Topic: 78 CB750F broken spark plugs

[ts354]

I've been working on bikes for a few years and have never run into this problem until now.  I broke two spark plugs off trying to remove them.  Never seen, or let alone done that before.  I probably should have used some heat trying to remove them but I noticed on one that the rust had started to eat into the threads so it probably would have broken anyway.  I'll add a couple of pictures for everyone to see.

So, what is the consensus on removing broken spark plugs?    ugg, I think I know .... (remove engine, remove head, machine shop, drill out, tidy up threads, rebuild engine.)   ...  but, has anyone had luck doing it themselves/their selves without going the "full rebuild" route?

[ts354]

Btw, here is a shot of the inside of cylinder #1.  Lots of flaky looking carbon, and of course some rust on the walls.

[Jerry Rxman Griffin aka MuthaF'er]

Uhhhh, you're going to be taking that engine apart....  good luck with what more you find

[pjlogue]

Yes, engine and head removal is needed.  I had a similar situation with a spare head I purchased for my GL1000.  Got it off flea bay and found the head had a broken off plug stuck in it.  What I ended up doing was  to drive out the ceramic core (carefully) then bought a  Jewlers hack saw mounted in a coping saw frame.  (very fine teeth on the blade)  I inserted the blade through the hole in the core of the plug, reattached the coping saw frame and started sawing into the broken off plug going from the center outward towards the heads threads.  When I knew I was getting close to the heads threads I went very slow and kept checking to make sure I just kissed the heads aluminum threads and not cut into them.  I was hoping I could get away with just one cut thinking it would relieve enough pressure so I could tease the broken plug out.  No luck.  I had to make a second cut on the broken plug to have a small section I could use a small punch on to drive the section towards the center of the opening.  This finally worked.  The threads that were left on the broken plug bent allowing the small section to come free.  This gave enough "give" in the broken plug to be turned out.  End result was a plug hole in the head with just a trace of the cuts from the hack saw but otherwise undamaged. This was a very, very slow process (2 days) and when I would get frustrated I would walk away from it.  It did work though.

When I was in my 20's-30's I would probably have ruined the head because of impatience.  I'm now pushing 70 and I know that taking time and being patient pays back 10 fold, time wise (and money) for projects I do.

-P.

[ts354]

I bought the bike for 300.  Thought I might be able to get it started and sell it as a runner, but, I don't know what I'm going to do with it now. 

I'm still just kind of surprised of how easy it is to break off spark plugs.  I've just never run across it before.  After seeing how the rust can creep in (probably from sitting outside and water being around them) they do rust and, that is the thinnest part of the metal of the plug, plus, just how deep those threads go too. Lots of surface area to stick to.

So, out with the engine.  I have a bore scope and will check up through the bottom oil drain hole to see what condition the bottom end might be in.   

[BenelliSEI]

Drop the small pan and see what you find in there and stuck to the pump pick up screen. That will tell you a lot……

[newday777]

I watched a video from Brickhouse Builds a week or 2 ago about them having a couple of busted plugs on a 750 they wanted to get running from a barn find K2, they had planned to try to revive it and ride it from the barn to the shop. It didn't happen......

[newday777]

[rotortiller]

This is what happens when you do not look after your 5hit lol, not mine though.

[HondaMan]

When Champion was a real sparkplug company, their sparkplugs didn't do that because the metal was properly plated (like with clear zinc) and the threads were machine-cut (an expensive way to do it then). When they got bought by whoever has owned them since the 1990s, they became genuine junk parts in Champion boxes. The threads are bare metal (low-grade potmetal steel) and are cast, not cut. I've also seen them rolled, and incompletely so, which damages the head's threads during install. At the very least, to use them required anti-seize on the threads at install: I just use better plugs, instead.

[bryanj]

Back in mid 70's we used to redo several Honda spark plug threads in situ with a proper helicoil kit, it was always done at customers risk on the understanding that the worst case was carry on and take engine out.
We usedcopious amounts of grease on the drill bit and tap plus turning drill bit by hand.
It was a very awkward job and took care plus skill.

