Logo
FULL SITE MENU

Advise needed. Buying a boat with a '04 Honda 150 with low compression

C

Chester543

New member
Hello.
I've found a boat that will fit my needs perfectly but both the main and the kicker outboards have low compression. They have even compression but they're all low.
It's on consignment at a dealership and I had their shop do the compression test.
They say the engine "runs and functions as it should". I live 3.5 hours away and have not had time to go check it out in person or do a sea trial.

Main engine:
2004 Honda BF150 - 477.5 Hours
#1 115 psi
#2 115 psi
#3 115 psi
#4 115 psi
They did a second test a day later after warming up the engine for a 20min or so. Tested at 125psi across all cylinders.
Here's a pic of their Honda diagnostics reading showing the hours, start count, etc.
Honda 150 hours.png

From the Honda service manual I found, compression specs are 222-250 psi. People on the interwebs seem to usually be testing around 170 - 210.
With it being 20 years old, I would not be expecting it to be in the 222-250 range but certainly in the 170-200ish range.

My thought is that there might be carbon buildup on the rings and/or valves thus causing the low compression. That would be my guess with the overall low hours, but I'm no expert...
Could doing some kind of decarbonizing/seafoam/etc return this engine to normal?
The owner says it works as it should but if I had to guess it might be losing some top-end rpm's and power.

Can anyone with experience with these engines shine some light on the situation?
Is the engine worth working on?
Should I just assume it's toast and needs a re-power?
The owner is refusing to do any engine work on it and is selling it as-is/where-is because "it's a running/functioning outboard"

There are not many boats like this one so it's not as easy as moving on to a different boat. Ideally, I would like to figure out how to make this option work for me.

Here is the info on the kicker:
2004 Honda 8hp - unsure of hours
#1 105 psi
#2 105 psi
Also testing low...

Thanks for any help on this!
 
Racerone makes a very good point. Common rookie mistake to leave the throttle closed during a compression test.

What bothers me too is the EXACT same numbers across all cylinders and on BOTH engines.
I call B S on that. I can't remember doing a compression test on anything where all the pressures were exactly the same.

If the compression is really that low, you might be right about sticking rings. But I would want to do a cylinder leak down test to narrow that down more precisely. Just not sure that I would trust that facility to do it after seeing those compression numbers.

I would like to see the valves adjusted on both of these old engines followed by another compression test to make a better determination of what you're facing there.

Tread carefully here.

Good luck.
 
Yes, it could be. But both of these engines are equipped with engine protection/limp home systems.

More testing is needed IMO. Not being willing to work through your concerns with you might be the biggest red flag of all.

Good luck.
 
Any shops in your area that have a dynamometer.-----A functional test to measure power output of this motor without any wrenching would be a good idea.
 
As already said, maybe the throttle was closed when tested.
Or it could be a compression gauge fault e.g. the gauge is under-reading either because it is faulty, or they are using a flexible gauge adaptor & the schrader valve which must be fitted to the engine end of the adaptor is missing or not closing.

Bob
 
jgmo said:
Racerone makes a very good point. Common rookie mistake to leave the throttle closed during a compression test.

What bothers me too is the EXACT same numbers across all cylinders and on BOTH engines.
I call B S on that. I can't remember doing a compression test on anything where all the pressures were exactly the same.

If the compression is really that low, you might be right about sticking rings. But I would want to do a cylinder leak down test to narrow that down more precisely. Just not sure that I would trust that facility to do it after seeing those compression numbers.

I would like to see the valves adjusted on both of these old engines followed by another compression test to make a better determination of what you're facing there.

Tread carefully here.

Good luck.
Click to expand...
This, having the exact same compression across all cylinders never happens. Have your own mechanic check the engines.
 
Thanks for all the input! Really appreciate it.

I had been thinking exact numbers from the tests seemed a bit odd. Guessing it was probably the tech just round up/down for the sales guy? They did use a brand new, calibrated gauge for the tests as the main tech was out that week and had the only gauge (so they told me...).
It could also be possible that the throttle wasn't held wide open during the tests as that would give slightly lower numbers.
I'm definitely going to see if I can chat with the tech who did the test, as the same numbers are suspect for sure. I have a mechanic buddy who said I should be demanding a refund as there's no way those numbers are accurate...

With the boat being on consignment, there is limited info I can get from the sales guy about the history or maintenance. It's also a tricky situation as the sales guy is representing both the seller and the buyer...

The joys of trying to buy something in a different city/state. Worse problems to have :)

I think the best option is to bite the bullet and drive the 7hr round trip and do a sea trial. That will give solid info if it's getting to the correct rpm/top speed under load.
And of course, check out all the nooks and crannies of the boat.


PS. I'd advise myself to use spellcheck in my titles next time I need advice 🤣
 
Throttle does not have to be open on a multi cylinder engine with a single throttle body, a common myth. Only a leak down test will reveal issue. Given age of motor I would steer clear
 
Back
Top