How to compression test an outboard

[@bradleyfarquhar2023]

Very good mate good explaining. I've done a compression test on my old outboard motor before come out pretty healthy for its age but I have my new outboard now its going so well had 2 hours on it before when I got it now its got a lot more hours I'm loving it cheers mate.

[@25hpboatracerman]

Hi Champion, Yeah, great skill to have 👍 Stoked your loving and getting good use of your new motor 👌 All the best, Aussie Boat Guy 😎

[@douger1517]

Hey, that’s a really good explanation and advice, I assume that this would be good for both two and four stroke. A very handy tool.

[@25hpboatracerman]

Hi Mate, Yep, exactly the same for 4 stroke All the best champion. Aussie Boat Guy 😎

[@michaelsimpson9779]

Good info.

[@Itsrajkumar2000]

Thank you for the video from srilanka ❤

[@25hpboatracerman]

My pleasure 😊 All the best, Aussie Boat Guy 😎

[@Brandon-km8fq]

How do you make sure there isnt any fuel being fed into the cylinders?

[@25hpboatracerman]

Fuel will be being fed into the cylinders but it doesn’t matter as the spark plugs are removed and the leads are to the side. Cheers 🍻 Aussie Boat Guy 😎

[@Diesr]

Hey how are you I’ve gotten another question for you concerning the mercury/tohatsu 5hp I’ve recently beheaded mine and looked at the top of the piston it was absolutely spotless and it looked great no blacking or anything carbon and no scoring on the walls, surprising be cause I’ve sank it twice and I thought hey could bump up the compression by shaving the head with sandpaper and give it new rings and a bone any idea how much i should shave and what hone and what size? And the ring gap Thanks a lot 👍

[@Diesr]

Oh yeah and I got this nasty squealing sound when I turn it over is this of concern?

[@25hpboatracerman]

Hi Mate, You really cannot shave much off the head without re-turning the squish band and combustion pot. when I shaved my head I returned the entire squish and pot. Honing is just to put some scuffs in the bore at a crosshatch pattern to help lubricant things. Sorry mate, I cannot remember the ring Gap, it might be in my outboard re-build video if that video is the same motor as yours. Keep in mind every outboard has a different and very specific ring gap. Cheers 🍻 Aussie Boat Guy 😎

[@25hpboatracerman]

Hi Mate, Yes, very concerning. You mentioned that it has sunk a few times, normally the bearings around the crank get rusty and damaged if the motor has not been properly flushed and given a good hard run for at least 45 mins after clean out. I would pull the crank case apart and view the bearings cheers 🍻 Aussie Boat Guy 😎

[@Diesr]

@@25hpboatracermanwell the bearings make no sound whatsoever it’s the piston rings I think cause if I get to a part where there’s no movement of the piston like bdc tdc and move the crank it’s just fine but anywhere inbetween it sounds, well I don’t no how to describe it it’s a squeal squeak ish but it’s not metal rubbing or anything it sounds more like the rings are skipping or something I really have no clue, well I’ll replace em and the bearings but the hone was for reviving the crosshatch do you know what type of hone would work best? (Stone or ball) cause my big hones don’t fit also got any tips for model year differences (if there are any) so I won’t order the wrong parts. Thanks mate😅

[@25hpboatracerman]

Hi mate, Definitely not a ball hone, just the normal one with the three long cutting stones and you don’t need to go crazy, I put up a video on the channel how to do it. Just occurred to me that it may be the reed valves vibrating and causing the squealing sound which is common at low turn over speeds with all of the small motors I have tinkered with. Cheers 🍻 Aussie Boat Guy 😎

[@bunndyboy]

G,day mate. My merc 15 super has been sitting for a few years and my compression drops on the gauge as soon as I stop pulling the cord. The head gasket looks like white stuff around it. I'm thinking the head gasket but wanted your input please mate. Keep the vids coming.

[@25hpboatracerman]

Hi Mate, Sounds like a problem with the compression gauge to me, they are supposed to hold the highest reading they take until you press the button on the side to let out the pressure. Also a motor won’t hold compression for too long and pretty normal to have the white salt band around the head gasket. Does the motor run ok? Cheers 🍻 Aussie Boat Guy 😎

[@bunndyboy]

@@25hpboatracerman yeah it runs ok just concerned about the dropping pressure. I'll try it on another motor. Cheers mate.

[@bunndyboy]

Hey mate, I think the gauge is stuffed, a good 5 hp ran 25 psi no drop but the 15 is around 70 still dropping. Its done stuff all work no rust and very clean under the hood. Want pull it apart for me 😂

[@25hpboatracerman]

Hi Champion, The dropping in pressure is 100% the gauge, don’t be worried about the drop in pressure. The gauges have a little button on the side to release the pressure and that’s probably stuffed and may be able to hold 25psi but not 50psi and leaks the pressure out above 50. I would invest in a new compression gauge, way cheaper than rebuilding a motor. Also if the motor is running correctly and we know that the gauge your using is very broken, why pull the motor apart? Please get a new gauge 😊 Cheers 🍻 Aussie Boat Guy 😎

[@jakehyland1202]

Hey mate, quick question, what brand compression tester are you using? I believe my toolpro one is out, I've tested my mates and it said 90 on each cylinder when he did it earlier with his uncles full on one and got 145, Im wanting a better one as I fix up motors for a hobby and also I've got a Yamaha 60 2 stroke I want to check, its nice and even but only at 75 on all cylinders, 1998 and still going beautifully💪 Cheers mate

[@25hpboatracerman]

Hi mate, My tester isn’t an expensive one, I think it was from gasweld tools. Definitely need one that reads the correct comp. Cheers 🍻 Aussie Boat Guy 🍻

[@ZachWardGolf]

Did a compression test on my 1978 evinrude 15 hp 2 stroke and top was 75 bottom read around 55ish. Not sure what to do now. Is this a big problem I should be worried about and how can i get the numbers to match.

