Leak Down Test

[imtb]

I was thinking about putting a new head on the L20B but thought maybe I should see how engine test out. I did compression check and had good compression 210psi. So i thought it was still pretty good. Then last night I did a leak down test to see where all my power is going since the car doesnt really run that great. Well on cylinder 1,2,4, i have 20percent lose blowing by the pistons rings into the crankcase and on #3 30 percent. The plug and top the #3 piston is has oil build up and always has some oil on the base of the plug. The vavles seem to sealing tight no sound coming out the carbs or exhaust.

 

Just curious if anyone else has done leak down test and what kind of reading you got. If you can let me know I would appreciate it.

 

Now i am trying to decide if I should pull the engine and rebuild it or what to do.

[hang_510]

double check that the valves are w/in tolerance. if there is oily build up you will see some loss there vs. rings.

 

try a squirt of oil in the CC and redo the test. if its rings the loss should be less.

[imtb]

I just adjusted the valves less than a month ago so they should be in spec.

 

Should I squirt some oil in the spark plug hole when the piston is at TDC?

Then do the leak test?

[hang_510]

squirt it in the test cylinder (@ BDC), crank it a few times to distribute the oil, install tester and procede. repeat 4X ;)

[imtb]

I'll give that a try tonight. I was wondering if the oil would help seal the rings when its running. I am curious to see if the valves will leak.

 

thanks,

mike

[hang_510]

I was wondering if the oil would help seal the rings when its running. I am curious to see if the valves will leak.

 

only until it burns off and then your batman smoke screen get-away kicks in :eek: mines awesome :lol: :lol: :lol:

so keep the crankcase filled at all times :sneaky: in case of emergency escape.

 

 

(a cracked valve or) carbon build up on the valve seats could cause minor leaks like your experiencing.

[imtb]

Now it seems to only be leaking past the rings into the crankcase. I am getting a lot of blow by coming out the breather tube, i guess that is an indication of bad rings?

[datzenmike]

Up to 20% is considered ok but there is no cut off point. As long as the cylinders are even, up to 30% would be of concern but not necessarily worth the trouble and expense of a rebuild for the small gain in output.

 

Make sure the motor is warmed up when doing a leak down test.

 

To check the intake valve sealing listen at the carb with throttle open. Hissing sound is air escaping. Tap the intake on that cylinder with a plastic hammer or piece of wood to snap the valve open and closed. Does this seat the valve and reduce the hissing sound? Does this reduce the leak down percentage? If hissing continues the valve could be burnt or bent.

 

To check the exhaust valve do the same if possible at the manifold outlet. Perhaps unbolt the EGR tube and hold a piece of hose to your ear with the other end in the hole?

 

To check ring blow-by listen at the valve cover vent hose.

 

In all cases you will have to compare the sounds relative to the other cylinders.

[imtb]

Motor was just warm(not hot) when I performed the test. I had the vavle cover off so I could make sure both vavles where closed. I had the butterfly on the carbs proped open. I could not hear any hissing coming fromthe throat on the carbs. The only sound i could here was coming from the dipstick tube and the crankcase up through the timing chain cavity.

 

When i would move the engine past TDC I would hear the hissing out the carbs or exhuast.

 

i was thinking about just keep running the way it is and and rebuilding another engine to swap out. I found a long block for $125.00 local and talked to a local machine shop who was pretty knowelagable about the L20B. I picked up an rebult A87 Head with 490/290 cam. So I could go this route and take me time. Then I could just put my carbs, header, and what everelse on the rebuilt.

 

Any input?

[datzenmike]

Can't argue with that logic.