Life of 6v92 TA

[Docs Holiday]

3000 hrs on my 550 hp DD 6v92.. so I am having them surveyed this week. Brief telephone conversation with mechanic and he mentions "probably time for a rebuild". He indicated and I have read on this forum that these engines are over powered for the size of the Pistons. These motors imo have been babyed...usually running at hull speed of 9 knots (1200)rpm taking them up to 2250 for 10 to 15 mins at the end of the run, maintenance with oil and filter changes at 150 hrs etc. Oil consumption is not excessive but there appears to be some blow by with oil coming out dipstick on port engine. My question is at what point should I consider rebuild...what on survey would be- absolutely needs rebuild vs. you can get another 2,000 hrs before rebuild?

 

[Glory]

3000 hrs on my 550 hp DD 6v92.. so I am having them surveyed this week. Brief telephone conversation with mechanic and he mentions "probably time for a rebuild". He indicated and I have read on this forum that these engines are over powered for the size of the Pistons. These motors imo have been babyed...usually running at hull speed of 9 knots (1200)rpm taking them up to 2250 for 10 to 15 mins at the end of the run, maintenance with oil and filter changes at 150 hrs etc. Oil consumption is not excessive but there appears to be some blow by with oil coming out dipstick on port engine. My question is at what point should I consider rebuild...what on survey would be- absolutely needs rebuild vs. you can get another 2,000 hrs before rebuild?

1, Your mechanic said " probably time for a rebuild", without looking at the engines? That's sales position, not a surveyor position. I would hope a vendor arrives at the job with an open mind, not anticipating a $20,000 payday in each ER

2, "what on survey would be- absolutely needs rebuild vs. you can get another 2,000 hrs before rebuild?" The wear or defects found. Like cylinder and ring damage/wear, low compression.

The one thing you didn't talk about was poor performance, you only mentioned an oil leak, on what sounded like just one engine.

A premature overhaul is never a bad thing, just expensive.

JM

 

[SeaEric]

A few years back I sold a Chris 500 to a customer in Fl. She was powered with 6v92 550's with 3500 hours showing on the meters. They surveyed fine with good compression. The engine surveyor commented "I can just about guarantee that these engines have never been run much over 1500 RPM's"

Hours don't tell the tale. If you want to know for sure, you must do a compression test.

 

[Finalee]

It's really more about fuel burned versus hours.

 

[rwappleton]

I would not let that mechanic on my boat!

As everyone has said here it's about usage not hours.

How does it cold start? That is the best single indicator of engine condition IMHO.

How long does it crank before it starts?

How long does it hunt (RPM varies)?

How much smoke?

Our 6-71 TI's have 2700 hours and at 55 degrees crank less than 5 seconds, hunt for less than 5 seconds and smoke less than 5 seconds. We are counting on another 2700 easy with good maintenance.

 

[jim rosenthal]

I hope that the gentleman you spoke of isn't doing the survey. If he is, he's probably already ordered the parts

I agree with a survey and a compression check. (I don't think you can do a leakdown on DDs, or it would be a bit complex- not sure on that one) If you can get a few more years out of them, then why not?

 

[rsmith]

Hey Doc if you walked into your Docs office and the first thing he told you before any testing was at your age you probably need a quad trouble bypass would you let him cut you open???

 

[Docs Holiday]

Motors fire up right away and pass
Genesis 30 second smoke test with minimal searching. Port motor is putting out a noticeable "sheen" on the water.
I have updated my galley and galley floor and recently brought her down from Eastport, Me to Florida with no major running problems (if I don't include dinging the props) but I need to replace the sagging whisper walls so I want to make sure there are no major problems with the motors before sinking a lot more money into cosmetics. I have been told that at 3000 hrs the after coolers should be cleaned but with the oil or fuel sheen I wanted to make sure that it wasn't something that requires a major overhaul.
I guess my question is, "is 3000 hrs the average life span of these motors and how accurate will a survey/compression test be as to the longevity of these motors
I think the person I talked to was just telling me what his experience indicated...after all, they probably see mainly the bad ones and get a somewhat skewed perception. That is why I'm asking forum members...for the most part y'all care for and look after your boats.

 

[Cricket]

Fuel sheen could be from a leaking fuel cooler, need to determine if it's fuel or oil. 3000 hrs on the after coolers sounds like way overdue for a cleaning.

 

[jim rosenthal]

Hey Doc if you walked into your Docs office and the first thing he told you before any testing was at your age you probably need a quad trouble bypass would you let him cut you open???

Not a chance of it. I'd walk back out. So would any rational person.

