Engine only revs out of gear

SimbaDog

SimbaDog

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Pete Bernfeld has a problem with his one remaining engine, it won't rev in gear! can anyone offer help?
Text below is from his latest blog:
In the meantime, a question for you tech types.
The engine will give full revs in neutral. In both forward and reverse I can only get idle rpm. Increasing throttle results in nothing so it isn’t the old transmission problem. Paul had removed debris from the prop and I don’t think he missed anything. The in-line fuel filter is OK, I haven’t checked the engine fuel filter yet but as I can get revs in neutral I don’t think it can be a fuel problem. Anybody got any ideas?

http://blog.mailasail.com/troutbridge
 
Try turning shaft by hand.

SimbaDog said:
Pete Bernfeld has a problem with his one remaining engine, it won't rev in gear! can anyone offer help?
Text below is from his latest blog:
In the meantime, a question for you tech types.
The engine will give full revs in neutral. In both forward and reverse I can only get idle rpm. Increasing throttle results in nothing so it isn’t the old transmission problem. Paul had removed debris from the prop and I don’t think he missed anything. The in-line fuel filter is OK, I haven’t checked the engine fuel filter yet but as I can get revs in neutral I don’t think it can be a fuel problem. Anybody got any ideas?

http://blog.mailasail.com/troutbridge
Click to expand...

Has he tried turning the prop shaft by hand or disconnecting the drive coupling.

If that is ok, look at the single lever control, try puting engine in gear and increase throttle at fuel pump on the engine
 
SimbaDog said:
Pete Bernfeld has a problem with his one remaining engine, it won't rev in gear! can anyone offer help?
Text below is from his latest blog:
In the meantime, a question for you tech types.
The engine will give full revs in neutral. In both forward and reverse I can only get idle rpm. Increasing throttle results in nothing so it isn’t the old transmission problem. Paul had removed debris from the prop and I don’t think he missed anything. The in-line fuel filter is OK, I haven’t checked the engine fuel filter yet but as I can get revs in neutral I don’t think it can be a fuel problem. Anybody got any ideas?

http://blog.mailasail.com/troutbridge
Click to expand...

I'm not an engineer or a mechanic. So what I say might be complete *******s.
Diesel?
With no load diesel will rev up with very little extra fuel required.
The more load the more fuel required to increase revs.
Check and eliminate the simple stuff first.
Lots of fuel in tank.
Your throtle leaver and cable are conected and not sticking.
Your shut off cable is not sticking or stuck partialy closed.
Fuel filters ok.
Air filter clean.
fuel pump? is pumping

You have already checked prop is clear?

Does it sound different in gear out of gear? is it struggeling?
Smoke, is it blacker in gear? or just the same.?
 
SimbaDog said:
Pete Bernfeld has a problem with his one remaining engine, it won't rev in gear! can anyone offer help?
Text below is from his latest blog:
In the meantime, a question for you tech types.
The engine will give full revs in neutral. In both forward and reverse I can only get idle rpm. Increasing throttle results in nothing so it isn’t the old transmission problem. Paul had removed debris from the prop and I don’t think he missed anything. The in-line fuel filter is OK, I haven’t checked the engine fuel filter yet but as I can get revs in neutral I don’t think it can be a fuel problem. Anybody got any ideas?

http://blog.mailasail.com/troutbridge
Click to expand...

This is an interesting problem.
So she revs fine until put under load hum hum hum !!!! ................Air Filter ???
 
Many years ago on a friend's boat we had exactly these symptoms, due to filter blockage by diesel bug. We were in Portpatrick, engine ran fine unloaded inside the harbour but would not rev at all trying to leave. Changing filters several times until it was clear fixed it.

Later, we bought an old diesel van for our son. Driving back down the M6 from Blackpool we were limited to 30 mph! Problem was a fouled fuel filter, once replaced it ran fine.
 
Rope around the prop or shaft? Bent shaft? Destroyed cutlass bearing, debris packed between prop and sterntube or p bracket.

As someone has said can the shaft be rotated by hand? ( engine off, gearbox in neutral just for safetys sake )
 
Very possibly a delaminated exhaust pipe. It happens if the exhaust (rubber) overheats at some time previous due to loss of cooling water then the internal layers come adrift & act as a valve increasing back pressure which stops the engine revving in gear as there is not enough volume remaining to evacuate the higher volume of gas when the engine is under load. Revving free does not increase the volume to the same degree. It cannot be detected externally usually.

John Lilley
 
johnlilley said:
Very possibly a delaminated exhaust pipe. It happens if the exhaust (rubber) overheats at some time previous due to loss of cooling water then the internal layers come adrift & act as a valve increasing back pressure which stops the engine revving in gear as there is not enough volume remaining to evacuate the higher volume of gas when the engine is under load. Revving free does not increase the volume to the same degree. It cannot be detected externally usually.

John Lilley
Click to expand...

Does an engine at 2000rpm not produce the same gas and water volumes into the exhaust regardless of being in or out of gear?
 
The quick answer is no, when you blip the accelerator on a car engine when it is out of gear it revs up to maximum at very low travel on the pedal but when in gear & under load you could use maximum travel & still not over rev the engine but the volume of exhaust gas created is considerably more than when running free.

John
 
johnlilley said:
The quick answer is no, when you blip the accelerator on a car engine when it is out of gear it revs up to maximum at very low travel on the pedal but when in gear & under load you could use maximum travel & still not over rev the engine but the volume of exhaust gas created is considerably more than when running free.

John
Click to expand...

I would have thought that the volume of exhaust gas produced per minute could be found by multiplying the total swept cylinder volume by the revs/minute and dividing the answer by 2 (since it's a 4 stroke). I can't see how load comes into it, but please explain what I'm missing.
 
DaveS said:
I would have thought that the volume of exhaust gas produced per minute could be found by multiplying the total swept cylinder volume by the revs/minute and dividing the answer by 2 (since it's a 4 stroke). I can't see how load comes into it, but please explain what I'm missing.
Click to expand...

That would be true if it was a compressor! Liquid fuel is burnt to gaseous exhaust with a massive expansion rate. If it didn't an engine would not work.
 
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