Twin plug heads -what plugs?

[fayeslane]

Any suggestions for what plugs to run for the lower plugs on my new R80G/S ?

Currently fitted with Champion L10s.

Should they be the same as the top plugs? (if not, why not?)

thanks

 

[Miz]

Try here

http://www.spark-plugs.co.uk/


or here


http://www.ngkpartfinder.co.uk/motorbikes_scooters.php

 

[(RIP) Proff]

A lot of the ones with same size twin plug holes suffered from cracking across to the valve seats
So they went with a 10mm plug for bottoms...
I don't personally like twin plug heads, in fact every time I've had one, I've blanked the bottom holes off with a nice bolt [cut to exact length of course] and copper gasket.

 

[fayeslane]

A lot of the ones with same size twin plug holes suffered from cracking across to the valve seats
So they went with a 10mm plug for bottoms...
I don't personally like twin plug heads, in fact every time I've had one, I've blanked the bottom holes off with a nice bolt [cut to exact length of course] and copper gasket.

Why don't you like them Proff? Is it the potential cracking problem or other issues? Theoretically they should be a good thing

I thought they might end up on my R80 cafe racer/track bike if the provide a bit more punch.

 

[(RIP) Proff]

Why don't you like them Proff? Is it the potential cracking problem or other issues? Theoretically they should be a good thing

I thought they might end up on my R80 cafe racer/track bike if the provide a bit more punch.

They'd be better on the st
On the g/s if you go through water you can lose bottom spark, don't matter as you will not notice any difference
One thing you will find out when you ride the st, is that you get pissed all over by the crotch rockets on the straights, don't worry cos when you get to the twisty bits you will wipe the smiles right off their faces. cos st is amazingly nimble bike..
IMHO The R80s/t is the BEST handling airhead BMW ever made !!!

Now this might just be an old wives tale, but I've spoken to people who developed twin plugged airheads for airplane use....
The reason the Airhead engine was first twin plugged was for CAA reasons..
they must have two separate ignition systems in case of failure of one whilst in the air...
I believe the conversions were first done on the R75/5 engine in the USA..
Then various places in UK copied them.................

 

[(RIP) Kaister]

surely you're aware of flame front travel, incomplete combustion, emissions, etc ?

there's lots of reasons to do it

 

[(RIP) Proff]

surely you're aware of flame front travel, incomplete combustion, emissions, etc ?

there's lots of reasons to do it

Of course, also lots of reasons NOT to do it !!

Only probs I've ever had with airhead heads is [apart from stub thread strip] has been on twin plugged ones, cracks, blown threads and even center of lower plug embedding in top of piston......
IF I bought another bike that happened to be twin plugged I'd convert it back immediately,

I use Splitfire TPC6 plugs, the best plugs by far.
give a nice spark 100% of the time......

 

[Kenny]

Bike ticks over smoother..otherwise little gain for the extra expense/setting up etc

 

[Rob Farmer]

I twin plugged an 80 GS a while back. The bottom plug came from a Honda 90 or other small capacity honda.

 

[Rob Farmer]

surely you're aware of flame front travel, incomplete combustion, emissions, etc ?

there's lots of reasons to do it

I'm sure there is but the biggest problem is controlling the ignition to make the most of it. You need the ignition to have less advance at lower RPM and the maximum advance to happen at higher RPM otherwise the twin plugging actually works against you. The recomended mod is to knock back the ears on the advance retard unit to limit the maximum advance of the bean can either from 26° to 22° or from 26° to 20° (where these figure comes from and who you believe is anybodies guess) - if you have ever tried to do this you soon realise the chance of actually doing it accurately is about a million to one. Most people simply retard the standard ignition a few degrees to try and make the timing correct at the top end: obviously this isn't ideal at the bottom. Without the use of a dyno you are simply pissing in the wind and you are simply relying on suggestion that this is the way to set up your bike.

The easiest solution is to buy a bean can from a 1980 airhead (the one with the points) and fit a Boyer twin plug ignition system --> Motorworks link This will at least give you the correct ignition curve.

There's a good article here on twin plugging --> http://www.airheads.org/content/view/281/98/

I fitted a pair of microlight coils from Scriminger (SED Link) . Scrimingers do the mod for their airhead aircraft engines so know what they are doing: drop them a line, however it may be they fit them to provide redundancy in the event of an ignition failure.

To be honest after weeks of messing about the best I could get was a slightly smoother tickover and easier starting. I think the best I can say about it is it looks pretty trick and it makes people think you know what you're doing so got to worth it for those points alone

My own advice would be to keep the twin plug set up for redundancy set the ignition to standard timing marks and just ride the thing.

 

[VAL. H.]

Any suggestions for what plugs to run for the lower plugs on my new R80G/S ?

Currently fitted with Champion L10s.

Should they be the same as the top plugs? (if not, why not?)

thanks

Stick with the same or eqivelent plug. Otherwise: What they say above. I don't know enough about them to make any mechanical suggestion. Only that Jill's 100GS is twin plugged and runs great.
If I ever actualy get myself and Airhead I won't be bothering about twin plugs personaly. I think it just over complicates things that I don't know enough about.

