Vibrations (possible spark plugs)

Background:

I have had a vibration issue with my bike for awhile, which occured suddenly after a full hot summers day of running my beloved VFR around a gocart track for a whole day at top speed. After that I rode it home on the highway and noticed engine vibrations that started at around 5.5k rpm  and continued all the way up to the redline. I may have described the issue elsewhere here, or possible there (points at some other forum). I've gone through the usual suspects, like compression, drive chain, engine mounts, starter valves and injectors, but nothing have cured the problem.

Current affairs:

I had a list of further things to check this winter to get rid of the problem, but had to order tools to get to it. Well, after doing my second hot compression test (I need to be sure after all) I thought I could prepare myself for the next step (HEI testing, with my new tool that will arrive shortly) when everything already was taken out of the engine, so I placed one of my current spark plugs into the ignition coil and lo and behold it fell right out again. Hmm, that can't be right, can it? Tried with one old spark plug I had lying around since my change (I changed spark plugs well before the background gocart run) and that trusty old NGK plug stuck inside the coil as a very warm sweaty hand in a goretex glove. I have checked what I could regarding the ignition, like signal levels to all ignition coils. I also have had no problem at all with jerky idle, it runs smooth as a babys butt at 1250 rpm (I do have very well performing starter valves after several syncs...).

Proceeding to check out the plug I took out of the bike. The plug is marked Denso IUH27. It was sold to me by Partzilla, as a replacement spark plug for a 2002 VTEC VFR. I double checked the part number at the time with Denso, and they said it would fit my bike. I checked it again tonight, and now Denso says that it fits a VFR from 2000-2001, ie a 5th gen bike.

The spark plugs are almost identical, but the 5th gen version is slightly thinner at the ceramic part. Another thing I noticed when closely examining the two different spark plug is that the Denso plugs have a noticeable bigger gap, even though they are supposed to be identical. Probably slightly worse quality control by Denso, I don't know. Or maybe my high rpm misfires (if the vibrations are misfires) have done bad things to the plugs, but they don't appear to be worn? There are no carbon traces on the Denso plugs and no miscoloration of the tips either, they look pristine.

I haven't concluded that they are the culprit, but new spark plugs are in the mail. Thanks to Brexit the pound is lower so I ordered these new NGK's from the UK instead of the US. I'll report back if there's interest.

What is the consensus here, are the plugs likely culprits? I hope so, I'm slightly tired of chasing these illusive vibrations.

It certainly could be spark plugs, but considering the RPM range where it becomes noticeable, I'd be looking hard

at the V-tec actuation. Maybe you have a valve or two that isn't actuating like the others when the V-tec kicks in.

4 hours ago, FJ12Ryder

It certainly could be spark plugs, but considering the RPM range where it becomes noticeable, I'd be looking hard

at the V-tec actuation. Maybe you have a valve or two that isn't actuating like the others when the V-tec kicks in.

I think FJ12Ryder is on to something. 

If it was plugs you’d have vibrations from the moment you fitted them. Sounds like it only started after your go kart track session? 

How many miles and when did you last check valve clearances? My inline four rumbles like a b@stard if the valves need adjustment. 

So plugs either fit or don’t they are the right thread length or not. Compare old to new. The plugs should have an alloy top screwed on to the top thread. That’s what makes contact with the plug cap. If a plug falls out of a cap there is something physically wrong. The runner boot does NOT restain the plug, the electrical connector does !

Plugs can crack & can create odd effects, but you can just swap them one at a time to test that. 

If the the gaps are wrong, why didn’t you check them at installation ? Plugs come with the gap set to something, but NOT always to your bikes spec, they are used on many engines, so ship with a common setting, but you should always confirm before using them that it’s right for your specific application ! 

Have ypu you checked the chain & sprockets ? Often a cause of apparent engine vibration on these bikes. If vibration is apparent when run on centre stand in neutral then it’s not the C&S ! 

Check all all electrical connections to coils & HT leads are secure.

Hope that helps.

PS Plugs are only designed to be fitted 3 times before the sealing crush washer is crushed flat & a seal is then not guaranteed. How are you fitting the plugs ? They should be hand tight using a plug socket plus 1/4 turn. 

NGK. Time and again issues seem to be with other brands.


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Buy the exact plugs as specified in the owners manual. The manual has part numbers. They come pre-gapped. Do not adjust the gap, especially with an old style tool.

Denso or NGK only on plugs, again, as specified in the owners manual. Looks like they sent you the pre-VTEC style, which is different.

