low compression 3.0 cobra (new)

[Randy stoner]

I totally agree Mark. But regardless the engine had good compression numbers when it went in and in the spring the first thing I did was check the compression and they were down by 25 to 30 pounds per square inch in every cylinder and that was the only thing that was done from the time. I got that boat back with a new engine to the time I checked the compression for the first time in the following spring

 

[markhodges78]

I totally agree Mark. But regardless the engine had good compression numbers when it went in and in the spring the first thing I did was check the compression and they were down by 25 to 30 pounds per square inch in every cylinder and that was the only thing that was done from the time. I got that boat back with a new engine to the time I checked the compression for the first time in the following spring

Did you check the compression cold or with the engine warm?

 

[Randy stoner]

Did you check the compression cold or with the engine warm?

Checked cold

 

[Grub54891]

Wow. Even if the compression recovers, future issues will crop up. I'm even not happy about this. What kind of shop is this?

 

[Randy stoner]

It’s a boat sales and service company. I’ve always had outboard engines and this is my first inboard outboard, and given that it was brand spanking new I want to have it winterized properly as such. I should’ve done it myself. No I’m not saying they did it but the boat was not put in the water from the time it came back brand new, and I took the compression at the end of the season and at the very beginning of the next season down, and the only thing that was done to that age and it was winterized and I watched him do it in? And question them as to why they let it run with the water going in at first

 

[markhodges78]

And question them as to why they let it run with the water going in at first

Not sure I understand this statement? Did they have water going to the engine while it was running?

 

[markhodges78]

As i waited i noticed they started the engine and let it run without water for a minute at about 2500 rpms. They said this is how they do it to get the thermostat open.

Did they have the lower unit removed from the boat if so then letting it run without water would not hurt anything I would say it could run for several minutes like this. If the lower unit was still on the boat then just a few seconds could destroy the water pump in the lower unit

 

[Randy stoner]

They stated that it would not take long to winterize the motor. They started the boat up and ran it for a min without ears on. I immediately asked them if that was ok and they said yes they do it all the time. Stated they did to get the thermostat open quicker. They then turned on the water and then lowered the unit in a tank of antifreeze. Never seen it done that way but who was i to argue. Last spring i started the boat up on ears to flush the antifreeze out and the pump worked fine. I then took a compression test and got the low numbers. The reason for all these tests was because i had purchased a new engine the year before and if you read the early posts you would see why i was taking readings. I am no idiot when it comes to motors. I look after my equipment and have rebuilt many v8s and customer harley engines as well. I should have done it myself and in fact this winter past i did my own winterizeing. The question i am also wondering is wht to set the timeing at on this new motor. In my opinion other than the compression issue it seemed sluggish as well and just want to make sure on that because the original seller of both engines told me they are very conserviative on timeing when it new or rebuilt.

randy

 

[markhodges78]

I am no idiot when it comes to motors. I look after my equipment and have rebuilt many v8s and customer harley engines as well. I should have done it myself and in fact this winter past i did my own winterizeing.

I'm not saying you're an idiot. What I am saying is there is absolutely no damage that can be done to the engine by running it with no water for a few minutes drag cars do it all the time.
What I am saying is I've personally seen water pump impellers ( That are located in the lower drive destroyed by running engines for a few seconds without water)
It is rubber and needs the water for lubrication

The question i am also wondering is wht to set the timeing at on this new motor. In my opinion other than the compression issue it seemed sluggish as well and just want to make sure on that because the original seller of both engines told me they are very conserviative on timeing when it new or rebuilt.

randy

The timing is determined by the distributor that's in the engine if the original distributor was used then set the timing to original spec..

 

[markhodges78]

Also I don't think it's been mentioned but if your exhust manifold is leaking you could be getting water in your cylinders and causing rust in the bores during winter lay-up

 

[Randy stoner]

Thanks mark

 

[Randy stoner]

Thanks mark

The bored are good there’s no rush them so what would cause the compression ratio on all four cylinders to drop by 20-25 psi each cylinder

 

[markhodges78]

The bored are good there’s no rush them so what would cause the compression ratio on all four cylinders to drop by 20-25 psi each cylinder

If this has been verified with a different compression tester then I would say possibly valves..
Also I purchased a new compression tester from advance when I went to buy a boat because I left mine at home and it was 3 hours away the compression was 90 93 and so on. They were all within 5 psi and the boat ran and idled good so I bought it. I'm glad I did because when I got home and tested it the numbers were135 + within 5 psi

 

[havoc_squad]

The bored are good there’s no rush them so what would cause the compression ratio on all four cylinders to drop by 20-25 psi each cylinder

You are going to know very quickly if you do a leak down test by hearing where it leaks. (Valves would be intake or exhaust, cooling would be head gasket, oil dip stick will be piston & rings)

There's no point in guessing what might be wrong, find out.

I am curious how much leakage percentage you have.

 

[Randy stoner]

Well I have egg on my face. On earlier posts here i had stated that a presumptiously new motor had poor compression. I based it upon the readings of a new digital compression guage. The number bothered me all winter. Moving forward my son bought a used older 9.8. It wasnt fireing on both cylinders so i loaned him my guage. He called to say it was reading 75 psi in each cylinder. I thought that is extrodinarilly low considering we finally figured out it had a bad plug wire and ran like a bear. Shouldnt be that low on a merc 9.8. This past weekend i was suspecting the new guage so i used a brand new pressure washer as a test because it was raining. 40 psi. I knew something was up. So i went to a local hot rod shop and bought a good analog guage and tried it. 85 psi on the washer. I again checked the old guage and it read 40.

I tested the new remanufactured 3.0 Vortec engine in the boat and my gosh 155-160 in all four holes.

There is a moral to the story. Stay away from those cheap Princess Auto/Harbour freight guages. Im sure some have luck but i finally have the readings i was promised and egg all over my face as well. Now to figure out the bog when accelerating. Sounds like an old cow LOL.

Randy

 

[Bondo]

Now to figure out the bog when accelerating.

Ayuh,..... Sounds like a lean condition,....

 

[Randy stoner]

Bondo, the plugs i pulled are sooted like a rich condition but the boat has only been running on ears so i havent had a chance to open it up but my experience with a lean condition is spitting through the carbs will suggest that. I have the fuel air set to 1-1/4 turns out. The left side was in to 1/2 and equalizing it really helped with a sharp throttle up. Still hesitates a little but nothing like it was. The original engine ran like the wind but it was replaced due to a cracked block. Had a new reman put in it and compression was awefull so the marina put in another. Last year out i was not getting up on plane like the original even though this one was rated at 140 over 120 hp. So i thought id check the compression. As it stand now my guage was bad and i have lots now. So I just have to figure out what the low end bog is under full throttle. i put on a 15p prop but havent had a chance to test it out yet.

incidently the original engine pushed this boat at37 mph by gps best i could get last year was 30 with a tail wind. boat is a sunbird corsica 175 and is not waterlogged

randy