I just changed the spark plugs on my 740 wagon (1992). I've only had it a short while and bought it used from someone who owns a shop. It has 222,000 miles. I'm not familiar with this car yet so this spark plug change goes down in history for me as the oddest spark plug change yet.

All the plugs came out fine, but the gaps were all off. I checked them and the gaps varied for each one. Two were at .035 . My book says they should be .028 (which none of these were) . I went to the volvo dealer and purchased plugs from them directly. I checked the gaps on all of the plugs they gave me and they were .028 exactly.

So, I took the old plugs out and put in the new ones. 3 of them went in perfectly. 1 of them gave me a lot of trouble. It didn't want to go in very far and after an hour of working it, taking it out, cleaning the threads a little with my finger, cleaning the outside a bit, putting it back in, taking it back out, i finally just said 'to heck with it'. I'll let it go in as far as it wants to and i'll fire it up and see what it does.

It seems to me like that one plug just didn't go in far enough. I compared it with the others and really analyzed them with a flashlight. On this one plug you can see some of the threads on the plug when you look at it installed. The other plugs seemed to go in normally and you can't really see the threads at all once they're torqued down.

I didn't want to break anything, and certainly didn't want to damage any threads on the plug or the engine. So, i snugged it down just a little and fired it up.

The car started right up but it left me feeling uneasy. The engine itself is very noisy, and it was very noisy before I swapped the plugs. It almost sounds like it knocks but without a good frame of reference I cant tell what this engine is supposed to sound like and what exactly I'm hearing. Since day 1 it has always been noisy and always had a bit of a knocking/rattling sound to it.

Maybe I bought a car with issues, I'm not sure, but changing the spark plugs didn't make it quieter and only left me feeling more uneasy than I did before I swapped the plugs. Figures.

I don't really have a question to post yet, I just wanted to communicate this and see what response I get from the community here. I'm going to do some further analysis in a day or two and post a video online so you can hear it. There's definitely something off about this engine, I just can't place it. I'm just now getting to 'making it mine'. If it were my Buick I'd tell you the moment something didn't sound right and be able to tell you what it is, or where it's coming from... but this car... It's like unknown territory for me.

I'll post images of the spark plugs and a video soon, so updates to this post are coming shortly.

EDIT: Here are 2 photos of the spark plugs I pulled. These are not the greatest images. It's dark here at the moment so what I'll do is take better pics in the light tomorrow and I'll have a video posted as well of the engine noise.

 

Spark plugs can never quiet an engine, may be if there's blowbye...
Should try to clean the treads, may be put some oil on the treads to make them go in better.
Hard to opine on your noises but these motors are not the quietest. Autolites don't work well in Volvos.

 

Oh I didn't set out to change the plugs because of the engine noise. As I said I'm just starting to 'make it mine' by doing a tune up. The noise however, is an ongoing thing I need to investigate further. This is my first time doing any work on this vehicle since I purchased it, outside of an oil change a few weeks ago.

 

These motors are noted for piston slap as they get older. You usually get it at 1st start up on a cold engine. The engine sounds a little like a diesel at idle. Both as it warms up and you increase the RPM it quiets down. You may get a little valve noise but that usually isn't to loud. What are your symptoms.

 

Really? I heard this from someone else too. It really does sound like a diesel when I think about it. It's always sounded like this since the day I got it but since it drove fine I gave it the benefit of the doubt. It seems like it has got a little louder in the last few months though.

My symptoms are.. well.. noise. Other than just noise I'm not having any problems driving. There was one time it felt like it wanted to stall when I was about to take off from a red light, but it was only 1 time (last week) and it never did that again. For the most part, its just noise and I want to know if its normal or not.

Here's my update on the plugs today:

The thread on one of the spark plug holes is definitely screwed up. Today I decided to pull the new plug out (it was only in partially) from that cylinder. It came out fine. No probs with the plug itself. I used a shop vac to suck up any thing i could from the hole, and that seemed to help a little, and i basically spent 2 hours with the original spark plug - torqueing it down a little, backing it out, torqueing it down a little more, backing it out, and in between pulling it completely out each time I brushed off tiny fragments of metal that were attached to the spark plug threads and I was lubing the threads with oil each time.

I managed to work the original spark plug in a little further than I could yesterday with the new plug... but it is still not seated all the way down like it is supposed to be. The reason i chose the original plug was because i wanted to see if the hole would take those threads over the new plug. It did seem to like the old original plug more than the new plug.

After about 2 hours of doing this - no joke - I gained a little bit more... a few threads or so, but that was really all. I fired up the engine with no probs and then while the car was running I pulled out each spark plug wire to see how the engine behaved.

One reason i did this was to see if that rattle/noise would go away if i killed the power to one of the plugs. It did not!

The other reason i did this was to see if that cylinder with the bad thread and half-installed spark plug was actually working or doing anything... which it seems to be doing something... because when I pulled it from that plug the engine reacted noticeably. I guess it's still firing??

I ran out of light so I was not able to do any filming but I'll be doing it tomorrow. I'm also going to give the car a drive. I have no choice really. Its my only operating vehicle at this time and I need to do things tomorrow.. I guess we'll see if the car fails on me.

I wonder if that spark plug being the way it is will do any damage or cause any problems. What do you think?

I know the solution to this is to retap the threads. What a pain. This is my far the most difficult spark plug change I have ever done on a car.

