1986 240 dl engine head

Is this the one where people were recommending getting an insert (eg Helicoil) fitted a few weeks ago? Is that what you did, or, when you say 'rethread', do you just mean a tap was run down the existing thread to clean it out? If the latter, then it will not help; if the former (and assuming the thread of the spark plug is not damaged) then something is seriously amiss here.

The amount of pressure needed to push a plug out of its hole when the thread is good is extreme - far greater than combustion pressure. Did the insert come out as well? If the plug came out and left the insert in place, I would suggest the plug is at fault. If the insert came out, was it fitted by an experienced engineer, or is it possible it was done badly?

As Stewart says, if the thread was repaired with an insert, something is very amiss. The threads strip because the aluminum wears and eventually the thread is too thin to hold the plug. The steel inserts make the repair much stronger than the original.

Mike

Local yard around here charges $30 for complete cylinder heads (u-pull), but prices are all over the map.

Well I looked all over town for a helicoil, no luck. I did find a spark plug repair kit, with an aluminum insert. My cousin is way more experienced than me with working on cars so I had him do the rethread job, he didn't even want to do it, he said that guys he talked to about the problem didn't recommend rethreading, just getting a new head. But he did it anyway, at first he said he didn't think it would work, but he finally got it to rethread. I was sceptical the whole time cause he had a really hard time with it. Anyways, the aluminum insert lasted about three weeks, until it finally popped out again. Somtimes It would make a whistling noise, that must have been the spark plug not sealed making the noise,after all. It was 12 midnight pitch dark out, I had just left my house so I only was abot five blocks from home, when it broke down again. I looked under the hood for the spark plug but it wasnt there, it was about 100 ft behind me sitting in the middle of the road, luckily I had my flashlight so I found it OK. It had melted just like the first time it happened, so I give up! I'm just gonna get a new head. Now i need to find out how much it is gonna cost to install by a professional, I don' have any experience with engines at all.

Weird - I've never heard of an aluminum insert. It seems kind of pointless.

If the newly cut threads for the insert are damaged, there really is no option but to go with a new head. The leakage was the kiss of death for the insert - the leaking gases will cut even steel inserts.

Mike

Probably a few hundred bucks, it's really not a difficult job but you do need a torque wrench, new stretch bolts, and you may as well replace the timing belt while you're in there.