Bukh DV36 - Will only reach 1500RPM when in gear

[Michael Siggers]

Hi

 

Hope everyone is well.

 

Just collected my new Narrowboat today and have experienced an issue with the Engine which was not present during the test when i was looking at the boat.

 

The engine is a BUKH DV36 with Skin Tank cooling and raw water for the Exhaust silencing.

 

When I tool the boat for a test, it performed great and the engine revs were no problem.

 

As part of the sale, the engine has been serviced.

 

So, picking the boat today you can imagine I was rather excited.

 

I did have a few incidents where the engine smoked more than what would be considered normal. As a result, I checked the weed hatch and the filter for the exhaust cooling. All OK, although did remove a couple of leaves from the raw water filter. There were quite a lot of leaves on the route.

 

One I got through Willington and past all the moored boats, (quite a few of them), I decided to speed up a touch and took the engine to 1200RPM. This is when I discovered it wouldn't go any further. Pulling over and checking weed hatch and filter again, all seemed OK.

 

Now, the engine revs freely in neutral and it not limited. For.some reason when in gear the maximum throttle is around 1500RPM.

 

Not that I am intending to race everywhere, but this does not seem correct to me.

 

The previous owner is coming out tomorrow to have a look and seems quite embarrassed by it, having sold the boat. 

 

Would just be interested to see if anyone has any ideas. It does seem to be since the engine service, but that was only an oil and filter(s) change.

 

Kind regards

 

Mike

[Tracy D'arth]

Its post purchase problem, always happens when you buy a boat.

See if big foot has trod on a control cable when changing the oil.

Lots of leaves stuck on the prop can do this, and they fall off when you stop so they are not there when you take the weed hatch out.

[Michael Siggers]

Thank you @Tracy D'arth

 

Yes, the control cable is going to be checked. Just odd that it seems OK when in neutral but not when in gear.

 

Mike

[magnetman]

I think the person who serviced it needs to come and have a look as well. Big foot is a good term. 

 

I've seen a lift pump mangled by an engine servicing person. 

 

Does the engine area smell of diesel at all? 

[Tracy D'arth]

Just now, Michael Siggers said:

Thank you @Tracy D'arth

 

Yes, the control cable is going to be checked. Just odd that it seems OK when in neutral but not when in gear.

 

Mike

Not odd at all if the problem is what is on the prop.

[magnetman]

 

 

Neutral does not use as much fuel as when in gear. 

 

To check the transmission line see if you can turn the propshaft by hand. If not then maybe something else on the propeller other than leaves. 

 

 

[Michael Siggers]

Hi @magnetman

 

Not really. Have checked the engine bay and all seems dry. The BUKH manual says this can be caused by a fuel supply issue, so maybe something has been upset when the Services was done.

 

Mike

[magnetman]

Air in the fuel seems a possibility. 

 

@J R ALSOP has a Bukh engine he might know about this. 

[Michael Siggers]

1 minute ago, magnetman said:

 

 

Neutral does not use as much fuel as when in gear. 

 

To check the transmission line see if you can turn the propshaft by hand. If not then maybe something else on the propeller other than leaves. 

 

 

Checked the prop and turns freely by hand. Checked the external shaft for any items as well and could not find any.

 

Mike

1 minute ago, magnetman said:

Air in the fuel seems a possibility

Thank you. Yes, that's what I'm wondering. If fuel filters were changed then maybe its gone slightly awry.

 

Just rather frustrating as you can imagine.

[magnetman]

Also if the lift pump (if there is one) was disturbed perhaps for cleaning during the service it seems possible it could have not gone back together properly resulting in sucking in air. 

 

"I did have a few incidents where the engine smoked more than what would be considered normal. " 

 

That sounds like air in fuel assuming a previous on-load engine test did not reveal any problems. 

 

 

[Michael Siggers]

Thank you @magnetman

 

Much appreciated.

 

So, stupid question of the day.......

 

What is the lift pump?

 

Mike

[magnetman]

Usually a pump on the side of the engine which is mechanically driven and gets fuel to the engine even if the level is too low for gravity to do it. 

 

Sometimes they are electric and some installations don't have them. 

 

 

[Michael Siggers]

And, just thought.......

 

I should check the fuel isolation valves to make sure they are turned on fully?

 

Mike

1 minute ago, magnetman said:

Usually a pump on the side of the engine which is mechanically driven and gets fuel to the engine even if the level is too low for gravity to do it. 

