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spark plug torque

21K views 36 replies 12 participants last post by  plinker17722 
#1 ·
I am replacing my bosch spark plugs with bosch spark plugs for my 2000 sl500.

Does anyone know of the torque setting.

I tried looking for it in past thread but dod not see.

Thanks

Terry
 
#4 ·
thread torque is dependent on lube or not and if lube what kind.

Since the plugs and WIS don't say to use antiseize compound the torque listed is for a dry plug, You would use LESS torque if you use antiseize.

How much less, would mean looking up a table for the plug listing torque spec's with antiseize.

Personally on disimilar metal joints, which this is, I use antiseize. a very very small dab on the plug threads. But it's your choice. you do NOT want to get any antiseize anywhere near the plug tip or on the ceramic. It is conductive.

And for torque, personally I have never used a torque wrench on plugs. In most cases, virtually impossible to get a torque wrench on them anyway. in the case of the SL, you can. However IIRC the plugs have a crush washer, If so, you will easily notice when the washer has crushed completely. then stop.
 
#8 · (Edited)
I have always used anti-seize compound but the trick is to use it very sparingly. Glob it on the threads and get some of it in the combustion chamber and you can mess up the O2 sensors.

As far as the torque the aluminum head I've worked with From my Toyota MR 2 to 300E to my SL it's always been the between 16 foot pounds and 20 foot pounds. It doesn't have to be critical but obviously over tightening the aluminum threads though ruin your day. Just as under tightening them.

That plug works it's way loose and strips the threads under compression and you'll wish it tightened it a little more.

20 foot pounds with a very light coat of anti seize has always worked for me.
 
#12 ·
Fouled Plugs on #1

On the '01 SL500, I removed the plugs this evening and had an unpleasant surprise: #1 has 2 fouled plugs (picture 1), the rest of the cylinders plugs are fine (picture 2).
Reading other plug-related posts suggests several reasons:
- bad valve seals
- bad piston rings
- plugged crankcase ventilation system
- weak coil and/or wires
One post suggested replacing all the plugs, swapping coil and wires on the fouled plug cylinder with the ones on a clean plug cylinder, and running the car for a while to see if the problem follows the coil from the dirty cylinder to the clean one.
I'd also like to do a compression test, but first need to search the forum for a 'how to' on that one.

Tomorrow I'll examine the crankcase ventilation system, but any other suggestions to diagnose the problem would be welcome! :bowdown:
 

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#19 ·
From my blurry photos it's hard to tell, but they're all identical:
Beru Platin 14F-8DPURX02, R1, Made in France.

Picked up the new plugs today:
Bosch FR8DPP33+, 7422, six of them made in Germany, the rest made in China. Yes, I know ... life is in the details, and this does not make me happy. However, I trust Robert Bosch was looking over their shoulders when they were made.

I also bought a remote start button to attach to the starter for doing the compression test. This will allow me to leave the ignition off and hopefully not disturb anything electrical. Must remember to put one plug in each cylinder first!

A question on thread chasing: the plugs came out fairly easily, but the 2 fouled ones were a little hard at first, so I loosened them, then ran them back in before completely removing them. Do I need to chase the threads?
Again, thanks for all the help!
 
#23 · (Edited)
Update on my fouled plugs on no.1 cylinder:
When I installed and torqued the new plugs at 75,000 miles, I swapped no.1 and no.2 coils around and renewed the no.1 plug wires. I've driven 2500 miles since then so today pulled the no.1 and no.2 cylinder plugs. Same thing: no.1 front plug was fouled and no.1 rear plug was a bit less fouled. Cylinder 2 plugs were fine.
Does it look like oil or is it a fuel problem? The car doesn’t use any oil, is getting good fuel mileage, and goes like a scalded cat. There's no evidence of smoke on start up, and the compression on all cylinders falls between 190 and 200.
I'd like to try pinpointing the trouble before I start taking things apart. Any and all help, suggestions & advice is welcome,
Thanks!
Peter.
Edit: the plug in the first photo was supposedly, if the records are correct, installed at 43,000 miles and I removed it at 75,000 miles in this condition.
 

