EMan 928

Is there a device available that lets you perform a leak down test (to check rings) with the heads off?

69gaugeman

Do you need the heads off? you can use the old heads and gaskets and torque it up but not necessary to go to 100% of the torque.

Engine in or out?

No one makes a plate that I know of, but you could easily get a piece of aluminum flat bar 1/2" to 3/4" thick and drill some holes in it, I suppose.

davek9

His engine is out and heads are at the machine shop Rob. I was thinking the same, that he could make up some kind of plate.
I'm thinking his compression issue's were due to the 10 "slightly" bent valves, as the cylinders all look great, no scratches.

Dave

Dave928S

You could fairly easily make an alloy plate big enough to be held by the four bolts surrounding a cylinder, stick some thin rubber sheet to the sealing side, drill and tap a hole for an air hose, snug down enough to hold 100psi (not much) and go for it a cylinder at a time. Won't be hard to find TDC. I'd test with the piston about 5mm down the bore before TDC to give a bit of volume, to approximate what you'd have if a head was fitted, which would also give clearance it there's any threaded air fitting spigot projecting through the plate.

If you have a broken ring, or bad rings, the blowby will be massive. If you do a simple elevation of pressure to 100psi (instead of a full leakdown test with double gauges), it should take about 10 to 12 seconds to leak down to about 10psi ... if rings are bad it will be down to that low pressure in a matter of a few seconds.

GregBBRD

On a 928 engine, with the heads off.....

The only "leakdown tester" you are going to need is your eyes.

If there is a ring problem, you are going to see it on the cylinder walls (scratches/gouges) or on the tops of the pistons (oil will remove the carbon in areas where it consistently washes on the pistons.)

If the cylinder walls look good and the carbon on the pistons is uniform all the way to the edge....you don't need to go any further.

A stock GTS engine is always going to "push" some oil up and into the combustion chambers....until the pistons are removed and have the oil return holes drilled......huge error in engine design, by the engineering department. There's no way around this.....yes, you can make it significantly better, with a good breather system that keeps oil out of the intake (like you have).....but it is always going to push some oil. Without the oil drain back holes, the rings wipe the oil off the cylinder walls.....and then have no place for it to go....except into the combustion chamber.

No one thought that one through, very far.....

Dave928S

Probably just incredibly lucky, but my 82 had a top ring snapped exactly in two equal sections, which rode up and down with the piston in the ring groove, without leaving a mark in the bore, and the piston crown was no different than all the others with a light carbon layer.

A leakdown picked up the issue with one pot, but I couldn't see any problem with an endoscope prior to stripping the motor, couldn't see any issue with the heads off, but when I took that piston out the two ring halves fell out of the groove.

I think what you see might be dependent on how long you run it with any ring problem ... ?? If you pick an issue up early perhaps it might not have time to accumulate carbon, or generate any significant scratches, or other visual clues.