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I have the Mitivac Compression testing kit and the 7.3L adapter.
The adapter will not thread into most of my glow plug holes.
The glow plugs thread in easily. I have run them in and out several times to ensure there is not thread damage. I am confident the threads on my heads are fine. The adapter, however, goes ½-1 full turn then just stops, I have tried turning it with a wrench and in some cylinders that will get it to thread. I was able to test 3 cylinders so far, but in all of the others it will not. The threads are not crossing, and nothing is damaged. Again, my glow plugs thread in and out easily by hand with a vacuum line used as an "extension".
I ordered a replacement Mitivac adapter and have the same issue - 2 of them have not worked for me. The truck has been down for weeks between this and the front end rebuild and this is beyond frustrating.
Has anyone had this issue? I can only imagine the threads on the adapter were poorly manufacturered and are just off by a hair. Current plan is to get a 10mmx1.0 die and see what I can do with the adapter, unless anyone has a better suggestion.
Pic for reference, glow plug is on left, adapter on right...
I had the same problem with a Lang tester, probably made at the same place. Went through several adapters (including one from Snap On) and finally found one (I think from NAPA) that worked.
You're not the only one that had difficulties with the Mitivac compression tester adapter. I also reinserted glowplugs many times to ensure the thread was clean. Stress was high and beads of sweat were pouring ensuring I didn't wreck a thread. The hose was used to thread the adapter in due to lack of a proper tool to tighten at the hex head. The hex head broken free from the crimp which caused many extra hours a work. (no leaks though) My experience, or both of ours, could be isolated. I would NOT recommend the Mitivac adapter for this job.
EDIT: broke free might not be the best choice of words. The crimp "broke" to allow the hex head to spin very easily on the main hose.
You're not the only one that had difficulties with the Mitivac compression tester adapter. I also reinserted glowplugs many times to ensure the thread was clean. Stress was high and beads of sweat were pouring ensuring I didn't wreck a thread. The hose was used to thread the adapter in due to lack of a proper tool to tighten at the hex head. The hex head broken free from the crimp which caused many extra hours a work. (no leaks though) My experience, or both of ours, could be isolated. I would NOT recommend the Mitivac adapter for this job.
EDIT: broke free might not be the best choice of words. The crimp "broke" to allow the hex head to spin very easily on the main hose.
That's what mine was doing. Glad to know I'm not the only one!
Something looks off with the helical angle of the threads on the tester adapter...
With a die threaded onto it check to see if the die shoulder is 90* to the rest of the unthreaded portion.
Something goofy, perhaps just the pic itself though.
Just drawing some lines across the image in cad I get 1.69* helical angle on the glow plug but 4.01* angle on the compression adapter.
1deg32sec is called for with a 10mmx1.0 thread so the lines i dropped on glow plug is very close to spec.
But again could just be something goofy with the camera angle
I had the same problem when I tried to check compression on my truck. Bought every single diesel compression kit in my, smallish, town trying to get one that fit. OTC, Mityvac, all the auto store brands. Never did find one. Didn't try any tool truck brands, none of them answered their phones on the Sat after Thanksgiving, I don't blame them. Gave up, I didn't have a real reason for testing, just wanted benchmark numbers for the future since I had the valve covers off to re-ring injectors.
All of them had the exact same problem though, thread pitch was off, slightly. They all matched each other. My guess is some contract machine shop in Huang Zhu China pumped out a lot of these adapters for a lot of brands with some questionable lathes, machinists, probably both.
Good luck! Probably best to borrow the one offered.
The write up and parts list created by @FordTruckNoob that I linked in the post above has information on a tested and proven method of completing a compression test for not much coin.
This may be too late for the OP, but should serve future readers well...
To the OP, did you notice that the wrench flats on the adapter are larger than the glowplugs? They're hanging up on the sides of the glowplug hole. Even the glowplug's wrench flats have barely any clearance to that hole. I cannot get my 3/8" drive socket to get in there. Only my 1/4" drive socket has thin enough walls to fit over the glowplug and into the hole.
The write up and parts list created by @FordTruckNoob that I linked in the post above has information on a tested and proven method of completing a compression test for not much coin.
This may be too late for the OP, but should serve future readers well...
This PDF is new to me. Thanks Sous and FordTruckNoob. I'm definitely going to try this custom made adaptor next time around.
To the OP, did you notice that the wrench flats on the adapter are larger than the glowplugs? They're hanging up on the sides of the glowplug hole. Even the glowplug's wrench flats have barely any clearance to that hole. I cannot get my 3/8" drive socket to get in there. Only my 1/4" drive socket has thin enough walls to fit over the glowplug and into the hole.
I did not see any clearance issues on my heads, at least on the cylinders I can clearly see. I was able to get the Mitivac adapter to thread succesfuly into the two front cylinders on the driver’s head, and the middle two cylinders on the passenger’s
The only clearance issues I had was with a deep-well, ¼ drive socket against the valve rockers on one side of the motor (passengers I think). I had to use the vaccuum hose to thread them, which is even more testament to my head threads being just fine.
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