Engine Hours (volvo) how do we know

Colleagues
I have a 22' aluminium boat which I am rebuilding, the Volvo Penta motor AD31B wich is removed at present showed on the Hour meter 256(white) 15(red)
I take this as 256hours 15min, but being new to this boat I can not confirm this. When I purchased the vessel The tacho therefore the hour meter did not work, they are connected but not operational.
I realise a question of how do you tell how many hours on the motor is futile and impossible to know.
I am assuming the hour meter is relatively correct if anything lets place another 20% on top of the reading as error and say the motor has 300 hours. Being new to this and judging that the motor was built in 1990 say 20 years ago with 300 hours would this motor be due for a rebuild?
I have no prior knowledge of the vessels past or even motor performance as when I bought the vessel it was not usable, due to corrosion in the hull. I do know that the motor starts, idles and accelerates and that's about it.
At What hour mark would you start looking at replacing parts? and which ones?

Katoh

 

a 31b is good for at least 5000 hours which is not a lot for a diesel but they are a high speed small displacement engine. generally if a diesel starts easy and runs okay there is nothing wrong with them. make sure you replace all the anodes . if it has an aftercooler make sure you clean it as any crap that gets in the system collects there and restricts cooling water flow.

 

Thanks for that.
While the motors out I was not sure how far to take it, I'm definitely going to change anodes, hoses belts even the raw water pump, but getting conflicting messages on the motor.
A friend owns a motor rebuild shop, and advised me to rebuild, but others have told me for the hours dont touch the motor, I am just opening a can of worms if I do. It definitely needs a good clean out and a re-spray to keep the rust under control.
300 odd hours in 20 years does not really sound right that's only 15hours a year, But who knows how long its being sitting. I think only way to know is pull the sump of and insect the bearings.
Cheers
Katoh

 

i like the volvo,s , very smooth and economical. the old detroit diesel worksop manuals had an excellent note inside the front cover, it said if the engine is running well leave it alone.

 

Katoh,

I usually consider a diesel ready for a rebuild any time after it hits 3,000 hours. Some engines seem to just keep going, and may go to 5,000 but for a maintenance cycle 3k seems to be a good start point for comparison.

As for 15hrs a year.... Just go take a look at the boats at your local marina, you will see many that haven't left the slip in year. Sadly a lot of people buy boats and never use them, or use them as cocktail decks to watch sunsets. Alternatively a lot of sailboats never use their engines at all, and just sail in and out.

 

Thanks Gentlemen
it seems the 3K mark is the magic figure and I dont think I'm anywhere near that, Even if it did 100hours a year it would still have some life left, and for a trailer boat I thinks that a lot, maybe?
That's great, I will leave the motor, a good clean and service and see who she go's.
Thanks Again
Katoh

 

Have the engine oil tested. This will reveal all about your motor, for very little money and not taking anything apart.

 

I have to remove the sump, in my wisdom when I removed the motor from the boat and went to put it on the engine stand I removed the fly wheel housing thinking it was bolt on like a typical petrol motor. Only to realise to late after the gasket had broken that it in fact was the back of the block, also ruining the sump gasket in the same movement.
While the sump is off it will just be a matter of inspecting one of the bearings to give me an indication of wear, my friend with the engine rebuild shop will gladdy do that for me.
Cheers
Katoh

 

A few year ago, I pulled 2 Cat D-342 diesels, for a repower. Both had 42,000 hours and never touched. I sold both engines, they fit D-8, H,K Cat dozers. They are still running today.

 

Wow 42k.
I think my boat would disintegrate first just leaving a running diesel on its mounts.
If you had to compare marine hours to say a vehicle diesel in Kms/Miles is there a conversion for that? Or can't you compare the two?
I would have thought that a marine diesel would be more like a highway driven vehicle, run at more a constant rpm and load, therefore making them last longer.
Cheers
Katoh

 

There's no true comparison to automotive application from marine. They run in to completely different modes. A marine engine runs at 90% output, 90% of the time, while an automotive engine runs in 20% output, 90% of the time. Aircraft engines and stationary engines do compare favorably to marine engines, as they too operate in a continuous, full load duty cycles.

 

Marine engines run in the cleanest environment. the Cat engines, that I had, were run in a work boat on relativity light duty.

 

Par
The 90% figure you speak about of load on the motor, would that be for all boats? Lets say a 22' aluminium planning hull with 2 people on board, would not be running at the same % power compared to say a 30' glass hull and a crew, both using the same motor.
I might be getting a little of track here, but we always seem to talk hp in boats, were does the torque come into things, I guarantee my 130hp Volvo has a lot more torque than any outboard comparable size. For some reason I can see the outboard working hard but than the diesel.
Would you ever have the occasion were a motor works at nearly peak on a small planning hull unless underpowered of course.
slow fred
I dont know about the cleanest environment, when I removed mine it was putrid underneath, the bilge was oil/ dirt and diesel coated and extremely rusty. one thing I found interesting there was no bungs, nowhere to allow a washout water to drain.
Thanks

Katoh

 

In evaluating truck take outs for marinization purposes , 50 miles is used as 1 hour.

"A marine engine runs at 90% output, 90% of the time, while an automotive engine runs in 20% output, 90% of the time."

Perhaps in commercial use this might be true , but something like a recreational "trawler" will have a weak 120 or 135hp engine installed and run at 2 or 3 gph , perhaps 14 to 16 hp per gallon of fuel , or 30 or so hp.

Same with many cruising sail boats "35" hp engine , .7 to 1 gph of fuel 10 -16 hp from 35!

FF

 

Fast Fred
Really good information you given me.
I sort of worked out in my head 50km = 1 hour, I think your closer to the mark, but I'm still in the ballpark.
I know this really means nothing but at least it gives me something to compare to that I understand a little more.
I was told prior to purchase of the vessel that it uses a mere 7ltrs/hour@ 20knots
I cannot confirm that figure but it sounds mighty low to me.
Cheers
Katoh