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Discussion Starter · #1 ·
I am the new owner of a 1984 Sirius 28 sailboat with a Yanmar 1gm and quickly learning the previous owner did very little regular maintenance on the engine. Despite the marine surveyor who stated the boat is in good shape, I have replaced the thermostat, zinc anode, primary and secondary fuel filters, oil filter, air filter, both engine and gearbox oil, seawater intake hoses, seacock, one rusty oil line and checked the exhaust elbow for blockages (none). The hull and prop have been cleaned and I am about to have the packing replaced in the stuffing box. Although this has been a terrific learning opportunity, the engine is still giving me some concerns. The engine starts easily and will reach a max of 3100 RPM in neutral, but only 2400 RPM when in gear which will get the boat up to 6kts. The exhaust is whitish in colour and there appears to be only a low amount of water being expelled from the exhaust, although I do not know what the normal amount should be. Additionally, when accelerating quickly there is a “clanking” noise in the engine compartment – there is no noise if the acceleration is gradual.
I’ve scoured the forums and internet to get some answers to no avail. I am able to perform some fairly basic repairs and would really appreciate any assistance you can provide to identifying potential reasons for the low RPM, whitish exhaust, low exhaust water outflow and “clanking” noise when accelerating quickly.
 

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rod bearings...the clanking happens cause you are loading up the engine...if gradual you arent pushing the engine much

whitish smoke can indicate among other things coolant into oil or viceversa...

there is a very similar thread here with a 2gm with similar issues except for the clanking...
 

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I think your 1gm is raw water cooled. Are you sailing in salt water? You say you replaced the thermostat- this is good. How did the cooling water passages look in the engine when you replaced tha anodes and thermostat? If they looked clogged, you can do an acid flush of the engine. The low water may be due to blocked passages. Contact a yanmar dealer and talk to them about what chemicals to use for the flush. You can do it yourself, just need to use right chems or you could damage the engine (you might need to remove t-stat and anodes during flush). Make sure the raw water suction strainer and screen on the outside of hull are clean and not causing blockage.

My engine will knock if rpms are raised to fast- make adjustments slowly and change gears 900 rpm or below.

I flush my raw water cooled engine with fresh water after each use to slow corrosion.

You did not mention if you replaced the rubber raw water impeller- that could be your problem with low water flow.

Another thing- not sure if the boat sat for a long time- might be a good idea to drain the old fuel and start with fresh diesel- small engin like that buy the fuel from a non marine source- less chance of having water in the fuel. Bad fuel can cause combustion problems.
 

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you shouldnt knock no matter what...changing the impeller will have no effect on that but it will help you water flow issue

it also will not do anything with the smoke you are experiencing

knocking in some extreme cases can be caused by carbon buildup too...



the other thread I mentioned will give you clues into the possibilities of what you might have going one with yours

a shop manual will go a long ways in helping you determine what course of action to take

good luck
 
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I had a Yanmar 1GM in my Cape Dory 25D. It had about ten hours on it when I bought it and sounded like someone banging on an anvil with a hammer when it was running. Despite that, it was absolutely reliable and used so little diesel it was easy to forget to even put any in the tank.
 

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I had a Yanmar 1GM in my Cape Dory 25D. It had about ten hours on it when I bought it and sounded like someone banging on an anvil with a hammer when it was running. Despite that, it was absolutely reliable and used so little diesel it was easy to forget to even put any in the tank.
I have heard the 1 cylinder yanmars run a lot rougher than the multi-cyclinder. One cyclinder does not have anything to counter balance.

OP- you may also want to check you engine mounts are good- lift up on the engine and see if the rubber has broken loose from the metal mount.
 

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I'm not totally clear what your problem is. As a few others pointed out, the 1 cylindar deisel is a loud engine. When you accelerate rapidly the engine does get louder until it gets to the requested RPM's.

I'm not convinced the sound you're hearing is a problem.

On the other hand not getting above 2400 rpm's is a tangible problem. It may just be that the prop is too large. 6 knots for a 28 ft boat with this engine is pretty reasonable (that's my maximum).

Also note that there is a difference between the 1gm10 and the 1gm, with the 1gm10 being more common.
 

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Discussion Starter · #9 ·
Wow, that is quite the response, thank you all. So to answer a few questions, yes the boat is in salt water and after I replaced thermostat and zinc anode which were in terrible shape I believe in hindsight that some "bits" may have clogged the cooling system. As suggested I'll have a chat with Yanmar folks to find out what to use to flush it, and how to do it as all of this is new to me. After reading some more about the white exhaust I have a theory. With a low flow of water out the exhaust the small amount of water entering the hot exhaust in the exhaust elbow is creating steam. So first step is to improve the flow of raw water cooling so see if this fixes the problem.

