2007 8.1 Horizon

[susanandlance]

What would be considered good compression #'s on a 300 hr Mercruiser 8.1 Horizon, freshwater engine?

 

[scoflaw]

175. Watcha got ?

 

[susanandlance]

Nothing near that but waiting on final results...….

 

[Espos4]

For the most accurate results, The engine should be warm, wide open throttle, battery on charge and the fuel injectors disabled.


Also get “dry” and “wet” numbers.

 

[susanandlance]

The engine should be warm for the test.

Also get “dry” and “wet” numbers.

I can't because it's not near me, I heard 120-140 but service dept will send numbers Tuesday, seems low to me but don't know if it was cold or hot check and leak down info...…..getting worried, service dept supposedly said great numbers for an 2007 with 275 hrs...……..

 

[sbw1]

130-175 is the range for a crusader 8.1 standard HP engine. HO is the same. I would think Merc should be the same. Important issue is all cylinders should be close to each other. Testing techniques can alter the results.

 

[susanandlance]

If it doesn't work out think I'll get a new Corvette, don't need the headache …..lol

 

[scoflaw]

Is this boat/motor new to you ? 120-140 no effin good news there
Do the leak down, and listen to the air coming out your exhaust.
Yup Corvette would be an easier toy

 

[susanandlance]

Is this boat/motor new to you ? 120-140 no effin good news there
Do the leak down, and listen to the air coming out your exhaust.
Yup Corvette would be an easier toy

Called off the deal, too many what ifs!!!!!! Not to say that I'm not PISSED!!!!

 

[scoflaw]

Called off the deal, too many what ifs!!!!!! Not to say that I'm not PISSED!!!!

Smart...don't need some ones worn out motor

 

[susanandlance]

View attachment 66846 130-175 is the range for a crusader 8.1 standard HP engine. HO is the same. I would think Merc should be the same. Important issue is all cylinders should be close to each other. Testing techniques can alter the results.

Numbers we're 123-130 across both motors, 270 hr. Fresh water boat

 

[CaptRonn]

How long has the boat sat with the engines not operating? How was the compression test done?

 

[susanandlance]

How long has the boat sat with the engines not operating? How was the compression test done?

How long has the boat sat with the engines not operating? How was the compression test done?

I wasn't there Captronn, I assume cold because they were changing the plugs as well, don't know how long it sat

 

[CaptRonn]

Too many variables here. Always ask for details, and if possible be there to see it done.

 

[susanandlance]

Too many variables here. Always ask for details, and if possible be there to see it done.

Understood, they were changing all the plugs and I requested a compression check, boat is 600 miles away, will be there for sea trial and survey

 

[CaptRonn]

How long has this boat been sitting?

 

[susanandlance]

5-6 months so I'm told

 

[scoflaw]

Would you rather have a motor with 130 psi cranking compression or 175 ?
Mercs number guideline is a joke and more of a disclaimer. Most of their literature says that 100psi is an acceptable number. Give me a break, just redid my tired 20 year old 502 and the lowest 1 was 125. Now they all be at 165 #, but this motor predated the 8.1 which has higher CC out of the box.

Do a leakdown on a couple of cylinders. Don't be bamboozled with "oh they just need to be run in everything will be fine"
Cause they just want to unload it.

 

[sbw1]

Agree with the leakdown test recommendation.

 

[susanandlance]

I will get some answers from service dept when I'm there, if I don't like what I hear I'll walk away from the deal. hardly my first rodeo guys, but I appreciate it, it's a 12 year old boat with 270 hours on it, numbers probably not going to be good as a new or fresh rebuilt engine, not to mention I'm sure tests were done with engine cold