 

Sometimes they are electric and some installations don't have them. 

 

 

OK, thank you. Will make sure that is checked too.

 

Mike

[mrsmelly]

When you initialy took it for a spin did you try to take it over 1500 rpm? It could be prop is a tad big and will not spin faster anyway or as others have said somett on the prop. My DV36 didnt go above around 1500 when I changed the prop up a size or two . Is it a velvet drive box?

[magnetman]

It looks like the lift pump is right up near the injection pump.

Picture of DV36. It is a single piece lift pump so not serviceable but I have seen an almost identical pump on a Beta marine engine where someone had stepped on one of the pipes when climbing down into engine bay resulting in one of the pipes getting a hairline crack. It was all aluminium. One piece unit. Older pumps are positioned in a different place and can be dismantled. 

 

Pump replaced all ok. It is in a position where unless the fuel is above it the symptom would be air drawn in rather than diesel leaked out. 

 

Might not be this exact engine model. 

Edited November 5, 2023 by magnetman

[Tony Brooks]

 I also had a DV36 and on the present info tend to agree with mrsmelly, especially if the smoke occurs when you are trying to get the revs up - classic over prop symptoms. Be aware the DV36 is direct injected and all direct injected diesels with mechanical governors often smoke a bit at low speed and load

[Michael Siggers]

47 minutes ago, mrsmelly said:

When you initialy took it for a spin did you try to take it over 1500 rpm? It could be prop is a tad big and will not spin faster anyway or as others have said somett on the prop. My DV36 didnt go above around 1500 when I changed the prop up a size or two . Is it a velvet drive box?

No, it was the brokerage guy who 'opened her up' and I think I quickly glanced at the ref counter but may have misread it.

 

Interesting about the prop too. Maybe it had a larger one fitted previously. When I put the boat in tick over, it revs at about 400rpm.

 

The name of the drive escapes me as its on my other paperwork which I don't have on me.

 

Mike

59 minutes ago, mrsmelly said:

When you initialy took it for a spin did you try to take it over 1500 rpm? It could be prop is a tad big and will not spin faster anyway or as others have said somett on the prop. My DV36 didnt go above around 1500 when I changed the prop up a size or two . Is it a velvet drive box?

It has an Aquadrive.

 

Mike

[mrsmelly]

5 minutes ago, Michael Siggers said:

No, it was the brokerage guy who 'opened her up' and I think I quickly glanced at the ref counter but may have misread it.

 

Interesting about the prop too. Maybe it had a larger one fitted previously. When I put the boat in tick over, it revs at about 400rpm.

 

The name of the drive escapes me as its on my other paperwork which I don't have on me.

 

Mike

I wouldnt be suprised if its deliberately slightly over propped? My dv36 was fitted to a 65 foot boat that started life for two years as a hire boat with a 15 inch prop. Reason it had a small prop was so it would whizz round and charge batteries as it was hire and didnt go fast but freely revved. I fitted a prop stuck in my spares bin which was iirc a 19inch so whilst it didnt rev it did push boat along well enough on canals where it spent most of its life anyway.  

[magnetman]

Aquadrive is a flexible drive linkage that allows the gearbox output to be higher or lower than the propeller shaft.

 

The gearbox is a different part. 

[Michael Siggers]

6 minutes ago, mrsmelly said:

so whilst it didnt rev it did push boat along well enough on canals where it spent most of its life anyway.  

Yes, I can say that this boat does move very well, so maybe that is the answer. I'll see if I can check/measure what the prop is, size wise.

 

Still want to get the fuel system checked.

 

Mike

[blackrose]

I don't know the area so this may be a stupid question but what was the depth of the water when it wouldn't go above 1200rpm? Since nobody else has mentioned it then perhaps they all know the waterway, otherwise I'm quite surprised this hasn't been mentioned:

 

If you had those issues on a shallow canal then that's probably because there simply isn't enough water available at the prop to produce higher revs 

 

It could be over-propped and I had my prop repitched in order to solve the same problem. However, if you're saying you saw it previously producing more revs in gear when the surveyor was onboard then that's obviously not the issue. 

 

If it was on a shallow canal when you tried it then before you do anything else get it into some deep water and try again. 

Edited November 6, 2023 by blackrose

[magnetman]

Yes good point and combined with autumn leaves it could behave very differently. 

 

I imagine the previous owner coming round will help as they will presumably know how it performs in shallow water.