The "clanking" sound described in my OP sounds more mechanical and only occurs when in gear and accelerating quickly vice gradually to full throttle. One suggestion is that it could be rod bearings, but I hope not as this sounds like a complicated and expense repair.

As for the low RPM, the original prop is still with the boat, everything has been cleaned on the hull and prop. Possibly the injector needs some TLC and or timing. Again this is a bit out of my comfort level to attempt on my own so may have to seek professional assistance.
 

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Discussion Starter · #10 ·
Could also be knocking caused by bad timing, if you don't have a shop manual for the engine, let me know and I can email you a link.
I would really appreciate the link to the shop manual. I am a newbie to this forum and unable to PM you as I do not have enough posts, but are you able to PM me with the link?
With thanks from your V.I. neighbour in Comox.
Mike
 

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Discussion Starter · #11 ·
Paul, thank you very much for the shop manual it looks perfect for what I need and it will really help expand my limited knowledge of our little 1GM.. I would gladly accept a copy of the parts book and official Yanmar manual when you get a chance. My engine is a 1GM vice a 1GM10 so there may be some differences. Once again, thank you very, very much. Now if I can find some time in my schedule to get down to the boat to do some tinkering, I might be able to do some sailing this summer down to Denman and Hornby.
 

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Hello,

A clacking sound can be caused by a bad cutless bearing that the prop shaft goes through. If you can rev it up in neutral and not hear a noise and then do the same in gear and you go get the noise it might be the cutless. It's hard to test a cutless with the boat in the water.

Lastly, I have never know of an engine with Rod knock to last more than hour or two.

Barry
 

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tell that to my old atomic 4! jajaja

little oil thickener and shed keep going

some engines are fine being all lose some other no

barry is right though...eliminate transmission and associated parts like shaft and cutlass bearing before attacking the engine
 

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Discussion Starter · #15 · (Edited)
Thanks again everyone, albeit the problem related to the "clanking" noise does not seem to be very good news. So it seems that it is either the rod bearing, main bearing or cutlass bearing. Any suggestions on which one is the simplest to check first? The boat is in the water and there is not a lift at the marina, although I could it on the grid if I can get the right tides and time off work.
 

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ummmm are you familiar with basic diesels

the cutlass is just the shaft tube that exits the stern tube, usually bronze with rubber inside...the best way to check that is to try and move the shaft from the outside...if there is a lot of play you need to fix that

determine wether its transmission related, cutalls bearing shaft and if neither of those then start looking at engine

but if its in the engine it means you have to tear it down...and not hard per se, but time consuming and a reabuild no matter what

a good way is to use a screwdriver a long one and with the handle to your ear try to pinpoint the noise while the engine runs...

good luck
 

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Cutless

Hey,

Do you have a fixed prop? If so you can test the cutless by sailing at a good speed, say 5 knots or so. Put the trans in neutral, the speed of the boat will cause the shaft to spin fairly quickly. If the cutless is bad you should hear the same or similar clanking sound. Put the trans in reverse and the shaft will stop and the noise should stop soon. If that happens then the cutless bearing is bad.

If you only hear the clanking when the engine is running, especially when the trans is in neutral, then it's not the cutless and you will need to look further (and perhaps have a good cry).

Barry

Thanks again everyone, albeit the problem related to the "clanking" noise does not seem to be very good news. So it seems that it is either the rod bearing, main bearing or cutlass bearing. Any suggestions on which one is the simplest to check first? The boat is in the water and there is not a lift at the marina, although I could it on the grid if I can get the right tides and time off work.
 

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You can get mask and snokel and dive on your boat. grab the prop shaft and shake it. If it moves more than 1/32 inch the cutlass bearing is worn. To replace, you will need to pull boat out of the water. If you do dive the boat, be careful of the sharp edges of prop and any barnacles growing on the boat- they cut like a knife.

FWIW, my cutlass is really worn- 1/16 inch play. I will use the boat until this fall and replace, along with a lot of other work. So even with a lot of play, you can milk a bad cutlass for a while using engine rpm that don't cause a knock.
 

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Discussion Starter · #20 ·
If the noise persists with the gearbox in neutral, it probably is not in the cutlass bearing.

However, it could be in the flywheel/drive plate. As mentioned earlier, if it is a rod, wrist pin or main bearing it will likely get worse fairly soon.

Paul T
Lots of great suggestions coming in, so thank you to everyone. So there is no noise when running the engine in neutral, nor when undersail and gearbox is is neutral. It only occurs when under power and accelerating quickly. I can avoid the noise if I accelerate gradually. Therefore, by process of elimination it must be somewhere in the engine. I'm thinking it is time to seek professional advise from a marine mechanic as opening up the engine is beyond my abilities.
 
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