leak down test numbers

September 24, 2013, 05:58:27 PM

posted in this separate thread to get opinions

Guys,
son came in for my birthday .
we were able to get leak down numbers on this 88sport 302 ho conv sd mkvii eec with explorer parts + 20 over pistons & 1.7rollers

i presurized the tester.. dialed in the adjustment to "zero" out the guage and the second guage usuall fell at 100lbs.

so upon connecting up the hose, sometimes we lost some air presure but anyway, that is the reason the psi numbers are a little different.. i think.

anyway.... in HO firing order

cyl 1 @ 86psi= 17% loss
cyl 3 @ 89psi= 18% loss
cyl 7 @ 82psi= 20% loss
cyl 2 @ 83psi= 18% loss
cyl 6 @ 84psi= 18% loss
cyl 5 @ 80psi= 42% loss (hearing air out the tail pipe
cyl 4 @ 89psi= 19% loss
cyl 8 @ 84psi= 18% loss

thoughts?

leak down test numbers

Reply #1 – January 18, 2014, 01:37:11 AM

this week we were able to examine some details about cyl 5

the last post above i told you all that we could hear air coming out the tail pipe.

took top end stuff off and removed driver valve cover.
we dialed in cyl 5 tdc then we continuied rotating the crank clock wise about 15 or so degrees to insure we were on the base circle of both I and E valves.
I noticed by feel that the exhaust valve push rod spun by hand just a tad harder than the intake.

we removed the exhaust valve rocker
we added to a bone cold motor (bad choice i know) 100lbs of air.
with no rocker installed , the leak down number fell to 23psi.. i feel it would be better if the motor were hot.
We made up a shim for the underside of the rocker pedestal from feeler guage materal which we chose .010 thick.

did a leak down again and it still held at around 20 or so psi

oddly enough, with no rocker on and with the leak down tester attached,,, with very little presure at all, we were able to cause a leak by pressing down on the valve stem ,, and from my perspective, it took very little effort to induce a leak.
my installed seat presure should be at 115lbs from what the machine shop measured,, i watched him put the springs in.

i am suspect to the work done on the heads when they did the bowl blend and cut / cleaned up the seats.
im thinking maybe on this valve they cut too deep and the valve stem is sticking up a little more than the other exhaust valves.. but didnt have time to anylize that part.

so,, thinking we need to also shim the base of the spring as well.
im not worried so much about the push rod length, we arent talking about that much gap needing filled.

just an update.

leak down test numbers

Reply #2 – January 18, 2014, 03:07:41 AM

id guess a bad cut on the valve or seat. if its leaking cold, it wasn't cut right or your rocker/pushed is too tight.