1 hour ago, ScottieDucati

NGK. Time and again issues seem to be with other brands.


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Denso are just fine. They're identical in quality to NGK and work properly. Having the right part # helps though

Stray, 3/12/2019 at 9:10 AM

I think FJ12Ryder is on to something. 

If it was plugs you’d have vibrations from the moment you fitted them. Sounds like it only started after your go kart track session? 

How many miles and when did you last check valve clearances? My inline four rumbles like a b@stard if the valves need adjustment. 

My bike's done 51.000 kms, and had the valves done at around 50000 kms (three tight valves, so obviously Honda don't manufacture magical engines that don't need valve checks). Vibrations started at around 47000 kms, and the valve adjustment was done as fault finding. Don't really know how to test actuation of separate VTEC valves, but the general VTEC kick is present at the right temp and rpm... Vibrations start before VTEC actuation, and are present during and after as well. Any tips accepted gladly! 🙂

Mohawk, 3/12/2019 at 12:26 PM

So plugs either fit or don’t they are the right thread length or not. Compare old to new. The plugs should have an alloy top screwed on to the top thread. That’s what makes contact with the plug cap. If a plug falls out of a cap there is something physically wrong. The runner boot does NOT restain the plug, the electrical connector does !

Plugs can crack & can create odd effects, but you can just swap them one at a time to test that. 

If the the gaps are wrong, why didn’t you check them at installation ? Plugs come with the gap set to something, but NOT always to your bikes spec, they are used on many engines, so ship with a common setting, but you should always confirm before using them that it’s right for your specific application ! 

Have ypu you checked the chain & sprockets ? Often a cause of apparent engine vibration on these bikes. If vibration is apparent when run on centre stand in neutral then it’s not the C&S ! 

Check all all electrical connections to coils & HT leads are secure.

Hope that helps.

PS Plugs are only designed to be fitted 3 times before the sealing crush washer is crushed flat & a seal is then not guaranteed. How are you fitting the plugs ? They should be hand tight using a plug socket plus 1/4 turn. 

The Denso plugs was supposed to have the correct VFR gap settings (specified on the box), but I'm almost certain now that they didn't. The reason I did not check them before was due to laziness, I don't own a wire type feeler gauge just classic rectangular type not suited to iridium plugs. The spark plugs fit, the 5th gen uses the same threads, and the tops are correct. My reasoning was that if the rubber boot doesn't seal there is the possibility of the current taking a different path to ground at speed, heat and compression. I'll soon have factual data on that, since my new plugs arrived in the mail today. What I might have failed to communicate in my first post was that the rubber boot seals to my old NGK plugs really tight, and holds the plugs in when letting them go when inserted into a lose ignition coil. If I try the same with the 5th gen Denso plug it falls out, ie no seal at all. The spring that makes the electrical connection to the plug does not hold anything, its just a spring with lower diameter fit to make an electrical connection to the top of the plug. Obviously you dont rely on the boot to hold the coil to the plug when normally running the engine, thats why you bolt the coil onto the valve cover I guess. 🙂 The boots themselves look pristine, but I guess thats no guarantee that they haven't cracked. Will check that there is spark with HEI tool, both cold and hot as soon as possible.

New chain, new sprockets. Yes, I bought the OEM front sprocket with the rubber damping. And yes, there are vibrations when standing the bike on the center stand.

The electrical connections and me have a rather rough relationship at the moment. I'm going over them for the fourth time with a file removing every sign of corrosion (have got the charging up to 14.2V at idle with headlights on at the moment without Vfrness or any modifications to a european 2002 wire harness, with original R/R and stator). But as I said, the signals to the coils are correct, both the 12V feed, ground and the signaling (checked with oscilloscope). Have not checked the coils as of yet, awaiting tool for HEI testing. There is traces of fine white dust coating on the rubber boots down by the plug connection...

First installation I did as you specify, after that I've torqued them to 12 Nm (as according to the shop manual). Interesting, I didn't know that they are deemed useless after three goes. Well, another reason to change them then...

Thank you for your response!

The traces of fine white dust are almost definitely old dried up dielectric grease.

Can you run the engine at the required rpm and push the rubber boots down into the plugs just to see if it’s a problem with poor contact? Plugs shouldn’t fall out the boot like that. 

Are all the headers getting hot at the same time? A slightly colder one might pinpoint the problem. 

Im really hoping your new plugs do the trick. 

