[DeTomaso] Cylinder Heads leaking

[sean mundy]

I ran out of time last night to put the rockers back on.  I will get the leakdown tester and do that test first and listen for leaks. Then I will reassemble the rockers and do the compression check again.  I'm getting a lot of great information.  Thanks all for the help!

Date: Mon, 23 Nov 2015 14:59:23 -0500
From: jderyke at aol.com
To: seanmundy at hotmail.com
CC: detomaso at poca.com
Subject: Re: [DeTomaso] Cylinder Heads leaking

 You're right- you do in fact need the rockers not only installed but adjusted close to the way you'll be running them, in order to ingest consistent amounts of air to compress. Further, the plugs should be all removed and the throttles blocked wide open during your tests to increase the speed of the engine turning over. More speed = more compression= more variance between bad cylinders & good ones so its easier to differentiate. Then turn the engine over with the starter at least 5 times per cylinder, & write down the results. If you change ANY of the above conditions, your results will not compare well with others'  results, some of which are published on line. The test is further described in all of Chilton's overhaul manuals & other similar places.



You have a cylinder with pressurized air in it with 
valves and a gasket sealing one end & a piston & rings sealing 
(more or less) the other end. The famous compression test is a fairly crude test from 100 yrs ago, but it should at least point one in the direction of the likely cause and narrow down possibilities to one cylinder. Using a stethoscope with a pressurized engine (air compressor at 100 psi), I'm able to hear air leaking in the carb (bad intake valve), the tailpipes (bad exhaust valve) or the breather cap (bad rings or a bad head gasket). If TWO ADJACENT cylinders are low or leaking, that indicates a gasket blown between two cylinders. If you're poor, my stethoscope is an ancient two-ear airline sound connector; just be careful to not touch hot metal with the plastic tips, which melt. Better ones are at any auto parts store.



You're looking first for consistent readings and second- significant variances in them. +- 15 psi is about normal on used non-race engines and should repeat 2-3 times. Variances beyond that either means the fitting is not being held in the sparkplug hole tightly ( i use the screw-in ones) or there's metal missing somewhere inside. Take the recovery tank off for better access to #4 plug. I cut the bracket welds and completely remove the whole assembly, then reinstall with a couple of sheet metal screws.



 






 Worst cases are holed pistons, a cracked cylinder with a
 piece of wall gone, a blown gasket or a chunk gone from a valve. But 
they are sort of rare and if the motor was running decently, none 
of these should apply. My best guess is a stuck ring. Several possible causes but the fix is replacement (with rings) especially if its a high mileage OEM part.

Good luck, Sean- J DeRyke






 






-----Original Message-----


From: sean mundy <seanmundy at hotmail.com>


Cc: detomaso <detomaso at poca.com>


Sent: Sun, Nov 22, 2015 10:13 pm


Subject: Re: [DeTomaso] Cylinder Heads leaking





I was thinking the piston needs to suck in some air from the intake valve to be able to compress it so I thought I needed the rockers


   installed.  I was only getting 30 to 40 psi on 5,6,7 cyl and on  8 I saw 200psi.  Those numbers dont make sense as the motor was running


   pretty good power just burning oil


   




 		 	   		  
-------------- next part --------------
   I ran out of time last night to put the rockers back on.  I will get
   the leakdown tester and do that test first and listen for leaks.
   Then I will reassemble the rockers and do the compression check again.
    I'm getting a lot of great information.  Thanks all for the help!
     __________________________________________________________________

   Date: Mon, 23 Nov 2015 14:59:23 -0500
   From: jderyke at aol.com
   To: seanmundy at hotmail.com
   CC: detomaso at poca.com
   Subject: Re: [DeTomaso] Cylinder Heads leaking
    You're right- you do in fact need the rockers not only installed but
   adjusted close to the way you'll be running them, in order to ingest
   consistent amounts of air to compress. Further, the plugs should be all
   removed and the throttles blocked wide open during your tests to
   increase the speed of the engine turning over. More speed = more
   compression= more variance between bad cylinders & good ones so its
   easier to differentiate. Then turn the engine over with the starter at
   least 5 times per cylinder, & write down the results. If you change ANY
   of the above conditions, your results will not compare well with
   others'  results, some of which are published on line. The test is
   further described in all of Chilton's overhaul manuals & other similar
   places.
   You have a cylinder with pressurized air in it with valves and a gasket
   sealing one end & a piston & rings sealing (more or less) the other
   end. The famous compression test is a fairly crude test from 100 yrs
   ago, but it should at least point one in the direction of the likely
   cause and narrow down possibilities to one cylinder. Using a
   stethoscope with a pressurized engine (air compressor at 100 psi), I'm
   able to hear air leaking in the carb (bad intake valve), the tailpipes
   (bad exhaust valve) or the breather cap (bad rings or a bad head
   gasket). If TWO ADJACENT cylinders are low or leaking, that indicates a
   gasket blown between two cylinders. If you're poor, my stethoscope is
   an ancient two-ear airline sound connector; just be careful to not
   touch hot metal with the plastic tips, which melt. Better ones are at
   any auto parts store.
   You're looking first for consistent readings and second- significant
   variances in them. +- 15 psi is about normal on used non-race engines
   and should repeat 2-3 times. Variances beyond that either means the
   fitting is not being held in the sparkplug hole tightly ( i use the
   screw-in ones) or there's metal missing somewhere inside. Take the
   recovery tank off for better access to #4 plug. I cut the bracket welds
   and completely remove the whole assembly, then reinstall with a couple
   of sheet metal screws.
   Worst cases are holed pistons, a cracked cylinder with a piece of wall
   gone, a blown gasket or a chunk gone from a valve. But they are sort of
   rare and if the motor was running decently, none of these should apply.
   My best guess is a stuck ring. Several possible causes but the fix is
   replacement (with rings) especially if its a high mileage OEM part.
   Good luck, Sean- J DeRyke
   -----Original Message-----
   From: sean mundy <seanmundy at hotmail.com>
   Cc: detomaso <detomaso at poca.com>
   Sent: Sun, Nov 22, 2015 10:13 pm
   Subject: Re: [DeTomaso] Cylinder Heads leaking
   I was thinking the piston needs to suck in some air from the intake
   valve to be able to compress it so I thought I needed the rockers
   installed. I was only getting 30 to 40 psi on 5,6,7 cyl and on 8 I saw
   200psi. Those numbers dont make sense as the motor was running
   pretty good power just burning oil