hitmanpty

I want to preform a leak down test this weekend in my vette.

i look all over the town and find only one place that have it. but is to profecional at $400 . is to much money for one time use tool.

i also look into ebay, and find some tools at a very good price, but it will take about 2 more weeks to get here from the moment i purchase. and i really want to do the test this weekend.

so I decide to make my own tool.

this is not a profecional tool. in any way. I just want to find out if i have a leak on my cylinder numeber 1. and like to know where is that leak.

here are some pics of my home made tool.

here is my compression tester
[IMG][/IMG]

this is the tip that go into the spark plug hole, on my compression tester
[IMG][/IMG]

here you have the tip disconected from compression tester. this is what iam going to use with the home made leak tester
[IMG][/IMG]

here is the tip install on the snap on part that go to the ari compresor
[IMG][/IMG]

i will set the air compressor to 100 psi. I dont have way to measure how much air iam loosing. but all iam looking for, is where the most air is leaking.

I guest i can compared with the other cylinders and look for big diferances.

iam guesing a vent valve.

383vett

That'll work. What you are doing is pressurizing the cylinder. They make an adapter for that and it's pretty inexpensive. Yours is even less!

hitmanpty

hitmanpty

ok just finishing preformence the test on my car.

i only test cylinder number one. try to check number 2 but had some problems with my home made tool

this are the results.

i hear no air from the radiator or bubbles.

I hear clear air leak on the exhasut pipe.

also hear some air coming out of the intake, but lot less that the exhaus

i remove the vlave on top of the valve cover. I can hear air coming out of that hole. also i can feel a little brezze on my face when i put it next to the hole.

I really try to test the other cylinders to compare with number 1 cylinder, but like I say I had some problems with my home made tester tool.

so in conclusion i dont really sure what the test is telling me. Iam getting leaks on intake valve ,exhasut valve, and also piston rings. i know some leaking is ok but sinse i dont have a profecional tool can not measure preasure lost

any sugestion is very welcome.

joe paco

I wondered how you would be able to verify anything without a gage. keystring has some good advice. but you can remove dist cap and turn engine to where #1 is firing to be sure valves are closed, rather than remove valve covers. every 90* rotation of engine is the next cylinder in firing order.
I believe the pressure will push the piston down anyway, if it is high enough. unless you remove rockers, valves will possibly be open.

without a gage to measure it, the test may be confusing.

hitmanpty

ok guys. I put the number 1 cylinder on TDC. I tell my soon to put his finger on the spark plug hole. at the same time I rotate the engine by hand. when he feel the air pushing, them we know the piston is coming up.

writing this I just realized that i put the cylinder on 6 BTDC not on 0 mark on balancer. when the piston was coming up

I ask now at that position will I have a open valve????????????????

I think i will repeat the test tomorrow with the valve cover off. just to be sure.

hitmanpty

one thing I want to confece.

any body remeber the time when i change my harmonic balancer.??? about 6 month ago not sure exactely.

well in order to stop the engine to rotated when aplying torque to the balancer.

I introduce a rope inside the cylinder. so when the cylinder go up will be stop by the rope.

that maybe damage one of my valve on cylinder one. after all i have low compression on that cylinder 110 to 115 psi,

by the way i saw the rope method on youtube. it was not my idea

Keystring

Although 6 BTDC is the 'timing' advance, your valves would still be in the closed position.

You should be fine.
What kind of readings did you get with a compression test?

If you're reading low on one cylinder, then that cylinder either has a burnt valve, worn or broken compression rings or possibly even a blown head gasket.

Do a full compression test on each cylinder first and compare the readings.

They should be within 5 to 10 lbs of each other.

hitmanpty

the other cylinders are arown 135 psi dont remeber exctely i dont have my notes here

hitmanpty

since i dont have a good tool to do a leak down test. I been thinking of removing the cylinder head. and inspect visualy

Tom400CFI

Several things need addressing in this thread, and for anyone doing what I call, the "poor man's leak-down test"...That is WAY too much pressure. All you need is 30 PSI and even that is a lot for the purpose of this test



BINGO! Frankly, you should hear zero air coming from the TB, exhaust or radiator. Maybe a little far-away sounding air noise from the oil fill as you'll have a small amount getting past the rings.

See above. You verify by 'measuring' leakage w/your ear, comparing cylinder to cylinder.


