Spark plugs on 455 compressed

Hi,


this weekend I took the GS 455 on a long trip, approx. 650miles in 2 days. Had a little incident and would like to hear your opinions on it:

Went on the Autobahn, my TH2004R shifted into OD like it`s supposed to. Accelerated a little more and the tranny shifted back into 3rd, sending the rpm to the sky (I guess so, happened too fast and didn`t see it exactly, but then, I felt that rush going through the car and heard the engine turning high rpm for an instant). Engine is a moderate build, not supposed to live far above 5000 rpm, car has a 3.73 posi out back.

Afterwards, and still some 250miles ahead of me, I felt quite a vibration, rocking the car, you could see the engine shake in idle, OD with a locked TC wasn`t possible, just too many vibrations being transmitted to the car.



Coming home and letting it cool off, I discovered the following (presumably, the driver`s side bank is 1-3-5-7 from front of the car to firewall, and 2-4-6-8 on the passengers side, right ?) :

Spark plug in pos. 7 and 6 had their spark gap pressed together, not crushed (see pic, note the missing piece of isolation. The rest of the plugs look like the one in the other picture). New spark plugs all around made it cruise nice and powerful again in midrange above 1800-2000 rpm. In idle rpm is going a little too much south, and it feels „unstable“ like it wants some more throttle, esp. when being cold, definitly more than before.

I don`t know what`s happening, but suspect either ignition (HEI) is off (why ? Can that hard down-shifting incident have modulated it ?) or something in the cylinder head, gasket or valve ?


Happy for your opinion on my case.



Jens

 

By some luck, the porcelain hit the plug and then went out the exhaust. if you have a vacuum reading recorded you can check to see if it is near the same as before. Just a guess ...

 

Valve float when the engine over revved? I don't know if it's possible for a piston to hit a spark plug or not? But, don't know of any other way to crush a plug electrode. (much less two plugs)

 

Yeah, the valve float was my guess too. Is that possible, spark plug being hit by pistion? Could the Piston come that close? Plug was an Autolite 665 , never a Problem before. Hopefully that porcelaine piece came out, not too interested of it dancing around in my chamber...Why that changed idle?

Jens

 

I don't believe the piston hit the sparkplug directly. This kind of mechanical damage is caused by foreign objects in the combustion chamber.
A large piece of carbon rattling around in the combusation chamber can do this also. The two damaged sparkplugs looking wet and oily, the other looks real clean a tad to clean.

Why are these so oily? Are they oily before the overev miss happen? Can the lean cruise mixture & over advance created in the two hottest cylinder a detonation?

I will do a compression test.

@Jens meld dich doch per messanger

 

Hi Rob, dank dir für`s Angebot,

didn`t check on them before, the two oily ones are actually the same one, the first I discoverd, no. 7, was compressed but not oily, no pic as I bent it back, put it in place again and fired her up, she was running quite better afterwards. Oil in that chamber, coming from a defect from either cylinder wall or piston ring? I hope it`s nothing like that...

 

Piston cannot hit the plug, something else did though, but I doubt it was carbon, check for missing screws on the carb bottom, or broken valve possibly. Oil after an over rev is a result of a bent valve not sealing properly.

 

And a bent valve, not sealing properly, would/could cause that idle issue I was talking about, right?

 

Maybe that BUICK 455 was trying to spit out those FORD spark plugs .

 

Ring butting for various heat related reasons lifts the piston tops as it widens the ring gap.
I don't have one of these near me today to see if it's possible, just adding to the discussion.
Borescopes are cheap on ebay. ($20?) Probably listed as "endoscope".
You should get two if you have devious intentions.

 

That's funny right there.....

 

3rd gear is 1:1, just like high gear of an older 3-speed TH400. HOW HIGH did the RPM go? How fast were you going?

It's not that the trans wouldn't shift into OD...you just chose to drive in 3rd gear?

Two-plane intake manifold? 6 and 7 are on the same runner. Any crap spit out the intake valve of one could go directly into the intake of the other.

Wild Guess: The missing piece of porcelain was a result, not a cause of the spark plug gap closure.

