Compression gauge for Flathead with 10 mm plugs.

[Tom Knoebel]

Does anyone know of an adapter for the 14 mm thread with the off the shelf gauges?
Thanx
Tom

[Steve Passmore]

You can get them with a tapered rubber end that usally fits all.

[harry s]

Tom, I was able to find an adaptor at one of the local speed shops years ago.    Harry

[Jim Stamper]

     Call me silly but when I have 10 MM heads off I drill them out to 14 MM on the drill press ( very carefully) and tap them out for the 14 MM plugs.

     The tap costs $8 at NAPA.     Jim Stamper,  CLC#13470

[John Washburn CLC 1067 Sadly deceased.]

Tom,

What I did was take a 10mm spark plug and remove everything off it but the metal base with the threads. I then braze a air compressor fitting onto it so I can hook it up to my compression guage. Works quite well.

Don't listen to silly, I mean Jim. Keep it original.

jw

[Tom Knoebel]

Jim, what 14 mm plugs are you using.
John in the mean time i will cut off an old plug an braze.

[Steve Passmore]

Tom, if you wanted to go down that route you could use the plugs from the earlier engines which were 14mm, they were AC45 or their modern day equivalent but 10mm can still be had.

[Jim Stamper]

     I just use a normal range 14 MM plug. What I like about them is they can be had in any heat range anywhere. In this neck of the woods it can take a day or two to get the 10 MM. 

     The tank engine in my 37-60 coupe is a long way from original anyway so when I changed the heads going to the more available plugs seemed the thing to do. If I had a very correct car I might not go to the bigger size but I didn't see the advantage to the smaller plugs in my first car over 50 years ago and I still don't. Does anyone know the reasoning behind them?

                                       Jim Stamper CLC#13470

[Steve Passmore]

I think I read somewhere it was something to do with heat reduction Jim but I cant be sure now, as a side note I have completely dismantled several early and late engines comparing and measuring every component to try and figure out how Cadillac obtained the extra BHP from 132 up to 150 by 1941 and there is absolutely no difference between all the working parts internally but there are tiny little differences that I discovered which added together maybe do it, could be the plugs are one of them.

[pauldridge]

here you go... a set of adapters for your gauge for just $11... I bought the same for mine, and they work fine on the flathead

Amazon

http://www.amazon.com/Equus-3618-Adapters-Compression-Tester/dp/B001QUHFQA

Phil - Austin

[Tom Knoebel]

Paul,
Thank you just what I was looking for.
Tom

[Tom Knoebel]

I think I read somewhere it was something to do with heat reduction Jim but I cant be sure now, as a side note I have completely dismantled several early and late engines comparing and measuring every component to try and figure out how Cadillac obtained the extra BHP from 132 up to 150 by 1941 and there is absolutely no difference between all the working parts internally but there are tiny little differences that I discovered which added together maybe do it, could be the plugs are one of them.

Steve,
All the work I am seeing others do is that the volume flow and compression of the heads kept evolving. 1947 heads are the best for flow and compression is 7:1.
Cam grinds did not change only the material. Mr Burell did most of this development for Cadillac during the war and his son freely shares that info and is making the high performance intakes that are period correct.
http://flatcaddy.com/products/index.php?product=2-x-2-Aluminum-Intake-Manifold

Tom