In your case, especially looking at that bore, i would remove the engine, head and block for full inspection

[willbird]

When Champion was a real sparkplug company, their sparkplugs didn't do that because the metal was properly plated (like with clear zinc) and the threads were machine-cut (an expensive way to do it then). When they got bought by whoever has owned them since the 1990s, they became genuine junk parts in Champion boxes. The threads are bare metal (low-grade potmetal steel) and are cast, not cut. I've also seen them rolled, and incompletely so, which damages the head's threads during install. At the very least, to use them required anti-seize on the threads at install: I just use better plugs, instead.

I worked at a Tool and Die shop in Toledo Ohio from 1998 to 2002, Federal Mogul owned Champion then. There were Champion plants all over the world and the blueprints had dimension boxes with different dims for each place. The company I worked for "CO-OP Tool" pin stamped every single part they made with the company name and address. The Champion plants had all switched to local suppliers, but when Federal Mogul bought them all of the sudden orders for parts started rolling back in again because they contacted us due to the pin stamp on the parts.

Bill

[Stev-o]

 Personally, I would source another head....

[ts354]

Thank you everyone who replied!!

Interesting knowledge about the champion plugs.  I personally have never used champion plugs unless it was in my lawnmower.  I've always used NKG's.  I'm not saying I know or prefer either brand, I just have never used champions. 

Like I said, I bought the bike cheap and was just going to try and get it to run, not a big loss.  I did learn some stuff though.  I will probably keep it and use parts off of it here and there.  I do have a '72 K model so maybe some things can swap. 

Thanks again everyone!!

Todd

 

[M 750K6]

It is interesting how different communities have their preferences.

I also own a mid 1970s Norton and as here, with my Honda, have had help on a good Norton forum, with various issues. THE plugs to have are Champion N7YC. Better than genuine NGK, plus less likely to get a fake. Also, 1st chance whip out your old fashioned points and condensers and fit a more reliable, never need to touch again, EI.

I guess, experiences vary, get reported and then you're better safe than sorry. No criticism intended on this, I very much follow what's offered as best or safest practise. The differences just struck me.

Happy with Champions in the Norton and NGK in the Honda. Came with EI on my Norton and points on my Honda. Happy with both. Love how bikes and fora can be so different, but also the same  👍

[rotortiller]

I've used Champion plugs in a lot of stuff however the thinner walled and smaller sized plugs with long threads do need to be removed from time to time with machines operating in a corrosive situation. Most bike manufacturers use and recommend them. I pulled and replaced my 2005 R6 CR9EK plugs due to a failed coil pack and they were fine with 30,000 kilometers on them, the bike lives indoors. My CB750 has 8 year old champs in it which I pull every 2-4 years. They have been in operation before 2017 when I replaced the CB750K ignition system with a Tytronics electronic unit, but so are the ones in my brother's OEM system. Anti-seize  applied sparingly on the threads is wise in any situation with all brands especially when pulled on a maintenance schedule. I prefer NGKs in my two strokes as they seem to last forever. Champion plugs are fine in 4 strokes. My car has Champs with no issues. My ocean going Jet Ski with the thin walled CR9EKs has the plugs pulled every year and replaced every 50-100 hours (12-24 months).
Back in the 1970s there were plugs that became seized in the SOHC cylinder head due to poor maintenance, today is no different except modern bikes run cooler and have rubber sealing methods that keep the plug area dry compared to the antique stuff thus allowing a larger maintenance window. Some will say it's a China thing, but we all know the best SOHC stuff comes out of there lol. Without China there would be a lot of parked SOHCs.

[HondaMan]

I grew up swearing by Champion plugs and used them in all my cars (except the Toyota Celicas). They had one to die for in the CB750: it would stay clean and self-clean after too much choke was applied for too long (I wish I could remember it's part number...) but that plug disappeared in the 1990s from their lineup. It was a great plug for touring, too. I was real sad when they became junk parts during the 1990s...