Bad day for team Yamaha

[ChuckB1954]

I purchased a 14 to 12MM adapter so I could do a compression check on my 1999 F50TLRX, which is a 50HP 4 stroke.

Cylinder one 140 PSI.. great I thought!
Cylinder two 80PSI.. not so great.
Cylinder three 80PSI..oh no..
Cylinder four 135 PSI

I added a couple squirts of oil in two and three and they came up to 120PSI.

Is all lost? Should I be looking for another motor?

I might add that this is the engine that was running rich causing the plugs to be black and sooty. (I posted a thread about this)
This was caused by the choke linkage being basically disconnected allowing the butterflies to close.

Maybe things will get better after I resolve the carb issues and run the engine? Or just wishful thinking on my part?


EDIT: I just realized that the throttle was not open when I did the test.. Also engine cold.

[boscoe99]

No reason to get excited
The mechanic he kindly spoke
There are many here among us
Who feel that compression is but a joke


The test you did was not worth a flip. Here is what Yamaha has to say.

[ChuckB1954]

Wow! good news and great info! Thanks!

[99yam40]

If still a problem you might try yamaha combustion chamber cleaner to maybe clean up some of the gunk that built up from the linkages being screwed up

[TownsendsFJR1300]

If still a problem you might try yamaha combustion chamber cleaner to maybe clean up some of the gunk that built up from the linkages being screwed up

Plus 1 ^^^. Below is the commercial grade cleaner.

Per Rodbolt, it's approx. 90% (as I re-call), successful.

http://www.2wheelpros.com/oem-parts/...129436146fff44



* Did you get the new linkages and other parts installed? If so, how's it run?

[ChuckB1954]

Plus 1 ^^^. Below is the commercial grade cleaner.

Per Rodbolt, it's approx. 90% (as I re-call), successful.

http://www.2wheelpros.com/oem-parts/...129436146fff44



* Did you get the new linkages and other parts installed? If so, how's it run?

Thanks for the info.

Got the parts in yesterday, but I am yet to put them on. Hopefully tonight. I will post an update in the "running rich" thread.

I was busy yesterday selling the crappy boat I was piecing together before I bought my beautiful Key West.

(btw: thanks for not ragging on me for not checking the correct compression procedures in my nice, new service manual!)

[rodbolt17]

compression test on a four stroke = a teat on a boar hog.
a leak down test is much more accurte,faster and will tell you WHY the cylinder wont seal.

[TownsendsFJR1300]

compression test on a four stroke = a teat on a boar hog.
a leak down test is much more accurte,faster and will tell you WHY the cylinder wont seal.

Not quite...

Second single cylinder B&S larger mower engine this month that came in for repair. (12.5HP) Both suddenly stopped running..

OHV's, cam in the block with push rods..

Checked spark good, compression (on both) about 40PSI.

Pull off the valve cover, both instances, the aluminum push rod for the intake valve BROKE..


A leak down test would NOT have found that pushrod as the valve was still sitting on it's seat, NOT moving.. Sealing is great, but No air/fuel moving into the engine...

[Masonmobilemarine]

Not quite...

Second single cylinder B&S larger mower engine this month that came in for repair. (12.5HP) Both suddenly stopped running..

OHV's, cam in the block with push rods..

Checked spark good, compression (on both) about 40PSI.

Pull off the valve cover, both instances, the aluminum push rod for the intake valve BROKE..


A leak down test would NOT have found that pushrod as the valve was still sitting on it's seat, NOT moving.. Sealing is great, but No air/fuel moving into the engine...

Agreed. Compression is important. It's the first step in seeing the health of engine. If compression is bad, then a leakdown is needed.

[boscoe99]

Get a big score in a cylinder wall and one can have perfect leak down results yet the compression pressure can be poor.

Either test in and of itself is not the definitive end all/know all. They are but tools to help with the assessment of either an observed problem or to try and forecast the continued apparent good health of a motor.