[@25hpboatracerman]

Hi Mate, Some of the older OMC motors did run a lower compression. Other thing is some gages read low too. If it is easy enough to start then I would keep using it with no issues. To fix the compression you would need to do a full rebuild and replace the rings and have a quick hone of the bores while hoping there is no deep scratches in the bore walls. like I said, if it is easy enough to start and runs ok I would just use it like it is. Cheers 🍻 Aussie Boat Guy 😎

[@ZachWardGolf]

@@25hpboatracerman thank you ❗️

[@boatsandoutboards9070]

Nice topic. Are these spark plugs standard size , or different for each brand or hp interval?

[@25hpboatracerman]

Hi Mate, thanks 😊 Yes, there are many different variants of spark plugs for different motors, make sure to replace with the same. Cheers 🍻 Aussie Boat Guy 😎

[@boatsandoutboards9070]

So we need to be careful with the thread size of the test gauge. It's not universal

[@Yamahaoutboardguy5090]

Why should the motor be at full throttle? I have done compression tests on the same outboard with the butterfly closed and the butterfly wide open and it seemed to make no difference in the compression reading

[@25hpboatracerman]

Hi Mate, On most motors it makes not much of a difference but on some the butterfly seals very well in the throat with no relief holes so affects the comp reading. Cheers 🍻 Aussie Boat Guy 😎

[@Yamahaoutboardguy5090]

ok. thanks@!@@25hpboatracerman

[@Tech_90599]

Quick question: Do Tohatsu CDI units have a bult in rev limiter? for my current project outboard, a suzuki 15- it has a built in rev limiter, which cuts in at about 5500. With a re-profiled the head and ported the reed block/new, bigger reeds, tweaked the ugly duckling carb out a little and now it easily hits the rev limiter on the stock prop at 3/4 throttle or before...

[@25hpboatracerman]

Hi Mate, There is probably a way to override the limiter in your 15hp yam. try asking Borneo boat racing on Facebook, I think they race them. a lot of the smaller HP Tohatsu (under 40hp) don’t have any rev limiters. Cheers 🍻 Aussie Boat Guy 😎

[@random_dude_99]

Hey i got a question. I have a tohatsu 9.9 2 stroke and i want to change the crank bearings but i cant find any bearings with the little locating pins on them. Do you think it would be fine if i put 2 normal bearings and leave the middle bearing that has the pin on it? Both bearings fit tightly in the crankcase so i dont think that the outer race would spin and cause damage. Thanks

[@25hpboatracerman]

Hi Mate, Are the original ones recked? a few people do just use normal bearings but it’s better to buy the factory ones with the retainers. I personally always buy original parts. Cheers Aussie Boat Guy 😎

[@random_dude_99]

@25hpboatracerman the original ones have quite alot of play,but I can't find oem bearings in my country,and if I find any they are overpriced, for example I found 1 crank bearing for a tohatsu 40hp that was 73€... That's insane

[@Tech_90599]

My Brother from another mother! I just found your channel, luv it , mate. I am also a member of the exclusive Tohatsu 5hp go fast club... In my case, I have fitted an entirely new reedvalve and carb along with high compression squishband head and cylinder porting. Would be cool to compare notes- not sure how to email you?

[@25hpboatracerman]

Hi Mate, That’s awesome 👍 Would definitely be good to compare notes, I am considering doing another 5 but going full out this time. I was still hoping to keep that one I did pretty mild and reliable but was still surprised at the gain in power. They definitely have potential. Cheers 🍻 Aussie Boat Guy 😎

[@Tech_90599]

@@25hpboatracerman Yeah for sure. I fitted the reedvalve block and carb off a honda NS-1, which is a hot 50cc twostroke roadbike. Bike slide carbs are so much better than the cr@ppy outboard carbs... drop me an email and I'll send some pics. I need to do the leg mods to go faster- and a new prop.

[@borismandrykin2761]

Pay attention to how bendix works! It's jumping!

[@25hpboatracerman]

Hi champion, can you please explain your comments cheers 🍻 Aussie Boat Guy 😎

[@borismandrykin2761]

@@25hpboatracermanPls, look at the starter at 1:42 and 2:23.

[@kevinwaller6572]

Plug leads should be earthed, or damage to coils and other electronic components can result. So I'm told.

[@25hpboatracerman]

Hi Mate, I really appreciate your input champ 👌 Interesting, will have to check that out. cheers 🍻 Aussie Boat Guy 😎

[@bunndyboy]

Hey mate, if the compression drops in the gaauge after the test would that be the head gasket ? I noticed its white around were the head gasket is. On a mercury 15 super. Love your work mate...