Leakdown test procedure info needed
 

OK, so I'm thinking about running a leakdown test on my engine to get a baseline to compare with later. I have read up on this a little bit, and I have a leakdown checker. I understand that you want the piston on the compression stroke at TDC. What is the best way to ensure that each piston is on TDC as I check it? TDC for #1 is relatively easy, and following the firing order every 90* of rotation should put me at TDC for each hole as I check it (if the balancer is marked all the way around). However, my engine compartment is very tight in front of the crank pulley, and I am not certain that I will be able to get a wrench on the crank pulley bolt to get the necessary leverage with all of the accessories in the way. Having the plugs in would make it very difficult to turn the engine over, but then there is nothing to keep it from "bumping over" when air pressure is applied to the cylinder being tested. Besides that, I have never been real crazy about using the crank bolt to turn an engine over. I have seen these strip out, and that would ruin my day.

Anybody got any good tips on this?

Thanks!

I'm guessing with the leak down you have plugs out anyhow? At that point turning crank would be easy with a breaker bar. I have never done or seen a leak down done so I'm just guessing here.

Articles I have read recommend leaving the other plugs in to lessen the chance of the air pressure trying to turn the crank.

If you want to do a leakdown test "by the book", you need to have each cylinder at TDC when you pressurize it. I use a 1/2" ratchet with an extra long handle to turn the engine. Don't use a wrench, use a socket on the crankshaft nut. Alternatively, you can use a remote starter button but you will be cranking that starter a lot. You want the cylinder at TDC before you pressurize it and start with low pressure 20-30 psi and gradually increase the pressure to 100 psi and if the cylinder is at TDC and the plugs are in, the engine should hold at that spot. However, if you are a few degrees off either way, its gonna roll over.

I've done it a little differently, but you have to be willing to remove your rocker arms and readjust your valves afterwards. I remove all of the spark plugs and all of the rocker arms so that the engine will turn freely and removing the rocker arms ensures the valves will not be hung open. When the cylinder gets pressurized, it will go right down to BDC and you can get your readings. The downside with this method is you might not really get a good read if the blowby is in the rings... but it will tell you very easily if blowby is in the valves..

You have to leave the other plugs in. With the plugs out, the engine will turn for sure once the pressure gets above 50 psi..

Hmmm, sounds like a much easier process with it sitting on a stand than down in the bilge of the boat. ;) You have to pretty much stand on your head to access the crank pulley on my boat.

Pull your drive. get a old drive shaft and go in from the back!

Hmmm, just like a big-azz rectal thermometer - I like it! I've always wanted to get back at that damned boat for all the money it has screwed me out of! :D

It would be nice to be able to do it as KWright described and hold it in position. That would allow me to pull all the plugs out and just rotate it into position for each hole. Might have to think about fabricating something that could bolt to the bell housing and hold the shaft in place. Might be a handy tool I could patent. ;)

Bud, back the valves of then leak Down the cylinder. Put the plug back in and move on to the next cylinder. Don't complicate it. It's alot easier to back the valves off than put each cylinder on TDC especially if your balancer doesn't have degrees all the way around.

Disconnect coil. Disable fuel. Put a remote starter button on. Remove your first spark plug, put your finger near the spark plug hole bump the starter button until you feel a puff of air come out of spark plug hole. Then you can use a drink straw in the spark plug hole to find true TDC by turning the engine over with a ratchet, when the straw gets to its highest point your at TDC. This Process might take two people one to turn the motor over while the other watches the straw. Use a good 6-point socket on a half inch drive ratchet on the crank bolt, you might have to remove the accessory pulley to allow the socket clearance to get on crank bolt. If everything is fine in the engine, the bolt won't strip out.

Black Baja's way is a pretty good way, probably take less time as long as you can get your valve covers off with the exhaust on.

That way will work, but you will be measuring leak down at bottom dead center instead of top, and any piston rock can effect your reading. TDC is more of a pain in the butt, but it measures how well you're sealing in a more critical area.

Are you saying my way is going to be BDC?

No, Blackbaja's

This is interesting and I never knew how to perform this test, so do you use the breaker bar to hold it at tdc?

