Compression tester
 

Does anyone have a recommendation for a compression tester that comes with
an adapter for a Flathead. Everything I see comes with mm adapters. Thanks Dave/Green Bay

Re: Compression tester
 

Aren't all spark plugs metric thread? According to Machinery's Handbook (24th ed pg 1650), there are four standard SAE spark plug threads, all metric: M18 x 1.5; M14 x 1.25; M12 x 1.25; and M10 x 1.0

Re: Compression tester
 

All ford v8 heads,flatheads from 39 aand up have 14mm spark plugs. some in the early 30s had 18 mm plugs if I remember right.

Re: Compression tester
 

Yup! My '34 has 18mm plugs....

Re: Compression tester
 

Thanks. Just what I needed. That makes the search much easier.

Re: Compression tester
 

I bought mine at Harbor Freight
John

Re: Compression tester
 

Model B and real early V8 had 7/8 plugs didn´t they ?
But after that metric.

Re: Compression tester
 

O'Reilly Auto Parts is where I bought mine.

Re: Compression tester
 

Ones with long rubber hoses tend to give lower readings due to hose expansion, I look for Steel cord in the hoses

Re: Compression tester
 

Don’t forget to check that the adapter for the plug hole doesn’t thread too far down into the opening.....it could hit moving valves. A guy I know used one with a long adapter plug on a fresh built engine and ended up having to replace a valve if I remember correctly.

Re: Compression tester
 

7/8" wrench but threads are 18MM

Re: Compression tester
 

Re: Compression tester
 

I've been told we ended up with mm spark plug sizes due to the influence of Robert Bosch' an early day electrical engineer and manufacturer, who was of German descent.

Re: Compression tester
 

Dave when doing the test, have all plugs removed and the throttle wide open for best results. You can test it dry then add a little oil to see if it changes the readings, do one cyl. at a time or the oil can drain by rings and give different results. I bought a Bosch tester from O'Rileys. Al

Re: Compression tester
 

When the gauges are checked to a standard pressure and read the same---then when used to check engine compression they read different, the long soft rubber hosed ones read lower, when you move into the high end recording testers the hoses are short, metal reinforced,and the passage is filled with wires to reduce volume

When testing compression it's not as much about how high the gauge eventually gets, it's more about what happens on the first few compression strokes, and testing all the cylinders the same ---you have to remember that to fire there is only one compression stroke

Re: Compression tester
 

If you have a 37 21 stud or earlier 18mm plugs. just get one of these for compression checks.


https://www.snydersantiqueauto.com/P...earchByKeyword


If using 18mm I like autolite as they still have screw tops and you can run raja ends.