Isuzu - Borg-Warner

[straban]

[warmrain]

[mimoza]

[warmrain]

[straban]

Thanks for the responses and I suppose I wasn't as clear as I could have been. The engine is installed in a HC43. The engine does run to full rated RPM without load, which is 2900 RPM but under load my engine guy, Klassen Diesel, says I should be getting 2700 under load with the specified reduction/prop combination of 3:1 and 22/16. I get 2100 and at that there is a little black smoke but hardly anything to be concerned about. Just to him it seems too low. The boat runs just around 7 kts at that RPM and I of course don't push it that hard.

Anyway, the RGB is missing its dataplate so I am faced with finding an alternative way to determine the ratio. Perhaps borrowing a tach strobe from my A&P and doing that way, although a rather inelegant solution.

Dave
HC43 Ketch

[warmrain]

So if it runs to rated RPM w/o load then it is not a governor or max RPM limiter issue. It is either a weak engine (lack of compression or the like) or an improper reduction OR prop. There really shouldn't be any black smoke in my opinion, and also I think that it should run to red line in gear (with the boat moving - not tied in the slip).

If the engine will not run to its designed max continuous RPM in gear the reduction OR the prop. If it won't go to max continuous RPM in gear then you are not developing the horse power the engine is designed to deliver, and that horse power you may someday wish you had.

~Cars

[mimoza]

Hi Dave,

Just for your peace of mind, you ~should~ "push it that hard." Even if black smoke pours out of the exhaust. You want to know how your setup will behave in extreme conditions. That's what this is all about. You won't break any components by running full throttle under load. Diesel engines are remarkably strong, and if something ~does~ give, it's far better for it to give when you are in no real danger than when you are being pushed onto a lee shore.
So.... Speaking of full throttle, is your throttle in good adjustment? It may be quite easy to reach 2900 (or 3000 as my research suggests) with no load, but is there any room left in the throttle? Or is it pegged? And why didn't I think of this sooner? Must be Oldtimer's Disease.
Sometimes a stretched throttle cable will mean that you can't open it up all the way. Check that first. It's a really easy thing, and in my experience, the easy and simple things are very often the issue.

Okay, your throttle cable has been adjusted.

The C240 is rated at 56HP @ 3000 rpm. Based on that and the additional data you provided, there may be problem with your engine. But before we jump to that conclusion, lets look at the prop and the gearbox.

The prop seems right. Michigan Wheel delivers the 22x16 size as a standard prop. It moves my HC 33 very well at 6.5 knots without cavitating. It is a very good prop for 700 to 850 rpm or thereabouts, and is perfectly suited for the speed range we run in.

The gearbox: Based on the prop and the rated engine HP and rpm, the reduction ~should~ be very close to 3:1. This would allow both your prop and your engine to work at maximum efficiency.
So we need more data. You should be able to figure out the reduction ratio.
Can you crank that engine without starting it? As in keeping the throttle in the "kill" position, or releasing the compression? (How you do this depends on the engine design...)
You might need an assistant. Just paint a little white dot on the crank pulley, and another on the shaft. Note the positions. Have your assistant watch the shaft while you watch the pulley. Crank the engine while in gear for, say, 15 or 16 revolutions. If the shaft goes around about five times, then you have a 3:1 reduction.
Note that standard gearing design does not have an exact 3:1 ratio. Otherwise you would have the same tooth fitting into the same three slots forever, promoting uneven wear. It is more likely that there would be something like 10 teeth and 31, giving a 3.1:1 ratio. 15 engine revs would give you 4.84 shaft revs and 16 engine revs would give you 5.16 shaft revs.
If you are getting something between 6 & 8 shaft revs for those 15 or 16 engine revs, then your gearbox may not be the right one. A lower reduction ratio like 2:1 would run the prop too fast, forcing the engine to work harder at a lower rpm, and preventing it from reaching designed output.

However, if the reduction ratio is 3.1:1 then you could very well have a weak engine, and that would be a topic for another day.

Let us know what you find. But be sure to check that stretchy throttle cable first.

[straban]

Thanks again for the responses, and I especially like the way to determine the ratio ... in fact it should be 2.98:1 or something like that.

I have indeed checked the throttle, actually the stop on the injector pump, to make sure it was hitting the stop, which it is. Soooo, I´ll confirm the ratio and go from there. I did speak with a marine engine specialist who seems to think that I am in the ball park and thinks that the prop is within an inch of where the pitch should be for that ratio so it leads me to think that I may be looking at an engine swap. Not bad insurance in the long run for a little over $5000 seeing that I am hoping to head offshore within the year.

Will report back with my findings soon as I am about to install a Max-Prop and I´ll pitch it a little less and see what kind of RPM I can get.

dave