Leakdown test kit , which?

[anthony1956]

Any recommendations please ?

I gather the cheap stuff is not good, but do not know why.

Anthony

[revilla]

I can't point you at a specific model but I can give you some clues. I ended up making my own. You would be welcome to borrow it but it's a bit late to get it to Ian to bring now!

The two main problems are:

Most of the ones you see for sale work at far too low a pressure, often around 20-25psi. You want one that works at 80-100psi to put decent pressure behind the rings.

There isn't a standard fixed calibration. What one gauge calls 5% leakage another may call 10% leakage. You are basically recording the percentage pressure drop across a restricted orifice due to the flow caused by the leakage from the cylinder. In rough terms you are comparing the size of the leaks in your cylinder with the size of a tiny standard hole, but the exact size and shape of that hole varies from one tester to another.

If you don't know the calibration of the tester, it's hard to know whether your leakage is good or bad unless you have something else to compare with. For example if one cylinder leaks a lot more than the others you have a problem. Or if the leakage is a lot higher than last time you checked it with the same tester. But if you just buy a tester and use it on your engine to assess wear, you won't have a standard to compare to.

There are a couple of standards although very few of the sets you see on places like eBay will conform to either of them.

One is a defined standard published by the FAA in the USA for testing light aircraft engines. The other is the "80 at 80" standard used by American drag racers (and therefore maybe not so appropriate to our engine capacities but at least a known quantity). This basically requires the tester to read 80% leakage when connected to a "test orifice" which contains a hole 80 thousandths of an inch in diameter (at 80psi) (I think - from memory). Somewhere there should be more detail on the shape of the hole, length etc.

In the end I made one as close to the FAA standard for smaller engines as I could. It reads pretty much zero on the engine in my car and clearly showed up some ring and valve problems I've looked at so seems to make sense, but the important thing is to get to know what it reads when the engine is healthy then I will know if it changes something isn't quite right.

So I would look for:

The two gauges both calibrated in absolute pressure scales with the same given units. For example both in psi. That way you know what pressure you are using. Ones marked just with some kind of "set point" on the input and then a scale of "good / ok / bad" on the output are unlikely to be scaled sensibly.

A working pressure up to 100psi.

Ideally on the more expensive sets, a calibrated test orifice that you can use to check the calibration of the gauge.

I did discuss some of this with Dave Andrews once and he mentioned what he uses and said he was happy with it, but I can't find his reply at the moment. From memory it was Sealey set of some sort but I may be wrong. May be worth dropping him an email and asking what he has?

 

[elie boone]

Convert a spark plug and put 10 bar on it and listen and or watch for bubbles in de header tank.

[anthony1956]

thank you both :-)

[anthony1956]

I’ve bought the Sealey offering.