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Old 03-19-2011, 06:26 AM   #1
Bill Harris OP
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Dual plugging the /5

Years ago when leaded Premium gas became scarce I did the "low test base gasket" modification to my /5. Took a slight performance hit, but didn't regret it since I am able to run even swampwater unleaded regular without pinging. Before that I had "upgraded" to the -010 advance unit with the slower advance curve.

Fast forward to the 21st Century. In a couple of months I'm planning to do a complete valve and ring job on the motor. At this time I will have the heads tapped for dual plugs so that I can go back to the "normal base gasket" with a CR of 9.6:1. This is about the only "free lunch" performance mod you can do and is my last blast bike hopup. :)

I have everything planned out, but have one question about the ignition setup. Currently the bike has newish stock BMW coils, stock points with a Dyna Booster and that slow ignition advance unit. The usual dual plug ignition nowadays uses a pair of Dyna dual-output coils. Not being a tightwad, but I'd like to not replace the new Bosch coils with new Dyna coils. There is nothing magic about dual output coils, except for having two outputs. What I am thinking of is using the stock coils, and modifying spark plug wires to have two wires per side. A nice soldered splice insulated with heatshrink tubing would be as reliable as you can get.

Do you see any problems with this? Eventually I may try a Boyer electronic ignition with the programmable advance curve, but for now I'm wanting to minimize that cost since I have other repairs to do on the bike.
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Old 03-19-2011, 06:43 AM   #2
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Years ago I saw an R100/7 that had been modified in exactly that manner.

I'd be thinking the result would be two slightly less energetic sparks instead of one fat healthy spark.

The owner of the bike said it ran just fine.

"The proof's in the pudding", I guess.

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Old 03-19-2011, 06:55 AM   #3
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To be really cheap therewillbe lots of dual output japense cols coils out there that you could pick up for a song.

Remember to set the timing at around 28/29 degrees on full advance.
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Old 03-19-2011, 08:01 AM   #4
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My /5 is dual plugged with Dyna coils, ignition booster and retains the original points set up. I've never felt a need for an electronic ignition on my bike. It runs to good to fiddle with it!

Splicing the spark plug wires makes me leery. I'd do it right the first time and be done with it.
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Old 03-19-2011, 11:26 AM   #5
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This is a common R650/5 problem. Dual plugging will only hide the problem, but not fix it. I cheaper fix is to go to the thicker cylinder base gaskets and de-carbon the tops of the pistons and the combustion chamber. As well find an advance mechanism from a 77-78 /7.

Here's the thinking here.
De-carboning the the pistons & comb. chamber will increase your chamber volume and lowering your compression as well as the thicker base gaskets. The /7 advance mech starts to advance at 1800 RPM compared to the /5 that starts at 1200 RPM, this will help with low end detonation.
Lastly- Ride the piss out of the thing. Do not ride around town in 3rd or 4th gear and every couple of fill ups and a bit of Chevron's Techrolin
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Old 03-19-2011, 11:48 AM   #6
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First off, if you have the slightest ring ridge in your bore and you probably do, removing your base gasket is going to hammer your compression ring against the ring ridge. Are you following me?

You'll need dyna coils. Lot's of stuff will work long enough to get you to a rally but you got get back home too?

I don't know from experience but dual plugging might let you go back to the original advance. Run as close to stock advance as you can at idle and just above and then retard the full advance to around 28 degrees via welding the slots up in the advance a bit and testing/filing it.
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Old 03-19-2011, 12:53 PM   #7
Bill Harris OP
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Great info, 'Shaft and 'Euro.

The -010 advance (which I'm thinking is a /6 part, but may be a /7-- I did that mod in 1977-ish) and low test base gaskets were indeed done to correct that chronic R60/5 pinging as well as in preparation for phasing out leaded Premium (in the first post y'all got the short version of "why"). This has worked flawlessly for some 30 years-- no pinging and I am able to run any brand of gas without problems. Back when, I carefully timed a series of 3000-5000rpm WOT runs and found that I lost a bit less than one second from the low-test gaskets, which I considered a slight performance hit and acceptable.

But, this top end work is a long postponed project-- valves and guides are high-mileage and the rings are about maxed out (I did a pulled stud repair a couple of years ago and whilst they were off did a de-coke and general inspection and assessment of the top end). Thie will be THE time to have the heads done for dual-plug, and with a hone/rings/pistons(?) this will be THE time to think about use/not the low test base gasket.

So in a way it's now or never, I'm not going to pull it apart again to do the modifications next year. And, honestly, I'm still on the fence about dual-plugging.

I've had good results from Points and Dyna Booster, but "I've heard" that the programmable Boyer kit is that way to go. I suspect that this may be a case of someone crowiing about My Latest Farkel ;) . The important thing is to slow up the advance curve from Lug to 3000rpm and limit the total advance.

I'll go with Dyna Coils then. It's just money...

Gotta go do yard work and then RIDE. Let's talk stock R60/5 camshafts later.
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Old 03-19-2011, 03:42 PM   #8
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Another solution for pinging is to remove all the sharp edges in the combustion chamber. The idea is that sharp edges radiate energy which ignites the mixture, rather than the spark plug. So smooth every sharp edge on the piston and head - like the spark plug hole, valve pockets on the piston, etc.