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#33 ·
... if the records are correct, installed at 43,000 miles and I removed it at 75,000 miles in this condition.
How long have you had the car? Anything in the service history that would indicate work done on the engine cooling system? I mean any previous evidence of overheating? This would point more to a leaking head gasket than valve seal I guess.

I would take a look to see if there are any signs - new rad? new coolant hoses, thermostat, water pump etc?

Just a hunch.

Regards
Rob
 
#24 ·
Do all your spark plugs thread down the same number of turns? You can achieve the proper torque specs against galled threads but you won't have a proper seal. Improper seal, improper combustion. The amount of buildup on your #1 plugs does look worrisome though.

If the threads don't go down all the way just by finger strength, check out one of these: https://www.amazon.com/Back-Tap-12-Millimeter-Reverse-Re-Thread-Tool/dp/B000NOX3KW

Works a charm.

If you haven't already, go ahead and replace all the soft vacuum and crankcase vent hoses. Shouldn't be more than around $100 to do.
 
#25 ·
brauhaus, I looked at that reverse thread tool before I tackled the plug change earlier. But they all came out nicely, except the two at cylinder 1 which had the carbon build-up. But gently reversing them a little way in then backing them out did the trick. Most of my mis-spent youth was spent working on Corvairs, so aluminum heads and galled or stripped threads are all too familiar! Anyway, they all wind in by hand the same amount, and torquing them only requires about a half turn, so I'm confident they are sealing well.
The fact that it's only one cylinder giving trouble has me leaning toward a bad valve seal. I don't even know what the M113 valve seals look like, but I'm probably going to find out.
Changing the hoses was on my winter maintenance list, but I'll move that up to "soon"!
The car is in such pristine condition ... always garaged and serviced, everything working ... it's not like some of the orphans I've towed home in the past. It's more like a three year old car than a fifteen year old one. My main concern is an excess of carbon building up in the number one combustion chamber.
Thanks for your suggestions!
 
#26 · (Edited)
Yeah, I would have otherwise guessed valve seals on any other car, but it's so rare on the M113. Could be though I guess.

I should also say, after I cleaned up my threads when I RE-did my spark plugs, there was no way I could get half a turn until I reached the proper torque spec. When I say the plugs should thread all the way down by finger strength, I mean literally all the way down to the point where the head, washer, and spark plugs are mating. At that point, I could not get anywhere near half a turn more before I reached the proper torque spec. The exact spec escapes me, but it is not much.

So, I guess to be more clear, I thought I was good too, then I cleaned the threads up and realized how wrong I was.
 
#29 ·
Thanks brauhaus.
Insurance expires on Oct 20, so it'll be laid up then for the winter. My original plan was to get the rear windows fixed, but this takes priority. Going to start by getting the injector for that cylinder tested as that's another possibility, and is probably the easiest thing to check first, plus a leak-down test of all cylinders. I'll also replace all the crankcase breather hoses as per your suggestion. After reading the process for changing valve seals on my Star Service Manual DVD I'll leave that as a last resort. Another thing I'll do is a borescope inspection of the no. one cylinder walls to check for scoring. Will keep the forum posted with finds and results.
Meanwhile I'll enjoy the ride until Oct 20 :smile
 
#30 ·
I finally got around to a leak-down test. One should start with a warm engine but my injectors are all out so it had to be a cold one. All cylinders came in between 6% and 12% leakage, which, according to info on the net, is well within the normal range for an engine with 77K miles. The 12% reading was number one, the cylinder that's fouling plugs, so I suspect some carbon build-up is the culprit.
While I wait for the injectors to arrive I'm going to do some research on changing valve stem seals.
 

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#32 ·
... While I wait for the injectors to arrive I'm going to do some research on changing valve stem seals.
Check codes as rorypff recommended.

But before you go for changing the valve seals, there is another possibility.

