Hi. I have developed a slight vibration throughout rev range. Nothing major but noticeable through bars, pegs and tank. Reading various forum posts I have tested all 4 HT leads. The readings I get are 1=4.75, 2=4.84, 3=5.08,4=0. If I understand they should read 5. Do I need to replace them all? Do I need to replace the lead and the cap or is there another test I can do to determine which part is faulty? And finally, with these readings should I be surprised that the bike is running at all? Many thanks.
HT lead testing
- Thread starter Howard
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jfheath
John Heath
When I replaced mine, the new plug cap resistances were a little out either way - 5.02, 4.98 I seem to remember, so I suspect the 5.08 plug is perfectly Ok. The other two may well be OK too - one of mine was something like 4.56 when I replaced it, and that definitely had a fault, but two of yours are somewhere between. I don't know. I just know that mine were faulty when the resistance showed 4.5 ish and 5.5 ish. I don't know if there is a tolerance or whether that was the cause of the fault or a symptom of some other fault in the cap.
But when you say that you tested the HT leads - what do you mean ? Did you test the plug caps by themselves, or did they still have the leads attached ? The leads unscrew from the plug cap - put a mark on the lead where it meets the cap so that you can measure the distance from the mark to the end once the lead has been removed. (See Pic) There is a fair chance that the leads themselves have corroded inside. There is a threaded spike inside the plug cap which screws into the stranded copper core of the HT lead.
Get yourself some standard, copper cored HT lead - I got some from a car auto-electrical supplier - it cost me a couple of quid. Put a mark on the lead the same distance from the end as the one that you removed (my marks were an inch from the end), and screw that in all the way to the mark - a little silicon lubricant helps. Then cut the other end to get a lead of the correct length. Doing it this way means you can have a couple of goes at getting it back into the plug cap - when it has been screwed in and out a couple of times, some of the copper core strands may have been cut by the threads.
Now check the resistance again - plug and new lead.
If they show an improvement, then its worth trying the engine with the new home made leads - but you will need to fashion something at the coil end so that the screw on gland can hold the lead inside the coil. The lead at that end is a simple push fit, and could work its way out. Roughen the outside of the lead, put the gland on and wrap some chord around the lead - or tape the lead onto the outside of the gland - just to stop it coming out. This is only temporary. You can ride the bike without the lower and fairing, if you secure the ends which might flap about in the breeze - you're only going out for a test run.
The fault on mine was the most noticeable when I put it into a higher gear and tried to go slowly uphill. I assume that at higher revs, there was enough electrical power generated in the HT coils for a decent spark to jump the gap of any electrical fault. At lower revs, there wasn't enough for this to happen and the bike ran more roughly - like riding over a bumpy road surface. Going up hill made the problem much more apparent.
What happens next depends on what you find. If the fault has gone away, then the leads were the problem, not the plug caps.
Depending on damage / corrosion, it may be possible to use the existing leads and chop a small amount off the end of the HT lead that plugs into the cap. This may be enough to cut out the part of the core that has been damaged by the threads on the plug cap 'spike'. A short length - maybe 5mm at a time - you judge. The idea is to try to get back to some decent copper core, but you run the risk of cutting off too much so that the lead is no longer long enough to reach the coil.
The original lead comes with a secured grommit, and tiny plastic washer, and a secured outer sleeve. You may be able to salvage these from any lead that you decide is beyond use, and re-use on your replacement HT lead. I found that properly securing that grommit for the coil gland to tighten against was a problem. I used superglue - it wasn't good enough for a permanent solution.
If you still suspect the caps, then buy one or two and see what improvement that makes.
When I replaced the leads with home made on mine, the bike improved massively, but it still wasn't right. I replaced two plug caps, and that improved things again - the bike was reliable, but it still felt a little like riding on a tar and chipping road surface all of the time. I switched in and out various combinations of new and old caps - but that made the problem worse - so the old caps got ditched. I eventually decided to replace everything. I still have one old cap and a brand new lead which never got switched out. They will be there for the next time this happens in about 10K miles time, if history is to repeat itself.
