Twin plug

[PW Cymru]

On twin plugged heads (R100) Is the secondary plug normally a 19 mm thread length.

I've got a pair of NGK CR8HS's fitted which according to the NGK chart is only a 12.07mm thread length. Which looks rather fouled unlike the main.

I'll measure the thread length in the morning but I suspect it should be a NGK CR8ES.

 

[Rugged Path]

Not in a position to measure anything but, I am using short reach plugs in the bottom second plug.

 

[Roger Chatterton]

I use same plugs top & bottom but bottom plug has a spacer fitted. Can't remember exactly which plug, but can easily check if you want ?
Andrew Sexton did the twin plugging originally before I bought the bike , so guess it's a kosher mod - bike goes like a rocket, so must be right ! ( Not compared it to a multistrada though ).....

 

[PW Cymru]

I think the short reach plug fitted to the lower position probably isn't reaching into the chamber far enough as its not being cleaned the same as the main plug.

As has been suggested I may need a 19 mm reach and fit a suitable spacer under the plug to set the immersion correctly.

Thanks for the responses.

 

[fayeslane]

! ( Not compared it to a multistrada though ).....

Why not Roger? They are both twin plugged

 

[pete.keys]

I use same plugs top & bottom but bottom plug has a spacer fitted. Can't remember exactly which plug, but can easily check if you want ?
Andrew Sexton did the twin plugging originally before I bought the bike , so guess it's a kosher mod - bike goes like a rocket, so must be right ! ( Not compared it to a multistrada though ).....

I've got an Andrew Sexton 1000cc and twin plug conversion too (also done before I bought the bike) with 800heads and 32mm Bings - very impressed by the performance.

Mine has tiny 10mm plugs top and bottom. Has the same plugs both sides and the spacer on the bottom plug. The bottom plug gets oily really quickly.

 

[Steptoe]

DON'T expose the bottom plug thread in the combustion chamber, nothing to do with it hitting the piston, but it gets carboned up it will tear the thread out in the head when you remove it.

I've had the joy of this happening a few times on customers bikes who'd fitted the wrong plugs.

I used to work on a racing bike used in the old classic racing which used honda C90 lower plugs.

 

[Roger Chatterton]

Just checked , and the plugs I use are;

NGK BCPR7ET

and I guess, as Steptoe says, that the spacer on the bottom plug is to keep thread out of combustion space.
In conjunction with Seiebnrock conversion, gas flowing, and Mikuni Carbs ans sump extension, it does go rather well, but not ridden a bog standard 100GS to compare.

Going to replace the Mikunis with the Bings as soon as I get them back & sorted, so be interesting to see if I notice any difference in power.