 

[saltshaker]

Find out what the problem is and if it would indicate a major. I've seen some high output Detroits that ran great with high hours. Sounds like yours are doing fine other than what you indicated. Get them checked out and find out if they need service or a major. Many will condem them when they are running fine but show signs of wear. If they start well, run well and compression is within spec, you probably have a lesser issue to deal with. Start with a mechanic diagnosing the problems and see if they need further testing or work. A survey is nice but shouldn't be needed unless you want make a determination before spending significant money fixing other issues with the engine.

 

[jim rosenthal]

Some of this would depend on the rating of the engines; if you included it and I missed it, my apologies. I recall a discussion here a few years back when the opinion was expressed that all other things being equal, the 6v-92s that were rated at 550hp were wound pretty tight, and that lower power rating engines would last longer.

All other things, of course, are seldom equal, and maintenance and use are very significant. Before I went to the trouble of overhauling an engine, I'd want to know for certain that it needed it.

I DID miss it- 550- well that's the highest rating, but it sounds like you take good care of them and don't beat them up.

 

[Docs Holiday]

Yes, I remembered the same comment....so the diesel mechanic is on my boat half way through the compression check right now...so far so good... I will report when he is done

 

[Fanfare]

I would estimate that I have about 2500 hours on my 550 hp 6V-92TAs, going on 23 years old. They run great and I am not changing anything until they act up. I did have a leaking fuel cooler on one. It was hard to figure out. I was getting about a half cup of water in one Racor after a long day's run. Thought condensation, etc. Then noticed it was fairly regular. I figure when the engine was running the cooler had positive raw water pressure on it and some got into the tank. Then the Racor pulled it out. Rebuilt both coolers, no more problem. I think replacement with new was about the same cost. But are new ones made in China?

These have been GREAT engines--even more reliable than my former 8V-71Ns were. Although with those engines I had more problems with the Allison transmissions than anything else.

 

[Docs Holiday]

Just finished compression check....all cylinders within specs....yea! I have never seen any water in my record but will have after coolers cleaned and injectors replaced.....now any suggestions about sagging whisper wall replacements

 

[SeaEric]

Just finished compression check....all cylinders within specs....yea! I have never seen any water in my record but will have after coolers cleaned and injectors replaced.....now any suggestions about sagging whisper wall replacements

I have seen those sagging wallcoverings on other 501's and in the pics of your boat. If I recall, it seems like the surface vinyl has cut loose from the padded backing and that's why it sags - is that correct? I have variously noticed that some Hatt models have that same issue. I think all of these installations pre-date the "whisper wall" product (I may be wrong). Whisper wall is pricey stuff and requires a trained installer. If it was my boat, I would pick an isolated section of failed wallcovering and pull it off to see what you have. If you can easily get to decently smooth plywood, I would prime it with an oil based primer and hang new vinyl wallcovering (not padded). It's important to note that the best choice of replacement wallcovering is something relatively heavy weight (commercial grade?) with texture that will disguise small imperfections in the substrate. The textures that seam up the best are those with a vertical texture so the seams disappear. A good paperhanger can make it look like new again.

 

[Docs Holiday]

Thanks Eric, yes you are correct the ?paper /vinyl has separated from the backing. I will look for the plywood but I think the whisper wall does supply some soundproofing. Also it appears to have been installed prior to all the trim! There has got to be a less expensive way than removing all the trim. A friend suggested covering up with fabric covered panels (? A product called Magilite). This would keep the soundproofing.

 

[oscarvan]

OP mentions blow by, to the point of oil spitting out of the dipstick tube. Now, don't know enough about these engines to say whether that's normal or not, but on all the engines I AM familiar with that's a bad sign....

 

[SeaEric]

Thanks Eric, yes you are correct the ?paper /vinyl has separated from the backing. I will look for the plywood but I think the whisper wall does supply some soundproofing. Also it appears to have been installed prior to all the trim! There has got to be a less expensive way than removing all the trim. A friend suggested covering up with fabric covered panels (? A product called Magilite). This would keep the soundproofing.

I Googled and found Majilite. Looks like some $pace age $tuff. You're selling this boat, yes? I'm not quite sure what we're sound proofing from. You need to do what makes you happy and what your wallet can bear. A sharp razor knife and a wide joint compound blade will separate the existing wall covering from the existing wood trim. Any remaining fuzzy edge, if any, can likely be caulked with clear to isolate it from a new wallcovering that runs up to it. The soft stapled on trim along the headliner and elsewhere can be removed and replaced as necessary.

This doesn't have to be a huge expensive job IMHO. This kind of interior refit is 90% art and 10% science.

 

[SKYCHENEY]

OP mentions blow by, to the point of oil spitting out of the dipstick tube. Now, don't know enough about these engines to say whether that's normal or not, but on all the engines I AM familiar with that's a bad sign....

That could easily be explained by stuck air box drain check valves.

Generally these old 2 stroke Detroits don't die a quick death unless overheated. Usually they linger on for many many hours and you know when they are due for rebuild.