engine swap need to find right prop

[horse_power]

Hi all Jim here I am a brand new member. I would really appreciate some advice. I have a Bayliner Classic 242. I removed the 5.7l V8 and fitted a 120HP Mercruiser diesel with Alpha one out drive. It is for the river so I do not need to be getting high speed. 6 to 8 knots at about 3k revs would be perfect. The maximum revs of engine is 4400 rpm. I currently have a 15x17 prop on it. I can travel at 2 knots max and the engine rpm only goes to 2500. Boat feels like its bogging down and only reaching 4psi on boost gauge so turbo cannot kick in. My limited knowledge tells me the wrong prop is on the boat. As this is not a factory combination of engine and boat how can I calculate the correct prop or can someone tell me the correct prop to achieve the performance I am looking for. Thanks for taking the time to read this.

 

[tpenfield]

I would go down a couple of increments on the pitch . . . so maybe a 15(dia) x 13(pitch)

15" diameter is actually a fairly big prop, so you should be much lower on the pitch. So, maybe even 11" pitch.

Your situation reminds me of when I had one dead engine on my twin engine boat. I tried running on one engine (330 HP), but could only go about 7 mph and the engine would bog at 2500 RPM. So, it seems when there is way too much boat for the amount of power, the engine cannot achive its normal 'specs' of performance.

 

[Scott Danforth]

the bayliner 242 is a way bigger boat than any of the 120hp diesels would have been fitted to. my guess is there is not enough motor to get the boat out of the hole and its just struggling.

did you reuse the alpha drive from behind the 5.7? because if so, you need different gearing. the diesel needs 2:1 gear ratio. the 5.7 had 1.47:1

 

[Bondo]

Hi all Jim here I am a brand new member. I would really appreciate some advice. I have a Bayliner Classic 242. I removed the 5.7l V8 and fitted a 120HP Mercruiser diesel with Alpha one out drive. It is for the river so I do not need to be getting high speed. 6 to 8 knots at about 3k revs would be perfect. The maximum revs of engine is 4400 rpm. I currently have a 15x17 prop on it. I can travel at 2 knots max and the engine rpm only goes to 2500. Boat feels like its bogging down and only reaching 4psi on boost gauge so turbo cannot kick in. My limited knowledge tells me the wrong prop is on the boat. As this is not a factory combination of engine and boat how can I calculate the correct prop or can someone tell me the correct prop to achieve the performance I am looking for. Thanks for taking the time to read this.

Ayuh,.... Welcome Aboard,..... I don't think they make props as small as Ted mentions, so you'll need a different gear ratio as Scott says,....

 

[Scott06]

Agreed you need a different ratio drive. You can swap just the upper to a 1.98 /2.00 that the 3.0 used, Merc also makes a 2.40 drive but I think you need the whole drive as lower gears are different too.

Would think if you went from the 1.47 drive that was likely in there to a 1.98 you would probably see a lift of 1200 rpm

 

[QBhoy]

Hi. Great comments above. Won’t add to that…
But what I will say, is that this 1.7 diesel engine you have now…is fast on its way to rival the horrid old 3.7l that mercruiser dabbled with, producing disastrous consequences.
Although a great wee engine in the many small cars and vans it powers here in Europe (based on an Isuzu GM), alas, some engines just don’t have the same success, when used in the marine world.
These particular things are now famous for turbo issues, turbo elbow issues (might arguably be consumable parts) and throwing the odd broken timing cam belt at you, destroying the engine at the same time. Even when the suggested replacement interval is followed. Known a good few of them locally here. Mainly in regal bowrider boats and some fishing boats. Powerful when they are working…but the one I know of that hasn’t had issues just yet…is a rare thing. They really need to be in the right application and crucially…propped well and working hard. What you want to do, is likely just about the worst possible exposure, most likely to cause issues. They need to be pitched to allow the turbo to come on boost, but also finely enough to allow their higher rpms seen regularly. Change the timing belt in half the interval suggested and under careful visual inspection too. Can’t tell you how well known or common it is for the belt to fail.
Personally I’d have thought you better with a 3.0 Petrol equivalent perhaps. Just far more robust and you can run them at any rpm or speed you like, in the lower range.

 

[airshot]

They are turning diesel engines at 4400 rpm ???

 

[QBhoy]

They are turning diesel engines at 4400 rpm ???

Yeah. Unusually high for an oil burner eh. High revving engine used in vans and small cars over here. Need to be worked hard in marine world to keep them working as long as possible. That’s not usually too long though…unfortunately. The belt snapping or the turbo spewing it’s turbine towards the engine…usually put an early end to things.

 

[horse_power]

I would go down a couple of increments on the pitch . . . so maybe a 15(dia) x 13(pitch)

15" diameter is actually a fairly big prop, so you should be much lower on the pitch. So, maybe even 11" pitch.

Your situation reminds me of when I had one dead engine on my twin engine boat. I tried running on one engine (330 HP), but could only go about 7 mph and the engine would bog at 2500 RPM. So, it seems when there is way too much boat for the amount of power, the engine cannot achive its normal 'specs' of performance.

