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Old 25-01-2020, 21:18   #1
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Nanni Diesel (14hp) will not rev in reverse gear

Hi ..

When I put the engine into forwards gear it engages and revs through full range. Idles nicely. But when I engage reverse gear It just remains at the same revs (although the throttle lever on the engine appears to move as it would in forward gear).

Does anyone have suggestions on how to trouble shoot this? WOuld it be a gear box problem? There is a clunk when gears (especially reverse are engaged - I have a 2 blade folding prop)

Alby
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Old 25-01-2020, 22:53   #2
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Re: Nanni Diesel (14hp) will not rev in reverse gear

when you engage reverse, does the shaft turn?

Jim
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Old 26-01-2020, 06:17   #3
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Re: Nanni Diesel (14hp) will not rev in reverse gear

Hi Jim,

Yes, the shaft turns in reverse - actually, the thrust is enough to pull the boat backwards out of the marina berth but I cannot regulate the speed at all. So, it would be hard to pull the boat up to a stop from going forward. Cant do a burst of reverse to stop forward motion quickly - eg when coming into a marina berth.
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Old 26-01-2020, 07:09   #4
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Re: Nanni Diesel (14hp) will not rev in reverse gear

If you have a single lever control (throttle and shift use the same lever), I'd guess the problem is in the control box. Or perhaps we need a more complete description of the problem.

As for troubleshooting, take the control out of the equation; disconnect it at the gear and engine, and operate the shift and throttle at the engine and transmission whilst tied firmly to the dock,
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Old 26-01-2020, 10:59   #5
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Re: Nanni Diesel (14hp) will not rev in reverse gear

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Originally Posted by jimbunyard View Post
If you have a single lever control (throttle and shift use the same lever), I'd guess the problem is in the control box. Or perhaps we need a more complete description of the problem.

As for troubleshooting, take the control out of the equation; disconnect it at the gear and engine, and operate the shift and throttle at the engine and transmission whilst tied firmly to the dock,
Great answer, Jim. I think the issue is that you have a single lever control that does not provide throttle to the same degree in FWD and REV. Not sure how this would happen, but many of the single lever controls are surprisingly complicated.

I would state the troubleshooting slightly differently.
  1. Remove the throttle cable from the injection pump so that you can move it manually. It would be best of the throttle naturally returns to idle when you release it.
  2. Use the current level to switch gears. Make sure the boat is immobilized with spring lines...
  3. Engage forward gear and use the throttle to test your theory (engine increases in revs and propeller appears to be turning faster and slower).
  4. Engage reverse gear and see if the throttle on the engine increases the revs and the prop shaft appears to be turning faster and slower.

If this is what happens, then it could be that the single lever control is damaged internally, but I can't see how an adjustment would resolve the problem alone.

If the throttle on the engine can't increase the revs when manually pressed, then I don't have the foggiest idea what's happening.

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Old 26-01-2020, 11:39   #6
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Re: Nanni Diesel (14hp) will not rev in reverse gear

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Originally Posted by Alby66 View Post
Hi ..

When I put the engine into forwards gear it engages and revs through full range. Idles nicely. But when I engage reverse gear It just remains at the same revs (although the throttle lever on the engine appears to move as it would in forward gear).

Does anyone have suggestions on how to trouble shoot this? WOuld it be a gear box problem? There is a clunk when gears (especially reverse are engaged - I have a 2 blade folding prop)

Alby
Sounds to me like a simple case of a broken reverse throttle cable. Have someone watch at the engine when you pull it in reverse and see if the throttle moves.

Al, S/V FInlandia
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Old 26-01-2020, 13:02   #7
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Re: Nanni Diesel (14hp) will not rev in reverse gear

Quote:
But when I engage reverse gear It just remains at the same revs (although the throttle lever on the engine appears to move as it would in forward gear).
this statement from the OP seems to rule out the control cable suggestions made in the last few posts.

But I'd still do the suggested experiment with the cable disconnected, just to be sure that the movement is indeed normal.

Jim
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Old 26-01-2020, 13:29   #8
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Re: Nanni Diesel (14hp) will not rev in reverse gear

With the engine off, put it in fwd gear and full throttle. Look closely at the throttle, maybe mark it if you need to.
Then put it in reverse and full throttle, the throttle arm should move just as much as it did in Fwd, it may help for you to watch as someone else does it.

The engine does not need to be running
The bane of single lever controls is that some are quite complex.
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Old 26-01-2020, 13:36   #9
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Re: Nanni Diesel (14hp) will not rev in reverse gear

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Originally Posted by a64pilot View Post
With the engine off, put it in fwd gear and full throttle. Look closely at the throttle, maybe mark it if you need to.
Then put it in reverse and full throttle, the throttle arm should move just as much as it did in Fwd.
Sounds like the best test yet to me. Give it a try and let us know what happened.

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Old 26-01-2020, 13:38   #10
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Re: Nanni Diesel (14hp) will not rev in reverse gear

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Originally Posted by svfinlandia View Post
Sounds to me like a simple case of a broken reverse throttle cable. Have someone watch at the engine when you pull it in reverse and see if the throttle moves.

Al, S/V FInlandia
Surely most throttles use the same cable for increase revs in forward and reverse, then a second cable to the gearbox to select forward or reverse. Should look something like this inside:

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Old 26-01-2020, 14:57   #11
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Re: Nanni Diesel (14hp) will not rev in reverse gear

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Surely most throttles use the same cable for increase revs in forward and reverse, then a second cable to the gearbox to select forward or reverse.
I donít know what I was thinking. I have a pilothouse motorsailer that has dual Helms. Therefore it has two Morse Controls and if one cable breaks I can lose engine control, but still be able to engage reverse gear.
I still think it would be a good test though to have someone watch the gears and throttle tables while someone else works the Morse control.

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Old 26-01-2020, 15:01   #12
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Re: Nanni Diesel (14hp) will not rev in reverse gear

Do you have some kind of feathering prop? It may not be pitching correctly in reverse.
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Old 26-01-2020, 15:11   #13
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Re: Nanni Diesel (14hp) will not rev in reverse gear

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Originally Posted by Alby66 View Post
Hi Jim,

Yes, the shaft turns in reverse - actually, the thrust is enough to pull the boat backwards out of the marina berth but I cannot regulate the speed at all. So, it would be hard to pull the boat up to a stop from going forward. Cant do a burst of reverse to stop forward motion quickly - eg when coming into a marina berth.
When you say you can't regulate the speed in reverse, what is the speed (rpm) when you do select reverse?

Normally it would be at idle until you advance the throttle but it sounds like it may be higher than idle from your description.

Said another way, what is the reverse rpm you are experiencing?
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Old 26-01-2020, 20:52   #14
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Re: Nanni Diesel (14hp) will not rev in reverse gear

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Originally Posted by svfinlandia View Post
Sounds to me like a simple case of a broken reverse throttle cable. Have someone watch at the engine when you pull it in reverse and see if the throttle moves.

Al, S/V FInlandia
I second this idea. One of my boats has a single lever control. I have a problem and when I took it apart I discovered that there were indeed two cables attached to one lever.
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Old 27-01-2020, 13:05   #15
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Re: Nanni Diesel (14hp) will not rev in reverse gear

I had a similar problem. As odd as this sounds, the problem was the solonoid controlling the fuel cutoff was out of adjustment and would open the lever about 90 percent. I guess reverse needs 100 percent. Problem was driving me crazy. It was just not obvious until I looked carefully at the cutoff lever.
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