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Thread: How To Avoid Machining

  1. #1
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    Question How To Avoid Machining

    I want to avoid a machining job. Here's the story: I'm refurbishing the aluminum cylinder head of an early '60s Jaguar engine, 3.8L DOHC. The head has three threaded core plugs in the valley between the cams. The JagUah gurus recommend removing these plugs when rebuilding the head, as it facilitates removing crud in the water passages. The plugs have straight thread, and they appear to be a weird size: the ID (not the OD) of the female threaded hole (measured on another head) is slightly over 3/4". Anyway, the plugs have a lot of surface area, they have been happily corroding in place since 1961, and I can't get them out. First I tried my longest wrench with a cheater bar, then my trusty air impact wrench. No joy. I tried heat (Mapp gas, not oxy-acetylene), but 75 lbs is a lot of aluminum, and I wasn't able to raise the temperature enough to make a difference.

    The machining job I want to avoid is having to helicoil the head because I stripped out the core plug holes. On the other hand, I'm not quite ready to give up yet and leave the (now battered) plugs in place.

    Anyone know how to get these things out?

  2. #2
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    Do the geniuses who suggest removing them have any brilliant ideas?

    Can these plugs be obtained? or are you stuck with having to re-use the ones that are in there?

    Aluminum corroded together in a water-tight seal is not a recipe for an easy removal. Plus, there may be, with straight threads, some type of sealant that is acting as a glue as well. The good news about a sealant would be that the plugs may have good threads, the bad news would be that the glue is now old and very thoroughly cured, stuck tightly to both surfaces. Unless that can be softened, if present, it does not sound promising.

    Heat, possibly a solvent, although I doubt the ability of a solvent to work into glue going "end-wise".
    1601

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  3. #3
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    So what kind of crud is in there that won't be removed by putting the whole head in an ultrasonic cleaner for an hour? Or sticking the nozzle of a high pressure steam cleaner in each end?

    Steve

  4. #4
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    Yes, the plugs are available and affordable. There is a copper washer under the 1 1/4" hex head, so there is no need for sealant in the threads, but that doesn't mean there isn't any. I can use oxy-acetylene to heat the plug. That might help break down any corrosion/sealant. But I really don't want to take a chance of melting the aluminum threads. Maybe I should heat the plug until the center of the head just begins to turn red -- that should still be below the melting temperature of the AL -- then let the whole thing cool down, then try the impact wrench again. What say you?

  5. #5
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    SteveF,
    The answer to your question is, it's impossible to know without removing the plugs. There are two press-in core plugs in another location in the head. I drilled those and pried them out. There was a substantial quantity of rust/mineral deposit behind those plugs. Some of it might get flushed out by a power washer. Some of it probably would not. That's why I decided to try to remove the threaded plugs. Anyway, after aggressive use of the impact wrench, the plugs now look like something a dog with titanium teeth chewed on. It's a vanity issue, I admit, but I'd like to get them out, deal with whatever is inside, and install new plugs.

  6. #6
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    Do you have a milling machine at your disposal?
    An O/A torch can get ugly with aluminum fast if one isn't careful, sounds like you know this already though.
    Didn't the Jag heads before mid 60s use pressed in plugs? My brother had one at some point and I remember they were plugged. I think, been a while. LOL

    The Jaguar head.

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  7. #7
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    Do not heat the aluminum too much to try and pull the plugs or you will pull threads along with it, it sounds like a nightmare and i know hindsights 20/20 and all that but I generally avoid allot of the "recommendations" due to them not considering all the other pit-falls it introduces - some that are total nightmares... if they have not leaked since 1961 they will most likely hang another 60 years or so, run a premium coolant and toss that sow back out to the universe *(if you don't think you did any damage to them trying to remove them)

  8. #8
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    Willy, Yes, I have a milling machine, and my head looks exactly like the one in your photo, except yours in nice and clean. The plugs in question are the ones with the orange washers under them. What do you suggest I do with the milling machine?

  9. #9
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    May 2006
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    hmmm - i was thinking internal hex and made of same material as the head due to what JT stated,

    i would soak the hell out of them over night with some good penetrating fluid - actually try somehow to get it in from the cooling side would be key, then set an impact gun to very mild and let it work at it for long duration's

    do not damage the hex just baby the gun and don't forget to use tightening on the gun about 20% of the time - you would not believe how many times iv actually got thing to crack loose by reversing the drive - it sounds crazy but it works


    other than that - I just would have ran that pig in the first place,,, those are solid and looks like easily accessible so was thinking you were changing due to them failing and leaking, jags are crap and don't make enough horsepower to even hurt themselves so even if things are half plugged up inside it don't matter - your dealing with a "hit and miss" motor, just get things close and ship it - not worth the time...

  10. #10
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    Steel bolts in alu seem to sit super tight and penetrating oils appear to have less effect. And you would need to get the oil to the water passage side.

    Household ammonia, dishwasher tablets or something caustic like that works sometimes. It dissolves ”rust” aka aluminium oxide but also aluminium itself so use in moderation.

    Few (about 100) whacks with medium size hammer to the bolt head also helps often.

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