New Yamaha F150XB compression test

[Seanic08]

Hello All, new to forum as well as owner of a new 2017 Yamaha F150XB. I was wondering if it's a good idea to do perform a compression check right now while engine is still new (under 10 hours) to get an idea of what the compression numbers are for future reference? Coming from an older 2 stroke that I bought used, i never knew what it's real compression numbers were. I would get around 120 PSI on all cylinders, but from reading online no one knows for sure what a good number is.

Figure if I have those numbers now while the motor is in good working order, I can use those numbers for reference down the road.

Thank you,
Seanic08

[fairdeal]

IMO it can't hurt to see what you get.

But there are some authorities who lack enthusiasm for compression tests on principle,
deriding it with crude animal references.

Don't know if a 2017 is different, a few years ago the F150 SM listed 128 psi as "minimum"

[99yam40]

would not hurt to take it now and write it down in you manual along with all of the mode and serial #s for reference later on,

I would take it again after it is well broken in or every few years to see if things change over time.

then if you have the proper test equipment take other readings in case you later what to see what has changed if you have problems

[boscoe99]

That is exactly what is done in aviation. Compression tests are performed annually so that one parameter of an engines condition can be monitored over time. It is called trend monitoring.

Compression might actually get better as the rings seat in a new engine as stuff wears together. Then over time, a long time, wear may cause the compression to diminish.

Keep in mind that how the test is performed is importantly to getting accurate results. Ideally the pressure gauge should have been calibrated within the past year to ensure accuracy, but few will do that.

[Seanic08]

Thanks for the response guys. I will do that when I get a chance.

Nothing different from the 2 stroke right?

1. Remove all spark plugs.
2. Ground all plug boots
3. Put throttle to WOT.
4. Lightly lubricate the thread of the gauge.
5. Crank motor for a few seconds or when gauge needle stops moving.

Thanks,
Seanic08

[99yam40]

You should just pull the kill switch to stop spark , not need to ground all plug wires

[TownsendsFJR1300]

I'd wait and break it in fully first.

Then do your tests...

Plus 1 on 99's post, yank the black safety clip.

And plus 1 on 128 PSI per the Yamaha Shop manual.

[boscoe99]

If that motor does not have 175 plus psi I would be very disappointed.

[99yam40]

If that motor does not have 175 plus psi I would be very disappointed.

my thoughts also, 4 strokes have higher compression #s than 2 strokes

[panasonic]

If that motor does not have 175 plus psi I would be very disappointed.

175 PSI?? What compression ratio does that engine have?

[panasonic]

Greater than 12:1?

[boscoe99]

9:1 compression ratio.

[dray0151]

2016 compression in SM is min 127.6 for F150

[panasonic]

9x14.5=130.5

Not going to get much more than that just cranking it over doing a compression test
..

[rodbolt17]

compression test = teat on a boar hog.
a leakdown is way faster and way more indicative of a problem.
read very carefully the Yamaha test numbers, you will find there are no definitive numbers. there are definite limits on leakage numbers.


it is kinda like the maint schedule. appears NO BODY understands the word OR.