Thanks very much for the info

 

[horse_power]

Hi. Great comments above. Won’t add to that…
But what I will say, is that this 1.7 diesel engine you have now…is fast on its way to rival the horrid old 3.7l that mercruiser dabbled with, producing disastrous consequences.
Although a great wee engine in the many small cars and vans it powers here in Europe (based on an Isuzu GM), alas, some engines just don’t have the same success, when used in the marine world.
These particular things are now famous for turbo issues, turbo elbow issues (might arguably be consumable parts) and throwing the odd broken timing cam belt at you, destroying the engine at the same time. Even when the suggested replacement interval is followed. Known a good few of them locally here. Mainly in regal bowrider boats and some fishing boats. Powerful when they are working…but the one I know of that hasn’t had issues just yet…is a rare thing. They really need to be in the right application and crucially…propped well and working hard. What you want to do, is likely just about the worst possible exposure, most likely to cause issues. They need to be pitched to allow the turbo to come on boost, but also finely enough to allow their higher rpms seen regularly. Change the timing belt in half the interval suggested and under careful visual inspection too. Can’t tell you how well known or common it is for the belt to fail.
Personally I’d have thought you better with a 3.0 Petrol equivalent perhaps. Just far more robust and you can run them at any rpm or speed you like, in the lower range.

Thanks for your reply. It is what it is If I can get 5/6 knots out of it without thrashing it to death it will serve my purpose

 

[horse_power]

the bayliner 242 is a way bigger boat than any of the 120hp diesels would have been fitted to. my guess is there is not enough motor to get the boat out of the hole and its just struggling.

did you reuse the alpha drive from behind the 5.7? because if so, you need different gearing. the diesel needs 2:1 gear ratio. the 5.7 had 1.47:1

I bought the engine and outdrive so it has the 2/1 gearing

 

[Scott06]

I bought the engine and outdrive so it has the 2/1 gearing

I think you are going to run out of available lower pitch props, so would look to get the 2.4:1 ratio drive, then play with props

 

[Scott Danforth]

Thanks for your reply. It is what it is If I can get 5/6 knots out of it without thrashing it to death it will serve my purpose

idle speed is 4-5 knots. so you are there.

Just dont try to climb the hole, as you dont have enough motor

 

[Scott Danforth]

They are turning diesel engines at 4400 rpm ???

and much higher

the diesel the OP is mentioning is either Isuzu or VW (TDI) would need to have specs to verify the VAG diesels will spin nearly 5200 RPM

 

[QBhoy]

and much higher

the diesel the OP is mentioning is either Isuzu or VW (TDI) would need to have specs to verify the VAG diesels will spin nearly 5200 RPM

It’s the GM/Isuzu Scott. Spot on.

 

[QBhoy]

and much higher

the diesel the OP is mentioning is either Isuzu or VW (TDI) would need to have specs to verify the VAG diesels will spin nearly 5200 RPM

It’s the GM/Isuzu Scott.

Thanks for your reply. It is what it is If I can get 5/6 knots out of it without thrashing it to death it will serve my purpose

I suppose what I might be getting at…is that running that particular engine at low rpms, not on boost or properly set up…won’t be too clever an idea. It will absolutely not be running as designed. Will be over fuelling and not combusting properly. Will almost certainly cause issues at some point in the future. Carbon deposits blocking valves, exhaust elbows and exhaust turbine side of the turbo. Running temperature will be lower than designed perhaps and the engine not getting to the design conditions to run efficiently or effectively. She’ll throw unburnt fuel down past her piston rings, wash the bores, lose compression at best, then usually end up lubricated by diesel diluted oil in the sump. Never a good situation at its worst case. Sorry to be pessimistic perhaps. But all a true story and frequent cause of failure with engines such as these.

 

[QBhoy]

Thanks for your reply. It is what it is If I can get 5/6 knots out of it without thrashing it to death it will serve my purpose

I think you’ll get a prop pitch for her, but urge you to find somewhere you are able to open the throttle up every now and then. Just to clear her out. Sustained low load running ok these engines isn’t good for them at all really. They need worked hard. Just the fundamental operation of any diesel really. As you know…they fundamentally and absolutely require the right conditions, load, pressures and temperatures, for them to create and sustain the compression levels high enough to physically ignite and burn the fuel thrown into them. The mechanical fuelling set up design and function, these engines have, are set up with the assumption that most of the running time and use, will be at rpms over a certain point, enough to spool the turbo, enough to produce a boost pressure sufficient enough to see the fuel/air mixture at a ratio suitable for clean burning. So anything less and not on boost, inherently results in a very overly biased ratio in favour of fuel. Anyway. You get my point. Hope that helps.

 

[airshot]

and much higher

the diesel the OP is mentioning is either Isuzu or VW (TDI) would need to have specs to verify the VAG diesels will spin nearly 5200 RPM

My, that has certainly changed since I last tinkered with them....