WHAT was the spark plug gap?

Time for the "Three Sisters" of cylinder diagnosis: Cylinder Balance test, Cranking Compression test, and cylinder leakdown test.

 

Yes, it would idle bad, run bad and show slight oil in the exhaust especially if the valve is the exhaust valve that's bent/not sealing properly. Also I agree with LARRY, the missing porcelain is the result and or cause of the messed up gap and possible valve problem. Solution: pull the head.

 

Where in this thread does LARRY say the missing porcelain is the result or CAUSE of the closed gap? The only post of his that I see, he suggests a broken piston.

agetnt9 says the porcelain "hit the plug and then went out the exhaust", but I think that's very unlikely.

Eventually, yes. NOT right now. Before he disassembles the engine, there's diagnosis to be done.

 

Hi everybody, I was wound up in work the last 2 days so I couldn`t get back to you. Thanks for your Input, really helpful.
@ Schurkey:
1) I think it must have been around 90-95 mph, accelerating, well, fast enough for the transmission to shift back from 4th, OD, in that case 0.64 to 3rd, 1:1. Putting the numbers into the rpm calculator makes this a sudden shift from around 2900 rpm to 4300 rpm. Car felt like it had been struck by a lightning(whitch is not unusual, but I think the gap between 1-2-3rd gear is not as steep as in comparison to 4th).
2) Concerning gears: yes and no, when I stayed in 4th(what I did for some time) I just switched out the lockup, this way it was possible to drive it without all the jerking of the engine being transmitted fully to the driveline and still making some 85-90 mph. Putting it lockup would shake the car quite a bit. If your thinking about transmission damage: After replacing those two spark plugs I`ve had no vibration problems in lockup position going faster than , say, 70-75 mph, rides smooth. No fluid loss, nothing.
Gernerally, I choose 3rd positon on the tranny for around town cruising and elsewhere from the speedways, I just put it in OD (locked up nowadays, drove the transmission for years without, no damage...but that`s another topic) when going on the Autobahn.
3)Intake is completley standard as is the rest of the engine, all iron, heads are Stage-1-converted. In fact, the engine is one of the last mules Mike Phillips of AM&P sold, as far as I know. It`s normaly a healthy, torquey engine without problems whatsoever, 517ft/trq and 425 horses.
@72STAGE1: sounds familiar to me. My last engine had a burnt valve, but that was an intake valve. She was banging through the carb when revving. Not so this time, no "shots" coming out of there. Exhaust note is louder, idling around 700rpm when warm(dropped a bit, not much, around 100rpm, I guess). Then, between 700 and 1800 rpm, she feels definitly rougher, even a little weaker, more vibrations. Going over 2000 rpm stabilizes her, you wouldn`t even know she had a problem.

Good hint with the intake connection between these 2 cylinders. I`ll bring in my borescope soon and will tell you what I saw. Thanks for the hint with the 3 sisters also, I see it coming my way...damn!

Jens

 

before my rebuild , the engine would run great to about 4000 rpm.When I would open it up it would start back firing and running like crap. Pulled the plugs and a few of them were slammed closed. Turns out detonation had caused the pistons to fragment and cause the blasting of the plugs at higher rpm. Never heard of it since then

 

I flattened a few plugs on a 430 back in the day. I had always assumed the rods had stretched when I over revved it.
Live and learn.
Cliff

 

Let's see what will show up, I'll keep you guys informed about the case. I' ll check the chambers with a borescope within a few days, next will be the 3 sisters...

Jens

 

So, here we go with pics from cyl. 4 and 6. The first is the surface picture from cyl 4, sorry, first time I put a borescope inside a chamber, Looks "caked" to me, surface of the pistion is crusty...but maybe that`s the way it`s supposed to be when exploding gas inside a little metal-surfaced room

Pic 2 and 3 are from that cylinder that had the oily spark plug. Changed the flattend plug, doesn`t seem to get soaked with oil again after the switch, fires and works. You can see a spot on the piston that looks like something was pressed/melted there...not the best of pictures, sorry!

Jens