Cylinder 2 incomplete combustion

[Fairlady5150]

So my recently acquired 1968 1600 appeared to be running very rich. I'm new to SU's so I did some homework before taking a look at them. Everything appears to check out okay, so I started looking elsewhere. Figured I'd swap the plugs while I'm at it. Before I removed it, I noticed #2 was at a slightly off angle, and wasn't seated as low as the others. New plug yielded the same results. So I'm guessing that I'm likely 'running rich' because cylinder #2 has little or no combustion. Any thoughts on this? Any recommendations? Definitely don't want to try to force the plug.

[keith0alan]

If the plug is at an angle and not seating then the plug is quite likely cross threaded. You have a bigger problem that running rich.

[theunz]

You might be able to correct the threads with a thread chaser. Use plenty of grease on the chaser to hopefully catch the shavings. Other, and the proper way is to pull the head and then address the threads.

[C.Costine]

I agree with starting with quick and easy with the thread chaser. It would be virtually impossible to get the plug in even halfway in at such an angle so you should still have plenty of good straight thread left. You will be told that you have to remove the head and take it to a machine shop for work like this, it depends on your level of confidence with your automotive repair skills.The key to getting the threads straight will be a long extension for the tap. It will enable you to hold it at the correct angle. You can google tap extension and find sources. To check mixture go to the carburetor section of the Tech wiki and look at Keith Olan's write-up. Checking and adjusting mixture is quick and easy. Another quick, easy, inexpensive analysis is to check compression.

[notoptoy]

I have done a helicoil on the car with the head in place. Not for the faint of heart. 1) Start with piston near top of stroke, but leave room for tap/chaser to seat fully. 2) get some foam, firm but flexible. Saturate it with oil. Stuff it into the plug hole, so that shaving and fillings are caught in the foam. 3) Run tap/chaser, using a shop vac to get as much as possible out of the hole. 4) Seat helicoil. 5 Using forceps/tweezers, and shop vac, remove the foam (you did use a fairly flexible but sturdy piece, right?) Vacuum out the hole meticulously. Install plug and see your results.
My father showed me this trick with a 1969 Fiat way back in 1970's, on an aluminum head. I never had any problems and had it up and running quickly with no drama. Everything and everyone will likely and rightfully tell you not to do it this way, but I did, and I would probably do it again faced with removing OHC components.

[keith0alan]

The best way to heli-coil a spark plug hole is with the head off the car. It is also a good chance to do a valve job and check the head for flatness. Pulling the head is not the cheapest or fastest answer but it is by far the best answer. Removing the head really isn't a horrible chore. At one time removing the head and cleaning carbon out of the combustion chambers was considered routine maintenance. Not so much any more with modern oils and gas but not rocket science.

[notoptoy]

Too be sure, make no mistake that I am in complete agreement that the RIGHT way is to remove the head to fix this. I am just suggesting an alternative based on the stated problem. If the spark plug threads are the only known problem, then this could be an alternative. I can tell you that for teenager who paid a whopping $50 for the entire Fiat, the $5 solution was a welcome one! As a responsible adult who knows better now, that solution is not necessary for me to choose today.

[keith0alan]

I certainly have done my share of no money on the cheap fixes. Ask me about my three cylinder Renault Dauphine trip some time. If he can scrape a few bucks together and someone with some experience can lend a hand he will be much better off. The proper repair will need to be done at some point. The sooner the better. If it is bodged now and the plug blows completely out a month from now when he is miles from home he will be really stuck.