When it's truly at TDC it will not try to rotate because it's pushing straight down. Trying to hold it with a bar can be exciting, and or dangerous. :D

Gocha, thanks for that little tidbit!

I have never heard of having to hold a breaker bar on the crank, but like haxby said you shouldn't have to. You could hold a dollar bill at the exhaust pipe to see if you have a Burnt exhaust valve, the dollar bill will be sucked back to the exhaust pipe. Just joking. I've heard a lot of older car guys use that method.

Reading this post i just devised a simple cheap tool that will guarantee tdc any cyl you desire no crank position cumpass, no removing parts, no straws, no second person, no bs.
This will only work with dizzie motors.
Requires cheap self powered conuinity tester.
2 ea plug connectors 1 connected at each end of tester.

Procidure:
Rotate engine to tdc #1 mark on ballancer ( #1 verified by rotor position).
Loosen dist. And retard.
Remove coil & #1 plug wire
install tester on coil tower and #1 tower on cap.
Advance dist until light just comes on.
Lock dist.
Now tdc can be found on any cyl by moving the tester "plug wire" to desired cyl and rotate motor until light just comes on.
You are at tdc for desired cyl.
Dont forget to reset base timing when done. If you are creative you could use this initially to mark current timing on crank and return to that baseline when completed, virtually eliminating the need for dynamic re-timeing of dist.
Call me an idiot but this is the way i will try it next time.
Hope this makes sense and good luck.

Why are you hating on my straw? :party-smiley-048:

What is a dizzie motor? I like your idea I'm just trying to pick up what you are throwing down.

dizzy+distributor.
I was typing as i was designing. I can verbally explain but quick posts are not my speciality.
Think of my test box as the ecu set to fire (light comes on) at 0* advance.. (tdc) #1.
If you get the box set for #1 just move the plug wire (from test box) to next plug (#8 on bbc) to fire rotate crank c-wise (std rotation)
until light just comes on there (that will be 90*) you are at tdc #8 etc, etc, etc.
If you mark your harmonic balancer at the timing mark on the block after 4 times you will not need the tool any more.

Don't know where it has beed or what has been inside.

I see what your saying good idea. All you need is a fluke 88 or similar to read continuity

And the light comes on!!

It kinda did.....

When actually doing the leakdown test.
If you use a cheap, i mean inexpensive, tool you will think you need to throw your motor away.
The cheap tool operates on about 12 psi for reference. They have a very bad regulator in them and your compressor also is most likely useless trying to regulate to 12 psi.
There is a youtube on how to convert the harbor freight cheap tool to work at 50 or 100 psi. (remove 1 gague and install a plug).
Remember at 12 psi a 5 psi drop is almost 45% at 50 psi that would be 10%. @ 100 psi reference = 5%you get the idea.
The regulator and gague are much more accurate at 50 or 100 psi on most of our garage style compressoers.
Also, the increased preassure will actually give you a much better test environment as it is much closer to operating paramaters.
I use 50 psi as that does not seem to try to rotate crankshaft even with all plugs removed.
If you have marked your h-ballancer position before each of the cylinder tests you can visually verify crank did not rotate.
Make sence?

I have a tool that I am improving upon that screws into the spark plug hole and is spring loaded that has a measuring stick that moves when the piston moves. It is very accurate for finding TDC and on the compression stroke of course. I should have this tool completely on the market in about 3 or 4 months. Takes all the guess work out of finding true TDC.

Believe it or not a lot techs in the marine industry do leak down tests on 2 stroke outboards engines as well and you have to lock down the flywheel when filling the cylinder(s) with air. The tool I am bringing to market will be a hit for the outboard tech using it on 2 and 4 stroke engines as well..

Also I sell digital leak down testers for 200 bucks and the analog ones for 100 bucks and they are not cheap quality ones like HF or Northern tools. HF are not accurate by no means. FYI

We use a remote camera in the spark plug hole if we don't have a degreed damper. 1 man job, works very well and is fast.

can you send me a pm with info on these tools.thanks

Mike sent you a pm.