Jagtoes, I'll have a video soon so you can hear the noise I'm taking about. It almost sounds like its coming from BEHIND the engine... possibly the tranny? Or maybe it's supposed to sound like this and I'm just used to quieter engines. I don't have a long hose or anything to be able to use as a stethoscope but I'm hopeful.

 

remember the head is aluminum, while the plugs are steel.

I think I'd try a bronze brush large enough to be a tight fit, and turn it while going in and out

 

I would get a spark plug tap and put grease on it and slowly retap the spark plug hole. Use the same process of threading it in and backing it out . Clean off the grease and do it again until you have it completely cleaned up. I also use "never seize" on the spark plug threads when I install them. You don't need to retap the holes but just clean up the threads. You just need to be careful when you start the tap so as to not cross thread the start. Take your time and it should be OK. Also looking at your old plugs they look fine and based on the pictures it looks like the engine is running OK.
As for the noise with the engine at idle and warm listen as you increase the idle and it should get quieter. Also i don't know what oil you are using but whether it is 10W-30 or 10W-40 it is thin (10W) at start and as it warms up it thickens out a bit. I run 10W-40 in our 89 740 with 353K miles on it. By the way the piston slap started at around 150K miles and it's still running.

 

Piston Slap happens due to the motor having been overheated causing piston(s) to shrink thus making them move laterally in the cylinder wall and this is what makes the "slap". Later, 1993 and up, motors have longer piston skirts which cuts on the space available to create the slap, so almost never a slap... Piston Slap doesn't just happen due to mileage or age--overheating is what causes it.

You may get various other clackety noises as the motor ages and things get looser but this is not "piston slap".

 

Michael9898: It is odd that the Autolite came out with no problem and no visible damage to treads but one of the new plugs has a hard time going in! I'd think some debris might be causing the issue and might have already done some damage to the treads in the head. I'd tap that whole, at least make sure it's clean and use oil to get the plug to sit in right.

 

Just assuming it to be piston slap but also considered a wrist pin but as I mentioned cold it idles like a diesel. As for the overheating we bought the car new in 89 and it has never overheated so I'll rule that out. Based on using a stethoscope the noise is in the block and not the head. As I mentioned it's been this way for 200K plus miles so I'm not to concerned about it. If or when it blows I'll just rebuild it. Not a big deal.

 

When you remove the head from a piston slapping motor, you can actually move the piston top back and forth with your finger and hear the "slap", more like a clunk. The rings are still there and good and doing their job but the piston has shrunk due to overheating then cooling--nothing else can shrink the piston. And yes, this can last for hundreds of thousands of miles without any other negative effect...

 

I'll have to remember that when the time comes to pull the head or rebuild it.

 

Update:

The car fired up with no problems today and I drove it about 20 miles doing my usual errands for the day (stop and go and some highway time). I had no problems at all and I did notice that the engine noise got quieter as the engine warmed up. By the time I got home it was a lot quieter although it does kinda sound like a diesel to me.

I'm still very uneasy about that plug. It's not installed all the way. I'm looking into some options and may just pay someone to fix the threads. I'm really pressed for time and If i'm going to do it myself it's going to take up 2 of my afternoons and I've already spent 2 afternoons on what should have been a simple spark plug change.

I recorded a video today of the engine starting up from a cold state. I'll get that uploaded as soon as I can and update this post. Thanks everyone!

 

Low-pitched engine rattle. If your ear pics up anything odd please do share your thoughts. The engine is quieter after being driven but the rattle never quite goes away. This video was taken just after cranking up from a cold engine state.

 

Interesting and it sounds to me like you have a few different noise that need to be isolated. The squeaking noise sounds like belts. I would remove all of the belts (alt , PS , AC) and start it up again and see what you have. I also think I hear FI clicking much louder then normal along with some valve noise. Has this engine had a valve adjustment or have the clearances been checked. Last would be to get a stethoscope and check the noise of the block under the exhaust manifold for piston slap. Just need to isolate. Do we assume some of the noise but not all goes away as you increase rpm.

 

Is there any wobble in the crankshaft pulley with the engine running?

 

Yeah. I believe the fan is making some sounds or maybe thats the crank shaft? The belts seem to be in good shape but I'm missing the AC belt. I bought a new one but haven't installed it yet (the old one just fell off while driving only a few days after i purchased the car).

I'm not sure if it's had any work or what. I know where the original owner is, he has a shop not far from me, but honestly I don't trust anything he's going to tell me. There were a few things off about the car when I bought it and more things I've discovered along the way.

I'll take some better videos soon. This is the loudest engine I have ever owned. Something is up.

 

How would I determine that? Just a visual inspection or?

The fan sure does make a lot of noise. I'll take some more videos soon.

I purchased a thread chaser today. A local shop wants $175 bucks to 'retap' the spark plug hole. I may be able to fix this (spark plug problem) with just a thread chaser so that's tomorrows fun. If that doesn't help, or if it makes it worse, I'll just pay the $200 bucks. I'm pressed for time at the moment.

Thanks everyone, I'll let you know my progress. Fun fun!

 

Yeah...just look at it while its running.

I ask because I've seen one that had a wobble and a rumble from the engine that was timed with the wobble of the crankshaft pulley.

 

The thread chaser should do the trick. Just use grease on it as you thread it into the hole. Take your time and it should work out. Also use anti-seize on the plugs when you install them. Next I would remove the fan unit and start the engine again and see what noise you get. As for the lower balance pulley I've replaced mine as the rubber rots with age. You can tell by removing the belts and then try to move the balancer by hand .