Spark plug cap update for Guzzi 8V models

Link to this great tip (with photos) from Micha at Moto International here in Seattle

Micha of Moto International wrote:

It has come to our attention that some spark plug caps on 4-valve-per-cylinder Moto Guzzis develop high-voltage shorts to the cylinder head covers. This results in frequent misfires as well as occasional flickering dash lights.In recent models, factory engineers attempted to correct this problem by insulating the cover from the cylinder head. Nevertheless we think it is a good idea to update components to reduce failures.To do this, you’ll need two NGK iridium plugs and two straight NGK 5,000-ohm spark plug caps. Procedure:

   Remove spark plug covers (2 tiny Allen screws under Guzzi logo clip)

   Unplug spark plug caps and cut plug wires close to caps

   Reroute plug wires behind frame tubes

   Remove & replace spark plugs after first removing threaded adapters from the cap ends

   Screw new plug caps onto plug wires and press them onto the new plugs

   Replace spark plug covers and miniature Guzzi logo emblems

You are done. Sit back, relax and claim mechanic’s rights by your loved ones. Even better, go for a ride!

Note: there is a hole on the bottom of the spark plug cavity to drain any water and debris.Once you have completed this update, before removing the spark plugs always blow some compressed air to clean the surrounding area and prevent any debris from falling into the combustion chamber.

Excellent idea. I just wish I lived closer to MI in SEA, so they could handle my Guzzi
services, mods, etc. But I think I can handle this spark plug mod on my own, due to the
clearly described procedure. Thanks for posting it, S.

Just happened to me yesterday - had checked the valve clearances and the spark plugs and back together and running well. Around 15-20km later after stopping off at a mate's house, it started running like crud. When at idle it was 2000 rpm then would go down to 900rpm and feel like it was on one cylinder. Then the other cylinder would kick in with a big surge. Just what you want when you are showing off the bike..

Pete Roper picked it in one. Took off the covers under the Guzzi logo and the left cylinder plug cap was arcing intermittently. Some electrical tape fixed it and will pick up some NGK SB05Es from somewhere next week hopefully. Went for a ride this afternoon with no problems.

I guess would ride it until it happens but put some electrical tape in the toolkit, a 2 minute job to fix it temporarily.

I have a video of the arcing but not sure how to embed it.

If you can upload the video to YouTube, embedding the video is then simple.  Just use the YouTube button in the post editor.

Then there is this:  [You must be registered and logged in to see this link.]

And remember, DON'T use the torque setting published in the MG shop manual when replacing plugs. It's way too much.

Hi all, has anyone done this mod?

I am going to replace one of my LHS valve covers (at some point) after a low side crash and thought it might be worthwhile doing it at the same time.

Cheers Taz.

Haven't had to swap my own, but I have done it for three other ham fisted Guzzisti... Easy fix and works just fine.

Thanks Steak.

The screwdriver method works everytime for me. I usually stick a piece of stiffish plastic tube over the top of the plug when replacing it so it can't cross thread then nip it up with a socket.

Tassiedevil71 wrote:

Hi all, has anyone done this mod?

I am going to replace one of my LHS valve covers (at some point) after a low side crash and thought it might be worthwhile doing it at the same time.

Cheers Taz.

I did it on a Stelvio while fixing low speed fueling issues because it was easy and cheap.

OK so just to make sure before I cut....  Is there enough wire to cut behind the sleave on the back of the cap or do I need to cut closer like the instructions say? Or cut at the buldge in the middle of the sleave.  Thanks...

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Cut closer, the sleeve will peel off with a little effort. The more slack you have left in the lead the better.

Are there any aftermarket plug wire sets that are better quality available?

NGK SB05E caps.

Pete Roper wrote:

NGK SB05E caps.

Yeh I used SB05E plus the end caps off the SD05F's to get the full effect. Cost an extra $10 that way but what the hey.

The only problem I had is with the little screw that holds the wire cover on. Went to put the cover back on and that screw was very tight. Backed it out and hand fit it without the cover in place and it was still tight so I put a little anti-seize on it. It went most of the way in and then started to get pretty stiff so I stopped. Hopefully in time. Will try a die tomorrow.

Bike ran for a quick trip around the block so I must have handled the rest of the chores o.k.

So after resolving the cover screw this morning I went for a 30mi ride. I believe this is a must do mod now. You can actually launch the bike normally not having to guess if it was going to stumble or not. It doesn't solve all of the issues down low but it puts a dent in them.

So in the books now:
Rollers
Spark plug update
KD lowering pegs
Onar's risers

To do:
Beetle map
Pete's swingarm service

I have a question. The new NGK cap + the rubber end doesn't seem to fit inside the tube. It is too tight. I did`t think it was a good idea to force it in, so I stopped. It seems that if I forced it in there was no way the rubber end would come out later.

While I’ve not had this problem it’s probably due to different manufacturing plants having slightly different tolerances. Just shave it down around the outside with a razor blade or craft knife and lube it with a bit of rubber grease. That won’t compromise its ability to do its job..

Pete

Thank you. I will try. Can I use the SD05F on the bike as well or not?

The ‘E’ or ‘F’ suffix relates to the type of top on the centre electrode of the plug.

Has any body tried NGK CR3 cables as a possible replacement for the spark plug cables on this bike?

Well, I used the SB05E replacement and impovised a rubber end cap from the SDOF's. I cut the rubber cap that is supposed to go where the cable enters the cap. It seems to make a really tight fit with the spark and it is fitting inside the head's tube. I hope this improvisation is not a stupid thing to do. Seems to be working.

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After reading this thread, I did mine as a preventative measure. No problems resulted at all.

jretanacr wrote:

Has any body tried NGK CR3 cables as a possible replacement for the spark plug cables on this bike?

On my fifth season with a set of CR3, no problems, easy swap.

This happened to me on Saturday !!! Just on my way back from visiting Sunbeam (Peter), when the bike started to run like a pig - felt like it was only running on one pot. No flashing dash lights tho. Remembered reading this post recently & as it'd just (like the week before) come back from being serviced, thought it may the same issue.

As I was only about five miles away from the dealer, I rode straight over there. They put it on the ramp & confirmed it was arching over. Temporary fix with some insulation tape to get me home & given the choice of replacing with original (£72.10 each) or NGK SB05E (£3.99 each). So there's a pair of NGKs on order.

Dealer reckons that removing the leads to swap the plugs was possibly the final straw.