kashurst
Well-known member
I've noticed on a few threads recently about engines people have suggested doing a fast idle test. What does this mean and what does it reveal? thanks
fast idle test on engines
- Thread starter kashurst
- Start date
volvopaul
Well-known member
Kas it reveals the governor setting result at high idle or lay mans term, flat out in neutral. It's all to do with what the pump is set at to give it's max rpm under load, an engines injector pump will have a higher max rpm setting not under load than when it's under load, all to do with governor stabilisation as a mechanical governor cannot work out if the engine is under load or not but it stabilises at higher rpm than under load as there is no load so the engine can rev freely out of gear, where as in gear it can only rev to it's capability related to load, ie the prop, hull fouling, what the other engine can achieve etc. The max rpm not under load is always higher than it's loaded rpm, so in your case 3000 is the figure 2800 is it's in gear loaded figure, so if you use a hand held laser tach with the strip of reflective tape on the front pulley and you don't get the high idle figure of 3000 rpm you need to find out why, otherwise your engine will never perform it's max rpm under load, eg 2800 out of gear you won't get 2800 in gear under load, hope that makes sense. My engines tamd62 will pull 2900 in gear when the bottom is clean which is 100 rpm more than it should which means in theory my props are not big enough and I could get more top speed out of her, but as the season gets on that figure drops, I'm down to 2500 now! So in your never ending task to get the speed and rpm buy a hand held tach and get some testing done when the bottom is clean, it's data collected that gets results when you have problems with prop size etc, but first you have to make sure the engine is doing what it did when it was new.
Latestarter1
New member
Around 40% of alleged low power complaints I come across are due to sloppy setting up of Morse throttle controls.
Unless fuel pump lever is hard up against the stop you may be getting NEAR maximum WOT rpm, you will not be getting maximum power. This is the very reason why the manufacturer puts the figure on the spec sheet of a mechanical engine. Taking engine to high idle first on the control lever, then dropping off the ball joint on the linkage and operating the pump lever against the stop can often reveal a difference of several hundred rpm.
In the old days we had break back levers on PT fuel pumps, real simple you adjusted control cable until the spring loaded lever was breaking and you knew that you were getting 100% throttle. Throttle lever not reaching the stop by as little as a few thou can make a big difference in power.
On a slightly different slant remember the poster who took offer on his vessel because it would not make WOT? Turned out to be net around the prop. High idle test would have eliminated the engine. Or the guy with exhaust system full of sea water causing corroded and stuck turbine end of turbo, engine would struggle up to high idle and black smoke even though out of gear, indicating investigation of base engine was required.
Remember only applicable to mechanical motors.
Unless fuel pump lever is hard up against the stop you may be getting NEAR maximum WOT rpm, you will not be getting maximum power. This is the very reason why the manufacturer puts the figure on the spec sheet of a mechanical engine. Taking engine to high idle first on the control lever, then dropping off the ball joint on the linkage and operating the pump lever against the stop can often reveal a difference of several hundred rpm.
In the old days we had break back levers on PT fuel pumps, real simple you adjusted control cable until the spring loaded lever was breaking and you knew that you were getting 100% throttle. Throttle lever not reaching the stop by as little as a few thou can make a big difference in power.
On a slightly different slant remember the poster who took offer on his vessel because it would not make WOT? Turned out to be net around the prop. High idle test would have eliminated the engine. Or the guy with exhaust system full of sea water causing corroded and stuck turbine end of turbo, engine would struggle up to high idle and black smoke even though out of gear, indicating investigation of base engine was required.
Remember only applicable to mechanical motors.
kashurst
Well-known member
thanks for that - I will give it a go next time I'm back at the boat. I will buy a laser rpm tester. I borrowed one in the summer to check out the tacho readings, which I did at 1000 and 2000 rpm and they were both spot on. I suspect they will be at max revs but it will be one more thing off the list to verify. I suspect I have now resolved my problem and I just have a furry bottom but I'm a bit of a perfectionist and like everything properly sorted or at least understood.