed out area that acts as a flame front to guide the burn of fuel towards the crown of the head maximising the efficiency of the combustion. The second shows both plug holes and bits of the valve heads and the last very hard to get with my camera - shows (badly lit) the tulip in the inlet tract where the valve stem comes through, previously this had a step around the base of the valve stem this was cut away to aid efficient flow the tract was further lightly flowed to take away cutting/ moulding edges and finished with a brushed finish to aid turbulance to mix the fuel/air. I did not get any other photos of note. Having just done 300 mile run this weekend the bike is very torquey and pulls extremely well from low revs and has a notable improvement of mid range power between 2300 to 4000 revs much better pick up on acceleration everywhere more so in the roll on speeds in top gear where before a change of gear was often a safe bet its no longer required.
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Has anyone read this?
I found this a couple of days ago, and found it interesting.
Published in 1994 I think, so cost figures are likely a bit out by now. I'd be very interested to hear what others think of this. The changes to MPG and power they got seem significant. Get More Punch out of your boxer - ADVrider |
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Luftmeister = ? California BMW Triumph Motorcycles: Motorcycle Parts, Accessories, BMW Apparel, KTM Parts ? Vanished in 1995. Motorworks - BMW Motorcycle Spares - home will make dual plugged heads for you. Moto-bins - BMW Spare Parts and Accessories for Motorcycles - Index I think they will do dual plugged heads as well. Siebenrock - BMW Motorräder & Teile ...alles ab /5 makes them. hpn makes them. www.israel-motoren.de makes them - this is the only remaining tuner company since CC and Luftmeister was swallowed up back in the 90-ties. Just to name a few known companies. Please read this as well: Svenska BMW MC Klubben • Visa trÃ¥d - Trasiga ITU - Tändimpulsgivare /7 1981-1995 http://www.horizonsunlimited.com/hub...oken-itu-41532 Daniel Dicke: Doppelzündung I strongly disagree with the CC concept using SuperTrapp mufflers/silencers. The s/s mufflers made in Australia is far better choice. The s/s megaphone are really nice. Parts sold in Sweden by www.midland.se You will get more effect at once by just swapping Bings for dell'orto PHM or Mikuni Flat slide or equivallent Keihan. I am playing with the idea to get a carburetor rack from a 1100-1300cc japanese bike = 4 carbs at rather good prices. The max power will hardly be affected. I fair guess is 1-3% based on the difference between the R80 and R100 air-intake (I have a dyna test showing the difference on one of my engines). What you will get is the power when you want it and mileage will drop more than dual plugging - however... if you combine dualplugging and throttle carbs you should be able to expect about 10% (or even slightly better) mileage improvement -:) Down-sides: - the old articles you have read and found on the net are based on one original article from late 1970-ties... braker-point engines... It took me over 15 years to understand and accept that these articles are -not- applicable to the 1981-on semi-electronic ignition but applicable the the brakerpoint aftermarket conversion supplied by Boyer Bransden Electronics Ltd ... i.e. we're ... we who have the semi-electronic ITU... if it wasn't for Daniel Derdick and his site -:) Options available: - dual parallell ICU; like Derdicke presents. I prefer that. - single special ICU from Kallenbach Electronic; Q-Tech Homepage For the last two years I have been hestiating whether or not to dual plug yet a R100 I have. Since I managed to get my R80/100 back rolling with dual plugging since I repaired my ITU this fall - I will dual plug this bike as well! The costs: - the drilling of the 2nd sparkplug hole. - modification of the ITU. - parallell wires/cables for 2nd ICU - new plugs - new gaskets and sealings for the barrels and heads To do at the same time, main things e.g.: - check valves, guides and seats - check pistonrings - check conrod bearings - camfollowers and cam for pitting If you do the jobs that does not require machining yourself the cost should stop under 450-500 GBP (2009/2010). |
I think the main issue is to get the timing right and I think it’s nearly impossible to do this without placing the hall unit in a motor-driven jig and modify it to get a proper ignition-curve.
When (you think) the ignition is correct and your carbs are overhauled you can start to worry about jetting, exhaust etc. IMHO twinplugging is not necessary for all airheads. It depends on a lot of factors. I’ve a bike with 80 Nm torque at 3500RPM and the mileage is typical 17.2 km/liter. It’s not twinplugged. But I will start to build another engine shortly and it will be twinplugged. |
After running the bike for quite some time now on the twin plugged heads, I had a few problems with the soot build up on the plugs and some blistering it was also not so great on the fuel. I have after trying different settings come up with the following settings and found the bike has now ran perfect for many months of use. It appears to run far smoother throughout the rev range, slight improvement in fuel usage, better spread of low down torque and sharper acceleration. None of the improvements are going to pull your arms out of the sockets but when put together make the bike feel and run far better than it ever did before in any configuration and I would be as bold to say probably as well if not better than almost all the airheads I have owned in the last 30 years. It is also very easy to kick start even from very cold conditions with snow etc.
I Have changed the plugs to a BPR7ES so upped the heat range - this makes sense as the ignition is retarded - two plugs doing the spark more fuel burning the burn quicker and I suppose hotter ? - and the heat as a result was affecting the standard plugs which could not dissapate the heat quick enough - this single change made a big improvement to the running, After another 2000 miles I also junked the y piece in the exhaust and re fitted the standard centre box this done I found it was easier to set the carbs and it ran better than before and I also ran them a bit leaner on the mixture screws 1st to 2nd phase in the carb operation was much smoother - still retaining excellent burn throughout the range with no excess fuelling - so saving fuel. I would say on average over differing conditions fuel has improved between 2 and 4 mpg. i think the centre box in the exhaust has made a big difference to the smooth running and low down torque, but its not possible to seperate all the component changes to see what has done what it all works together and gives an overall improvement each part doing its bit I suppose. |
I've had good luck
When I lived in Venezuela a few years ago I bought a '78 R100RS. As you know, this bike came stock with a 9.5:1 compression ratio, which normally requires high octane gasoline. After the purchase, I looked closely at the bottom of the heads and noticed it had been dual plugged but the job had not been finished. There was a broken off spark plug at the bottom of each head, indicated the heads had been machined, but the coils had not been modified, etc. I bought a set of dual tower coils and finished the job, and was immediately rewarded with a bit more oomph. I also later found out that when the PO had the heads reworked, he had neglected to replace the piston rings. Although the bike ran better with a functioning dual plug system, it really didn't run optimally until I redid the entire top end of the engine. In addition, it is critical that the timing and carbs are also properly adjusted. I've been able to run regular gasoline in this bike without issues, but I wouldn't recommend dual plugging simply to allow the use of cheaper gas.
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