Went to buy a compression gage today at the local auto parts store and we asked them specifically if it would fit all spark plug holes and were told, YES.
Of course, when we get home, it has no way to thread into the Model T spark plug threads.
Can anyone receommend a part number or sku on a gage that they have purchased? Or tell me what thread size I am looking for so I can make sure the kit contains the correct size for the T?
Thanks in advance. And, that's not Advance Auto.
A rubber tip would fit any spark plug hole. But then you would need help to crank the engine while you hold it tight at the plug hole.
The 1/2" pipe thread the T uses for plugs has been obsolete for like 90 years, so it's understandable the guy at the auto parts store didn't know about them.
You can probably find a fitting adapter at a plumbing store, the pipe thread is still used in plumbing. http://www.mtfca.com/discus/messages/599638/672099.html?1472745282
T Vendors have the plug adapter set for $15.00
or try a plumbing supply for a single one.
You can buy the 14mm spark plug to 1/2" pipe thread hole adapters from the suppliers or make your own. All you need is a male 1/2" NPT reducer with 1/8" NPT hole, drill it out with the proper size drill and tap to 14MM.
I bought a good quality compression guage with various fittings for practically every spark plug hole imaginable at O'Reilly's. Except for a model T plug. For that I went online and found an exact adapter for less than $5 shipping paid but can't remember where I got it from. Didn't have to do any of that drilling and tapping crap. It was "plug and play". Works great.
I built a compression tester that was a no hands, T specific, by just standing in the local ACE by the miscellaneous fitting racks. The bicycle repair stuff was right across the aisle and the check valve and gauge came off of a bicycle pump repair kit.
Mr. Thrifty would have been proud of me...In an out for less than 20 bucks.
All the parts dealers sell the adapters only in sets of four. Apparently they don't realize that a compression tester needs one also.
Get a modern compression test gauge
And get or make modern plug adapter and done
I wish I could remember where I got mine, but one of the vendors, at least at that time, sold them in singles. I thought it was Lang's or Snider's. Maybe they don't sell singles anymore?
You can easily make an adapter out of an old hollowed out spark plug and a few minutes with a torch or welder.
The gauge I had was one that you could swap the thread sizes out and it would just click on, similar to an air compressor end.
I went to Lowe's and grabbed a 1/2 inch NPT adapter with the same fitting on the top. They call it a barb fitting or a crimp fitting, you'll know it when you see it. Screwed right in for about $5.
Just bring your gauge in and try if it fits.
I think this is the one that I have:
You can buy single 1/2" pipe thread to 14 MM adapters here:
Thanks to all. Loooks like I'll keep the tester I just purchased and work on getting an adapter. Worse case scenario is that I'll get a set of 4 for the vendors and offer the other 3 up to forum members whom might need one for just such a situation.
The vendors also sell adapters in sets of four for those folks who choose to run modern 14mm plugs in their original cylinder heads.
My old compression gauge had the rubber tip which is of course too small to fit 1/2 pipe so I took a broken old Champion take apart spark plug and removed the porcelain and then tightened the collar back down. Works great as an adapter for the rubber tipped gauges.
A couple of months ago a Club member brought a 1941 Mechanics Illustrated Magazine to our meeting. In it was a short DIY article on how to make a compression tester from a high compression "shotgun shell" tire gauge. I followed the instructions using JB Weld rather than solder. Here it is.
If you make an adapter as Mark Gregush suggested, remember that the 14mm spark plug thread is a special 14mm thread, 14 X 1.25, not the common 14 X 1.5 thread.
Tod thank you for the clarification. I would not have even thought about the difference because all my 14mm taps are for spark plug thread. Thumbs up!