Guest Posted January 10, 2012 Share Posted January 10, 2012 I've a Isuzu 25 hp diesel, 2 cylinder aboard the yacht which makes a loud clanking sound at some revs. Engine seems good , that is no noticeable oil used between oil changes, starts easily and runs well. I can dial in say 1800 rpm at which it seems to be fairly quiet and smooth. So I doubt its problem with the bottom end of the motor. Just wondering what it is thats making the noise. Engine has around 1700 hours. Thanks . Link to post Share on other sites
Guest Posted January 10, 2012 Share Posted January 10, 2012 Engine mounts? Link to post Share on other sites
Guest Posted January 10, 2012 Share Posted January 10, 2012 Chickens? Link to post Share on other sites
Guest Crafty 1 Posted January 10, 2012 Share Posted January 10, 2012 Chickens? No Isuzu's are more Clucking. I think the clacking sound is a craking sound of the man working the horses. Link to post Share on other sites
Guest Posted January 10, 2012 Share Posted January 10, 2012 Might be all the chicks aboard Yes engine has flexible mounts and they seem to be ok. Link to post Share on other sites
idlerboat 116 Posted January 10, 2012 Share Posted January 10, 2012 Yeah well apart from the solutions above,... I run a izi 53 hp. A clacking sound could be a few things but best ask a few questions. First is the oil colour all good ? Second if you put you hand on the engine does the clacking sound correspond with a vibration to your hand ? Third...go aft and put your ear as close to the prop as possible... If you can run the engine up and down its rev range without a load and the clacking sound is not there then it may be comming from the prop.(or shaft) Even a small amount of out of balance will create a sound up through the hull...this will be way noisier at some revs than others. A slightly slack stern tube bearing will be enough for this to occur and in the short term is not a problem. Crap on the prop is enough for a balance problem. If you have broken something in the engine itself....bummer....a clacking sound is going to show itself very quickly. Any sign at all of grey oil...blue smoke or unusul running...shut her down. It may save a lot of dollars in a rebuild. A further thought is that if the timing has gone out this can also cause an unusual sound. Checking this depends on the engine injection system (single rail or individual cylinder pumps) . To be blunt can be a real hassle and dosnt happen often on an engine of your hours. A blocked injector may throw the engine out of balance and/or create an un even burn in that cylinder. Another help is to the engine doctor thing...serious. Use a length of hose and stick one end in your ear and move the other end around the engine and after that the hull it can be a great help to localise where the noise is coming from. good luck.... Link to post Share on other sites
wheels 543 Posted January 10, 2012 Share Posted January 10, 2012 Dampner plate. It's the metal plate that bolts to the flywheel and has the spline that drives the gearbox. In the middle, you will have a series of springs. These springs take what is called "Injector shock" out of the drive line. Injector shock can wear out gearboxes. Over time, the springs wear and become lose and can even break in two and rattle or fail to take out that shock, which is also heard as a rattle at different RPM's. The big problem is trying to diagnose the problem, because it is not a noise you can easily locate and it is not made all the time, just seemingly at different RPMs and sometimes even then it can be intermitent. Link to post Share on other sites
Guest Posted January 10, 2012 Share Posted January 10, 2012 Just had an idea...... I'll take my phone and make a recording of it today.. Try to post it and see what you think it might be. The oil is black but dosn't have any metal in it. The engine does not leave a smoke trail. The shaft rotates freely and quietly when in neutral. I'll try the hose trick today Idler. It does seem worse when first started. Could it simply be the exhaust system not muffling well? It has a plastic wet muffler. I'll try the hose trick on the dampener Wheels and see if it is the culprit. Thanks for the help guys , really appreciate your efforts. Link to post Share on other sites
Guest Crafty 1 Posted January 10, 2012 Share Posted January 10, 2012 Just had an idea...... I'll take my phone and make a recording of it today.. Try to post it and see what you think it might be. The oil is black but dosn't have any metal in it. The engine does not leave a smoke trail. The shaft rotates freely and quietly when in neutral. I'll try the hose trick today Idler. It does seem worse when first started. Could it simply be the exhaust system not muffling well? It has a plastic wet muffler. I'll try the hose trick on the dampener Wheels and see if it is the culprit. Thanks for the help guys , really appreciate your efforts. Watch out for chickens! Link to post Share on other sites
Guest Posted January 10, 2012 Share Posted January 10, 2012 Its Old Chooks I'm scared of, especially mine!!! Link to post Share on other sites
Noodles 0 Posted January 11, 2012 Share Posted January 11, 2012 a flywheel damper can make a noise when you shut the engine off so try to check around bell housing when shutting down engine or as the engine is revved up or down , the damper will absorb the shock, but as the springs have worn or are gone, there is no smooth place for the shock load to go hence clunking noise.... Link to post Share on other sites
Guest Posted January 11, 2012 Share Posted January 11, 2012 I took a sound bite yesterday on my phone but can't find the bloody cable to load it onto the puter. The noise is only a problem below 1800 revs. Very noisy at idle. Seems some of it is from the air filter intakes. Is there a better exhaust system that will quiet the motor? What about these oil additives, do they help? Link to post Share on other sites
