I have a 93 f2 with 72,000 miles and i was doing a tune up on it and changed all the fluids and filters but then when installing the last of the new plugs on the right outter side i stripped the threads! I was told bout the helicoils and got one from the auto store but i need to know what the number is or what size one i need? The one i got is a m10-1.5, is this correct? The coil screws onto the threads of the sparkplug but as you screw it more and more it gets real tight and looks as though its ever so slightly getting bigger than it is off of the plug! Im womdering if i have the wrong size and im scared im gonna mess the hole up more. Also if you do know what size tap and coil kit ill need can you explain the best way to go about fixin it? Im hearing remove the heads but ive never done that before either! I do have a clymer book so that of course helps but if you could just give me a good rundown of what i should do id really appreciate it!!!!!! Thanks to anyone who answers!!!!!!!!!!!!

 

I'm sorry to say, but you will need to remove the cylinder head.

Not only will it make it easier to fix the threads, but it will also prevent you from dropping metal shavings and other crud into your cylinder.

This will be a lot of work, especially if you've never done it before because you'll really need to take your time.

It may be worth it to take it to a shop, because you're really going to be getting in over your head on this one, but if you insist on doing it yourself then good for you! And I will do my best to help you out along the way.

First thing you want to do is get a CLEAN bench space to work on, you don't want any dirt anywhere near any engine parts! I also recommend washing your bike before starting any work, so there's no dirt that can fall into the open engine

I hope you have a set of stands, or at least a front stand.

I'm going to give you a general rundown, but I will probably miss a few details like piston/valve timing that you'll need to get from your manual.

You'll want to get the front end off the ground so that you can remove the front wheel and forks to get them out of the way.

After that you need to remove all of your plastics, gas tank, air box, carbs, radiator (and pull the coolant hose off the thermostat housing on the head), exhaust header, and anything else around the cylinder head.

After that you need to remove the valve cover.

Now you'll want to refer to your manual, but I think you remove the cam chain tensioner then the cam sprocket bolts to remove the cam chain. I would tie a string around the cam chain so that you don't lose it when you drop it through the head.

You can leave the camshafts in the head, I don't think it's necessary to remove them for the head removal.

However, if you can't access the head studs you may need to pull them out.

Locate the head studs and remove them in a particular order hopefully explained in your manual (sort of like a criss-cross pattern)

Once the head studs are removed take a rubber mallet or a piece of wood and knock on a lip of the head in an upward motion trying to crack it loose (it will be stuck on the gasket).

Once loose, lift it evenly straight up off the engine block. There will be some alignment studs stuck in the base of the head or in the engine block, be careful not to lose these or drop them into any coolant/oil ports on the engine.

So, now you've got the head off... Congratulations!

Now on to the thread diameter/pitch/length/

In our bikes we use NGK CR9EH-9, and in NGK code this means:

C(10mm dia.) - R(resistor) - 9(heat range from 2-10) - E(19mm thread reach) - H(Half thread) - 9(0.036" gap)

I went down to my shop and measured the thread depth on my cylinder head that I have on the bench, and it's approx 12mm.

So, you're going to want a 10mm diameter x 12mm length x 1.0 pitch Metric helicoil.

You said that you've got a 10-1.5, you'll have to swap it for a 10-1.0 and see if you can get one close to 12mm length.

Let me know if you need help with anything else.

 

Oh, and the auto parts store should be able to tell you what size tap you need to use for the m10x1.0 helicoil

 

I've had a spark plug jump out and strip the head of my cbr 600fy (2000)
I was thinking rather than helicoiling it I would replace the head
I was wondering what part I would need to buy or would you suggest I buy the entire head and cams?

Steph

 

Sandman is right about the Helicoil with the head off being the best way, however ...
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I'm going to play devil's advocate. Many, MANY stripped plug holes have been fixed with the engine in the bike, car, tractor, etc. I would be surprised if you took it to a shop and they wanted to be pull the motor for this job. Some would take the job and not bother mentioning that they were leaving the engine in place.

Typically the Heli-coil tap is packed with grease to trap the metal waste (swarf) that's created. Once the tap is started and threading true, you back the tap out and clean off the grease and swarf. Grease it again, put it back in, cut a few turns, back it out and clean it. The more times you clean it the less likely you are to contaminate the cylinder.
The minute amount of material that gets into the cylinder if you're careful is unlikely to remain past the first exhaust stroke.

 

Any helicoil I've ever used required the original hole drilling out to a larger size, the helicoil tap running through to cut a brand new thread and then the helicoil installing. Excuse me if I am mistaken but you appear to be suggesting just running a tap through the original thread... I can't see how this could ever work as the OD of the spark plug and the Major diameter of the spark plug hole are too close (within a knats whisker) to insert anything between them.

Once you have identified the thread on the spark plug.. lets assume a M10x1.0, you will need to buy a helicoil kit for that thread which will come with a twist drill, a tap and coil. The length of the coil shouldn't exceed 12mm but shorter is ok, bearing in mind they expand slightly when installed.

I would absolutely not attempt this procedure with the head in situ. So once the head is removed, use the drill to open the spark plug hole to the correct size.. aluminium likes a fast cutting speed so don't attempt to drill it with a slow RPM or you will maul it to pieces. Then run the tap down the hole, after every half rotation of cutting with the tap in the clockwise direction you should move it anticlockwise by a quarter turn to break off the chips. Then screw the helicoil in (I would use some high strength Loctite for peace of mind), break off the tang and start the re-assembly.

 

As I said at the beginning of the post, head off is the best way, but in-situ is possible. Here's an article describing the same method I mentioned:
https://www.popularmechanics.com/cars/how-to/a1350/4212608/

I also wouldn't drill into a head without a milling machine or at least a drill press, in either instance with the work held securely at the correct angle.

​​​​​I respectfully disagree that the drilling is needed at all, especially in aluminum which is soft enough for a heavy cut with a brand-new tap. I also think that a novice mechanic is more likely to be successful doing the job with the engine together, rather than navigating the mine field of engine disassembly.

One thing I'm sure we can agree on is that this is not a job to be taken on lightly.

 

As a seasoned (and qualified) engineer I stand by my comments... trying to force a tap through a hole too small for its diameter, you are likely to break the tap (aluminium may be soft but the head a very thick rigid slab of it) and small chunks of tool steel can be a b'#@h to deal with. I agree that a mill or a press would be ideal but I have done the same job with a 100% success rate with a battery drill in the past, at the end of the day as you are enlarging a pre-existing hole, you would have to try pretty hard to get the drill to follow a significantly different path than the one already there. As far as taking the head off, I would 'always' but I have seen it done with success in-situ so you pays your money and takes your chances - although I will throw in that the novice should even consider shortcuts until a bit more experience is gained.

In the trade we would refer to such practices as 'bush maintenance', the kinda thing you do if you're in the middle of nowhere and that's all you have to get you home. But in my opinion the novice mechanic should either accept their skills are not adequate and take the job to someone who can do it competently or they should take the time to learn the proper technique and reap the rewards for years to come.

 

I love a good, gentlemanly debate. I threw the topic up at a machinist's forum I belong to as well:

http://bbs.homeshopmachinist.net/thr...rk-plug-holes/

 

I too love a good debate, and don't get me wrong I also love a bit of bush maintenance - I had a plug blow out of an old ford escort once and I used some gunk from Halfords called liquid steel to get me home, wonderful stuff but I couldn't recommend that method in good faith to a fellow member of the biking community.