Slowly checking off the to-do's getting a used truck (7.3l) in better shape, this project: replacing autolites with motorcrafts. Following the instructions here and elsewhere I've started replacing plugs, making sure corresponding pistons are tdc. Halfway through the process and the new plug won't fit one of the old holes. I tried several new ones and a different old one, the only plug to fit in that spot is the one that came out of that hole (and will go back in again no problem). The tip is fully intact, with some carbon buildup. I am hypothesizing that particular plug is slightly worn down and there is buildup in the hole preventing the new one from going in.

Poking around online the first suggestion was to try cranking the engine without that gp in to blow out whatever crap is in there. Had someone else watching, and cranked the engine a couple of times. They saw some gunk fly out of the hole (good) but the new plug still won't fit. Suggestions? Scrub it out with something? Keep cranking and try to blow more gunk out?

Thanks in advance!

 

Are you sure the threads are the same. Try the old plug in a different hole to see if it fits in there.

 

maybe try running a tap down that hole (grease it first) to try to clean out the threads. if you don't have the right tap (10x1mm IIRC), a round wire brush made for cleaning tubes/holes, or a gun cleaning brush would also work

 

Sounds like that hole was cross thread, and the old plug is also matched for it.
You may have to re-tap it, or bite the bullet and leave the old one in.
Closely inspect the threads on the old, compared to the new, there must be a difference,
only thing I can think of.

 

It's not the threads - the new plug stops short about 1/4" above where I'd be able to start threading it in. It feels like the blockage is starts right below the threads, because the tip will insert about the depth of the threads before it won't fit.

 

I'm thinking you have some carbon build up in the GP hole. Try a gun cleanin brush as stated above, along with some carb cleaner to help desolve the carbon. Be sure to turn the engine over to get all liquid and debres out of the cylinder before installing the GP.

 

x2
You might be able to find a drill bit sized just right and be able to use it (by hand) to scrape the carbon off where the tip goes through.

 

i wonder if the parts conter guy sold u plugs for a psd a pic would help

 

your plugs should be a motorcraft zd9 - what do you have
on second thought, you said the rest of them fit, so its either one plug thats different or one hole thats different

 

Ok, I am still having trouble here. I can only work on the truck from time to time so it has been a little while since I first posted.
In any case, I am certain all the plugs are the same: new ones are all motorcraft zd9, and all the old one's I've pulled so far have been autolite 1108's. I currently have 2 holes (1 and 2) that won't accept my new plugs or old plugs pulled from different holes.
Farmert and tecgod13 have the right idea, I know these new plugs are the right ones (they have fit some of the other holes) so I am thinking carbon buildup. I tried spraying carb cleaner in there and then using a copper-bristled gun cleaning brush (the one for my .22 fits perfectly) to scrub the interior of the hole as well- new plugs still don't fit. I'm at a loss of what to do- I would have thought that a tight copper brush + carb cleaner + serious scrubbing would have done the trick, but apparently not. I took a couple of photos but can't figure out how I can upload them if people still need a visual clarification of what's going on.

Last problem is somewhat different but still troubling, not sure how it could be related but it still affects this issue: when I tried to turn the engine over the blow residue out of the gp hole after cleaning, gp light time was good, then I tried to crank it, heard what sounded like my passenger's side solenoid "click," and then power died before the engine cranked. Tried jumping the solenoid and nothing happened apart from hearing the snap of making that connection - so I know the batteries are at least decent and it should crank.
The next day the engine cranked on my first try, but when I went to try it again got the same issue. At the moment it still won't crank. I may need to make another thread for this but if someone has a nifty idea of why my messing with gp's could have caused this that would be great.

Thanks for all the advice and input so far.

 

How sure are you that the batteries actually have a charge? Charge them up and then see what happens.
Another option is your starter is going out...

 

Find yourself a "good" chemical that will dissolve this carbon gunk and soak a rag with it. Then twist it in the hole and let it sit overnight.
This should eat away at the buildup. Maybe oven cleaner or something similar.
As for your starting issue, sounds like your batteries aren't up to par.

 

download the pictures to photobucket, them post the link here.
as for the carbon buildup, you will need to clean that out, maybe with oven cleaner as suggested.
the no crank sounds like either a low battery, or more likely a bad starter.

 

Finally got everything straightened out - starting problem was indeed batteries, I think the tender I was using is broken because it was registering good batteries and full charge after I let it sit overnight but I was still having the starting issues. Brought them back to walmart to get tested (and charged up) and now they're working just fine.

4 of the glow plugs had enough carbon buildup that the new ones wouldn't go in, and each was a huge pain to get sorted out but after several overnight soakings and a ton of scrubbing with a bronze .22 cleaning brush the new plugs fit. I think the problem was due to burning dirty used motor oil (previous owner, I had nothing to do with that). I know the IP was replaced but it makes sense that I found a whole bunch of junk in there.

Firing up like a champ right now and runs great.

 

Glad to hear that.