Read My Spark Plugs

[nicfranc]

New owner here.
I bought a 1980 Sc with over 275,000 miles from a friend.

So far I deleted the CAT & stock muffler and installed M&K Pre Muffler and M&K Sport Muffler. The O2 Sensor is not connected.

Transmission and engine oil changed.

Today I Changed the plugs and started to adjust valves on the left side.
Slow going at first.

The plugs were dry and the car runs well.
I do get slight rumbling on deceleration.
No broken head studs yet (fingers crossed)

Too Rich ? Too Lean ?

Thanks for looking.

[fasterlaster]

Plenty of other much more experienced mechanics than me around here, but if I pulled out 3 that looked like this, I'd just keep on driving and smiling. The look mostly consistent, with the slight difference in coloration in the porcelain likely due to the postion of the plug in the head.

[bgyglfr]

The plugs look ok to me. If it isn't running hot I wouldn't worry. The rumbling is probably from the exhaust changes. I had an SC that had SSIs and a Bursh muffler that did the same thing.
Kirk

[redstrosekNic]

That is what my plugs looked like when I changed them. I have a grumbly exhaust after disconnecting my deceleration valve... I really dig the sound

[James Brown]

275 on the clock, keep running hard, looking good!!

[nicfranc]

Tomorrow I will tackle the right side.

After reading all the horror stories of Broken Head Studs I was expecting all this hardware to fall out when I removed the valve covers.

Hopefully I will not have any broken studs on the right side either. (again fingers crossed)

I think if I had to do it again I would just pull the engine and work like a Gentleman.
and then throw it back in.

…..but I was afraid I would just keep drilling down till I was cracking the case. LOL

I want to "ABD" ……..Always Be Driving !!

Love this Community.
Without you guys I would never have bought the car.

[mytoy]

I have to presume that this was a street driven car with a normal shut down and not a new set of plugs with a max rev shut down. If this is the case then # 2 is running perfectly with little oil contamination, #1 is running a little leaner but well within reasonable specs, #3 is running a little leaner than the other two.

All plugs show little contamination from oil residue which is a good thing. All plugs show the timing is almost spot on. If you want to delve further into this I would check your injectors for even flow. But I would not worry about it at this time till we look at 4,5,6.

If 4,5,6 look similar to these then I would not worry about any thing as these look very good. It takes a lot to get even distribution of fuel as well as air to all cylinders equally. and small differences shown here are not worth the effort unless you are looking for every last ounce of performance.

[snbush67]

Looking good for 275. You should double check the tightness of the intake nuts, and perhaps the rubber sleeves as well. It is likely that they have been replaced but if not, that would be a recommended maintenance item.

[T77911S]

more or less what mytoy said.
for the mileage on the car AND the plugs, they look exceptional.

with old plugs like this, look for then to be the same. #2 is either too rich, or 1 and 3 lean. "I" would like to see more like #3.
with them not the same, 2 could be fine, 1 and 3 have an air leak or starting to get injector problems. 1 and 3 could be fine, 2 could have an injector problem. with that said, they are still very close and not covered in oil. me, i would run some injector cleaner and tighten the intake, check the runner boots and maybe change the injector O rings. i would not go overboard trying to get the to look better. they still look very good.

you did not say what heat range the plugs are but it looks like W5. that is a cool plug and that can make a difference too.
your mixture can be correct and if the plug is too cold, it will look like these. thats not a bad thing. you want to run as cold a plug as you can without fouling. with that said and them being a W5, they look really really good. you could go to a W6 but i would stay were you are.
also, hi mileage plugs will look like this. you really need to check them early in their life.

here is what i would do, and just did in my 930.
put in a new set. go run the car hard a few times and get them good and hot. make sure you do a few runs to redline. this will put the heat line on the ground strap and tell you your timing.
see how the ground strap is a different color. you should see the color change on the bend of the strap. dont worry, yours looks fine. it gets that way after hi miles. even though mine were correct, they look like yours now. that why you have to do it early. i did not shut my car down at the end of a run. i pulled back into the garage.

as for your backfire. as above plus timing can do it too. you want to make sure your advance and retard are working.

[pete3799]

Adjust the valves before you change the plugs. Those first 3 look good but if you pull one out that's all carboned up you might dislodge a chunk and it could get caught under a valve ( not likely but possible).

[OsoMoore]

That's awesome, its great to see someone else with a high mileage SC that is in good shape. I'm now up to 248K. Its very likely that an earlier owner replaced the headstuds long ago - there has almost certainly been a rebuild and that would have been addressed.

Good luck with the valves! I did mine a few weeks ago and I think they are still loose. Fortunately its not a danger to the car - I'll just do it better at the next oil change.

[nicfranc]

Originally Posted by pete3799

Adjust the valves before you change the plugs. Those first 3 look good but if you pull one out that's all carboned up you might dislodge a chunk and it could get caught under a valve ( not likely but possible).

I rigged up a plastic tube snorkel onto my air gun and blew out what debris I could.
The Porsche supplied spark plug tool made the plug removal and installation much easier.

I am up to my armpits in hoses with this CIS system.
Maybe I should do a partial engine drop to get behind the Beast to sort out some off these hoses. Replacing what I can get to.

Do I need a WUR if I don't drive the car in the winter ?

Learning on the job here.
"It Ain't No VW"

I am going back in.
"Cover Me"



I would like to delete the fresh air fan and clean up the engine bay.

[T77911S]

you have to have the WUR.

i dont know what your plans are as far as a rebuild in the future, but unless you are having problems, i would not go too crazy with it yet. my point, if you see a topend/rebuild in the future, save some of this stuff for when the engine is out. you can then do injector sleeves, Orings, intake runner boots and all the other rubber hoses.

if it runs good, you might just have the fuel pressures and mixture checked and just drive it.

[hbkramer]

As a comparison, here are the plugs from my 79 SC non-sunroof coupe.
88K mile valve adjust. on St. Paddies day 2013

[nicfranc]

Today I unmounted the AC pump and replaced the 4,5 & 6 Plugs
And adjusted the intake valves.

The number 5 and 6 plugs were a bit easy to remove.
Almost as if the mechanic did not tighten them enough when installed.

The good news is no broken head studs on the 4,5,6 intake side.
Tomorrow I do the Exhaust Valves.
From what I understand this is where I will find broken Head Studs.

Close to 300,000 miles on the original 1980sc engine which has never been opened and has no Pop-Up valve and original non pressure fed chain tensioners.

If all goes well I will set the timing and check out the chain tensioners.
My plan is to rebuild the existing tensioners and install collars to prevent catastrophic failure. I will also replace the ramps.

[James Brown]

6 a little sooty, could be oil.valve guides but don't sweat it. yep backdating to clean up the engine bay is a popular "up" grade. from there there is no return to sanity. the cliff is very steep. your tools of the trade look great, plenty of fluids and TLC should make a half million in no time