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by Bob Hagin Q. I have a 1991 Toyota 4Runner with the V6 engine. I recently took it in for a tune-up. The mechanics informed me that the number one spark plug that was already installed was in crooked so they would not remove it because of the possibility that the threads would be too stripped to install a new one. They even said that it might require removing the top of the block just to rethread the hole. Will this crooked spark plug create that much of a problem? And if so, is there any easy fix to it besides removing the top of the block? N.W. Springfield, OR

A. Rethreading a stripped spark plug hole on a V6 while the head is still in the engine bay is a very tricky proposition. The correct procedure is to bore out the faulty threads, re-tap the hole to accept a steel insert, install it, then "clean" its internal threads to accept a new plug. Leaving the cross-threaded plug in the hole is dangerous. The heat range of the plug is altered because there isn't enough thread contact to dissipate the heat and the base of the plug isn't sealed and can leak compression. This could lead to a fried plug as well as an overheated cylinder and a burned piston. Eventually you or the next owner will have to deal with it so I advise you to have the technician take out the old plug and try to install a new one after "chasing" the thread with a special spark plug tap. If it doesn't work, you can go on from there but removing the head may be the only permanent cure. The 3.0-liter V6 engine in your 4Runner is something of a problem child. They blow head gaskets a lot and often as not, the heads are corroded and require machining and valve grinding. The preventative maintenance for this corrosion is a radiator cap with a sacrificial anode on it to neutralize the electrolysis that's set up in the cooling system.

Q. In April of 2001, I bought a new Nissan Altima GXE four door sedan with the 2.4-liter engine and an automatic/overdrive transmission. I now have 12,000 miles on it with no problems. I intend to keep it for a long time. I have a few questions that I hope you can answer for me. Does this engine have a history of problems like blown head gaskets or other serious problems? Can I expect the transmission to go 100,000 miles? Does this engine have a timing chain or a belt? Does this car have any other problems in it's history? J.K. Rocklin. CA

A. The Nissan Altima is one of those rare cars that doesn't seem to have a single blemish on its record with the exception of a couple of steering gear lockups on older cars that the company didn't resolve. Japanese cars have a reputation for blowing head gaskets and I believe that it's most often caused by electrolysis in the cooling system so change your coolant at least as often as the owner's manual calls for. Relatively high-speed small displacement engines like your Altima don't take much abuse and I suggest that you change its oil and oil filter about twice as often as is called for on its maintenance schedule. The automatic transmission fluid and its filter should be changed every couple of years too. Your Altima uses a chain to drive the camshafts so replacing a belt isn't a maintenance factor.

Q. I just bought a 1984 Toyota Tercel station wagon with four-wheel drive. It has a four-cylinder engine. The body is in very nice condition and so is the interior. I bought it for my 17-year old granddaughter so that she could have a four-wheel-drive vehicle for the winter. It smokes a bit so I plan to overhaul the engine as well as the brakes. Is it a hard car to work on? P.H. Renton, WA

A. If you're going to do the jobs yourself, buy a good repair manual like the one offered by Haynes Publishing company and follow its instructions to the letter. The only problem I've heard of in overhauling an old Tercel is that it's hard to get the piston rings to seal. I pay particular attention to roughing-up the cylinder walls, make sure they're washed down with soap and water and use non-chrome piston rings. Break it in on inexpensive non-detergent oil for 500 miles, change the oil and its filter, then give it to your granddaughter. Young drivers usually doesn't understand the term "take it easy" so do the break-in yourself.