Vacuum testing a cylinder head for leaks

Here is a video of my vacuum test rig i have designed and made to test cylinder heads.
this test rig will check inlet and exhaust valves for leaks and test the cylinder head for cracking.

here is the video.

It is a youtube link but it is my limited channel.

https://www.youtube.com/watch?v=e1MdSnNp8v8

tell me what you think of my design.
i know you can put a cylinder head on its side and fill the exhaust and inlet ports with fluid to see if leaks past the valve seats. but it is a very basic test. this vacuum test rig gives a good indication of how bad a pair of valves seats are and it also checks to see if the head has any cranks in it.

the valve tests pulls a vacuum in the direction of the intended seal direction, e.g. the valve will be pressed against the valve seat as it would when a combustion event occurs.
the cylinder chamber test pulls a vacuum against the intended direction of the valves as it creates a vacuum in the chamber. but this test is designed to check for cracks in the head. So a slight increase in the leak rate is to be expected but only slight increase.
in all of these vacuum tests you are looking for a major difference between maintaining a complete vacuum and loosing it very quickly which indicates remedial work is required on the valve seats the valve guides or suggest the head is scrap in the event of a cracked head.

My intention is to remove all the valves in this head and do a mild valve seat regrind. Then retest the head and hopefully it will show perfect seal on all valves. i will have to wait and see.

One modification I could make is to create a couple of blank plate to block off the inlet and exhaust valve ports while doing the chamber test to give a better indication of chamber integrity.

That would be a more complete test.

@adaxo

Great piece of kit, well done.
Have few thinks to thought about, while you do vacuum test on inlet or outlet ports, wonder how much can escape through top of the valve? if any? can this lose vacuum through valve guide/valve steam seal?
Other thing to consider is, while you do head checks, especially for cracks, head need to be hot, at least 70'C, for this test to make sense as they can be all good while cold but leak when in operating temp, similar to compression test.
I think only way to find out is to lap valves where vac drop and see the difference b4 and after.

yes some good points there adam.
one way to ensure the heads are hot is to put them through the dishwasher again, my dishwasher goes up to 65 degree wash cycle and it does a steam drying cycle at the end of the program, when the heads come out they are way to hot to touch so i would expect them to be at about 60-70 degree.

yes valve guides and valve seals can leak. one easy way to test this is to squirt a bit of water/light oil on the valve seal/guide and the vacuum pressure will change if under vacuum pumping or the vacuum pressure will stop dropping while the water/oil is sucked into the leaking area when not under vacuum pumping but at static vacuum pressure with the valve closed.

i could flip the heads over and test the inlet and exhaust port and when the vacuum pressure is dropping, drip some light oil or water around the edges of the valve and see if the vacuum pressure drop slows down or stops completely until the water/oil gets sucked through the leaking area, this would allow me to pinpoint the rough area where the leak is happening. but when the engine is running the valves will naturally be rotating in there seats so the valve needs to be able to make a good seal at any rotation angle on its seat.

this could be checked after the valves have been lapped. There should not be any need for spring pressure to hold the valves down to the seats to make a good vacuum seal once the valve have been lapped. the vacuum should hold them tightly shut on it's own.

hmm something to think about. maybe i will retest and use the water/oil to rule out particular areas for leaking.

the reason for me going down the vacuum test route is because part of a mass spectrometers is the vacuum chamber where the chemical analysis down to atomic levels is done. so i need to understand hole vacuum pressures work and how to control them.
you can buy all the stuff i used for this test rig for under £100 the vacuum pump can be one of the ones used for air conditioning testing and they can be bought for about £50 new then the valve and gauge are only cheap things, then there is the chopping board and closed cell foam pad, again only cheap stuff. so yes £100 would get it.