I've done this to a few of my bikes - one of them the 90/6 with the 9:1 compression. I run it on regular and it never pings.

I've heard that doing this to diesels eliminates the characteristic knocking they make.
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Old 03-19-2011, 06:01 PM   #9
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I'll play the "I have a degree in electrical engineering that I rarely use" card here. By splitting the single output into 2 outputs you halve the effective resistance of the sparkplug lead, plug and cap. The result is that while the voltage and current would remain the same resulting in an increase in the wattage the coil is delivering there is a possibility that the current being delivered at high RPM will be diminished if the coil cannot charge fast enough.

I would imagine that its also possible to do some damage to the coil given the increased discharge rate from the extra load on it.

I'm not familiar with these setups but inductors are inductors for the same Henry value, why would you need to replace both?
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Old 03-19-2011, 07:13 PM   #10
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It's unlikely to damage the coils, once an arc forms they are driving into a short circuit anyway. So halving the open circuit impedance won't matter at all.

A weaker spark at best and a high chance that only one of your plugs will actually be firing at any time.

It's also unlikely you can splice the HT leads well enough to not have them break down when they get wet.

Do it properly if you are going to do it at all ;)

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Old 03-19-2011, 07:27 PM   #11
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You don't go to short circuit current once the coil fires in most cases, the resistor in the HT lead cap is constant (plus the plug if its a resistor plug). The HT lead has negligible resistance in series with the cap.
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Old 03-19-2011, 08:36 PM   #12
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Let me email Rick @ motorrad... and see what he thinks-- he knows Dyna as well as /5's. Seems that two 1.5ohm coils in series will be needed (for 3 ohms total).

I had some references on the internal makeup of dual-output coils, but I can't find it now. I seem to remember that a couple of arrangements-- one has the outputs at each end of the coil windings, the other has similar outputs, but with a center-tapped ground, I'm not sure, it's been a while and technology has changed quite a bit.

Anyways, here is my esoteric question on camshafts:

The R60/5 has an unusual cam timing that doesn't seem to fit what is "expected":

IO: 40* After TDC
IC: 40* After BDC
EO: 40* Before BDC
EC: 40* Before TDC

Yep, intake opens after TDC, for 180* duration.

OTOH, the R75/5 has somewhat more "conventional" cam timing:

IO: 10* Before TDC
IC: 50* After BDC
EO: 50* Before BDC
EC: 10* Before TDC

The bike has run flawlessly for 180K, but I'm wondering about this oddball camshaft and wonder what another cam (such as an R75/5) would do?

This is something I've puzzled over for decades now. Come to think about it, this might also be THE time to think camshafts.

Arrrgh, "this project is snowballing".


PS-- cam timings for the R60/6 (and other models) are at Duane's website:

http://w6rec.com/duane/bmw/engine.htm
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Old 03-20-2011, 02:37 AM   #13
Boxer Metal
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Quote:
Originally Posted by supershaft View Post
First off, if you have the slightest ring ridge in your bore and you probably do, removing your base gasket is going to hammer your compression ring against the ring ridge. Are you following me?

You'll need dyna coils. Lot's of stuff will work long enough to get you to a rally but you got get back home too?

I don't know from experience but dual plugging might let you go back to the original advance. Run as close to stock advance as you can at idle and just above and then retard the full advance to around 28 degrees via welding the slots up in the advance a bit and testing/filing it.
Sorry Supershaft but dual plugging is a bandage. All your doing as allowing the problem to get worse. Re-read my first post.
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Old 03-20-2011, 03:11 AM   #14
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Quote:
Originally Posted by airheadpenguin View Post
You don't go to short circuit current once the coil fires in most cases, the resistor in the HT lead cap is constant (plus the plug if its a resistor plug). The HT lead has negligible resistance in series with the cap.
Cap resistor is 1k. Arc is ~0 ohms once it forms, coil is 12-13k. Plug resistor is also ~1k .

So the change in impedance at the coil is < 10%, not enough to damage it unless it's marginal. Normal battery voltage variation will cause more problems than that.

But - only one of those plugs will fire in most cases - which is the biggy.

Pete
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Old 03-20-2011, 04:49 AM   #15
StephenB
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This thread comes quite handy: I am in the process of building a 600cc engine from parts myself. I have sourced most of them but since I have not been in an engine that deep before (done everything EXCEPT crankshaft and camshaft installation), I am unsure what kind of cam I have:





It is marked with

247 - which is most likely the model (247 for /5/6/7 etc, 248 for R45/R65, etc)
155 - near the points cam, most likely the casting number
1 250 249 - near the points cam, opposite to the #155

I don't have the means of dialing it out so I have to rely on visuals. From the above, can somebody tell whether this is a 600cc or 750cc camshaft?

Thanks,Stephen


Quote:
Originally Posted by Bill Harris View Post
The R60/5 has an unusual cam timing that doesn't seem to fit what is "expected":

IO: 40* After TDC
IC: 40* After BDC
EO: 40* Before BDC
EC: 40* Before TDC

Yep, intake opens after TDC, for 180* duration.

OTOH, the R75/5 has somewhat more "conventional" cam timing:

IO: 10* Before TDC
IC: 50* After BDC
EO: 50* Before BDC
EC: 10* Before TDC
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