Stripped spark plug threads 75 Dart

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gregpurcell

gregpurcell

Greg Purcell
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I just bought a 75 Dart Sport 225-6 "parts car" that the seller said was a low mileage driver until they broke off a spark plug in the head. Apparently they tried drilling it with the head attached and what was left was a hole with no threads.

I was amazed with how complete and unmolested the car was, so I decided to start it. After a bit of gas in the carb, the indestructible slant fired up, running on 5 (and, of course, spitting compression loudly out of the open hole). During the brief run, I was able to put the trans in both gears (it went right in), make note that the alternator was charging, and see that the engine had oil pressure!

With a good trans and oil pressure to the engine, it occurred to me that it might be worth a "low buck fix" to have an extra "transportation car" in the yard, as we are down to one right now.

What I'm thinking is a "quick and dirty" head pull with the manifolds attached (I saw a good thread on the subject here I think, and yes I would use an engine hoist to remove the heavy piece!). I could try to redrill and tap (or Helicoil) the head on the bench or if that fails, plan b would be to bolt on one of the many other heads I have laying around the shop.

I don't want to get into head resurfacing or any other machine work. The cost of the gasket set is all I'm willing to spend before relegating the car back to a parts piece.

I'd like to open this thread to a non troll discussion about the job from people with more 6 cyl experience than I have. That would probably include most people on this thread!

Has anyone used the Helicoils? Hopefully the job would be easier on the bench. The 75 head has the newer design spark plug holes without the tubes. Is that better? Worse? Will it be a problem swapping an earlier head to the block?

Thanks in advance for your input!
 
Don't know if they still make them or not but my absolute favorite for fixing plug holes was an actual sleeve.
They were threaded for the plug on the ID and came with a tap for the OD.
Not a heli coil but a solid threaded sleeve.

The only real deal with the heli coil is you have to use clean threads, red Locktite on it and trim the ends smooth after it's installed.
Other than that they have always worked for me.
 
Ford Triton Engine Insert Kit No. 39300 | VehicleServicePros.com
For Ford Triton engines. I think the plug threads are the same (size and pitch) Worth a try. Talk to a local shop or Ford dealer that has the tool or may be ask your local Mac Tool dealer as to who he sold the tool to locally. It might cost you a hundred or so but easier than taking the head off. The insert is a permanent fix.
tmm
 
mcmaster.com has a generic version of the timesert


look up 'threaded insert' Once you know what you're looking for, you could probably find it on ebay or amazon.
 
Ford Triton Engine Insert Kit No. 39300 | VehicleServicePros.com
For Ford Triton engines. I think the plug threads are the same (size and pitch) Worth a try. Talk to a local shop or Ford dealer that has the tool or may be ask your local Mac Tool dealer as to who he sold the tool to locally. It might cost you a hundred or so but easier than taking the head off. The insert is a permanent fix.
tmm

I think the head will have to come off regardless. There is no way to get a drill in at that angle and it looks like whoever removed the plug did not do a very good job. It will most definately have to be redrilled with a larger hole and a correct angle and the only way to get that will be on a bench (at least from what I can see)
 
I've used one similar to what Rusty posted (autozone version) on my Crown Vic with great success (at least 30K since the repair). The tap cuts the new hole and threads it, no drilling required and it can be done without removing the head. That is on aluminum heads though, I don't know if cast iron makes a difference or not.
 
If they drilled the old spark plug hole out with the head on, I would recommend pulling the head and removing any chips from the cylinder so they don't mess up the rings...

The thread for a small block spark plug is 14 mm x 1.25, I believe the slant six is the same... I bought a tap from my Mac Tool guy to chase the spark plug holes...
 
krazykuda said:
If they drilled the old spark plug hole out with the head on, I would recommend pulling the head and removing any chips from the cylinder so they don't mess up the rings...
Click to expand...
I am with KK and the OP on removing this head, because there is another reason to put in a new head gasket while there: The original steel shim head gaskets tended to rust out in 2-3 spots on the /6's, where the head gasket blocks some of the coolant flow from going through the wrong casting holes between head and block. So it will restore the proper coolant flow.
 
I have a correct tap for the spark plug threads but it won't come close to threading in the hole that's there now. As soon as it cools down below 100 (the outside temp not the motor), I'm going to pull the head and post some pics.
 
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