Vacuum Tester - test your valve job or test for cracks

[Greg]

One really cheap, really handy tool you can make yourself is a vacuum tester.
I use mine to check cylinder heads and blocks for cracks. you can test a head in less that 5 minutes and pick up cracks that wont show up using fluid pressurised inside the head.
All you need is:
1 small pneumatic venturi vacuum generator. You can buy these from a pneumantic/hydraulic supplier, mine is an SMC brand. About AU$40.

2 ball valves, telfon type valves seal better. About $15 each.

A few different plates, i use 5mm aluminium cut to diferent shaped to suit the holes you are covering. you need to tap an air fitting into the back and glue high density foam rubber to the front, this will seal the plate to the head. you also need some plates to cover other water ports or bungs to plug water pipes.

A large foam rubber pad to sit the cylinder head on face down to seal the water galleries.

some 3/16 or 1/4" vacuum hose.

a T-piece

A vacuum gauge.

A supply of compressed air.

you assemble it all in this order from the compressed air supply-

air supply - ball valve - vacuum generator - ball valve - t piece - one line to vac gauge/one line to pad.

i have a bit of a schematic


To use it, clean the head face, wet the large pad and sit the head on it face down.

turn on both valves and sit the pad on the end of the line over a water port, cover any other ports with another foam pad.

once the ports are all covered the gauge will rise to a certain level (depends on the air supply but doesnt really matter).

once the gauge has reached its max reading, turn off the ball valve closest to the head, this will seal the head, then turn off the other valve (because it makes a horrible noise)

watch the gauge, if the head is sealed and has no cracks to the water jacket the needle will not move. If the head is cracked through to the water jacket the gauge will leak down. I give it 5 minutes and if it hasn't moved the head is ok.

This method doesnt show you where the crack is but does show if you have a leak. If it leaks down, I pressure test it to find where.

You also need to remember to remove spark plugs, as these will seal a combustion chamber and not show up a crack.

I think air is 7 times less dense than water, so this will show up practically anything.

You can test your valve sealing by putting the pad over the intake or exhaust port and doing the same thing.

I hope this makes sense because this is such a handy tool, I would say it makes us $100-$150 a day in all of 1/2 hour. you shouldnt be without one.

[Shawn L]

How many Inches of vacuum do you use?

[Greg]

Shaun,
On my gauge it draws around -80KPa which is around 23.6in/hg, 320 inches water or -11.6psi. It doesnt really matter if you use a little more or a little less, what you want to do is see if the head will hold that vacuum.