A motor that appears to be deficient in a static condition (leak down test) or in a less than a real world dynamic condition (compression pressure at but a few hundred RPM's) might be just fine when being used in a full dynamic condition, as will be the case when the motor is hot, lubricants are being circulated and the motor is running at normal operational RPM's. Rings and valves might just seal better at 4000 RPM than they do at 0 RPM or at 400 RPM.

Let's say one owns a motor that runs just fine. It starts, idles and runs well. Makes rated power. Uses nil oil. Produces nil blowby. Operating temperatures are completely normal. But it has low compression pressure or a high leak down value. Would anyone in his right mind do major surgery on the motor to try and correct a perceived problem?

[TownsendsFJR1300]

In regards to my engine listed above(12.5 Briggs), got it running with a bunch of popping thru the intake / carb (valves adjusted correctly.)

9% leak down, all thru the intake. The borescope showed a bunch of carbon buildup at least atop the piston.

Worth noting, once started, WOT was maybe 2500 RPM's.. This engine SHOULD max out at 3,600 RPM's. I strongly suspect all the carbon build up is from the engine NOT running at full RPM's...(engine is at least 20 years old)

Initially, I couldn't get it to rev past 2,800 RPM's. Re-adjusting the governor, a strong dose of Ring Free ran thru it yesterday and checked this am has the "popping" reduced dramatically (almost nill) and RPM's now easily reaching 3,600...

[ChuckB1954]

Changed the oil in the F50.. it was filthy, but what was worse was the gear oil.. 1/2 cup of yellow froth and another half cup of clear water.. I flushed it out at least three times with mineral spirits, followed by a couple cycles of 30 weight motor oil. Added some quality gear oil after that. I wish I had checked it before taking it out a week ago. I am taking it out tomorrow to see how the engine runs. I will drain it again when I get home. Lesson learned..

[zenoahphobic]

Changed the oil in the F50.. it was filthy, but what was worse was the gear oil.. 1/2 cup of yellow froth and another half cup of clear water.. I flushed it out at least three times with mineral spirits, followed by a couple cycles of 30 weight motor oil. Added some quality gear oil after that. I wish I had checked it before taking it out a week ago. I am taking it out tomorrow to see how the engine runs. I will drain it again when I get home. Lesson learned..

The lesson about the water in the gearbox oil should be to repair the leak; usually being in the seals, either prop shaft , gear shift shaft, or prop shaft. I presume you are only going out to test the engine, but realise the gearbox oil will need changing again and then eventually fix that problem.

[zenoahphobic]

Get a big score in a cylinder wall and one can have perfect leak down results yet the compression pressure can be poor.

Either test in and of itself is not the definitive end all/know all. They are but tools to help with the assessment of either an observed problem or to try and forecast the continued apparent good health of a motor.

A motor that appears to be deficient in a static condition (leak down test) or in a less than a real world dynamic condition (compression pressure at but a few hundred RPM's) might be just fine when being used in a full dynamic condition, as will be the case when the motor is hot, lubricants are being circulated and the motor is running at normal operational RPM's. Rings and valves might just seal better at 4000 RPM than they do at 0 RPM or at 400 RPM.

Let's say one owns a motor that runs just fine. It starts, idles and runs well. Makes rated power. Uses nil oil. Produces nil blowby. Operating temperatures are completely normal. But it has low compression pressure or a high leak down value. Would anyone in his right mind do major surgery on the motor to try and correct a perceived problem?

True, the real "test" should be the actual performance in service. If it runs alright no major work obviously needs to be done.
However you qualified your example providing it meeting a number of other tests (rated power, nil blow by, temperature.....) in placing lesser or no value on "pressure" testing.
Ofcourse, the usefulness of any number of possible tests is to highlight future problems or to indicate the direction a working motor may be going in, that can be "fixed" before the problem arises. And repeating those tests will be the most useful information because they will importantly indicate the rate of deviation, the actual deterioration.

[ChuckB1954]

The lesson about the water in the gearbox oil should be to repair the leak; usually being in the seals, either prop shaft , gear shift shaft, or prop shaft. I presume you are only going out to test the engine, but realise the gearbox oil will need changing again and then eventually fix that problem.

Thanks, what ever needed will be done.