Guest Crafty 1 Posted January 11, 2012 Share Posted January 11, 2012 I took a sound bite yesterday on my phone but can't find the bloody cable to load it onto the puter. The noise is only a problem below 1800 revs. Very noisy at idle. Seems some of it is from the air filter intakes. Is there a better exhaust system that will quiet the motor? What about these oil additives, do they help? The noise will travel more clearly thru any aperture in the motor so that why you hear it louder at te air intake. Wheel is correct on this. Oil Additives that are sold to reduce Knocking and engine noises are dodgy at best. What they do is add a VII (Viscosity index improver) to thicken the oil at temp and disguise the noise. they also add other additives to reduce the "knocking affect" but they will ruin the chemistry of your motor oil and ultimatley reduce the oils cold start up flow and its ability to cool and lubricate. If these aditives were so good the Oil Co's would put them in their oil. (which they actually do but to prescribed and test formulae's) Also the chemistry and application of them is naff! how can one 500ml additive work the same in a Jag engine that takes 8 litres compare to a Fait engine that take 3?, It is NOT science but Smoke and mirrors!.... more smoke Link to post Share on other sites
Guest Posted January 12, 2012 Share Posted January 12, 2012 Thanks Crafty. Have you heard of using 1% Ethyl Nitrate in the fuel? Link to post Share on other sites
Guest Crafty 1 Posted January 12, 2012 Share Posted January 12, 2012 Thanks Crafty. Have you heard of using 1% Ethyl Nitrate in the fuel? No. But i am not knowledgeable on fuel just oils (many years with Burmah oil Co When theyowned Castrol) Link to post Share on other sites
wheels 543 Posted January 12, 2012 Share Posted January 12, 2012 Never heard of anyone using it in Diesel BB and i wouldn't suggest it being added. It is very explosive and would only result in increasing detonation. Plus it gives off some very toxic nasties when it burns. Air induction into a Diesel has always been an issue of producing loud noise. Some vehicles have specially designed intake boxes designed as sound traps to stop that problem. Link to post Share on other sites
Guest Posted January 12, 2012 Share Posted January 12, 2012 Thanks Wheels, yes I read its just the vintage of the engine and its ok. Apparently these old engines make a heap of clacket at low revs. If it were a petrol engine something would be broken for sure! Seems its just a product of the way these old diesels are injected. Listening carefully to the motor it all sounds good apart from the heavy clacking. I was hoping there was something that could be done to quiet it but seems apart from sound insulation or a more modern motor just turn the stereo up a lot. Just where I'm berthed is right in front of a bar and its not a good look coming in, mucking up the approach and having to have a another couple of goes with the engine sounding like its going to explode right in front of 40 or so people who have nothing better to watch. Link to post Share on other sites
Guest Crafty 1 Posted January 12, 2012 Share Posted January 12, 2012 Thanks Wheels, yes I read its just the vintage of the engine and its ok. Apparently these old engines make a heap of clacket at low revs. If it were a petrol engine something would be broken for sure! Seems its just a product of the way these old diesels are injected. Listening carefully to the motor it all sounds good apart from the heavy clacking. I was hoping there was something that could be done to quiet it but seems apart from sound insulation or a more modern motor just turn the stereo up a lot. Just where I'm berthed is right in front of a bar and its not a good look coming in, mucking up the approach and having to have a another couple of goes with the engine sounding like its going to explode right in front of 40 or so people who have nothing better to watch. There may be something you could do... check the engine spec's for what type of oil (weight) they use and just ensure you are on Spec. Won't fix the problem but if the oil is to light or it has reduces in viscosity then this would make the engine more prone to wear etc... and may reduce some noise. Wheels might want to comment on this as i am not to familia with your motor. Just on another story, but this show what technology can do even in the oil indutry... When Mitzi introducd the Sigma it had two issues.. 1. Most Multi grade oils (especially Mobil) would go thru them like a dose of salts 2. They had a difficult shift from 1st to second gear (stiff synchro) with normal mineral oils. It was a real issue .... until Castrol Put GTX2 into the motor and VMX (part synthetic) into the Gearbox and Viola the probems vanished in all vehicles. Also i was involved with many the Lada's that came into NZ in the 80's. We did some tests (two identical motors on a test bed) in Pangbourne UK and by changing from the OEM Russian oil to GTX we doubled the engine life! Link to post Share on other sites
Fusion 0 Posted January 12, 2012 Share Posted January 12, 2012 Old style diesel engines do clatter a lot at lo revs. My old Perkins has a very low RPM 1350 flat out. At idle it would clatter and jump around, so slow it would not even charge. I just turned up the idle until it was smooth. The result is 4 kts at idle in gear Link to post Share on other sites
Marshy 30 Posted January 12, 2012 Share Posted January 12, 2012 T When Mitzi introducd the Sigma it had two issues.. 1. Most Multi grade oils (especially Mobil) would go thru them like a dose of salts When i bought my Mitzi i remember one mechanic telling me if it ya Mitzi doesnt chew through oil or stops chewing the oil then its a darn good sign something is wrong with it! Link to post Share on other sites
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