2011 F300 compression standards

[boscoe99]

and you wasted about 1/2 hour of your labor money on a STUPID compression test.
waste of time on a 4 stroke.



Boscoe.
F80TLRY.
cyl 1 140 PSI.
cyl 2 135 PSI.
cyl 3 138 PSI.
cyl 4 135 PSI.

motor GOOD? motor BAD????

motor went to 3 other techs before me.

If the motor starts well, idles well, runs well and does not use an excessive amount of oil then I would say that mechanically there is no problem with the rings, cylinders and/or valves.

Yamaha would say that the motor exceeds their performance requirements for compression. If you can find in the service manual where a leakdown test go/no go value is provided I would like to hear about it.

What did you find out?

Now all along I have been talking about compression results on a motor that is otherwise in good condition. If there is a problem which cannot be found then certainly a differential pressure check would be a good idea after a direct compression check has been performed.

[Rustygaff]

We will see soon enough. I plan to sea trial the boat next week to see how it runs under a load. The motor is date stamped 03/10 so I assume it is one of the early 4.2's with the potential thrust bearing issues. Thanks for the advise.

[rodbolt17]

motor bad.

cyl head had corroded under the gasket and was leaking a bit o wawa.

leak down on #3 was 85%.

previous techs should have spotted the tell tale water marks on the plug.

compression test I would have bought.
leak down test failed.

industry standard is on a 4 stroke articulated rod engine is compression must be within 20% highest to lowest or leakage within 15% highest to lowest.
goes for chebbys,fords,kias, yamahas or whatever else uses an articulated rod piston engine.

works even on them there areo plane thingys.

its really really this simple.
seal the cyl and the rest is fuel or ign issues.

if you CANNOT seal the cyl NO amount of tuning.plugs wires , wailing or ghasshing of teeth will ever make it run correctly.
this standard has been about since I started this stuff in the 1960"s.

[Rustygaff]

Huh?? Did I miss something?

[bajakeith]

I did

Sir RODBOLT...can you fill us in ???? PS.. Ok Iwent back to the first page and reread the whole thread..I think they are talking about two different motors..but cly #3 is showing something....I'm feeling like a mushroom about now kept in the dark and feed ___ !! LOL

[Rustygaff]

I believe that if the leakdown is below 15%, it should be OK.

[rodbolt17]

most any leakdown test below 15% is industry acceptable.
there may be a manufacture with tighter standards.

I was pointing out the inaccuracy of a compression test vs a leakdown test.

the F80 I was referring to was an actual case. the reason I knew the compression numbers is the last tech wrote them on the cam cover .

if one went just by the numbers it passed,in fact 3 other techs passed it.

the water leak was small enough it would run WOT, complaint was it idle funny after a period of idling.

cust had already spent over 1000 dollars before I pulled the head,sent it to Flagship and had it welded and reinstalled it.

its why I don't do compression tests on 4 stroke outboards.

that and I am lazy, a leakdown test is faster and less trips up and down the ladder.

[bajakeith]

Rodbolt

Thanks for the clearing the mystery..I thought like I said in my last post we were talking about two (2) different motors... LOL.I know what ya mean about the latter........I have said for years..."if I had a nickel for every time I walked a dock for that one last tool,,I'd be rich"...............any how,, was the #3 plug "washed/clean ??" on the 80 hp

[boscoe99]

A differential pressure test is a wonderful tool. But, it is only one of many and is not without its flaws.

It won't indicate a scored cylinder wall, if and when the score is below the point at which the rings reside when the piston is at top dead center, which might be detected with a direct compression test.

It won't indicate a worn out camshaft lobe which might be detected with a direct compression test.

Dare I bring up the use of a bore scope?

[bajakeith]

question

Note to self: don't forget to ask rodbolt what he uses to hold the flywheel still on a V 6 and how in the hell is it faster than a compressin test ???? I can do compression test in 2/3 mins !!! I have a flywheel holding tool but doing a leakdown test does have some issue's...like a flywheel decides to spin and the need for air on a mobile job !!

[rodbolt17]

I don't do much mobile work anymore.
if its that bad it comes to me or a local backyardigan/mobile tech gets the job.
flat spot on the cam I spot with either the vacuum guage or the laptop .

scuffed cyl??? I simply turn down the set point of the incoming air pressure and move the piston.

once TDC is found there is no reason to hold the flywheel.
once TDC is found on one piston I simply follow the fireing order and quickly hit the rest of the cylinders.
on most Yamaha 4cyl 4 strokes its 1 3 4 2.
on most Yamaha V6 4 stroke its 123456.
like I said, I am lazy and its faster and more accurate.
doesn't hurt that I do have extensive training since about 1975 and done this monkey work for a living since about 1975.

the fuel and ign controls have changed a bit but the cyl block assy hasn't .
it still goes like this.
suck
squeeze
bang
blow.

[boscoe99]

Rodnut,

What type of device are you using for the test? Yamaha brand or other?

Do you try and maintain a particular pressure value on the input gauge while the test is being done or do you let the pressure vary as it will?

Do you know if there is a calibrated orifice between the first gauge and the second gauge?

[boscoe99]

To those that are wondering what in the hell we are talking about, here are some words and a picture that might help in understanding this subject. When you read the word "propeller" (this comes from aviation) just substitute the work "crankshaft" for an outboard motor.

[bajakeith]

To Sir rodbolt

Thanx for a reply..I have had a few times over the 35+yrs that I did not have exactly TDC and the motor liked to rotate.. also lost my TDC plug hole tool awhile back....was looking more along the lines if you had some sorta locking tool ?? most my work isn't much on the guts anymore but everything else that's attached to the block...LOL I also do way to much I/O'S...but what do they expect with a (usally) SMB based in a system with a million parts and then dunk it in saltwater......Friends don't let friends buy I/O's for salt !!

[rodbolt17]

I/Os suck but I make a lot of money on them.

what this differential pressure tester is based on is simple.

in theory at TDC compression stroke that cyl is sealed.

however with ring end gaps it may leak a bit.

so the tester uses a set input pressure, on the K&L tool I use its about 100 PSI.

the second gauge measures how much make up air is needed to maintain that 100 PSI set pressure in that sealed cylinder.

on I/Os with distributers I simply remove the cap and follow the fireing order.
on some,like the 8.1L GM its a pain cause there are NO timing marks nor distributers.

the F350 has no timing marks so I manually find TDC on #1.
then I count the flywheel teeth,do a bit of math, mark the flywheel with a sharpie and get after it.

yep math does bite but its required occasionally.