Wierd compression

V4F

V4F

Well-known member
CONFUSING QUESTION : I have asked this before but still need ideas .
stock model "A" motor . rebuilt recently . after a back fire , compression : #1-4 … 75# #2-3 45#
pulled head & resurfaced , magna fluxed , all new ignition (stopped backfire) , set valves , tried different carb …………. no change in weird compression readings . any ideas appreciated … steve
 
Sounds like you checked all of the normal things. You don't say but did you check the pistons and rings? Maybe stuck rings or collapsed ring lands from the back fire? Hard to believe it would happen to two cylinders but...

Just thinkin' outside the box.

Have you done a leakdown test?
 
It sounds like you have a weird engine rebuild. It is hard for me to connect 2 low compression readings with a backfire. Maybe you should explain what the rebuild included.
 
great ideas , all . thank you & I will try the 2 I haven't done ………… steve
 
Was the compression even before the backfire?


*** do not know as not my motor . but ill check ! …….. thanks
 
I agree with the leak test. Could be

crack
leaking valves [ which I would doubt, but, possible]
Rings [ not lined up correctly]

First thought of course was head gasket, but, you did all that related stuff.
 
For the leakdown test take apart an old sparkplug or buy a adaptor from Brattons or Snyders thread in a male adaptor from an airline into the sparkplug base.Hook up your airhose and pump 30 to 35 lbs into the cylinder which is at tdc with the valves closed,make sure the car is in neutral or hand brake on in case the engine turns over from the pressure.Listen for air escaping from carb,exhaust or into the crankcase.
 
rocket1, I put the car on high gear, and the e-brake on while doing a leakdown test, thus preventing the engine from turning if it is not at exactly TDC.
 
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