It makes sense that when the crank throw and rod are fully extended in the bore TDC that it wont try to rotate, good read

And I will add as people will ask how can you make it easier to find your leak source. ie: ring seal -cylinder - piston or valves intake or exhaust or even the head gasket.

What I do is tape Kleenex one side of it only over the exhaust tips and another kleenex over the intake = carb or throttle body then add the air in the cylinder - if leaking watch for the Kleenex blowing if not blowing then stick your mechanics stethoscope way down the oil dip stick tube to hear air leaking past the rings / piston / cylinder. Also Kleenex tissue over the oil cap hole in the valve cover works also.

If it is a head gasket and you have closed cooling watch for air bubbles in the coolant - if no closed cooling use a real doctors stethoscope and use it to listen around the head area. You will hear the air leaking past the head gasket by useing the docs scope. I use this as a tool all the damn time. It is great for finding bad bearings in pulleys, lifter noise, crank bearing noise as well, when you can not figure out what and where is that noise coming from.

FYI Volvo Penta pulleys do not last that long and this how I can find out exactly what the noise is. I can not tell you how many times shops and owners think they have an internal engine problem but it is just the darn bearing in the pulley..

Pretty good leakdown thread . If you want to get it done fast and effective hyfive had it down . It will take some practice . I vote remote starter , a quality dual gauge gauge (google what the faa specs for leakdown tests and call it a day ) let it spool at 30 psi stop hold pressure to 100 with breaker bar and good short socket .remember what smoky yunic said , all the important stuff happens at the top 2/3of the piston stroke .a go for the gusto buildwill return 3% or a late obd2. If your not that guy get a reading from the 2nd gauge at 30 move the breaker bar while tecnician b manipulates the air pressure to 100 psi and get a feel of whats happening in the engine .if you have a leakdown tester that reads in percent , toss it and get one that reads psi.

Once you get it , if your going to get it , you got it ..

so just tape a tape measure around the balancer with 0 inches at tdc. see the number where it hits tdc again? 7 inch balancer will be 21 and some inches. 11 inch balancer 34 or so. divide that number by 4 and that is your 4 tdc marks on the balancer.

On 2s mx motors and I assume outboards, you want the piston at bdc to open all ports. plug the exhaust and intake then pressurize to around 6 psi and let it sit for 10 minutes.If it drops more than 0.5 psi start looking for the problem. with 2 strokes air leaks are deadly.and the motor will lean out and stick, so your checking head gasket, base gasket, intake and exh. gaskets, case seal, main bearing seals etc.

I have a feeling i am about to get slamed but here is my thoughts anyway.
As usual with technical threads, this thread has come to the corner of neophyte and pedant, and made a hard left at pedant.
If we go down neophyte instead, this is an easy test to perform and if not done exactly perfect no harm no foul. This is a great way to assess the condition and isolate falts of the upper end of the engine. (lots of good info on this thread).
By the time you get it done the first time you will have devised your own tricks for success. It does not take long.
If you are doing it for the first time do it twice to verify repeatable results. Now document all readings and observations ie. Leakdown numbers, where the air is excaping engine overall performance etc.
Do this every time you change or read your plugs or having performance issues, document and compaire to previous reedings and you can get a good idea of any degration in your top end and plan accordingly.
This test, if done as a scheduled maintenance is kind of an engine top end barometer and indicator of things to come. Coupled with a compression test (heck the plugs are out already) and you know what is happening over time within the cylinders.
Most of us are not race engine builders and are doing this test to verify all is ok. Exact percission is not essential for valid results or trending.
Not trying to offend anybody, there is a need for perfection in the professional world but if you are asking how to and seaking advice you are not at the professional level, just trying to help.
Just my 2 ct. Go ahead and slam away.

To further add some say 10% leak and under U are good - some say 15% and under leak and you are still good, some say 20% and under leak and you are still good. Merc lists in one of their service manuals 30 % and under is still good for leak.

Really if you are good at reading spark plugs and good with a vacuum gauge in which really is a forgotten test these days, you can determine a lot. Also a cylinder drop test using a digital rpm gauge set to a 1000 rpm scale is another good test.