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Thread: Cylinderhead pressure tester
08-15-2007, 04:42 PM #1
Has anyone here ever tried to build their own pressure tester and how did you do it?
08-15-2007, 10:05 PM #2
What are you testing for?
I have made fittings to put air pressure in a cylinder to hold the valves closed to replace the valve seals. I took a spark plug, knocked the ceramic center out of it and brazed an air fitting to it.
If you are doing leak down testing you can make a simular fitting.
08-15-2007, 10:57 PM #3
A cylinder head pressure tester is basically a flat plate, a flat gasket, a gauge and an air pressure inlet. Not high tech. The difficulty is in sealing it against a variety of heads.
Commercial head shops have plates made for a variety of heads, with the spaces in the combustion chamber removed. A gauge on a solid plate can show a leak, but if it is in a combustion chamber, it isn't visible. Not a serious problem, as most cracked heads are not worth the cost of welding, machining and the warranty cost of those which don't stay repaired.
08-16-2007, 01:22 AM #4
I really shouldn't jump in on this, but what do you hope to determine? If a particular cylinder is leaking?
Pull the plugs, screw the air input in, pressurize.
Cylinder by cylinder, if you have air coming out the carburetor, or plenum, intake valves are bad.
Cylinder by cylinder, air coming out the exhaust, the exhaust valves are bad.
Cylinder by cylinder, air blowing by the rings and coming out the valve cover says the rings are bad.
You, of course, have to bring each piston to TDC, both valves closed to learn anything.
Why the hell am I following the above?
I assumed from them that it was a cylinder leakdown.
You might want to pressure test high pressures.
You might, from S Africa, want to test metals for hardness.What IS your question?
08-16-2007, 02:22 AM #5
Basically a cylinderhead pressure tester is to check if your top has a crack that allows combustion gasses to enter into the cooling system.
Usually a warped head lets gases into the coolant but if you've checked that the head is level, allowing the head gasket to seal correctly, then a pressure test is needed to see if there is a leak.
Packard is right in that the machine is pretty simple, that is why I'd like to see if I can't make my own. But the problem is all the different variations of heads needs its own method of blocking the water flow.
The most popular tester over here comes with hundreds of different 'plugs' so as to test as many a variety of heads as possible.
What I'd like to know is if anyone has tried building their own tester, and how did they do it?
08-16-2007, 05:10 AM #6
Not that difficult, bore size and bore centres don't differ that much between engines, if you cut say 3" holes in the plate for observation that will accomodate quite a bit of variance between bore centres. The testers I have seen have all been profile cut from 1" plate with no bolt holes, the cylinder head is held to the plate by some style of clamp a thick rubber gasket to match the plate is used. At a guess 5 or 6 plates would cover most passenger car engines.
Don't stuff around trying to make a unit which will work on all heads, make one which will work with the engines you normally see, for me it is 4 and 6 cylinder with bores between 3.8" and 4.1" and bore centres between 4.3" and 4.4" then if an odd engine comes in either send it to another shop or make another plate to cover engines around that size.
08-16-2007, 05:39 AM #7
I have been at engines and engines both in a professional teaching establishment and as an ordinary punter.
A pressure tester to many is no more than a dial pressure gauge with a shrader valve to lock the reading and a tapered piece of hard rubber to go into each sparking plug hole- and the engine cranked over on the starter.
It will tell if the valves are shot or the rings have gone but it will not tell which head valve or which ring or both or all.
Again, removing the head itself will reveal more and it should be fairly easy to run a set of tests. you don't need a machine to check for warp- you need a good straight edge. To see if the head gasket has gone is obvious but it might lead to coolant problems. To find out if valves are leaking, one needs paraffin and oil- overnight. To find out whether the waterways are shot, needs a rig which will seal the waterways and blow water or oil through. The same will be needed for oil ways.
Repeating on the block again needs something similar.
You are looking for leaks which under normal tests under normal atmospheric pressures will not be obvious.
It all begs the question of whether once the fault is discovered whether you will be comepetent to effect the repair.
Don't get me wrong but I once spent many hours than enough to rework a cylinder head on a MiniCooper. I thought all was well but it wouldn't fire up. It wouldn't even turn over.
Removing the plugs gave me an eyeful of antifreeze. There was a hairline crack. End of head!
I have also done it on human heads. Surprising just how little it takes to end life.
The fun is trepanning and fitting a hinge!
08-16-2007, 07:02 AM #8
The problem with pressure testing cylinder head water jackets on the bench is that the majority of cracks that develop in a cylinder head that cause a leak will test good on the bench and not open up enough to leak until the head is at operating temperature
08-16-2007, 07:14 AM #9
Sounds like you need to have the head magnefluxed(spelling?). Uses magnetism and iron dust to find cracks. At least that's how we did it 30yrs ago. [img]smile.gif[/img]
08-16-2007, 07:36 AM #10The problem with pressure testing cylinder head water jackets on the bench is that the majority of cracks that develop in a cylinder head that cause a leak will test good on the bench and not open up enough to leak until the head is at operating temperature
08-16-2007, 07:48 AM #11
The point of cylinder head pressure testing is often to avoid putting a lot of time into a head which should be scrapped, not 100%, magnaflux is better on iron and dye penetrant better on aluminium but it has a good chance of finding cracks anywhere, visible or not though the combustion chamber is the usual place to crack.
08-16-2007, 09:12 AM #12
I agree with HelicalCut on the need for various block off plates. We have several plates that we use on various industrial engines, but they are for that particular engine series. You can use hot water by strategically placing valves on the block off plate to circulate water until it reaches engine-operating temperature. A hot water heater or a pressure washer like a Hotsy, which heats the water, can provide this. You can generally reuse a head gasket or make one that will let you pressure up. I have also seen guys use gasoline in the old days to check for cracks. Gasoline in the coolant passages will find the crack. I have seen a fire that resulted from this practice so keep that in mind. I have used both of these techniques with success. In automotive applications why not collect blocks that are water tight but no longer economically serviceable (overbored or bad mains) they could be easily rigged to allow for pressure testing although set up time and storage would be downfalls.
The block off plates work well, allow for hot water usage when desired, and when labeled store quick and neat.