Cylinder leak down test

[johnmr12]

I have a 2001 Optimax 225 3L DFI SN OT305247

I want to do a cylinder leak down test on all 6 cylinders and I am doing it alone. Any tips on how to get the piston to top dead center? can I put something in the cyulinder and turn the prop in gear until the object reaches the top and starts back down?

[ChrisCarsonMarine]

My opinions on leakdown testing procedure are a little different than most,and render the most accurate results,again my opinion.Most folks follow the directions and put the piston at top dead...where there's no wear,and usually get low leakdown results accordingly.A poor mans leakdown test is really better,and is faster,cheaper,and easier...do a comp check,just write down the compression numbers,squirt a couple shots of 30 wt oil in each cylinder,spin the motor over a few seconds and recheck the compression...the amount the compression goes up will be close to overall leakdown percents.
Now my way.Follow the normal procedure but instead of locking the flywheel near tdc,pull the motor from ports open to tdc on every cylinder,stopping at several spots along the way,and look at the resulting leakdown along the working stroke of the cylinder.
We do this with a ratchet on the flywheel nut,with a long bolted in place tube extention on the ratchet handle...(3 foot long,specificly for this task).
DO NOT USE A BREAKER BAR for this job...when you pull the piston over tdc the 40-50 pounds of pull required will turn to push and may DE-BRAIN you...the ratchet will allow the flywheel to spin to to open the ports.
This procedure will locate bulged cylinders,scoring above the ports etc.,that a locked flywheel test won't know about.
Also,for the most accurate results check the port side of a "v" motor by pulling the flywheel clockwise,and the starboard counterclockwise to place the piston in its thrust position.I test
at 75 lbs.
I figure if you're going to test you might as well get the best results you can,I should'nt have to tell you to keep fingers clear,and be careful,as the flywheel is going to spin as it goes over tdc,but i will anyway,BE CAREFUL,Chris

[EuropeanAM]

As a general rule, you're going to want to bring the piston near to TDC and hold the crankshaft with a large ratchet and socket, or a flywheel holder.

Be very careful when doing a leakdown test- it is very easy to make an error and end up getting hurt pretty badly. Personally, I would recommend following the instructions from your Leakdown Tester TOOL, or Factory Service Literature, unless you are very versed in performing such tests.

DO NOT, UNDER ANY CIRCUMSTANCES attempt to hold the propeller, or use the propeller to turn the engine over.

[johnmr12]

So you turn the flywheel manually to reach TDC? How would I get hurt?

[basspro57]

So you turn the flywheel manually to reach TDC? How would I get hurt?

You use a leak down tester to apply air pressure to the cylinder at TDC. If you don't hold the flywheel then the motor spins. In order to keep the motor from spinning when pressure is applied to the cylinder being tested, you have to hold the flywheel (that is where they are telling you to use a ratchet with a pipe on it for leverage). Be careful as it can whip around and clobber you if you are not holding the ratchet when applying pressure to the cylinder. It is best to do this with two people. Understand???

[johnmr12]

I do understand and Im getting less enthusiastic about doing the test because I have nobody to help.

[EuropeanAM]

I will say I know of a couple co-workers over the years that had dental claims related to attempting to perform leak-down tests.

[blackboat]

On a related note,what percentage of leak down is acceptable and at what piston location in the cylinder? Why is it that compression can be in the normal range on all 6 but leak down is all over the place on some cylinders? The leak down test has it's place as a diagnostic tool but is it relevant on a 2 stroke when it runs good and compression is normal? Chris....the ratchet thing you mentioned is a great idea!

[EuropeanAM]

Many OEM's use the "10%" figure.

Personally, I'm wanting to know "why" and "where" if the leakdown is exceeding 4%... and at 6% teardown and rebuild are in order (JMHO).

[lpugh]

^^^^^^

[johnmr12]

If I were to put the engine in gear and block the prop to the lower unit housing to prevent it from turning, why can't I do the leak down test alone?

[EuropeanAM]

Because it is likely that either something will break, you will get hurt (or both).

[johnmr12]

I realize you have to warn me about injury for liability reasons but there is zero chance that I would get hurt. I also realize you are a professional and you don't like giving advice to someone trying to do something outside the box, but can you tell me what is likely to break so I can then make an informed decision on whether or not to risk it. I wont even come back here and report on the outcome. With compression reading between 70-85 I expect there to be significant leak down loss but I need to confirm it and I literally have nobody to help, and I have had far too many bad experiences with local mechanics to ever lety them near my boat again.

[JOE54]

water pump impeller /gearcase internal damage john,if breaker bar or ratshit slips from your hand air psi is gonna spin crank (duck ) just be careful good luck JOE

[Macsimus]

Interesting autocorrect ^^^

[EuropeanAM]

Far to high a probability of damage to pinion, driveshaft, clutch-dog, or even prop/hub.

Using a flywheel holder, it is definitely possibly for one person to perform a leakdown test. Have done it many times, but I'll admit there were one or two in the early days that knocked some "cents" into me.

[johnmr12]

Do you have a part number for a specific flywheel holder that would work on my engine or will pretty much any one work?

[EuropeanAM]

You can get a good-quality arm/tooth type flywheel holder that's designed for use with many Automotive Flywheels (example: GM 14" Smallblock V8 flywheels).

It works just fine on the Opti flywheel as long as you are reasonably careful.

[DewRonInc]

Mac tool truck has a nice one