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Micadog, order of cylinder test will make a difference if the starter motor or the battery are a little weak, as you crank the engine the revs decrease as you move from cylinder to cylinder - it can affect the result but as I said, the spead is not too bad
cheers
Craig
hi thats quiet a difference there myself working around alot of outboard engines.id have to say shes on her way out normally 5psi difference in a outboard engine is ok. but when you start getting those results.your best of walking away from it as in the long it will loose power run like rubbish and then go bang.
cheers shane.
Hi fellas, this compression test was done on my motor. A bit of history on motor bought in Brissy 4 yrs ago c/t 127,126,126, 250hrs on motor. I then put 50 odd hrs pushing vc 4.7. Restoration done on boat motor sat in shed for 9mths, put back on boat and have done 10hrs. Mechs think rings gummed up advice was to fill 80ltr tank with preium fuel spray carby cleaner in pots,give motor a good run on 5000 for a few hrs, do c/test if not good lift head clean or replace rings. Polky. Apprently 310 hrs is stuff all on motor, and doubtfull rings worn that quick.
polky, does your motor acheive full max RPM with a normal load?? if not, it could very well be carboned up and need a decarb, and then check RPMs and swap prop to get full WOT.
From the internet
David Compression is the heart of an outboard. If one or more cylinders are damaged due to improper timing settings, lean fuel condition, overheating, or stuck rings from carbon buildup, your outboard is about to become history.
Does a compression test alone always determine that my outboard is in good shape? Suprisingly the answer is "no".
A good compression reading does not completely determine internal conditions. To correctly diagnose condition of pistons, rings, and cylinders, a leakdown test should also be performed.
Using a quality leakdown tester, each cylinder should not show more than 10% loss. If any do, there is certain to be an internal problem in the making. For example, a compression reading of 120 lbs would be viewed upon as a good cylinder by the average person.
This may or may not be the case. If a leakdown test of the same cylinder indicates say...20% to 25% or more leakage, it would be a good bet that excessive wear, scored cylinder, the cylinder scratched, and/or the rings stuck or damaged in a way that does not show up with a simple compression check.
In any case, wear or damage is present and advisedly requires attention before further damage and/or exceptionally poor performance and efficiency results.
Most common effects from diagnosis of excessive leakdown would be in the idle range of the motor. If all other motor functions check out attempting to diagnose an idle problem, then its a good chance that blowby is the culprit. It is advised that leakdown tests should be performed at the beginning of the compression stroke (rings just above exhaust port opening, which is the critical point), and NOT at TDC. Make sure you have flywheel locked down securely when doing a leakdown test. If you try to hold the motor from turning with a socket and breaker bar, you are putting yourself in a dangerous position should the breaker bar slip from your hand. Purchase a compression gauge and leakdown tester to go in your boat's toolbox and check cylinders a couple of times a year to ensure there is nothing unusual going on internally. Using proper grade of gasoline and outboard oil is essential to preventing internal problems. Proper winterization procedures will also do wonders to prolong the life of the internals of your outboard. If compression check shows more than 15 lbs difference on any given cylinder from highest reading of other cylinder/s, or if leakdown test shows excessive loss, you have a problem in the making! DO NOT continue running the motor until problem is diagnosed and repaired! It could result in causing much more internal damage than you already have.
Thanks fellas, FNQ 1994 yama 70hp 2st, Nolem will check full revs on weekend, plan to fill with preium fuel and take her on a good long run. Nolem when you say decarbing, is this somthing I can do or should the Marine tech do this. Since the c/test I have had 2 buyers keen to buy boat,both say c/test is ok. But if it not to hard of a task I would like to decarb motor for my own learnings and peace of mind. Again fellas thanks for your imput, Micadogs thanks bud. Polky.
a decarb is done with a "miracle" can of various chemicals, most say that use the one made by the Engine manufacturer, may cost $5 more, but at least it is the "proper" one, as a general guide, an engine run with the correct prop (that can acheive full RPM) has used quality oil and good fuel, will not need a decarb, but I guess it is one of those "it can't hurt" things so why not? I have seen some absolute miracles from old engines that have used cheap oil, dodgey fuel and bad maintenance, and after a decarb, (and smoking out the entire neigbourhood) the motor went like a dream, but as a general rule I am not a big decarb fan, I guess because I always use synthetic oil, premium fuel and so on, it never seems to make any difference to my Motors, My son in law did my Subaru yesterday, he thought there would be smoke and the car would go like a dream (it did before) but there was no smoke, no mess or any difference!
there is lots of those 'do it yourself" things around, one guy reckons that if you get the Motor very hot, then introduce plain old water while it is running (via the manifold) it will do the same thing, who knows huh! not too sure I would be trying anything but manufacturers recomended though, unless the Motor was stuffed anyway! for the sake of $30 why take the risk, kind of like saving $2 a litre on oil by going to a Supermarket or something (don't want to start an Oil war here!!!!) better off to use the proper stuff from new and be done with it.
Yep I'm guilty of the above, well I was playing with water injection on a new Sigma (country boy with nothing better to do) Anyway the car did have more squirt and used around a litre in 2 miles cause I had it hooked straight up to a spare vaccum line in the manifold.
Looked like a steam engine flying down the road but when I looked behind the car the boot was covered in soot.
So yep It works Oh yeah the old Boeing 707 use to be water injected on take off 10% more power and all the smoke you see was due to the water De- carbing.
But they stopped carrying water for that cause it needed to carry more fuel to lift the water, Still scratching me head over that one how come some one took so long to work out it was false economy.
hehe, must have been a sight, a steam Sigma! maybe Steam power may make a comeback, we could just stoke up the fire half hour or so before we need to go fishing, carry a Coal/wood pile for fuel, plenty of water around when Boating, might be a tad smokey and hot, and polute the air, but at least it will be cheap!, the wood pile could be just a bit inconvenient, as well as the extra Spiders and Cockroaches and stuff in the Wood, but you never know!
Yeah water works wonders and has for near a century, a de-carbon is the go (if there is anything wrong with it) if only for the experience of doing it.
If this is for sale it's good to go! If you have the report and pass it on to the new owner you are totally in the clear, for all we know the mechanics guage could be out, the mechanic down the road might get the same spread around 129psi with his.
Just for interest, it has been known for dealers etc to own more than one guage, the known low reading one and a high reading one can you guess when either may be chosen for use!!!!
that is very true FNQ i was once at a Dealer to check out a Motor for a friend of mine (a V6) and the shonky Dealer ( I am not inferring that all dealers do this by the way) had two gauges to do the test while I watched, there was two guys, one did one bank, while the other did the remaining bank at the same time, not too sure why I "twigged" that something might be a tad dodgey, I asked if I could just test the second bank again, and the guy reached for the gauge, but I asked if we could use the same one on both sides, the "mechanic" went all sort of flustered and said he would prefer to use his own method, but I sort of insisted, and guess what, one bank was way below the other, and I mean really way below spec, just left with the usual "I'll let you know" and never have been back there ever since.
That's a telling story! the whole area come under the weights and measures regulations I would suspect, the only guage a person can trust is their own or a known re-calibrated one.
For $30 Polky can do his own test, takes less than 15 min and on a 3 cyl is about as hard as making 3 cups of coffee.
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