puzzler for ya

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like_A_pike

like_A_pike

that's not factory
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I pick'd this 68 cuda with a 76 360 up last April. You all are starting to know that I'm learning as I go. (thanks for your patients) About a month into it I take it down the road and decide to give it some gas, OK all it would take! and I thought it jumped time. Limped home and found a little carbon on the rotor and the No. 2 spark plug gap was closed. ?? Yesterday I finish putting in a new distributor and ECU. Took it out to time it up (by ear) tonight. It's starting to run good right. Put the vac line it's going well. Then I decide to let it go to 5000 and then it runs like crap !!!!?? turn it off back the vacume down 180 and no change. Bring it home and guess what that No. 2 plug gap is closed up again. I notice it's got a tiiny little nick on the tab at the bend on the side really. It's only the one plug.

what the h&!! is smacking that spark plug?? thanks in advance!

lap
 
Should be able to shine a light down number 2 plug hole with piston at TDC and see if piston is shinny or ?
 
there's about 2000 miles on these KB pistons. I don't think it's build up.

lap
 
are all the plugs identical? sure number 2 isnt a hotter longer plug? Maybe someone replaced one piston with a different replacement piston.
 
Definitely check down the spark plug hole with a flashlight with the piston at TDC to see if you can see any obvious problems or obstructions. Other than that maybe run a compression test on all the cylinders and if you can't see anything through the spark plug hole maybe you'll have to pull that cylinder head off to really see what's going on.
 
If you cant see anything down the plug hole......put a plug in it and turn it over manually....remove the plug. If the plug is closed again......there is ONLY ONE thing in that cylinder that CAN hit the plug and that is the piston....Unless of course some idiot dropped a washer down the intake( unlikely) good chance your pistons are matched but that is a possibility as is the connecting rod. If the CR is just a TAD longer than the rest or if your heads were decked....you might have found your problem.
Either way it will likely NOT be a simple fix....not trying to freak you out...just trying to sanity check the options......Chance favors the prepared mind.....you may be lookin at a partial rebuild
 
How about putting a light checking valve spring, and get ahold of a dial indicator, and compare valve travel at tdc on all cylinders. That would tell ya if # 2 is moving up in the bore more yes?
 
post a pic of the plug, and what plug are you using? (brand and part number)
 
thanks all!

after work I'll take a look inside the No.2. I think I have a little screwdriver with a magnet mounted on the end . I'm a little freaked out about loosin' the magnet in there!! You know, there is this gap between the Weiland 8007 intake and the head? I've dropped one of the choke screws in there before. Took a couple hours with a magnet and pliers to fish that thing out.

I fixed the gap and cleaned the contact already. It just looked like it got dropped or something. (both times) They are Autolite 66, they were new (and set @ .35) after the last time this happened. Suppposed to be "hotter" than the 65 which crossed w/ Champion RN12Y

My fear is that yes, it's the piston, and things just are not set up the same in there. If so, can I use a plug with a slightly shorter reach? can I double up on the washers?

when the gap is ok this thing runs fine normally, It only happens when I punch it.
 
Any chance its a over sized valve with a worn guide that allows to valve to move over a bit and hit the plug?
 
like_A_pike said:
I notice it's got a tiiny little nick on the tab at the bend on the side really. It's only the one plug.
Click to expand...

From your explanation it sounds like whatever is making contact with the #2 plug is hitting at the bend of the side electrode.
Take that plug out and mark the position of the side electrode on the ceramic insulator with a vertical black marker line.
Now put that plug back in and note where the black mark is.
Take out the other 7 plugs and mark them.
Now try the plugs one-by-one until you find one that will put the black mark 180-degrees opposite of what was in the #2 hole before.
Install all the other plugs, fire it up and see if you now have clearance and if it solves your problem.

This is similar to an old racer trick of "indexing" your plugs to put the spark gap in optimal position to fire the fuel mixture.
 
I asked if it was a hotter plug. This is because the colder they are the shorter they are.
 
slant6/4speed said:
Any chance its a over sized valve with a worn guide that allows to valve to move over a bit and hit the plug?

I don't think so with that recent rebuild and low run time.
but something unique is different in no.2 and different only at high rpms

ocdart

that took me a couple reads but I'm with ya. get that tab in a different position inside there. I can see a bit of an edge along the wall of the cylinder at the top of the piston at TDC. I'll find that 180* plug and try it out.

daredevil & UOP

I'll do some research to see what I can do. these are "hotter" plugs w/ 3/4" reach. all I need is an eighth and only one.

Car runs fine now (I haven't greased again yet) magnet came out empty, no obvious marks on the piston, until I touched it with the magnet.
Click to expand...
 
It is hitting at high RPM due to rod stretch. That is pretty close! You can run a couple of plug gaskets to shorten the reach too.
 
Every one of those electrodes wind up with the bend up against the outside wall of the head within 10* of each other!!!

My research finds that while there are lots of options for plugs, you either get .750 or half that for a reach across brands! Oh and Champion sells sport bras too, who knew! :cheers:

So I'm thinkin that I kinda want some or most of that 3/4" but will they all start kissin' Keith Black at 5500 ??? really hard @ 65K???

I'm going to try an extra set of gaskets on all 8.
If I still have one gasket on them would it be bad to use washers? (if I can't get a set of gaskets that is)

let ya know what happens

lap
 
I'm pretty sure the engine will grenade before twisting it 65K. Just kidding, buy a new set of plugs and reuse the gaskets off the old ones along with the new ones.
 
Put on 8 washers and shortened them all down .125 (or an eighth) with gaskets it comes out to .575 reach on my modified autolite 66's. Took it to town (an hour away) and brought it up to 5000 a couple times on the way home. I think it's gonna work. (65000 might be too much, good point!)
 
SGBARRACUDA said:
I'm pretty sure the engine will grenade before twisting it 65K. Just kidding, buy a new set of plugs and reuse the gaskets off the old ones along with the new ones.
Click to expand...

All the other posts were entertaining and great to read through, but this one cut right to the point.
There is rod stretch, possible piston mismatches, and so on but the main point is he can drive his car, not hurt it futher by this solution and it cost a set of plugs.
At 6500 it might hit the plug again. (I know that was mean sorry)

I love endings like this.:burnout:
 
Glad it worked out for you. More than likely your heads have had a lot milled off of them for them to be so close to the plugs. I once tore down a 289 Ford that the pistons came so close to the head a TDC that you could read the TRW and part number on the closed chamber part of the head!
 
It happened again! this time I also broke the insulator on #3 in addition to closing the gap on #2. I never mentioned that I had been racing this thing and using 110 octane off and on all summer. I think the slower burnin' fuel was keeping me outta trouble at the track (I must have run 15 passes with burnouts) As soon as I went back to just pump gas AND stomped it, boom!

Ok so the summit racing website lists lots of plugs with a .375 reach and the same threads as the longer autolight 65 and 66's. (the two I've been working with so far)the applications are all over the place but none for a 360. Parts store guys think I'm nuts! Has anyone used a shorter plug in their LA? Do ya think a plug for a big block will work in my motor? How much room do I have to play with this "heat rating" #?

lap
 
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