Bad compression test on 1995 Sport Nautique

I get the impression that you're relatively new or "less than experienced" when it comes to boats. Not meaning any disrespect, mind you and if I'm wrong I certainly apologize.

With that in mind I concur with what Joe said. Those compression numbers are not horrible and I personally feel you could get several good years out it with those numbers before you have to worry about. The mechanic says it runs strong and based purely on those numbers, I would probably whole heartedly believe him. My stock engine had numbers very similar to that for 6 years before I did anything with it and it still ran pretty strong. We put over 100 hours a year on it like that.

Buy it and use it and get a feel for the old girl. Get some experience on operating and maintaining it with the help of this forum and go skiing for Christ's sake. Have some fun.

Thanks, this has been very helpful. I spoke to the mechanic that did the test and here is the info.

- The boat was last run 2 weeks ago for a test drive and that the only time it's been in the water this year. It did get new battery at the time.
- Mechanic says the boat runs great. No noticeable issues when they did the test drive.
- Engine is a Pro Boss GT-40.
- Compression test was run cold, going to get it run again when I go for my test drive.
- I may have miss spoken on the 'new heads' recommendation, speaking to the mechanic in detail they recommend 'inspecting the heads and replacing the values'.

From what I have read, if the engine is running well then we could be good here and since it hasn't really been on the water this year getting it on the water a few time may clear up the issue. A hot compression test will also give me a more accurate reading, and if that comes out better we should be okay.

If the compression is bad on the hot test, would I still be able to run the boat until the issue becomes noticeable without causing additional damage? Or is this something I should get fixed ASAP.

If your comfortable with it and know the costs you'll be fine. A leakdown would be best,but you could maybe use that compression test to help in the negotiations. A leakdown test would indicate to you better what is exactly wrong but is not easily done unless you have the tool and a compressor.

Its too hard to see from over here how meaningful that compression test is. Relative numbers on a gage mean something, ie the 25% difference on the two cylinders but the absolute numbers have a lot that go in them. I have engines where 130 on a gage is a new and happy engine, and others that run 210 plus. If the gage was solid and the battery was strong and you are checking an HO engine then they are low, but not hugely low. If they are significantly low you would need to do a leak down test to determine if you have a problem with the heads, rings, or both. Assuming it is related to the heads simply from the compression test is a stretch. If it was the heads and you spent a grand on two newly rebuilt gt40p heads you would likely end up with a very new feeling and strong engine that you would expect to stay that way many many years.   If it leaks through the rings then changing the heads would be useless.   All that being said I would run that engine with good oil, good gas, and some fuel system cleaner maybe the occasional snake oil treatment for a season and see if you didn’t run the rough right out of it.

looks like it was done cold. engine may be OK, test again warm

$7,500 without a trailer, interior looks good in pictures but I haven't seen it in person yet. I plan to see the boat this weekend (its a 4 hour drive but close to my in-laws). Owner already offered to knock $500 off after the test.

Personally I like the idea of getting it down to $6,500 and getting the engine done. Total cost of $8,500 with new heads seems good to me, but like I said, I am no expert. Which is why I am here.

So I am looking at a 1995 Sport Nautique. I had the marina it's at do a compression test on the engine with the following results.

1     120
2     100
3     120
4     110
5     120
6     110
7     90
8     120

So I am new to this but I know this is bad, Overall the compression is low and 2 and 7 are very bad. Can you guys help me with my options. Should I still look boat if I can negotiate a discount. I plan to buy the boat now but won't really use it till next winter. What would I do to fix this. Marina has suggested I replace the heads for an estimated cost of $1,500, which I would negotiate the owner covering some of cost of the rebuild.

What is the likely result after the new heads are put, in. Does it mean I have brand spanking new engine that will last another 1000 hours. Would it be better to just do a full rebuild or repower)?

I am buying this boat partly to use but also because I want to have something to work on mechanically. I want to learn about the engine and parts, Get the boat fixed up and looking great. Basically something to keep me busy both in and out of the water,

Lastly, is fixing this something a novice could tackle with lots of time to learn and get it done, or is this best left to the professionals.