'79 GS 850 Spark plug cross threaded

[Michigander]

I have a '79 GS 850 that I purchased last fall. I knew it had some problems, but one I need to fix is the threads for the plug on one of my cylinders.

The bike runs and starts easily, but obviously that cylinder is not firing, I was wondering if anyone has delt with an issue like this. Is the best solution to take the top end off and re-tap? (I typically like to keep metal fragments out of my engine) or is there an easier solution? Will I even be able to do that without weakening the threads and/or loosing too much compression?

Also- it runs rich, carbon deposits on the remaining plugs occur quickly. Will fixing this cylinder help to solve this issue? I know my choke operates properly, and my air filter is clean. What would be the next step to getting the right mixture? The bike has 27K miles on it, and I know nothing of its maintenance history. I should check the valve clearances, and have the carbs rebuilt, but that takes time and $$$ and the weather has been much too nice to strip my one and only bike down. - or is it stupid not to perform that maintenance on this bike?

This is my first bike - Had to buy one after getting rid of my '87 Jeep Wrangler - I am capable of doing almost anything (not quite as familiar with motorcycles as I was my jeep) I can usually figure it out though, but I lack a place to do it being a college student living in a house with no garage. I love this forum and got plenty of good info from it already.

Thanks for any advice

[tkent02]

Why not just pop a good tight used head on it?

[Michigander]

Well that is a damn good idea, it seems much simpler!

Where is the cheapest place to get one?

[tkent02]

From me.

[979roadrunner]

If you are good with threads there is a way to fix this without removing the head, I believe.
The thing I don't know about this is if they make spark plug hole rethreading kits for motorcycles, as they do for cars.
If so, it'll come with a tap and treadserts (steel sleeves that replace the original threaded area) and an insertion tool.
You use a tap to rethread the spark plug hole, then screw in the right threadsert, and you'r done. If doing it without removing the head, just apply a bit of heavy grease to the tap when cutting the threads, and the shavings will become trapped in the grease, preventing them from entering the engine. Back the tap out frequently (every 2-3 turns) to wipe off the contaminated grease, and apply more.
This, of course, depends on accessibility. You may have to pull the head anyway

[Michigander]

Well how much would it be to ship one to Kalamazoo?

[SqDancerLynn1]

Go to www.jcwhitney.com search plug rethreading kit about $16.99 item 1ja-144235
it's in the auto catalog. You can also get extra inserts

[blowerbike]

install a heli-coil in the bad hole in the parking lot...
a little aluminum in that cylinder isn't the end of the world.
grease the tap and go for it.

[BassCliff]

Greetings and Salutations!!

Hi Mr. Michigander,

The PO (or one of his hack mechanics) of my bike had cross-threaded a spark plug in my #1 clyinder. It really wasn't too bad so I used a thread chaser to clean it up. It works fine now. But if yours is really bad then some kind of insert may be best, or a new head as a last resort. Your call. I just stopped by to welcome you to the forum and invite you over to my website for all the GS850G lovin' you can take.

If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", the Carb Rebuild Series, and the Stator Papers. Now let me roll out the welcome mat for you...

Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

[Michigander]

Thanks BassCliff, I have been there and read plenty of good info off your site!

I am definitely in favor of not removing the head if I can. A re-threading kit is perfect and easily within budget! I'll to be working with the cylinder under the tank, so I'll have to pull that off to gain access, but I appreciate the help and we'll see how it goes!

[bwringer]

I've installed a thread insert successfully without removing the head.

1) Use grease on the tap to catch the chips, and clean and re-grease often

2) For the love of all that is good and holy, do NOT install a Helicoil or any other brand of wire insert. Helicoils SUCK more than you can possibly imagine for any application requiring sealing (they're better than nothing in solid metal). A Helicoil WILL leak, it WILL fail and it WILL come out, leaving you with a real problem. Install a solid insert -- I believe the kit I have was called Perma-thread. They're easy to find -- I got a kit at Pep Boys. After installing the insert, you use the included tool to expand the top rim of the insert and retain it in the head permanently. There are a few other brands that work well, but make sure you get the thinnest one you can -- there's not much room.

3) Once you get the tap started, use a socket and press EXTREMELY HARD to keep it cutting. Back up and clean out the chips often.

4) Make sure that piston is out of the way (at BDC) before starting.

5) Clean the chips out of the cylinder afterwards with a piece of tubing duct-taped to a shop vacuum.

[Michigander]

I ordered a kit with solid inserts,

This may be a dumb question, but will I have to bore/drill the hole to a specific (slightly larger) size before tapping to allow for the larger O.D. of the thread insert? or simply use the provided tap and go to town on it.

Also, what kind of tolerance do I have as far as the angle of the threads to the cylinder head? i.e. if it's not precise enough, will I not get combustion in the cylinder still due to an incorrect position of the plug when its all done?

thanks again,

[bwringer]

I ordered a kit with solid inserts,

This may be a dumb question, but will I have to bore/drill the hole to a specific (slightly larger) size before tapping to allow for the larger O.D. of the thread insert? or simply use the provided tap and go to town on it.

Also, what kind of tolerance do I have as far as the angle of the threads to the cylinder head? i.e. if it's not precise enough, will I not get combustion in the cylinder still due to an incorrect position of the plug when its all done?

thanks again,

No, you will not have to bore the head. The tap in the kit has a threaded "nose" that uses the remains of the existing threads to pull itself forward and cut new threads for the insert.

This gets a little dicey when the old threads are in bad shape and when the insert section of the tap first begins to bite in. Hence the advice to use HEAVY HEAVY inward pressure when turning the tap, especially when you're just started to cut the new threads.

Tolerances aren't what I'd call extremely critical -- you can do this by hand, and it's not really possible to get the angle off by enough to matter without totally destroying the cylinder head.

[Michigander]

After installing the insert, you use the included tool to expand the top rim of the insert and retain it in the head permanently.

Ok, I see what you meant with the "heavy" pressure, it worked great and the threads are perfect.

I have not installed the insert yet because I do not have (I don't think) the tool to expand the top rim of the insert. So far it appears I will need to take the washer off of my plug to gain clearance, ???

Without the tool to expand, would using a high-temp thread locker work? j-b weld is good to 600F or 315C. But I don't think that will be enough, will it?

>Thanks,

Eric

[Nessism]

The insert kit should have the tool to seat the insert. What kind of kit did you get? Some kits recommend high temp silicone around the insert but I wouldn't use JB weld or similar.