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Old 03-09-2007, 08:40   #1
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My Perkins Prima engine only goes at 2000rpm

Hello,

When I have the lever in nuetral, the engine will go up to 4000rpm
but when driving the boat forward, it will only reach 2000 rpm.

My engine is a Perkins 500 series (Prima I think) and is 2 lt with turbo rated at 80hp.

I dont know if the turbo is working - not sure how to check either - but I wanted to know if these revs are "normal".

My boat is a 13m 8 tonne wooden cruiser, The engine has not done a lot of hours ( about 100 ) so it should not be worn out. Could be its not working properly - ... OR maybe this is normal.

Please let me know what you think.

Thanks
David.
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Old 03-09-2007, 09:14   #2
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Check your running gear and prop. $5 says it's full of growth.

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Old 03-09-2007, 15:25   #3
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Depends on bottom condition, hull configuration, vessel displacement, prop size and pitch, type of prop, type of transmission and mechanical condition of engine. Low hours on a diesel = engine problems.
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Old 03-09-2007, 16:54   #4
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Don't bet that the RPM Gage is correct. They do go bad. Get a scope on the fly wheel and measure the the rpm's. If you have growth on the prop you could be in trouble. It makes the shaft unbalanced and can cause lots of problems too. Make sure of the dumb stuff before you go to the expense of a compression test.

You said Perkins "Prima" are you sure it's not "Perama". These were marinized Detroit Diesel engines that were re branded by Perkins here in the US. I have a 35 hp.
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Old 03-09-2007, 17:06   #5
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Dave hasn't been back in the water long enough for Growth to be an issue. Everything should be clean as a wistle underneath.

Dave, I would expect you shoudl be able to hear a slight wistle as the turbo winds up. I also doubt the engine would run very well. Normaly if the turbo is not spinning, the engine is being mightly over fueled and large quantities of black smoke are often produced.
I would imagine you need to look at propellor pitch. It sounds like you have to much pitch.
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Old 03-09-2007, 22:08   #6
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Check for proper movement of throttle lever....I had a Perkins Prima a coupla months ago that exhibited the same symptoms. The throttle cable was damaged.

Also look at your fuel filters....and air restrictions.
If you can get a hand held tach use it. As another poster said, tachs can be unreliable.

If you need a good person to talk to Sheri Moon at Transatlantic Diesel migh be able to help. TAD for perkins engines, perkins diesel, perkins marine, perkins parts, perkins generators, perkins service
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Old 04-09-2007, 01:21   #7
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I whole hartedly agree with getting the RPM checked with a digital tach. However, if the current Tacho is registering higher RPM when the engine is out of gear, I suspect the engine is reving up much higher. The tach maybe out, but I suspect not that much in this case. Same woudl go with fuel filters and restrictions and blah blah. I doubt the engine will rev to full RPM in or out of gear. The throttle cable is yet another. Because the engine is speed governed, the RPM range would be similar in or out of gear. So once again, I suspect the issue is prop.
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Old 05-09-2007, 00:23   #8
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How fast is the boat going at 2,000 RPM and is the engine smoking?
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Old 05-09-2007, 03:03   #9
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Thanks for the replies.

Took a look at the prop and I was pretty annoyed to see that it had nylon string all over it. I saw this nylon string foating in the water a few days ago and thought that I'd fished it all out. Either I missed a pretty long length or some more got chucked into the sea !

Anyway, I dived underneath with a saw and wire cutters some 15 times and managed to get pretty much all of it off.

I hope that it hasn't done any damage to the engine. The engine was blowing black smoke for about 15 minutes - I guess it was struggling - but I didn't notice anything else.

I assume that the string was acting as a brake - but it shouldn't be any worse than when a heavy truck is going up hill - the engine just has to work a bit. Well I hope thats the case.

I ran the engine today, and it sounded fine - no black smoke. As we are going away for a week and I have just tied her up, I will not be able to test her on the water until I get back.

When I get back, I will try and hear if there is a whistling sound at all.
I recently replaced all the fuel filters and got rid of the air.

Cheers
Dave.
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Old 05-09-2007, 04:03   #10
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Dave - Working on the boat never ends! Sounds like you found at least one problem. Let us know what happens next!

Depending on the size and amount of nylon that could be it. Low RPM in gear and black smoke is a definite indicator that the engine is trying to work too hard - i.e. has too much load for the available torque/horsepower.

BTW - I found this website earlier but didn't post it. It could be a source of parts and advice for you if you need it. Looks to be a professional outfit in France.

SECODI / PERKINS : PARTS - Prima / 500 Series - m80T=
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Old 14-03-2008, 10:10   #11
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Dave, I have exactly the same problem on my Perkins prima m60
It does not run above 2300 prm but run at 4000 rpm in neutral.
did you solved your problem?
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Old 14-03-2008, 15:17   #12
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I had my prop fouled so bad this summer that I couldnt get above 1800 rpm on my 4.236, i was actually getting worried when we brought it to the dock to get scraped, but it was fine afterwards.
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Old 18-03-2008, 09:56   #13
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looks like some folks owe SvHyLite a $5 fee .... haha, think what a mechanic would have charged you !

PS no i am not working on commission.
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Old 20-03-2008, 10:19   #14
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Hello all,
I am a newby to this forum.
I am contemplating the purchase of a sailboat with a Perkins Prima 50 with about 2500 hours.
I have seen some negative reports.
The boat wold not be a good buy if it required a re-engine.
Can anyone share their knowledge and experience.
Thanx,
Mike
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Old 20-03-2008, 11:20   #15
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Mike,

Welcome. All engines have negative reports. Perkins has a lot of them mostly because it is one of the most widely used having been in use a very long time. For a well cared for engine 2500 hours is not old at all. Not even middle aged really. If the boat required a new engine it may not be a good deal.

One thing you can get with any sail boat engine is built up carbon in the exhaust manifold. It's mostly from running a long time at low rpm's. Sail boat owners tend to do that more often. If you want to spend the money to replace the seal pulling the exhaust manifold isn't a bad thing to check on a sail boat engine.
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