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Valve Stem Seals, or maybe throw in the towel

Just swap 2 of the caps, put 4 on 3 and 3 on 4 and see if anything changes. I'm really interested in what caused this [NODE="4"]Groups[/NODE] cyl. to quit.... Also what ron said in post #50, remove the resistors, replace them with a piece of heavy copper, and reinstall. Now no resistor to be bad... I can't imagine why you would want one, but if you think you need a resistor, put in a NGK DR8EA, you'll still have a resistor just in the plug and not the plug cap.... $20 for a plug cap??? that's crazy.... Wish you were closer I've got 2 new XD05Fs new in box out in the garage.
 
Agree, there's little sense in running resistor caps when NGK resistor plugs are cheaper and easier to find than non-resistor NGK plugs. There are probably some other brands of non-resistor plug out there but at $4ea at the local automotive chain store I'll stick to NGK.
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Rich82GS750TZ said:
Diaphragm is in perfect condition.

RSIVwfuh.jpg
Click to expand...

Turns out the diaphragm isn't my problem either as I swapped slides and the problem didn't shift. I'm beginning to think coil/ lead/ cap....
 
Update:
sX2Dv74m.jpg


Have disassemble, cleaned and reassembled all plug caps. 2,3, 4 read low to high 9K ohms. So they’re no better. # 1 cap I can’t get a reading at all no matter how many times I take it apart and put it back together. So I now have a new problem I didn’t have before my bigger problem of a mostly dead cylinder.
I will not be modifying these plug caps.
These caps are done.
Moving on.
I will be buying new caps.

Non- resistor caps and switching to resistor plugs seems like a good idea.
Known solutions, specific links for what I need would be appreciated. Parts that are known to work with the 16 valve 750 engine. I don’t know what to look for now.
Would like to put the coils and plugs to bed so I can get into rebuilding one of my other heads.

Endoscopic camera arrived today. So played with that a little. All pistons have quite a bit of carbon buildup on top. This is the offending cylinder # 4. You can see oil pooling in the indents.
p7HFn0ym.png
 
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Rich, don't get too excited with these caps. They're really simple, $80 for caps NO, though that [NODE="1"]Home[/NODE] seems odd. anything conductive, to replace those resistors will work, we think copper, but a screw with a small enough head to fit in there, cut a 10 penny nail or a piece of coat hanger to fit, I like to make just a little longer than the resistor to be sure both ends fits the inside connectors tight when the little brass thing is screwed back in. then you have non resistor caps. should have a complete full connection, no resistance, from the little pin that screws into the wire through the little brass part that connects to the plug. Heck just play with it, only takes a minute. Some will argue but I've ran them without the resistors forever never changed to resistor plugs and have never had any firing problems. I think the resistors are to restrict static on radios.... The compression test will tell a lot, the carbon on that piston looks normal, I can't see the oil you mentioned.
 
Rphillips. I appreciate you taking the time to write. I really do. Please understand. I am not going to modify these 41 year old caps. I’m done playing with them. I’m moving on. If you’ve got links for what I need in NEW caps, I would sure appreciate it.
 
Last edited:
Todd, thanks. I’m sure I can get these just about anywhere. If you have a part number that would help. I don’t want to get the wrong thing. I think now I want to go with non-resistor caps.
 
That carbon deposits on your pistons could cause detonation or ignite the fuel mixture too soon. This oil leaking into the pistons means in the very least you need valve stem seals, but you may also need new valve stems. Catching it now could prevent touching the lower end of the bike. Polishing the top of those pistons could only lead to good things. IMHO
:)
 
Last edited:
Rich82GS750TZ said:
Update:
sX2Dv74m.jpg


Have disassemble, cleaned and reassembled all plug caps. 2,3, 4 read low to high 9K ohms. So they’re no better. # 1 cap I can’t get a reading at all no matter how many times I take it apart and put it back together. So I now have a new problem I didn’t have before my bigger problem of a mostly dead cylinder.
I will not be modifying these plug caps.
These caps are done.
Moving on.
I will be buying new caps.