Don't forget that when you have finished testing, that the HT lead that fits into the coil needs to be securely held in place by that green threaded cap. The makeshift tape or chord-wrap solution isn't a good long term thing. If it isn't secured, that lead WILL work its way out of the coil and leave you stranded, and it isn't really accessible at the roadside without removing the fairing.
I assume you saw the thread I wrote as the fault was developing ? Link
But when you say that you tested the HT leads - what do you mean ? Did you test the plug caps by themselves, or did they still have the leads attached ? The leads unscrew from the plug cap - put a mark on the lead where it meets the cap so that you can measure the distance from the mark to the end once the lead has been removed. (See Pic) There is a fair chance that the leads themselves have corroded inside. There is a threaded spike inside the plug cap which screws into the stranded copper core of the HT lead.
Get yourself some standard, copper cored HT lead - I got some from a car auto-electrical supplier - it cost me a couple of quid. Put a mark on the lead the same distance from the end as the one that you removed (my marks were an inch from the end), and screw that in all the way to the mark - a little silicon lubricant helps. Then cut the other end to get a lead of the correct length. Doing it this way means you can have a couple of goes at getting it back into the plug cap - when it has been screwed in and out a couple of times, some of the copper core strands may have been cut by the threads.
Now check the resistance again - plug and new lead.
If they show an improvement, then its worth trying the engine with the new home made leads - but you will need to fashion something at the coil end so that the screw on gland can hold the lead inside the coil. The lead at that end is a simple push fit, and could work its way out. Roughen the outside of the lead, put the gland on and wrap some chord around the lead - or tape the lead onto the outside of the gland - just to stop it coming out. This is only temporary. You can ride the bike without the lower and fairing, if you secure the ends which might flap about in the breeze - you're only going out for a test run.
The fault on mine was the most noticeable when I put it into a higher gear and tried to go slowly uphill. I assume that at higher revs, there was enough electrical power generated in the HT coils for a decent spark to jump the gap of any electrical fault. At lower revs, there wasn't enough for this to happen and the bike ran more roughly - like riding over a bumpy road surface. Going up hill made the problem much more apparent.
What happens next depends on what you find. If the fault has gone away, then the leads were the problem, not the plug caps.
Depending on damage / corrosion, it may be possible to use the existing leads and chop a small amount off the end of the HT lead that plugs into the cap. This may be enough to cut out the part of the core that has been damaged by the threads on the plug cap 'spike'. A short length - maybe 5mm at a time - you judge. The idea is to try to get back to some decent copper core, but you run the risk of cutting off too much so that the lead is no longer long enough to reach the coil.
The original lead comes with a secured grommit, and tiny plastic washer, and a secured outer sleeve. You may be able to salvage these from any lead that you decide is beyond use, and re-use on your replacement HT lead. I found that properly securing that grommit for the coil gland to tighten against was a problem. I used superglue - it wasn't good enough for a permanent solution.
If you still suspect the caps, then buy one or two and see what improvement that makes.
When I replaced the leads with home made on mine, the bike improved massively, but it still wasn't right. I replaced two plug caps, and that improved things again - the bike was reliable, but it still felt a little like riding on a tar and chipping road surface all of the time. I switched in and out various combinations of new and old caps - but that made the problem worse - so the old caps got ditched. I eventually decided to replace everything. I still have one old cap and a brand new lead which never got switched out. They will be there for the next time this happens in about 10K miles time, if history is to repeat itself.
Don't forget that when you have finished testing, that the HT lead that fits into the coil needs to be securely held in place by that green threaded cap. The makeshift tape or chord-wrap solution isn't a good long term thing. If it isn't secured, that lead WILL work its way out of the coil and leave you stranded, and it isn't really accessible at the roadside without removing the fairing.
