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Old 08-02-2016, 15:08   #16
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Re: Differing revs in fwd and reverse

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Originally Posted by Warby12 View Post
[*]I have just checked the throttle linkage and it's correct My wife actuated it from the cockpit and I watched on the engine and it reached the same point on the injection pump in neutral and in both gears.
Still could be the linkage or the throttle cable. Remove the throttle cable from the engine and move the lever by hand. You should easily hit max rpm (4000?)
in neutral. The point you saw it reach could be short of the stop.

No sense worrying about the prop unless the engine hits its maximum rpm in neutral.
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Old 08-02-2016, 19:55   #17
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Re: Differing revs in fwd and reverse

G'day,
Perkins 4.108 motors have to be Marine special order, Ag or Transport spec engines to 4,000 high idle. To advice someone to max out an engine without knowing the Maintenance & service history of unit is being careless!!

If you want to make contact. 43southdiesel@gmail.com
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Old 09-02-2016, 03:00   #18
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Re: Differing revs in fwd and reverse

Typically the Perkins 4.108 comes with a hurth gearbox 2.25:1 (sometimes with 2.01:1).

Correct prop diameters for that engine are the following:

if 2.25:1 prop diam 17"
if 2.01:1 prop diam 16"

If your prop is larger than this you are overpropped.

Cheers !


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Originally Posted by Warby12 View Post
Wow! Thanks all

So it is not abnormal to have different speed

Coming out of the water today for a new shaft seal and I will go all over this prop.
  • It may be over pitched, I will check. (thanks for that link Deblen!)
  • The prop can be setup for left and right turning shafts so need to check this too (ours is left).
  • The boat is new to us so I can't say if it's a new problem.
  • It definitely blows blue smoke when pushed hard (not black which is more likely with over pitching, yes?)
  • Hull moderately dirty but the prop itself was scraped clean last last week
  • I have just checked the throttle linkage and it's correct My wife actuated it from the cockpit and I watched on the engine and it reached the same point on the injection pump in neutral and in both gears.
  • I didn't push the revs all the way in neutral as I didn't know the safe limit, I will see if it hits 4000 today.
  • Yes I wrote the revs wrong by a factor of ten sorry.
If no luck, I'll look deeper. Blue smoke and low power might indicate worn rings?


I did report some issues with this in an older thread but that turned out to be dirty fuel making the engine race. identifying the transmission was impossible Identifying a Hurth (I think) Gearbox


Thanks enormously everyone. We want to go cruising in a few weeks and 2.5 knots max speed in flat water is just plain unsafe
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Old 09-02-2016, 13:59   #19
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Re: Differing revs in fwd and reverse

Hi all, Continuing thanks

We have a propulsion guy coming this morning at 8. I was able to get a good recommendation on someone. Not as clever as you guys but local
On the phone he said sounds like overpitched because of the low revs in gear and smoke. I thought blue smoke was engine oil but we shall see today. He said becasue of the low revs it would be like trying to drive a 15 ton boat with 17 hp . This would explains my grey hair. We will run the engine in the yard and since we have no idea of our transmission he is going to check the reduction speed and reconfirm the prop size and pitch

Fingers crossed we can solve the problem with the lower range of trouble and expense but whatever happens we need a lot more power.

Re the throttle and linkage I have checked it from top to bottom but I will cover that this morning with him too.

Let you know how we go
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Old 09-02-2016, 15:06   #20
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Re: Differing revs in fwd and reverse

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Originally Posted by Warby12 View Post
Hi all, Continuing thanks

We have a propulsion guy coming this morning at 8. I was able to get a good recommendation on someone. Not as clever as you guys but local
On the phone he said sounds like overpitched because of the low revs in gear and smoke. I thought blue smoke was engine oil but we shall see today. He said becasue of the low revs it would be like trying to drive a 15 ton boat with 17 hp . This would explains my grey hair. We will run the engine in the yard and since we have no idea of our transmission he is going to check the reduction speed and reconfirm the prop size and pitch

Fingers crossed we can solve the problem with the lower range of trouble and expense but whatever happens we need a lot more power.

Re the throttle and linkage I have checked it from top to bottom but I will cover that this morning with him too.

Let you know how we go
Just as a PS. The forward and reverse reduction is not necessarily the same? I replaced forward gears on a Twin Disc. crash box The nice guy that I got the gears from said reverse is often times not changed. All he had to lose was selling me more gears.
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Old 09-02-2016, 20:20   #21
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Re: Differing revs in fwd and reverse

Hi again

Propulsion guy has just been! David O'Shea in Brisbane, very happy
He said the prop is too big (diameter) for the engine. We ran the engine in the yard and he worked out the reduction of the transmission 1 to 1.7 and what prop should be in there. He adjusted the J-Prop to less pitch but said if this is still too much when back in the water there is room for one more reduction in pitch before it's time to start trimming the blades and put the pitch deeper again.

He also said on the Perkins 4018 I should be looking for max power at 3200 to 3500 revs.

Thanks again everyone for all of the help. Now it's onto removing the Vetus Flexible coupling which is seized on, may require another thread

Once it's off should I replace it with another fexible coupling or can I just buy a plan coupling off the shelf, Will it need to be machined?
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Old 10-02-2016, 03:45   #22
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Re: Differing revs in fwd and reverse

Quote:
Originally Posted by Warby12 View Post
Hi again

Propulsion guy has just been! David O'Shea in Brisbane, very happy
He said the prop is too big (diameter) for the engine. We ran the engine in the yard and he worked out the reduction of the transmission 1 to 1.7 and what prop should be in there. He adjusted the J-Prop to less pitch but said if this is still too much when back in the water there is room for one more reduction in pitch before it's time to start trimming the blades and put the pitch deeper again.

He also said on the Perkins 4018 I should be looking for max power at 3200 to 3500 revs.

Thanks again everyone for all of the help. Now it's onto removing the Vetus Flexible coupling which is seized on, may require another thread

Once it's off should I replace it with another fexible coupling or can I just buy a plan coupling off the shelf, Will it need to be machined?

Congrats on solving low rev problem.

Flex coupling or not? These are used for two reasons:
1. Allows for a bit of engine movement on it's flex mounts without bending shaft out of alignment & makes a more quiet drive line.
2. Should break before transmission or some other expensive component does if prop hits something or gets wound in rope,nets,etc.

If you remove it,do you have enough excess shaft length o make up for it?

Flex couplings are an option-not a requirement,so it will be your choice.

Since you will be removing old flex coupling regardless,plan on checking your engine-shaft alignment,motor mounts,cutless bearing,etc.

Here is a link to Maine Sail's excellent tech articles on a variety of things including shaft coupling machining & fitting,etc-good reading & reference.

Welcome To MarineHowTo.com Photo Gallery by Compass Marine How To at pbase.com

& Cox Engineering of UK

https://coxengineering.sharepoint.co...Couplings.aspx

Cheers/ Len
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Old 10-02-2016, 12:57   #23
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Re: Differing revs in fwd and reverse

Hi Deblen and all, I've got most the coupling off. Just the pin which is driven into it. Weird system this vetus flexible. The end of the pin has broken off so considering options
Not enough on this shaft to cut it all off, maybe the coupling alone if I cannot get the pin out.
The fun! The fun!
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