MikeC5 Posted April 7, 2011 Share Posted April 7, 2011 Any ideas on how to adapt a 'modern' thread compression gage (14 & 18 mm) to the 7/8-18 spark plug thread? I took apart an old spark plug and the threaded part that holds in the insulator appears to be 24 tpi (.8" diam at thread peaks). Maybe this size is more adaptable? I haven't had any luck finding fittings to work with the 7/8-18. I may have to weld something up to the spark plug base? Link to comment Share on other sites More sharing options...
Guest 1930 Posted April 7, 2011 Share Posted April 7, 2011 If you keep your eyes on e-bay you will see the older kits being sold that have correct TPSI Link to comment Share on other sites More sharing options...
MikeC5 Posted April 8, 2011 Author Share Posted April 8, 2011 Thanks. Link to comment Share on other sites More sharing options...
Guest M R Simpers Posted April 8, 2011 Share Posted April 8, 2011 Mike,Years ago I took the base from a Champion C-4, which is a Model "A" Ford plug with the same thread size as my 1927 DB, Series 124. With a few fittings I permanently attached my pressure gage to it. It's worked great. I can't remember the thread size.I'd run out and check this rig in more detail; however, it is boxed up with tools, parts, etc. for the Model A Ford Club of America Natchez Trace Tour. We leave tomorrow at 9 am and return on April 19th.If you want more details, post a response, and I'll give you more details upon my return.M.R. Link to comment Share on other sites More sharing options...
MikeC5 Posted April 8, 2011 Author Share Posted April 8, 2011 Hi MR, It's funny, the plug I took apart is also a C-4. The thread is 7/8-18. I have had no luck in locating an adapter to go from this thread to 14 or 18 mm 'modern' spark plug thread. I would be interested in where you procured the fittings. I think I may end up just tapping a 14 x 1.25 mm hole (spark plug tap) in a steel plug and then welding it to the C-4 body. Link to comment Share on other sites More sharing options...
MikeC5 Posted April 8, 2011 Author Share Posted April 8, 2011 Oh and I forgot to mention, I hope your tour is enjoyable and goes well! Link to comment Share on other sites More sharing options...
Guest 1930 Posted April 8, 2011 Share Posted April 8, 2011 I hope you bring back pictures Link to comment Share on other sites More sharing options...
Guest DodgeKCL Posted April 8, 2011 Share Posted April 8, 2011 (edited) Actually any compression guage I've seen,including my own,has a hard rubber 'cone' affixed to it that you 'jam' into the spark plug hole and hold down while the engine is cranked. It does mean you need a 2nd person on the older foot operated starters but on the 'modern' key starters my hand held remote starter button makes it a one man job. The 'system' came as a kit. I've had my rubber nosed compression tester for 40 years and it's never failed me. It has a tire valve buried in the rubber which is pushed off it's seat when the compressed air hits it and then holds it so you can look at the number. You then just tap the tire valve stem which sticks out beyond the rubber nose against a solid surface and the guage drops to zero. Push the rubber nose down on another spark plug hole and crank away. I've never had to worry about having the right size threaded end. Maybe you could adapt a piece of rubber hose with a buried tire valve in it? If you're interested I can scan mine and put a photo on the site. Edited April 9, 2011 by DodgeKCL (see edit history) Link to comment Share on other sites More sharing options...
Guest 1930 Posted April 8, 2011 Share Posted April 8, 2011 I have that style also and your right works great but there is the screw into hole kind also which they say are more accurate. Less tendancy I guess that the compression might lift the rubber off the head I guess Link to comment Share on other sites More sharing options...
MikeC5 Posted April 9, 2011 Author Share Posted April 9, 2011 I have seen the rubber tip kind before although not in a long time. I machined up a steel plug and welded it to the spark plug body tonight. I just need to get the tap tomorrow and finish it up. I'll post a pic when done. Link to comment Share on other sites More sharing options...
brian1925tourer Posted April 9, 2011 Share Posted April 9, 2011 Hi , here in Australia I bought 4 plug adaptors that bring plug size down to 14mm so I use standard 14mm plugs, not original but 4 times cheaper. these plugs work great. You only need one adaptor if you do not want to change plug size. Maybe someone over there makes something similar.regards Brian Link to comment Share on other sites More sharing options...
Guest DodgeKCL Posted April 9, 2011 Share Posted April 9, 2011 I don't think the accuracy is any different- rubber nosed versus screwed in. My rubber nosed version does kick back off the cylinder head if you're 'not ready for it'. But it settles down when you realize you have to push down harder 'on this one'. The air pressure readings are held,one after another, and when I'm sure in about 3 or 4 cranks 'Ive got it' I just stop and the guage lets go with a snort. But it will have held ONLY the highest reading during the cranks because the tire valve keeps getting pushed up and off it's seat by the next compression stroke which 'resets' the reading all over again. I can't see it not being as accurate as any other. In fact I'll put it up against a screwed in one in a test any day. I bet the readings are the same. Link to comment Share on other sites More sharing options...
Steve9 Posted April 9, 2011 Share Posted April 9, 2011 Moral of the story... If you don't like rubber, get screwed! Link to comment Share on other sites More sharing options...
Guest 1930 Posted April 9, 2011 Share Posted April 9, 2011 Dont you mean if you dont like the rubber eventually you will get screwed Link to comment Share on other sites More sharing options...
MikeC5 Posted April 11, 2011 Author Share Posted April 11, 2011 Finished Product. Link to comment Share on other sites More sharing options...
dwollam Posted April 12, 2011 Share Posted April 12, 2011 Don't forget to hold the throttle open when cranking the engine to check compression. Link to comment Share on other sites More sharing options...
MikeC5 Posted April 12, 2011 Author Share Posted April 12, 2011 Yup. Or remove carb from engine... Link to comment Share on other sites More sharing options...
Guest Knucklebuster Posted April 14, 2011 Share Posted April 14, 2011 I may be wrong but I was thinking I had one of those that I bought for my small engine shop. Since lawn mowers use the older style plugs instead of the new 14mm stuff Im fairly sure thats where it came from.Hope you get it figured out. Good luck. Link to comment Share on other sites More sharing options...
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