Twin plug single plug heads?

[DrAlf]

Is it possible to convert single spark heads to twin spark? If so, who should I be talking to? Scriminger used to be the place to use but it looks like they have may closed down? Anyone got any experience or info? For reference, a mate has offered me some breathed on single spark heads but my bike is a twin spark.

Ta……

 

[Nin]

Just a straight swap I think ? Flog your singles, buy some twins.

(Later) Ah, a bit slow. I see your point now. Probably easier to breathe on your own heads? Then you can replace the exhaust studs, which means you don't have to hacksaw off your tele lever .... Doh!


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[(RIP) trickytree]

Cylinderhead Shop do twin plugging......or rework your twin spark heads.

 

[Roger 04 RT]

You'll need a new Motronic and new wiring.

 

[DrAlf]

Just a straight swap I think ? Flog your singles, buy some twins.

(Later) Ah, a bit slow. I see your point now. Probably easier to breathe on your own heads? Then you can replace the exhaust studs, which means you don't have to hacksaw off your tele lever .... Doh!


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Too late - I've chopped the telelever bolt and the telelever is off. I've now got a new problem - there's two different sorts of telelever bolts - My heads have already been worked on but these ones are better - better work and bigger valves.

Cylinderhead Shop do twin plugging......or rework your twin spark heads.

Thanks for the info, I mailed them yesterday.

You'll need a new Motronic and new wiring.

Thanks Roger - I'm going the other day though. I've got a twinspark bike and I'd like to fit some single spark heads but convert them to be twin spark. If that makes sense

 

[Flipfly]

Sorry Dr Alf but you'll have to explain that one.

You have a twin spark, but want to fit single spark heads to then twin spark them.......Why?

Is there some performance advantage?

 

[DrAlf]

There's not normally an advantage Flip - but I've been offered a pair of single spark heads at a bargain price that have had a load of work done to them - bigger valves and gas flowed. The exhaust studs on my heads are fubar so it might make both financial and performance sense to swap - if I can convert the single spark heads to twin spark as my bike is 2003 hence twin spark. Hopefully that makes sense?!

 

[Nin]

I think I read somewhere that you can run single spark heads on a twin spark bike using the secondary HT leads.


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[Roger 04 RT]

There's not normally an advantage Flip - but I've been offered a pair of single spark heads at a bargain price that have had a load of work done to them - bigger valves and gas flowed. The exhaust studs on my heads are fubar so it might make both financial and performance sense to swap - if I can convert the single spark heads to twin spark as my bike is 2003 hence twin spark. Hopefully that makes sense?!

If you can get someone to bore the head for a second plug, it may well work. There is a description of how to do it for airheads and your bike and ECU are many steps ahead of that.

Good luck with the project.

 

[Flipfly]

There's not normally an advantage Flip - but I've been offered a pair of single spark heads at a bargain price that have had a load of work done to them - bigger valves and gas flowed. The exhaust studs on my heads are fubar so it might make both financial and performance sense to swap - if I can convert the single spark heads to twin spark as my bike is 2003 hence twin spark. Hopefully that makes sense?!

Makes more sense now

 

[west coast traveller]

I think I read somewhere that you can run single spark heads on a twin spark bike using the secondary HT leads.


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I think I recall a post (either on the "John GS1100" or Adv Rider threads) about running both plugs off the primary plug circuit. If memory serves me correctly it was to do with converting coil sticks to run off standard coils. As a matter of interest, is it not possible to disconnect the secondary coil and run single coil head using the twin coil loom and Motronic as the secondary coil/plug is more to do with emissions than power? Roger and others will probably have the answer to this, but just a thought...........

 

[Ijustwanttoseethephotos]

Did you buy the heads via eBay from the Newcastle area? If so, they might be from my 1100.

 

[Steptoe]

Did you buy the heads via eBay from the Newcastle area? If so, they might be from my 1100.

1100GS or 1100S ?

If the 1100GS they'll have three stud exhaust ports and the 1150GS has two stud.

 

[Roger 04 RT]

I think I recall a post (either on the "John GS1100" or Adv Rider threads) about running both plugs off the primary plug circuit. If memory serves me correctly it was to do with converting coil sticks to run off standard coils. As a matter of interest, is it not possible to disconnect the secondary coil and run single coil head using the twin coil loom and Motronic as the secondary coil/plug is more to do with emissions than power? Roger and others will probably have the answer to this, but just a thought...........

Here's the issue and why you should have a twin-spark Motronic for a twin-spark bike, and conversely a single-spark Motronic for a single-spark bike.

The twin-spark motronic uses less advanced spark timing than the single spark Motronic. The reason is, when you fire two plugs at different points in one cylinder the mixture burns from two places. It burns faster, reaches peak pressure sooner and reaches a higher peak pressure.

So if you use only one plug on a twin-spark Motronic you will reduce maximum HP. Pilots with twin spark engines know this and the two mags are checked by shutting them off sequentially and watching for a power drop.

 

[west coast traveller]

Here's the issue and why you should have a twin-spark Motronic for a twin-spark bike, and conversely a single-spark Motronic for a single-spark bike.

The twin-spark motronic uses less advanced spark timing than the single spark Motronic. The reason is, when you fire two plugs at different points in one cylinder the mixture burns from two places. It burns faster, reaches peak pressure sooner and reaches a higher peak pressure.

So if you use only one plug on a twin-spark Motronic you will reduce maximum HP. Pilots with twin spark engines know this and the two mags are checked by shutting them off sequentially and watching for a power drop.

Thanks for the explanation. So the post referred to wouldn't work, or would but with resultant reduction in power.

 

[Ijustwanttoseethephotos]

1100GS or 1100S ?

If the 1100GS they'll have three stud exhaust ports and the 1150GS has two stud.

1100GS, three stud.

 

[Ijustwanttoseethephotos]

Update: I've checked a photo and they were 2-stud heads, I remembered that made a one-off exhaust system as well.
They were single spark with larger inlet valves.

 

[DrAlf]

Update: I've checked a photo and they were 2-stud heads, I remembered that made a one-off exhaust system as well.
They were single spark with larger inlet valves.

That's them. It would be good to talk - I'd love to know the history.

 

[Ijustwanttoseethephotos]

Brief history: I bought a R1150GS single spark as a project, 100% standard. A spare pair of heads were fitted with larger inlet valves, (I think the seats were left as standard), and the ports were cleaned up.
The bike was dynoed as standard, then again with the heads fitted and the fuelling optimised with a power commander.
From memory it gave about 10-12% gain in the mid-range, (the most useful area on the road), and about 8% at the top-end. This was with a standard exhaust system.
Interestingly, a K&N filter was then fitted with no discernable difference. According to the advertising, there should have been a massive increase in power!
The 1150 was sold and I fitted the heads to my R1100GS. This engine was already modified, squish, carbs, mappable ignition, exhaust, etc. Motorworks leant me a pair of R1200 camshafts and the bike was transformed!
It revved like there was no tomorrow, the engine would be well past the redline and still accelerating strongly.
I realised that it was not going to last long so I removed the heads and a mate had them.
After that I discovered K100s and turbos but that's a different story!

 

[DrAlf]

Interesting update – thanks a lot. Do you know how many miles the heads had on them? Were they originally R1100S heads or are they modified R1150GS heads? What R1200 did the cams come from and are they likely to be still fitted – R1200S? R1200GS? Last question – who did the head work?

I’ll put them to good use