Non- resistor caps and switching to resistor plugs seems like a good idea.
Known solutions, specific links for what I need would be appreciated. Parts that are known to work with the 16 valve 750 engine. I don’t know what to look for now.
Would like to put the coils and plugs to bed so I can get into rebuilding one of my other heads.

Endoscopic camera arrived today. So played with that a little. All pistons have quite a bit of carbon buildup on top. This is the offending cylinder # 4. You can see oil pooling in the indents.
p7HFn0ym.png
Click to expand...

Mirror polished bores. Pull the head ffs. Swanning about with changing caps is a ludicrous sidetrack.
 
I never remember seeing this size caps without resistors. You got me nosey, I just went out in the garage and took one of my new XD05F's apart, they are made exactly the same as the OEM, not a clue about how the K & S brand is made, NGK can easily be changed to non resistor, just as the OEM can... Did you find non resistor caps? both of these say 5K ohm, one in title, the other in description
 
Cipher,
All in good time. I know the top end all needs redone. I'll get to it. If you've followed from the beginning, you know I'm going to rebuild the top end for the '82 engine that was originally in this bike. In the course of looking at things, coils/wires/caps came up to investigate. Investigation lead to where I am now - needing new caps, Then I'll get to building the other engine to put in this frame. When I do that, I'll have reliable coils/caps. This is a long-term project. I'm in no hurry now. As you saw and commented on my other thread, I will likely have another bike to ride before too long. Sorry if my story, the way I choose to work on my bike, or the order in which I choose to work on it doesn't agree with you. I have seen you rarely contribute helpful advice in threads such as these. If can do so here and give me link to the correct non-resistor or resistor cap (I don't really care at this point), then please do. Or you could just scroll on.

rphillps, yes both of those of the links I posted above from Z1 are resistor type. only this one is available. I had thought one of them was a non-resistor, but as you saw, it was in the description.
https://www.z1enterprises.com/spark-plug-cap-10mm-12mm-102-degree-terminal-stud-5k-ohm-black.html
If I can get someone here to tell me this will definitely work, I'll buy it. Right now I'm second guessing myself, because I have never done this before. Trying to learn.
 
Don't discount the coil. Mine measured perfect and when I ran it with one lead disconnected from the plug (the cylinder I was having issues with) I got this.

AIL4fc_G51gNS0lGL-uaokeAVo2rk0vhTs524_m19IDR3d1wY6q_4-imVb1ORzqRIZlvheHDdRlwPLAhf7mGHemTywQMdBizxWh3i-qelYx_YNT2Qs9jk9cd=s0
 
Last edited:
Rich, IIRC, the inner cylinder’s caps are different from the outer cylinder’s caps on the 16-valver.
Can someone confirm?
 
KiwiAlfa156 said:
Don't discount the coil. Mine measured perfect and when I ran it with one lead disconnected from the plug (the cylinder I was having issues with) I got this.

AIL4fc_G51gNS0lGL-uaokeAVo2rk0vhTs524_m19IDR3d1wY6q_4-imVb1ORzqRIZlvheHDdRlwPLAhf7mGHemTywQMdBizxWh3i-qelYx_YNT2Qs9jk9cd=s0
Click to expand...

don't really understand what you mean.
But i can't quite make out what i am looking at, is the plug cap still on ?

Cool picture, that looks like a powerful coil/spark.

Made me think of the Suzuki service bulletin for GT750, how to do a rudimentary test of a coil without the Suzuki testing equipment.
Clip off the whole arm of the spark plug and check out how it sparks.
Spark should at least reach the side of the plug, preferrably a strong blue spark.
Yellow spark is already considered weak and a weak yellow spark means bad coil.
 
Jim, that's what others have said. As you can see in pic where I have them all apart, all 4 caps on my bike are exactly the same, right or wrong. I have no fitment issues. And I have every reason to believe the the coils/wires/caps on the bike are original from 1982.
 
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