I assume you saw the thread I wrote as the fault was developing ? Link
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Thanks John. I was hoping you'd chip in. Yes, I've read all your thread several times. I checked with leads still attached. I'll check without to see if there is a difference. I'll report back. Still intrigued why it runs relatively well with no4 clearly kaput. As I say, it's a subtle vibration throughout the rev range. I would have expected an obvious issue, as you describe with yours.
jfheath
John Heath
Most welcome. Not that I am an expert - but apparently more of an expert than the nearest official Honda dealer who told me that it was running normally for a bike with 60K on the clock ! Needless to say, I have never been back there.
Well just because there is no continuity with a multimeter, it doesn't mean that an HT spark cannot jump the gap. If there is a corroded or broken section, this is possible. After all, that is how the spark is created. But mine wasn't an obvious issue at first. It was a vibration - the best I can describe it is as if I was riding along a slightly roughened road surface - not as bad as cobblestones - more like the surface prepared just prior to laying new tarmac. Then it started getting worse when I was setting off, in the lower rev range. Then going uphill, I really had to rev it to get enough current flowing for all cylinders to fire. It still started up Ok though. It went on for a couple of months like that before I got it sorted. It is quite possible that a previous owner hasn't seated the plug caps on the lead properly, and the pin is no longer making contact with good copper core. If your number 4 lead has such a fault, I would expect that the engine would still run, if a little roughly, and it would struggle at low revs.
I used to have a Cossack Ural with a sidecar. It had bog standard NGK plug caps and HT lead. I used to carry spares of both with me all of the time. The cylinders were horizontally opposed - in fact they were manufactured using the tooling for early BMWs, so the leads and the plugs were exposed to the elements. The first sign of winter and wet salty roads, and the wear an tear on the HT leads during the summer would be immediately apparent. I could see the spark emerging from half way down the HT lead and jumping across to the cylinder head as the engine spluttered its way along at walking pace.
Thank you John. I've tested just the caps and got same results so have ordered just one new cap and will see how it runs before possible splashing out on more caps. Once I've got the new cap I'll test them all with HT lead from shop before attaching OEM leads. Watch this space
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Hmm it seems there's a fair degree of tolerance on the resistance rating.
https://www.ngk.de/en/technology-in-detail/ignition-cables/diagnosis/testing-of-ignition-cables/
https://www.ngk.de/en/technology-in-detail/ignition-cables/diagnosis/testing-of-ignition-cables/
The resistor can be removed from the boot and measured. Put a flat screwdriver in the end where the plugs goes and remove the end. There should be a small spring and a resistor.
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jfheath
John Heath
I don't know Howard. I read that plug caps were either 5K or 10K ohms, at some point when I was trying to find a non-Honda replacement. I know that two of mine that were suspect were 4.5 ish and 5.5 ish k. Both of these were proved to be faulty when I put them back in one at a time. That doesn't mean that the fault was related to the resistance though. I bought 4 new plug caps and all four were within a few hundredths of 5k. ie 5.0x or 4.9x - I don't have a record of the details - but I was surprised and how close to 5k they were. I measured them with the short copper cored cable attached. I have an unused brand new ignition lead - I'll check the resistance of that - I don't believe the resistance is very high at all, but I'll check.
Returns from garage.....
Just over 1m of bog standard copper stranded cored cable that I used - 2 ohms. (Not Kohms) ie hardly anything
Brand new OEM Honda ignition cable for ST1300 - shortish one - just over 1ft is 0.8 ohms - even less.
I just found the 4 plug caps that I removed 5 years ago. I probably kept them as I suspect that 2 of them are OK, but don't know which ones apart from #3. Once I had established that the fault lay with the HT plug caps and leads, I just replaced the lot.
#1 cap 5.29k ohms
#2 cap 5.8k
#3 5.08k labelled as faulty
#4 5.57k
Which is odd as one of them was 4.5k ohms when I removed it 5 years ago !! I wonder if I measured them with a faulty lead. Maybe I did.