Stray

It was not the spark plugs. Well, it could still be a misfire at higher rpm's I guess, but it runs beautifully at idle.

I've since started to suspect the clutch. I've got problems shifting gears as the clutch don't disengage so I dismantled everything. The clutch center has grooves in them that could very probably explain the sticky clutch, but its another thing that puzzles me. When I manually quickly turn the clutch center alternativly between directions (the proper word eludes me), see attached Youtube movie, there is a noticeable rattle. Is this normal?

Is there anything in the clutch that could produce vibrations? What should I check? There is no give at all in the clutch basket when mounted as in the movie, it's steady as a rock in every direction. Some grooves in the basket as well, but not as deep as in the center. Could it be the needle bearing? Should I notice some movement from the basket at all if the needle bearing or the clutch outer guide were worn? Or is the main drive gears preventing such movement to be noticable without dismantling stuff further?

I'm at a loss.

I believe what you're hearing is the gears banging around and hitting one another.  In fact I'd pretty much

bet a bit of money on it. The gears are free to move around so there will be some noise when you rotate

the clutch center around. There's no oil there so you will hear metal to metal clanging. The engaging dogs

will have clearance and rotating the hub back and forth will knock them together.

Yeah that’s normal. 

I’m still concerned your plug falls out of the plug cap. The plug top should either be a threaded rod of said rod with an alloy screw on cap. Either way a plug cap to plug connection should NOT allow the plug to fall out. The cap seal is a water seal nothing to do with electrical path, that’s why the plug body is ceramic. 

So adjust the inside side fitting in your plug cap, you can reach in with a flat blade screw driver & bend the connector petals in. They are supposed to be in PERMANENT contact with the plug top. The plug should stay in the cap even with the bottom seal removed from the cap.

as before, check your chain & sprockets. Worn front sprockets can produce horrible vibrations.

18 hours ago, Mohawk

I’m still concerned your plug falls out of the plug cap. The plug top should either be a threaded rod of said rod with an alloy screw on cap. Either way a plug cap to plug connection should NOT allow the plug to fall out. The cap seal is a water seal nothing to do with electrical path, that’s why the plug body is ceramic. 

So adjust the inside side fitting in your plug cap, you can reach in with a flat blade screw driver & bend the connector petals in. They are supposed to be in PERMANENT contact with the plug top. The plug should stay in the cap even with the bottom seal removed from the cap.

as before, check your chain & sprockets. Worn front sprockets can produce horrible vibrations.

+1

I'll fix that, thanks for the tip. At the moment my bike is disassembled waiting for a new clutch center and some filing on the clutch basket. But as soon as that is taken care of I'll get back to tracking the vibrations.

Mohawk, 3/27/2019 at 4:00 PM

I’m still concerned your plug falls out of the plug cap. The plug top should either be a threaded rod of said rod with an alloy screw on cap. Either way a plug cap to plug connection should NOT allow the plug to fall out. The cap seal is a water seal nothing to do with electrical path, that’s why the plug body is ceramic. 

So adjust the inside side fitting in your plug cap, you can reach in with a flat blade screw driver & bend the connector petals in. They are supposed to be in PERMANENT contact with the plug top. The plug should stay in the cap even with the bottom seal removed from the cap.

as before, check your chain & sprockets. Worn front sprockets can produce horrible vibrations.

I've checked now. There are no petals to adjust, there is just a spring pressing on the plug top from above. I think it's by design, as all four COP are the same. I also checked a modern Volvo COP and its the same, no adjustable petals in the plug connector. The spring will push out the plug when inserted in the COP if there is no tight water seal, just as being done when inserting a too small plug into the COP. The plugs are being kept in permanent connection with the spring by securing the COP to the valve cover... My springs don't look worn or rusty, so I guess they're fine. Mind you, I've recently experienced misfires on a GM engine when the spring, even though looking in mint condition, in their COP vibrated sideways inside the COP during running so still not 100% sure.

I guess the 6th gen differs from the 5th gen petal wise. 🙂

I've attached a photograph of a COP where you can see the spring. Sorry for the slightly blurry picture, it was hell to get the flashlight to light up into the plug cover... The springs diameter is slighty smaller than the spark plug top so that it is kept in contact by pressing the COP down onto the plug by securing the COP onto the valve cover.

[image: COP_spring.jpg]

Well I have to say I’ve never seen a 6th gen one.Do they screw down to the valve cover if yes fine, but the plug should have its alloy hat on it should not just be a threaded rod at the top !