legacycentral bbs

I was sitting at a stop light adn when the light turned green i started to go, except there was a loud pop and the car started running really rough/loud. I pulled over and figured out the problem was a spark plug. It just wasnt there anymore. I had a set of NGKs I've been meaning to put in in the car, so I tried putting one in. It woulnd tighten, so I took oneo f the other spark plugs from the engine and tried putting it in. it never tightened either. After putting the NGK in the other hole I tried starting the car to see if it would work. It didnt.
Anyone know what I should do besides take it to a shop? How bad is the damage/how much is it going to cost me? Thanks

Uh oh.

It sounds like the plug that blew out chewed up the threads on its way out.

It's possible to repair spark plug threads with a Helicoil-type threaded insert. I don't know how you could do it safely, though, without removing the head. With iron/steel engines you can use a magnet to pull out all the chips from the drilling and tapping process, but that won't work with aluminum.

Damn, that's crazy!

If you're going to remove the head to fix it with a helicoil, then I'd go ahead and consider just picking up a head from a J/Y to swap in. Just my .02

I agree. It's possible you would have to tap the hole a size bigger, so finding a plug to fit it would be an adventure...

Yeah, you guys are right, a replacement used head is probably the way to go... Depending on how much you like labor, it might be a better option to get the entire engine from a junkyard car.

Helicoils and their kin actually end up with the threads back down to the correct size and pitch. You drill and tap it bigger than the original hole, and then thread in the insert. There are a few different brands made specifically for spark plugs.

If you really want to try to do this on the cheap you could try running a tap through the threads and then using some kind of vacuum to try to suck any tiny chips out. I believe you'd need an M14x1.25mm tap. Depending on how damaged the threads are (and how far the plug backed out before it blew out), this might get you usable threads again. The crush washer at the base of the plug should still provide enough preload to keep the plug in the head. And if it didn't work, Helicoil is still an option.

I don't know how you could be sure to get all the chips out, though...

I could sell you a head really cheap. Either that or it goes to the scrapper where I would be grateful to get $.50/lb.

Steve

I had the same thing happen to my toyota 4runner. I was able to use the tap on the end of a ratchet and the I put alot of grease on the tap and the shaving stuck to the grease. Do it slow and use fresh grease every tine you reinsert the tap. take your time you get one shot at it.

BI wrote:take your time you get one shot at it.

A truer statement has never been made.

My XT stripped one of its exhaust studs out of the head, and I had never tapped threads before. So this very idea went through my head, that if I didn't do this right, I'd probably be buying a new head. I did everything by the book, used kerosene as a cutting oil as is recommended for aluminum, and tapped it out very slowly, making 100% sure I had the tap straight in there. I did it right, and I put heavy-duty threadlocker on the new stud, haven't had a problem since.

I was able to tap it out to the original size, so it's possible you could do the same. But you'd have to take the head off, I don't know how you'd get the shavings out of the cylinder, and hell, if you're taking the head off, spare yourself the tapping job and get another head.

When you say that the plugs you tried to put in didn't tighten, do you mean that they bound up and you couldn't thread them in any further without using a lot of force? Or do you mean they just spun around after threading in part of the way?

Repairing a stripped spark plug thread is a fairly common repair that can easily be done with the head in place. A competent shop should be able to quote you on this over the phone. Basically you drill, tap for helicoil, vaccum out the chips with a hose-thingy, seat insert which is already tapped back to regulation size, and reassemble. I did the exact same thing on a BMW 2002 head, had it fixed, and proceeded to drive 9 more years on it (and would still be if not for an unfortunate incident with a large Buick).

Aluminum chips won't stick to a magnet, but they also won't do much damage unless they find their way into a coolant hole. I'd change the oil soon afterwards for peace of mind.

Here's areference for a kit for such a repair, that obviously would be cheaper to have done professionally

http://www.thetoolwarehouse.net/shop/LIS-65900.html

Now, why did the plug blow out ? Must have been nearly stripped already, or you have some monster knock !

how did you drive for 9years on a BMW 2002 head?

http://www.cardomain.com/memberpage/362487

9 years isn't too much to ask. Is it?

a 1972 BMW 2002tii to be exact. Rock stock and in damn good shape until the Buick incident. My first car, I bought it at 15 and fixed the mechanical woes before even getting my license.

A good car once you: 1. learn how to remove the camshaft, change the rockers and valve seals with the head still on the car; 2. learn to jump out and clear the debris out of the idle jet while at a stoplight, reassemble, and take off without missing the green

BTW I called around and it looks like around $100 to do the spark thread repair around here, but with no guarantees (naturally). I don't like to take the head off of anything if you don't have to, I bet the failure rate for non-professional R&R of a head would exceed the failure rate for getting the plug helicoiled. Plus you could be buying a bad used head, been there and definitely done that

Sorry for the long response time, I wasnt informed there were replys...
I had the car towed to GB Motorsports in Hayward, so its in good hands. He was going to try and figure out the least expensive option for me, so we'll see what happens. Thanks for the replys, I'll keep you updated as I get word from the shop.