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Old 03 April 2006, 20:30   #1
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lots of revs = short engine life

One thing that has been nagging at the back of my mind since I got the new toy is how to treat it...

On most engines I am used to dealing with (in vehicles) the redline is really something to be avoided by a wide margin if you want the engine to live a long and happy life. On the other hand some engines (aero engines and tractor engines for example) the "rated speed" is fine to use all day long.

What about 2 stroke outboards?

The spec in the Johnson 115 manual gives 4500-5500rpm as the wide open throttle setting, and with the prop that is on there at the moment it settles at exactly 5500 once you are up to speed. Over 5000rpm it sounds really harsh though, but at anything up to about 4500 it sounds fairly "mechanically contented" - and I have a fairly good ear for funny or unhealthy noises in mechanical things.

I have already discovered that any sustained high-throttle use leads to scary, scary fuel consumption (3500rpm/20kt uses about half the fuel of 4500rpm/28-30kt) but what about the long term effect on the engine - what do you all think is a sensible "day to day max revs" to use, or is this type of engine usually pretty much OK with anything as long as you don't mind the fuel bill....

I guess the engine life must depend to a certain extent on how you treat it and I don't intend to thrash it senseless all the time but it would be handy to know what the accepted practice is on this type of engine.

Thanks

Stephen
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Old 03 April 2006, 23:18   #2
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I disagree about avoiding the redline - my engines tend to outlast the cars themselves. I rev to the redline all the time - golden rule is though NEVER until the engine is up to full operating temp. Also very regular opil changes etc.

Having said that it a car you don't hold it at maximum revs for long periods as you can in a boat.

Marine diesels are rated depending on use - a pleasure rating could be 800hp for a given engine - for commercial use it could be down to 400hp for the same engine!!!

2 strokes seem to thrive on revs - ask the crazy frog!!!
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Old 04 April 2006, 03:02   #3
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All engines are different, some bike engines will rev to 10 000 rpm or more. I have a 30 tonne truck that 'red lines' at 2500 rpm, its a 9 litre six, but it has masses of torque at 1800, where it sits at its happiest. Engine temp is indeed very important, especially if it has a turbo on it. I never ever rev any engine till its warmed through properly. I never rev 2 strokes without a load either, ie in gear

My view is that if you dont use it, you lose it. I have always used any engine I've owned to its full rev range. I agree though, constant use at extremes cannot be good all of the time, but it is definately not bad some of the time. In the end, you are shoving a lump of metal up and down in a cylinder, Its going from start to stop to start again, in fractions of a second. From a point of physics, thats quite hard to do quickly, but with modern engines so well engineered and balanced, using modern lubricants that are so much more efficient makes it all possible. The next thing I do is not to skimp on servicing, use top brand oils and filters, or the best you can afford and do it regulary.

I have no worries running my opti 150 up to 5600, for periods of time, no outboards i've ever had, have complained running flat out, only the wife does that!

If the plate on it says thats what the manufacturer rates it at, well they designed it, they have to warranty it when new. Just about all 2 trokes have very poor consumption when running fast, its a kind of exponential rise in guzzlement. If it doesn't sound happy stick to what you prefer, but run it full bung now and again.
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Old 04 April 2006, 03:27   #4
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The other thing to think about is how many hours you are going to use the engine in any one year?

Don't worry about it!
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Old 04 April 2006, 06:34   #5
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Sorry I was talking about sustained use at or near to WOT rather than short bursts for the hell of it - which I agree is good for an engine, to clear all the muck out of it. The amount of smoke and crud that comes out of my V8 if you give it a good burst up a hill after it's been pottering round town for a few days is remarkable.

Codprawn as you say you don't/can't hold a car engine at near to max revs for any length of time.

Put it this way if you took the average car, sat a brick on the throttle (assuming it has a rev limiter of course so would not over-rev and destroy itself) and walked away, how long would the engine last? Not very long at all compared to its normal life expectancy, even less so if it was on a dyno and under full load at max revs. I remember a few years back when there was a lot of adverse comment about the UK MOT test on diesels where some engines were blowing up when they had to be held at max revs for 30 sec (?) for the emissions test!!

I agree on temperature, I always treat any engine gently until it is fully warmed up, not sure how long this takes on an outboard (I haven't studied the book of words yet to figure out whether it is a direct or indirect cooling system, and there's no temp gauge only the warning light) but in using it so far I usually start it and let it idle before untying lines, putting on life jacket etc (so 3-4 min at idle) then do the first 1/2 mile or so at about 2500-3000rpm before giving it any more, I guess that is probably about right.

I was thinking that the engines were probably designed for sustained use at high revs and the general view seems to be that this is fine - which is what I wanted to know, thanks

Now just gotta live with the fuel bill
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Old 04 April 2006, 12:21   #6
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How many hours does an engine generally take before it is 'run in'.I have a 2004 Merc 60 2 stroke with less than 5 hours on it so I want to treat it with respect.
Also it has oil injection.Should I be mixing some oil in the petrol tank to keep it slightly rich, or do the more modern 2 strokes come from the factory run in on the bench?
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Old 04 April 2006, 12:29   #7
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Some of the latest 2 strokes will use more oil during the running in period - older ones will need oil in the fuel as well as oil in the engine tank so you are running at say 25:1 instead of 50:1.

I would always err on the side of caution. At 5hrs the engine will still be tight - don't think you should go over 1/2 throttle until you hit 10 hours - then gradually start opening it up - avoid more than short bursts of full throttle for the first say 25 hrs.
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Old 04 April 2006, 13:14   #8
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The yam F80 we have takes a total of 10 hours run in according to the manual.

First 10 mins just idleing

up to 1hr = quarter throttle

up to 3hr = half throttle

then full throttle after but not for long periods no more than a few minutes

No trawling the power should be varied, theres a noticeable difference as the engine is run in.
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Old 04 April 2006, 13:52   #9
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Quote:
Originally Posted by codprawn
Some of the latest 2 strokes will use more oil during the running in period - older ones will need oil in the fuel as well as oil in the engine tank so you are running at say 25:1 instead of 50:1.

I would always err on the side of caution. At 5hrs the engine will still be tight - don't think you should go over 1/2 throttle until you hit 10 hours - then gradually start opening it up - avoid more than short bursts of full throttle for the first say 25 hrs.
ISTR the engine manual for mine (made in 2000) says that - for the first X hours you have to run a mix in the petrol tank as well as the usual oil injection.
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Old 06 April 2006, 15:10   #10
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Just found out the new Yamaha R6 600 cc 4cyl inline bike revs to 18,000 RPM

Holy Jesus thats fast. Bet Valentino Rossi thinks its still too slow
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