8n compession test results

OLD FORDS

New User
Hello all, just bought a not running/no spark 48 8N, took some doing (new carburator, tune up and coil)but got her to run, however it runs very,very rough and seems to be not firing on all cylinders. I did a dry/wet compression test and the results were (DRY) 105-105-105 85, (WET) 120-120-120-105 I'm guessing it needs to have the pistons and rings looked at and most likley rplaced. Comments please ?
 
Assuming your gauge and technique are accurate, you have only one very minor problem and that can probably be solved with mmo or atf in #4 to free up sticky rings on #4.

A new engine has about 120 lbs of compression.

Compression is not your problem.

Have you changed the points, plugs, condenser, cap and rotor and set the timing?
75 Tips
 
Check your timing order,it easy to get crossed up.
a234029.jpg
 
I've replaced all ignition componets, and my wife says I can go check the firing order afetr I'm done with supper and help her do the dishes
 
I agree with Bruce , your compression is good
I would recommend not using Champion plugs
I use Auto Light or NGK
if it had been setting for a long time
try running some Sea Foam in it
 
(quoted from post at 19:05:44 08/08/16) Just saying that a leaky valve could account for the lower compression on #4.

Yes, a leaky valve could result in the 85 dry reading. But, how do you account for the significantly higher reading on the wet test? I' m having a hard time believing that adding oil to that cylinder sealed a valve leak.
 

"Yes, a leaky valve could result in the 85 dry reading. But, how do you account for the significantly higher reading on the wet test? I' m having a hard time believing that adding oil to that cylinder sealed a valve leak."

at first, i was thinking this too. but the more i thought about it, the more it made sense, if looked at a little differently.

let's say each cylinder has a roughly equal amount of wear - let's call it 20 PSI worth. in addition, cylinder # 4 has a leaky valve.

add liquid to all 4 cylinders, and all of them go up 15-20 psi. but cylinder 4 still also has a leaky valve, which is why it was an extra 20 psi low, and still is.

i don't know if that's the case here, but i can see how it could be.
 
That was the point I was trying to
make. All cylinders came up in
compression on the wet test, but #4
was still lower than the other 3.
 


OK, I understand your point.

Too bad he didn't write down the first reading on the dry test. That would have told him if the valves were seating.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top