The Honda caps are manufactured by NGK and have the code XC05FMGG stamped on them. I looked up the code ages back, and it describes things like the length, head angle and the rubber casing. I wonder if you could contact NGK.
Returns from garage.....
Just over 1m of bog standard copper stranded cored cable that I used - 2 ohms. (Not Kohms) ie hardly anything
Brand new OEM Honda ignition cable for ST1300 - shortish one - just over 1ft is 0.8 ohms - even less.
I just found the 4 plug caps that I removed 5 years ago. I probably kept them as I suspect that 2 of them are OK, but don't know which ones apart from #3. Once I had established that the fault lay with the HT plug caps and leads, I just replaced the lot.
#1 cap 5.29k ohms
#2 cap 5.8k
#3 5.08k labelled as faulty
#4 5.57k
Which is odd as one of them was 4.5k ohms when I removed it 5 years ago !! I wonder if I measured them with a faulty lead. Maybe I did.
The Honda caps are manufactured by NGK and have the code XC05FMGG stamped on them. I looked up the code ages back, and it describes things like the length, head angle and the rubber casing. I wonder if you could contact NGK.
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are you looking to find a misfire or a vibration ??
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I think he's wondering if a vibration is caused by a misfire.
Hi, yes I'm trying to cure a harmonic vibration. Not really sure what a misfire sounds like unless it's the popping on deceleration? I only occasionally get this when riding quite vigorously and don't consider it an issue. I have sent an email to Fowlers, asking them if the cap they sent me needs replacing. I suspect from John's experience of main dealers they won't be too helpful. We'll see.
Hi David. I read that article as well. I took it to mean that there can be that sort of tolerance in different set ups, not in HT leads on the same machine. No idea if I'm right. Read soooo much and can't seem to find definitive answer.
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Honestly Howard, if it were me I'd stick the new lead on and see how it goes.
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Appreciate it Howard. I'm not sure my ‘05 is quite right so I'm curious about the outcome.
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Just got off phone to Fowlers workshop. Initially said it would be in tolerance as they are either 5 or 10 ohm and then when I repeated that I was asking if 4.35 was in tolerance he didn't know and suggested I return the plug cap. So no further forward on tolerances. Just going to try it and see. Trouble is I will always have the niggling thought that it could be better if all caps were closer to 5. Think I might need therapy...
jfheath
John Heath
I got in touch with NGK today saying:
I have a friend who has just purchased an OEM plug cap for a Honda ST1300 - manufactured by NGK. He checked the resistance and it read 4.35k ohms. We are now curious - I had told him that when 2 of mine failed, their resistance showed around 4.5k and 5.5k. I bought a full set of 4 caps, and all of the resistances measured within a few hundredths of 5K ohms. Two questions - is the resistance a good indication of whether or not the plug cap is faulty And - is 4.35k ohms an acceptable value for a 5k ohm plug cap.
They were kind enough to respond fairly quickly with a detailed reply:
So now we know.
I think its safe to say that the one that measured nothing is duff !
I have a friend who has just purchased an OEM plug cap for a Honda ST1300 - manufactured by NGK. He checked the resistance and it read 4.35k ohms. We are now curious - I had told him that when 2 of mine failed, their resistance showed around 4.5k and 5.5k. I bought a full set of 4 caps, and all of the resistances measured within a few hundredths of 5K ohms. Two questions - is the resistance a good indication of whether or not the plug cap is faulty And - is 4.35k ohms an acceptable value for a 5k ohm plug cap.
They were kind enough to respond fairly quickly with a detailed reply:
Thank you for your E-mail. The resistance is a range, not an absolute. For example a 5k ohm resistor spark plug cap may ohm out from 3-7k ohms. The ceramic resistor used in spark plugs and caps are not as precise as coiled resistors. If the resistance in Ohms doubles from the spec, then I would say they need to be replaced. Modern ignition systems generate a lot of voltage, so a small difference in resistance is not very important to generate a good spark
So now we know.
I think its safe to say that the one that measured nothing is duff !