static compression check on 1941 coupe engine

[kkarrer]

Can anyone help with what the compression variance is on a 41 flathead.  The shop manual (boy, is it sorry...not nearly as good as the one I had for my 50 coupe) only gives the compression  @ 1000rpm.  There should also be information on what the compression should be when the engine is rotated by hand for a static compression test.
Thanks,
Ken Karrer 41 6227D coupe

[Dave Shepherd]

Rotating by hand was never a way to check compression, throttle open, all plugs out, cranking rpm, look for no more than 20% variation.

[kkarrer]

The tranny is out of this car (replacing original with a rebuilt 48) and so hand cranking is my only option.  Just  wondering what a "norm" is for that.  Either way, I'll check for variation between cylinder readings.
Thanks,
Ken 41 Coupe 6227D

[Bill Ingler #7799]

Hi Ken: As Dave pointed out, I don't`t think you will ever find the figures for a compression check by hand. Below is the compression check details as described in an early Cad 346 diagnostic manual. The only true way to get a meaningful check is with the starter doing the cranking.   Bill

[kkarrer]

Thanks.  When the tranny comes back in I'll hook it all up and see where I'm at.  I'm hoping not to have to do a rebuild on the engine.
Ken Karrer 41 6227D coupe

[pauldridge]

I disagree that the only way to check cylinder/rings/valve condition is by cranking the engine.  A leakdown test is equally as effective, in fact, sometimes more so, because it makes it pretty simple to determine whether leakage is from the rings, or either intake or exhaust valve.

An inexpensive leakdown tester can be readily found on eBay... here's just one example (new) for $35:

http://cgi.ebay.com/Engine-Cylinder-Leakdown-Tester-Dual-Gauge-Kit-?cmd=ViewItem&hash=item519b224014&item=350495064084&pt=Motors_Automotive_Tools&vxp=mtr 

You may need to get a spark plug adapter set for the smaller plugs on the flathead engine.. I got a set on Amazon for $9

You DO need to have compressed air source to use this.

The basic process:
1) bring the cylinder to top dead center on the compression stroke (verify by noting if the distributor rotor is pointing to that cylinder's plug wire
2) Block the crank from turning  (the air pressure will try to push the cylinder down)  One method would be to just put a socket and big breaker bar on the crank pulley, and have a buddy hang on while you CAREFULLY open the air pressure valve
3) Using the gauge with the unit, input 80 PSI of air pressure
4) Open the valve on the testor to admit compressed air to the cylinder
5) Read the "leakdown pressure" on the second gauge  A reading of 65-70 PSI would be considered a reasonably operable engine... anything higher than that is just extra gravy

If a specific cylinder reads much lower than 60-65 PSI, you can listen at the exhaust port (exhaust pipe), or intake (carburetor) for hissing air.. otherwise, if rings are the primary culprit, you should be able to hear air coming from the oil filler tube

[Dave Shepherd]

I disagree that the only way to check cylinder/rings/valve condition is by cranking the engine.  A leakdown test is equally as effective, in fact, sometimes more so, because it makes it pretty simple to determine whether leakage is from the rings, or either intake or exhaust valve.

An inexpensive leakdown tester can be readily found on eBay... here's just one example (new) for $35:

http://cgi.ebay.com/Engine-Cylinder-Leakdown-Tester-Dual-Gauge-Kit-?cmd=ViewItem&hash=item519b224014&item=350495064084&pt=Motors_Automotive_Tools&vxp=mtr 

You may need to get a spark plug adapter set for the smaller plugs on the flathead engine.. I got a set on Amazon for $9

You DO need to have compressed air source to use this.

The basic process:
1) bring the cylinder to top dead center on the compression stroke (verify by noting if the distributor rotor is pointing to that cylinder's plug wire
2) Block the crank from turning  (the air pressure will try to push the cylinder down)  One method would be to just put a socket and big breaker bar on the crank pulley, and have a buddy hang on while you CAREFULLY open the air pressure valve
3) Using the gauge with the unit, input 80 PSI of air pressure
4) Open the valve on the testor to admit compressed air to the cylinder
5) Read the "leakdown pressure" on the second gauge  A reading of 65-70 PSI would be considered a reasonably operable engine... anything higher than that is just extra gravy

If a specific cylinder reads much lower than 60-65 PSI, you can listen at the exhaust port (exhaust pipe), or intake (carburetor) for hissing air.. otherwise, if rings are the primary culprit, you should be able to hear air coming from the oil filler tube

Agreed, this is the best engine check for valves, head gaskets and compr. rings, standard procedure in my shop, but most home mechanics don't have an air compressor and it is somewhat more complicated then a compresion test.

[kkarrer]

Right.  I do have a compressor in my shop and I think one of my friends in the neighborhood has a Snap On leak down tester.  We may have to come up with an adaptor, but we'll see.  Would any of you all out there happen to know of  good way to test the shocks?  I don't see any obvious leaks and I know these were supposed to be lifetime shocks.  Since I have the body off the frame I thought there might be a good way to at least "ballpark" test them.
Thanks,
Ken

[Dave Shepherd]

No outside so only internal leaks would be an issue, no weight on the suspension makes it hard, you have to pull them out to get an idea.

[sly37]

I have always used the adapters that come with compression testers for leakdown tests. Can cobble something together with fittings laying around.