Warning: Be very careful tightening the lower plugs. I felt that the threads were very soft and could easily strip when I changed the lower plugs before our trip to Europe.

PS: for your reacurance; Jills bike has covered over 133000 miles now and runs faultlessly.


Val.

 

[fayeslane]

Stick with the same or eqivelent plug. Otherwise: What they say above. I don't know enough about them to make any mechanical suggestion. Only that Jill's 100GS is twin plugged and runs great.
If I ever actualy get myself and Airhead I won't be bothering about twin plugs personaly. I think it just over complicates things that I don't know enough about.

Warning: Be very careful tightening the lower plugs. I felt that the threads were very soft and could easily strip when I changed the lower plugs before our trip to Europe.

PS: for your reacurance; Jills bike has covered over 133000 miles now and runs faultlessly.


Val.

Thanks Val,

I always treat plug tightening with kid gloves after having f**cked up in the past

This Motobins page sheds some light on which plugs for the bottom hole. -http://www.motobins.co.uk/displayfinal.php?q=twin plug&s=1

I agree with above comments on twin plugging, theoretically it should be a good thing but it seems in real life experiences it makes bugger all difference. The negative of extra complication is probably balanced by having a spark fail safe.

If I hadn't inherited it I wouldn't pay to get it done. Cos I've got twin plugs I'd like to have them performing as best I can.

After studying quite a few of the airhead performance modifications it seems to me the best and cheapest way to get more performance from your airhead is to buy a different bike

The best piece of airhead advice I have been given is: "just ride it and appreciate it for what it is".

 

[Beemerboff]

Bottom 10 mm plugs on my 1000 cc G/S are NGK D6HA but they look a little cold .

The PO fitted the twin plugs and just retarded the ignition 4 degrees, but that doesn't work, especially if you fit two 3 ohm resistance coils with it, as he did.

I fitted the latest Boyer Micro Power set up into an points bean can, although I could probably have fitted it to the later one as it replaces everything from the bottom bob weight plate up. Apart from the top bearing and circlip.

Boyer recommend 3-4 degrees less advance than stock at 3700, but mine works better with even less. My testing ground is a long steep hill so I am not testing peak HP, but how it pulls between 2500/5500 revs.

I bought it from Gremlin, cheaper than Bins and quite an acceptable price considering that it includes two matching coils, plug leads and caps.

It is a noticeable improvement over the old set up, but it still isnt as good as either of my single plug bikes - there is more to making a airhead go than twin plugs, and if you get the rest right you probably dont need the twin plugs.

 

[Steptoe]

Bottom plugs should be smaller. make sure they aren't too long.

If you do have the same sized plugs the bottom plug must be shorter.
If not it'll protrude slightly into the head and when you remove it the build up of carbon will damage thread as it's removed.

But i really wouldn't bother twin plugging. vastly overated mod.
It'll give you more grief than benefit.

 

[Voyager]

Bottom plugs should be smaller. make sure they aren't too long.

If you do have the same sized plugs the bottom plug must be shorter.
If not it'll protrude slightly into the head and when you remove it the build up of carbon will damage thread as it's removed.

But i really wouldn't bother twin plugging. vastly overated mod.
It'll give you more grief than benefit.

My 100GS was twin-plugged by Motobins.

The lower plugs are NGK D6HA (6512 - whatever that is).

These are 12mm plugs, screwed into threaded "Timeserts" that come loose !

I found starting a bit easier but no other advantages and I wouldn't do it again.

Bob.

 

[(RIP) Proff]

Bottom plugs should be smaller. make sure they aren't too long.

If you do have the same sized plugs the bottom plug must be shorter.
If not it'll protrude slightly into the head and when you remove it the build up of carbon will damage thread as it's removed.

But i really wouldn't bother twin plugging. vastly overrated mod.
It'll give you more grief than benefit.

Exactly my thought on twin plugging as well.
Unless its a legal necessity like in aviation, it's a lot more trouble than its worth ...

But feel free to disregard any advice you get from me, make up your own minds

 

[VAL. H.]

Unless its a legal necessity like in aviation, it's a lot more trouble than its worth ...

I suppose in a way it could have the advantage of getting you home if one of your coils goes down.

But then considering the above thoughts on the advantages (or not). If one coil did go down, would you know about it? Maybe not, until the other one goes down too?


Val.

 

[Backroader]

Message for Val.H.

Not exactly continuing the theme of the thread I know but as the previous owner of Jill's bike I am very glad to hear it's still going fine, not that I expected otherwise. You can tell I miss the old girl (bike that is).

 

[(RIP) Proff]

Update

Only reason for Twin plugging
IMHO

 

[fayeslane]

Only reason for Twin plugging
IMHO

Won't the propeller interfere with the front end?

Could have a cooling advantage in an Oz summer