valve job or complete overhaul?

[glazingguru]

I have a 1995 355 Aft Cabin with 454 carburated Crusaders with 480 hours. In June we did a comression test and both motors were all over the place. We knew we would be having problems. The port motor began to run a little rough, was kind of hard to start and would die while docking at the worst times. I used spray and cleaned the carbs and air cleaner.eventually it wouldnt start but it would turn. I had a guy look and we tried to start it and he said the starter was dragging and then the starter wouldnt even turn. He thought a new starter would get it going. Then we pulled a plug and found a slight rust on it. Since then, I have been going around with different mechanics who all have different ideas on repower. Some say rebuild what I have, some say get long blocks and start over from there, some say change to a 5.7 Mag, some say 6.0 minimum. Prices are all over the place and really high from 18k to 40k depending on the option. Last night I was speaking with a mechanic who suggested a valve job might be all we really need. Is there a way I can determine that? Any options? I am going to the boat this weekend. I am anxious to get it going again quickly. There are a lot of bad mechanics out there. I am not a mechanic, but have a small amount of knowledge and ability.

[AaHubb]

Sounds like you need to get a better idea as to the condition of the engine. I think I would start by pulling all the plugs (keep track of which cylinder each came from) and examine them carefully. The starter should be able to spin the engine easily now. Now do your compression checks again keeping notes of the results. Next squirt a little oil into each cylinder, spin the engine over for a bit to work the oil into the rings and check compression yet again. If your readings don't even out some then you may have top end problems. This won't be as accurate as testing a warm engine but should at least point towards further tests. Disclaimer.. I probably have about the same mechanical ability as you so others may have better ideas. Good luck.
..Aaron

[waybomb]

Better yet, find somebody that can do a leakdown on each of the cylinders.

[Santego]

Sound like you need a good mechanic. If you do choose to check compression, make sure you disable the coil. If you pull all the plugs at once, you will get some fuel coming out the spark plug holes and one spark from a ignition wire could heat things up in a hurry.
All you need to run is 1) fuel 2) proper compression and 3) ignition source at the correct time. If you have that, and are still running bad you may have a tuning problem, partially clogged jet in carb ( dirty fuel injector if injected) or electrical problem killing spark.
I would check it over before considering repower at 400+ hrs.
Just my .02 cents

[waybomb]

A '95 with 480 hours? I just caught that.

Seriously speaking, a compression test is nice, but a leak down will be tell you much more, exactly. Not dependent on cranking power, carburetor, or anything other than valves and rings and headgaskets. Were all the plugs out and carb wot when doing the compression test? If the engine was cranking slowly, that test is useless and the numbers will be all over the place.

But I am betting your carbs need a teardown, clean, and reassemble.
And probably new plugs, wires, caps, and rotors. Fuel filter. Replace the antisiphon valves, and if you can pull and inspect the pickups at the same time, do it. Check fuel tank vents and clean them. All stuff you can do all by yourself.

I bet you'll be good to go.

As for slow cranking, load test the batteries, dissassemble all heavy battery connections and clean the terminals and the mounting surfaces. A slow cranking engine is an electrical problem usually.

[Steamboat Willie]

I have a 97 325 Aft Cabin that I have owned for a year. Crusader carburated 350's. Two days ago, the starboard engine started running rough and I noticed a significant amount of black oil being discharged from the exhaust. Oil pressure and temps were normal. Put it back in the slip and started trouble shooting. Starboard carb was recently overhauled and was working fine. The oil level was down a little bit. The oil was fairly dirty looking. (about 25 hours since last change). Mechanic came to the boat the next morning and performed a compression check on the engine. Five of the eight were at about 100 and the other three were 150 and 160. These engines have about 700 hours and are original to the boat. They had been run less than 100 hours in the five years prior to me acquiring the boat. The mechanic, (who I know and trust) seems to think that a repower might be the best option, given the age and history of the engines. He is suggesting going to a long block. Did not have time to check the port engine compression, but will do so today. Port engine runs great, good oil pressure, good temps, makes RPM, clean looking oil, and no smoke.
I am thinking that if a repower is what I decide to do, perhaps I should do both of them given the fairly significant boat disassembly and labor issues to do one now and then be forced to do the other one in the future.
I would like to hear from you all with suggestions and thoughts about my choices here.

[waybomb]

I'd again do a leak-down test. You need to find out why you have low compression. 900 hours is not that much so long as they were maintained.

While you have the plugs out, borrow a borescope and inspect the cylinders and valves.

I do not believe you have enough info to justify pulling the engines out yet. But that's just me - I hate doing too much work. I am lazy. I'd want to be certain the things needs replacement.

As for one or both, that's a financial decision and peace of mind decision. Just remember there are way too many marine mechanics that claim they can rebuild an engine. They probably can, but not correctly. It's more then sending stuff out for machining and bolting it together.

Me, I'd personally rebuild both. If I did not have the skills, I might chose to buy 1 <new> longblock. I would not buy a reman. My opinion; just what I would do.

[glazingguru]

Well, I ended up having both motors completely rebuilt from the bottom up. Leak-down test only confirmed my original suspicions. The Starboard motor was still running and seemed somewhat okay but tested bad. It was expensive. While I had it out I had the seals replaced. The bottom paint is only a year old so I was okay on that. I am in to the re-power about 18k now. Good luck finding a good mechanic, there are a lot of flakes out there. I found a good one, but his communication is terrible.

[Lyndon670]

A '95 with 480 hours? I just caught that.

Seriously speaking, a compression test is nice, but a leak down will be tell you much more, exactly. Not dependent on cranking power, carburetor, or anything other than valves and rings and headgaskets. Were all the plugs out and carb wot when doing the compression test? If the engine was cranking slowly, that test is useless and the numbers will be all over the place.

But I am betting your carbs need a teardown, clean, and reassemble.
And probably new plugs, wires, caps, and rotors. Fuel filter. Replace the antisiphon valves, and if you can pull and inspect the pickups at the same time, do it. Check fuel tank vents and clean them. All stuff you can do all by yourself.

I bet you'll be good to go.

As for slow cranking, load test the batteries, dissassemble all heavy battery connections and clean the terminals and the mounting surfaces. A slow cranking engine is an electrical problem usually

I have to totally agree with this opinion. A total of 480 hours is absolutely nothing. "Well" maintained gas engines (regardless of displacement) should have a lifespan of 2000hrs. During that 2000hrs, valve jobs would probably be requied at the 1000-1200hr mark, with carb rebuilds thrown in there as well. Oil changes, proper engine loading and RPM managment will help get you to the 2000hr mark. My '93 Silverton 41C with 8.1L Crusaders had 942hrs on her and it ran like a top. The new owner had a compression test, leakdown test and a bore scope check done as part of the survey. All came back well within the limits, or as quote in the engine analysis "like new". I changed the oil 2 times a season, impellers every other year, never warmed her up beyond the thermostats opening up, and only pushed her to WOT at the start of the season to make sure all was well from the winter. Other than that she ran at 3000rpm MAX wich was a fast cruise of 17kts.

You are best to have an engine surveyor give you advice, not the local marina mechanic, an automotive mechanic, or worse yet - your buddy who restores old Chevy's. Pay the $500 and have one of these experts give you the non biased opinion, then talk to your marina mechanic based on their information.

[George D]

I just left a website. Re manufactured.com. With a great section on diagnostics. One part very interesting about how just doing the heads could cause problems due to misdiagnosis af actual problem. Might be worth a look