cranking compression test 2006 F250??

[stoker2001]

Finally got to change belts on the twins and decided to do comp test (cold) befor i did belts.Port motor Cyl#1 was down to 160 with others maxing out at 180-185.motors have not been started for 10 weeks prior to the crank test and we have 1500hrs on them now.Thoughts?concerns?

[boscoe99]

No problemo.

In the future the motor should be hot, battery fully charged, throttle wide open, crank until the pressure stops rising.

Be prepared for some to say that a compression test is a waste of time. Or teats on a boar hog. Yamaha disagrees with these nattering nabobs of negativity. I agree with Yamaha.

[stoker2001]

No problemo.

In the future the motor should be hot, battery fully charged, throttle wide open, crank until the pressure stops rising.

Be prepared for some to say that a compression test is a waste of time. Or teats on a boar hog. Yamaha disagrees with these nattering nabobs of negativity. I agree with Yamaha.

thanks,the 25lbs diff from high to low raised my eyebrow a little.I have been building race 2.5 Merc 2smokes for decades,this is my first goround with 4s.these F250s are growing on me with the quad cams and VVT,they push this Parker 28XL with full pilot house amazingly well!cant wait to get back out on Salty pond to rip some lips

[stoker2001]

anyone here do the chemical clean with combustion chamber cleaner to help remedy low comp test readings?i will try the yamaha brand fuel additive also (ring free?)

[walleye1]

I have used mercury power tune, follow the directions on the can.

[99yam40]

ringfree would be good for maintaining after you clean it

[DennisG01]

Before you do a combustion chamber clean procedure (which certainly can't hurt), I would do like Boscoe mentioned and get the engine good and warm - even put the boat in the water a time or two - then do the compression check again. You may not need to do anything else. A snake camera is a cool tool to have and you can look into the chamber. It may not 100% tell you if anything is wrong or not, but it could. And, again, it's a cool tool to have around.

Merc Power Tune is good stuff - RingFree is also good for a chamber clean. As mentioned, just follow the directions.

[stoker2001]

thanks for all the input,great group here

[99yam40]

why has no one mentioned doing a leak down test to see what is leaking.
valves or rings

[boscoe99]

why has no one mentioned doing a leak down test to see what is leaking.
valves or rings

I (and Yamaha) for one don't recommend a leak down test unless a compression test indicates something is amiss. With a compression test being called for only if something seems to be operationally amiss with the motor.

OP has not reported anything untoward with respect to the operation of the motor.

In the OP's case, I don't see anything amiss.

I am surprised that rodnut has not come along and poo poo'd the compression test. As a teat on a boar hog.

How many do a compression (or leak down) test on their non-amiss automobile motors?

[DennisG01]

why has no one mentioned doing a leak down test to see what is leaking.
valves or rings

I think until he does the compression test again after the engine has been run for a bit, it's not necessary. If after a few hours of runtime (and a cleaning) the psi hasn't changed, then maybe. But even at that point, 160 isn't that far off from the rest that I'd worry about it, yet. Probably just monitor it. But it's still high enough that, in my opinion, it doesn't warrant taking any extra steps. Besides, the leak down is typically done with the anticipation of fixing the issue - and that engine isn't at that point, yet. Sort of a waste of time - again, my opinion. But a compression test can be seen (especially if done at regular intervals) as routine mainteance, giving a general (cursory) health of the engine and can warn of things to watch out for. As in this case, IF it is still a little lower than the rest, then just keep an eye on it.

[TownsendsFJR1300]

Re Ring Free, I use it in every gas machine I own, regularly..

I also use it in customers small yard machines (repaired by myself, Echo's, Stihls, cheaper residential machines).

Reg mix is 1oz / 10 gallon, Shock mix is 2 oz / ONE gallon.

I've done the shock mix many times on different machines, no downside to it or issues.

**After doing a carb clean (or other repair on a small machine-with RF in everything) , I'll re-check and re-tune the carb (if possible).
About 50% of the time, sitting over night, (of course after being run the day before), I can re-check with a portable tach and re-tune getting
MORE RPM's out of the engine. That's with doing NOTHING ELSE.

IME, highly recommended..



*I recently had to adjust the TWO exhaust valves (#4 cylinder-shim and bucket) on my Yamaha 600cc motorcycle (below pic) @ 26,600 miles.
They were too tight by .001". Had it been carboned up, the valves would have been looser. I don't run the bike as hard as it's designed to run and run Ethanol fuel. I strongly suspect the RF helped keep the clearances close to spec's. (The rest of the valves were dead nuts on across the board-4 valves per cylinder)







Synced cylinders after valve adjustment(spec's allow 10mms variance, within about 2mm's):

[rodbolt17]

compression test= teat on a boar hog.
leakdown test is so much faster and way more accurate.
at 100 bucks an hour did I mention FASTER?
2004 F115.
#1 135 psi.
#2 135 PSI.
#3 130 PSI.
#4 135 PSI.
good or bad readings
motor idles poor and is down on power.
real motor real numbers.

[boscoe99]

#3 is below minimum compression specifications. Others are right on the cut line.

Now if the motor was running just fine I would leave well enough alone. However, as you say it idles poorly and is down on power. In which case a leak down (differential pressure) test would be called for following the compression test. Which hopefully will give some indication as to whether the problem is related to the combustion chamber.

You may very well be able to perform a leak down check faster than a compression check. For me it is just the opposite.

For the average boater a compression gauge is less expensive than a leak down tester. The latter also requires the use of an air tank.

A compression check can be readily done with the boat in the water. A leak down check, not so much.

[pstephens46]

I assumed the owner was using an AGM battery.