81 SH (?) coils different (?)

[oldnortonrider]

Many times, since I originally acquired my 81SH, in '94 >> in the process of doing whatever I would have to take the tank off, to do, >> I've not been able to resist glaring at the coils being "different". I'm not sure what models did this. My manuals don't mention anything about "the difference". RH coil going to #2 & #3 (inside cylinders), LH coil running #1 & #4 .
LH shaped different than the RH.
Does anybody know why Yamaha did this ?

[Mike Hart]

I looked on the fiche for a few models, they all list a different part nr for the two coils, but all 'appeared' the same. That's a stumper

[oldnortonrider]

?? I'm not sure what you mean : "appeared the same" .

[Bill__Woods]

It must have something to do with the 81 models using a different Ignition Box. The coil primary resistance is 2.5 ohms on the 81 models. somewhere on the web page i saw it incorrectly listed as 3 ohm. my service manual says 2.5 ohms. They probably done it as a prototype for the XJ series bike, dunno bout that, just a specualtion.

weird ways of the world

[MartyA]

My Clymers shows the coils as mirrors of each other, for the left and right, but similar in design. Did someone "repair" one of them?

Also Clymers mentions the coil primary primary resistance as 1.5 ohms +/-10%. Is this one of those cases where the manual is wrong?

I will be tracking a minor misfire with my meter as soon as the rain quits. Which resistence is correct?

[Mike Hart]

coil primary
78-80 1.5 ohms +/- 10%
81 and later 2.5 ohms +/- 10%

[Mike Hart]

Originally posted by oldnortonrider
?? I'm not sure what you mean : "appeared the same" .

The drawing on the fiche pages showed no difference in appearance.

I'm not sure what you meant by "different"

[Bill]

There's a picture of an '81 RH coil (OZ) in the New Wires in Old Coils tip. It's the same as the '81 SH, with one of the high tension wire tunnels running only half the length of the coil body.

[oldnortonrider]

[QUOTE]Originally posted by Bill
[B]There's a picture of an '81 RH coil (OZ) in the New Wires in Old Coils tip. It's the same as the '81 SH, with one of the high tension wire tunnels running only half the length of the coil body.

One of the reasons I'm persistent about wanting to know the
difference ; is cuz, couple years ago, I started to interchange the
coils from my '79Standard, to the '81Special
When I saw, that one wuz different; I wondered if something in my ignition electrics would "get messed up". Turned out it was something else; didn't need to switch coils. But , what if, some other day, in the future, I did need to?
I don't think there'd be a problem; I'd still like to know what Yamaha had up their sleeve(s).

The "New Wires in Old Coils" thread is very well done. More than well done. I wonder if the other contributors to that thread : Blaine Hoopes, Shane Thomas, or Dave Norton , (?) would have a theory on this ?

[oldnortonrider]

I ain't believin', this thing pulled bold type, all the way down , nearly to the end. I tried to change it to look like a sane person had written it. My 5 minutes wuz up, before I got 2 lines done.

[Mike Hart]

the vB close tag from the quote part got snipped, so it went bold on ya! (bracket /b bracket) also the quote close tag.

The 81 and up coils have a primary resistance of 2.5ohm, while the 78-80 had 1.5ohm. As to whether that would fry something, beats me, I'm not gonna try it! Maybe safe with a 1 ohm resistor in series with each coil?

[oldnortonrider]

Originally posted by Mike Hart
I looked on the fiche for a few models, they all list a different part nr for the two coils, but all 'appeared' the same. That's a stumper

Years back when I first noticed my coils being different on this bomb ,>> right off, I thot; ...."PO has replaced one of my coils off
another different make of motorcycle.......(?) "?
SO; a few days later, I'm in the local dealer store, at the parts counter.....(I think, I'm remembering this accurately )....I sez to the parts man, "Hey, I think the PO of this 81SH, has swapped
one coil with another different type of coil; surely this M/C doesn't
use two different kinds of coils, if I was to order 2 coils, DOES IT?"
.....He looks everything up; sez, "Yes, it takes 2 different coils."
I didn't dare ask him what would be the difference between the 2 coils, to come on the same motorcycle, brand new, outta the same crate. BUT, I did ask him "Then they're different prices for the 2 coils "that I might need" , to go on the same engine??"
....He sez, "Yup, about $3 difference."
(I never did get another set of coils; still using that pair.)

I have the two different coils that are showing in the repair thread; I've tested the coils. Ohms are the same, the coils ain't.

[Mike Hart]

Originally posted by oldnortonrider
I did ask him "Then they're different prices for the 2 coils "that I might need" , to go on the same engine??"
....He sez, "Yup, about $3 difference."
(I never did get another set of coils; still using that pair.)

I have the two different coils that are showing in the repair thread; I've tested the coils. Ohms are the same, the coils ain't. [/B]

All models have 2 diff part nrs for the coils, they are mirror image and so are different. In 81 the coils became smaller physicallyl as well, and I don't recall noticing anything weird about my xj coils.

I'm curious about your resistance measurements: the 78-80 are supposed to be 1.5ohm primary, 15kohm secondary, while 81 and later are 2.5ohm and 11kohm. At least, that's what the service manuals say Are you using an analog or digital meter to measure?

[Mike Hart]

do those other coils have stamped on them "with external resistor"?

[oldnortonrider]

Originally posted by Mike Hart
do those other coils have stamped on them "with external resistor"?

YES; on one coil >>, the one on the right, feeds the middle two
cylinders.
SEZ : USE WITH EXTERNAL RESISTANCE .