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plug cap prices


jcr
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have just been looking at spark plug caps for a Thunderace.  prices are £60+ each, around £250 for 4 plug caps. i was quite shocked to be honest.

does anyone know of cheaper alternatives?

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I too am a little shocked, spark plug caps are not something I've had problems with on my Thunderace so far.

You may have to bite the bullet, after a cursory search, this is all I've found..:

YAMAHA YZF 1000 THUNDERACE 4SV 96-03 - IGNITION COIL CAP PLUG CAP - ONLY 3 | eBay

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thank you for the link blackhat, are you sure they will work?

ive just taken out the innards and 3 of the four brass screw in bits that the plug end slots into are badly corroded. the springs in them that grip the spark plug have disappeared.
are these bits the same in other caps?

was thinking i could buy some cheap caps and swap them out?

 

and yes snakebite it is a shocker. £250 for 4 plug caps is crazy!

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25 minutes ago, blackhat250 said:

I saw those, but it says they're for threaded terminals, I'm pretty sure the Ace doesn't use threaded plugs.

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Don"t you just screw off the  end bits  ,leaving the threads visable ? 

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4 hours ago, blackhat250 said:

Don"t you just screw off the  end bits  ,leaving the threads visable ? 

Yes Blackie, you are correct as usual, if I remember right I used to screw off the ends then just push the cap onto the threaded part of the plug not actually screw them on.

Mike.

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thanks for the replies fellas, they seem to be for a yzf750, but for the price i'll give them a try.

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5 minutes ago, jcr said:

thanks for the replies fellas, they seem to be for a yzf750, but for the price i'll give them a try.

Brill jcr, no probs that's what here for.

Mike.

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the caps were about 10mm smaller than the originals, the internals were smaller too, so couldnt swap over.

i fitted them, the bike still isnt right, but is a lot better. it has a missfire when revving and will only idle on the choke.

the bike was fine before i changed the spark plugs, which i believe were the originals and had never been touched.

the caps kept twisting on the ht leads rather than screwing tight, could this cause an issue?

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Posted (edited)
9 hours ago, jcr said:

the bike was fine before i changed the spark plugs, which i believe were the originals and had never been touched

Does putting the original plugs back in resolve the misfire?

if it does then there's something wrong with your new plugs

if it's a single faulty plug it's a case of putting in one new plug (with three old ones) at a time until the misfire occurs, then you've found the faulty plug.  Don't stop there, just test all of them to ensure you don't have more than one.

Occasionaly you can get cracks in the porceline that can cause misfires,(you'd never know if they've been dropped before you bought them) They may not show up visually on a brand new plug, they do on dirty ones as the dirt gets into the fine crack.

If it's the set of plugs: hear me out first! sometimes a full set can collectively cause a misfire if the set is not fully compatible to the correct rating.

I have an example where a friend changed a set of plugs on a Ford Mondeo and it transpired there were two different plugs depending on which HT leads were fitted NOT the engine size.  So the length of the spark plug head were identical, but the porceline was slightly longer on one set yet they both had the same spark plug number except for a letter on the end. The shorter porceline meant that the HTplug didn't seat properly and caused the misfire on all the plugs. Therefore don't just take the length of the plug head as being correct, check the top for correct dimensions as well.

 

Edited by NE0
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There are a lot of fake NGK plugs out there atm, so make sure you buy them from a reputable source

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The Thunderace will take two different plugs (they're listed in the manual).

If you don't have a Haynes Manual, say so, I'll dig mine out...

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its the correct plugs, identical to the ones i removed. NGK DR8EA.

i might try putting the old plugs back in. it is a pig of a job though

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Those sound right offhand.
 

So I've heard, I've not done it yet lol.

 

Stupid question, you did check the gaps on the new plugs before you put them in, didn't you?

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Posted (edited)
40 minutes ago, Snakebite68 said:

Those sound right offhand.
 

So I've heard, I've not done it yet lol.

 

Stupid question, you did check the gaps on the new plugs before you put them in, didn't you?

yes. i set the gaps to the recommended 0.6mm. curiously all the old plugs had gaps well over 2mm.

from the begining-

first time i started bike after plug change it sounded awful and would just cut out instantly. so i went back, rechecked the plugs and then looked at the coil. all the plug caps were very badly corroded inside and three of them wouldnt even grip the plugs because theyed lost the little springs inside that grab the plug thread. cleaned them as best i could then tried again. this time the bike would run on choke but had a bad missfire .

third attempt with the new caps, bike starts keenly and ticks over on choke, very occasional slight misfire, but increases when revved. bike stalls if choke full off.

this is why i thought the problem was with the caps? 

Edited by jcr
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Posted (edited)
47 minutes ago, jcr said:

set the gaps to the recommended 0.6mm. curiously all the old plugs had gaps well over 2mm.

That's interesting!.....and may have some significance.

You see modern engines now use very lean fuel mixtures and subsequently have their plug gaps set much wider than they used to be. They apparently are set wider as there needs to be sufficient molecules of fuel in the gap to ignite. Smaller gaps may result in misfiring and incomplete combustion. If you say you're having to run it on choke, you're decreasing the air ratio thereby increasing the molecules of fuel.

I appreciate it's a pig to keep removing/replacing the plugs but it's all part of fault tracing and the process of elimination.

I'd be inclined to match the plugs to their previous conditions with the same gap and see what happens, there may have been a very valid reason why they were set so wide in the first place.

 

 

Edited by NE0
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Posted (edited)
53 minutes ago, NE0 said:

 

I'd be inclined to match the plugs to their previous conditions with the same gap and see what happens, there may have been a very valid reason why they were set so wide in the first place.

 

 

thank you for the suggestion. i think ill put the old plugs back in first and take it from there. 

i just assumed the gaps on the plugs had widened over a couple of decades of running.

the fact that every time ive played with the caps the running has improved, made me think the problem was above the plugs. 

Edited by jcr
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42 minutes ago, jcr said:

assumed the gaps on the plugs had widened over a couple of decades of running.

Contrary to popular belief plug gaps don't open up much at all, maybe a few thousandths of a millimetre yes, as the central electrode wears down, but not by a couple of millimetres. The plug gap arm gets extremely hot for sure but it needs a physical force to open the gap up, it doesn't get so white hot in normal running that it melts and moves away from the electrode.

Furthermore if the widening gap was detrimental why would it run perfectly normal? I like these sort of puzzles and problems, it makes you think.😀

Keep us informed of your progress bud.

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maybe the Haynes manual has the incorrect spec for the plugs?

hopefully will have another bash at things tomorrow.

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