Since the affected cylinder #1 is at the end of the block, I would also suspect a leaking head gasket. When the head gasket starts leak, oil can be drawn into the cylinder on the intake stroke from the nearest oil gallery.

Head gaskets tend to start to fail from the end of the block first if they are going to at all. On a M113 I am not sure what is more likely; a leaking valve seal or head gasket. My hunch would be the latter.

The leak down test would show a leaking head gasket. Another test would be to check the cylinder head bolt torques to see if they are all uniform.

Any running issues? Rough idle? Tapping noise in vicinity of #1?

Regards
Rob
 
#31 ·
I see you have asked this question on another post too and advice given, as well as in this post, was to have a diagnostic test to pin point any codes - not done yet?

Doesn't use oil, goes like a scalded cat and good on fuel consumption - strange.

Have a diagnostic done.

Finally are you using good premium fuel?
 
#34 ·
rorypff,
No diagnostics yet, waiting for my C3 system to come. Yes, I'm using the best fuel I can get here on Vancouver Island.

Check codes as rorypff recommended.

But before you go for changing the valve seals, there is another possibility.

Since the affected cylinder #1 is at the end of the block, I would also suspect a leaking head gasket. When the head gasket starts leak, oil can be drawn into the cylinder on the intake stroke from the nearest oil gallery.

Head gaskets tend to start to fail from the end of the block first if they are going to at all. On a M113 I am not sure what is more likely; a leaking valve seal or head gasket. My hunch would be the latter.

The leak down test would show a leaking head gasket. Another test would be to check the cylinder head bolt torques to see if they are all uniform.

Any running issues? Rough idle? Tapping noise in vicinity of #1?

Regards
Rob
Rob,
Leak down test on cylinder one is good, as is compression test. No running issues , smooth idle, and no strange noises. I'll check the cylinder head torque if I remove the valve cover.

How long have you had the car? Anything in the service history that would indicate work done on the engine cooling system? I mean any previous evidence of overheating? This would point more to a leaking head gasket than valve seal I guess.

I would take a look to see if there are any signs - new rad? new coolant hoses, thermostat, water pump etc?

Just a hunch.

Regards
Rob
Rob,
I bought the car in December 2015 and drove it for the summer of 2016, about 3K miles.
(See service history in attached pdf.)

I found no evidence of overheating. I changed out all the rad hoses when I did a coolant change and everything looked original (dirt build up and MB part numbers). There was a minor water pump leak that had been ongoing for a long time, judging by the sticky goo build up down the front of the engine and in the pan underneath. It turned out to be a minor tear in the rubber gasket, right at the little alignment tab that protrudes out the side. Maybe someone gave it a pull and tore it? Anyway, a new gasket solved the problem, as the pump was still in good condition.

Thanks to all for your suggestions!
Cheers,
Peter.
 

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#35 ·
These engines head gaskets never give problems (unless the coolant has never been changed and it was filled with brine) and I have never heard of the cylinder head bolts being retorqued either. And your leak down and compression test picks up any problems too which can only point to a coil or HT problem.

The detailed service history looks exemplary.

Maybe what is left is to give it a Ferrari tune up - on the open road with foot flat in a lower gear

I would suggest you take the cam covers off and you might even find the cam lobes on that cylinder have been worn down.
 
#36 ·
I liked your post right up to the worn cam lobes part :eek
Ah, Ferrari tune ups ... I most have done a dozen on the way home from Oregon at every rest area. "Dear, are you sure you don't need to stop at this rest area coming up? I think I'll pull in anyway". And then another trip up the merge lane close to 100 mph!
Seriously though, if I remove the valve cover I'll check the lift on the lobes ... thanks for the suggestion.
 
#37 ·
I have never fitted a spark plug yet, with out copperslip or a spot grease on the thread .And i have never had one stick in the head or break off .This can be a problem with nothing on them .I have seen them shear off and brake in two .Thus rendering a head removal to extract the broken half of the plug.So it is up to you what you do ,i know what i would do. By the way its worked for me for 50 years ..
 
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