Not true. The piston can and will get pushed either way if not precisely at TDC -even more so if 100 PSI is used. "Either way", being backward toward the intake stroke OR forward toward exhaust. EITHER WAY, the valves DO stay open past BDC and therefor, if the piston is pushed down to BDC in either direction, one of the valves will come up off the seat...and leak like crazy.

Gotta keep that piston at TDC firing ONLY, and that is way, WAY easier to accomplish using a much lower test pressure.

joe paco

you've obviously experienced it, Tom. the engine can rotate either direction of the circle. that's why I said valves will possibly be open.

OP has the FSM. should have a method of doing a proper compression test in there. if he's going to be listening for air, he needs a calibrated ear, otherwise this test is useless.

I doubt that anyone on the forum understands what he means by "mumero one dead." hard to believe it would pump that much oil to foul the plug in a few starts, only running in the garage.

I think that he needs to describe and show the current problem -in a long history of problems. even at 115 psi, that will fall within the GM guidelines on compression variance. certainly enough to run decent.

the reality is that not everyone will be capable of maintaiining their C4.

hitmanpty

ok i just dont trust the leak down test i did on my car yesterday. the tool is not the correct one. and i only use my one cylinder test, have no point of comparationIam getting ready to remove the cylinder head.

the true is at this point I have no idea why cylinder number one is not working

383vett

Actually, it is very possible to bend a valve doing this. If the piston is on the compression stroke and the valves are closed, the rope trick won't hurt anything. However, if the piston is on the exhaust stroke, the exhaust valve is hanging down being pushed by the rope and piston. If 60 ft/lbs is applied to the balancer bolt, it the only thing preventing the motor from turning is the side of an exhaust valve. It doesn't take much to bend the valve and keep it from seating.

hitmanpty

see that is what iam saying. because I did not check the position of the cylinder when i did this. probability is that the piston was not at TDC.

hitmanpty

I need advice here. sure I open the cylinder heat ????????????????? or not.

remeber I will do this my self. I will have to get me a torque tool but i can get that. no worry

desertmike1

This is the best way to perform a "static" leak check, and at the same time you can observe the Variance between Cylinders. This Tool can be hand built with off the shelf parts with the exception of the "orfice" I had my Machinest Brother in Law make my orfice out of solid brass..some 32 years ago..still works good.

http://www.engineersedge.com/power_t...sion_check.htm

http://www.precisionmeasure.com/test3.htm

These can also be purchased through an aircraft (tools) supplier for cheap, or ebay.

http://www.ebay.com/itm/Never-Used-A...-/250923241627

desertmike1

one more thing...this is how you find TDC for each Cylinder.

First of all...there is two complete crank rotations in order to fire all eight Cylinders, so here is the simple calculation;

360° X2=720°/8= 90°

Fire order 18436572

So all you have to do is locate #1 @ TDC then rotate the Crank in the normal rotation (90°) now your at #8. Rotate another (90°) and your at #4..now you keep doing these 90° rotations until you complete the fireing order, while conducting the leak checking...

Caution

Never leave a tool on the crank when you apply air...the crank may try to spin on you..

joe paco

]

hitmanpty, read your FSM concerning compression test. no cylinder below 100, or less that 70% of the highest. your engine is within guidelines, per my 91 FSM, so what is your problem, exactly? you need to show it or describe it so we understand.

if you already have decided that number one is "dead" what does that mean? plug fouled? is it the correct plug?
these important questions have been asked before, with no response -or maybe I missed it.

is it possible that number one plug wire is damaged? have you been puncturing it to check timing? etc.
if the cylinder has been showing compression -finger test, whatever- it isn't dead. maybe not ideal, but may be normal for an old engine.

before I tore an engine apart I would be certain what the problem was that I intended to solve. as you said, it has been over a year, and you are back to the same issues.

add: I agree: forget the leak down test, and start a new thread

coupeguy2001

A leak down tester has two gauges. one tells you how much input line pressure you have, and the other one tells you how much pressure is holding in the cylinder.

So if a good cylinder is on the leak down tester, each good cylinder would have a measurement of like 90/100. This would be a ratio. The ratio would indicate PERCENTAGE of leak. 20-25% leakage is the last leak test you want to do, because if it is any higher leak rate, it has to come apart for repair.

The 90 would be how much pressure the cylinder holds and the 100 is how much pressure you are putting in.

You can't just pump a 100 pounds of air into a cylinder to see what the compression is, because you have no gauges to tell you what the pressure is in the cylinder.

You can tell where the pressure leak is by listening, but a more coordinated test is needed.