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BrandonC
BrandonC

Posted: Wed Sep 19, 2018 8:33am

Post Subject: Yanmar engine vibration

The three cylinder Yanmar on my boat has never been a particularly smooth runner but recently increased vibration in the rev band 1100 to 1400 RPM (canal cruising range) has become uncomfortable to the extent I'm worried about damaging the engine. Above and below this band it seems normal. The vibration is engine derived as it also occurs when the drive is in neutral. Additionally the engine starts ok, no excessive smoke, but during the warm-up the engine sometimes suddenly runs more smoothly leading me to think that perhaps it started only on two cylinders. The valve clearances have not been adjusted during my ownership (8 years), I intend to rectify this. Could this be the cause? The engine has done about 3500 hours. Regards John

Tony-B
Tony-B

Posted: Wed Sep 19, 2018 9:33am

Post Subject: Yanmar engine vibration

A tight valve clearance could cause a misfire so the valves are worth checking but I would expect it to start at idle and then lessen as the speed increased. Check the bolts holding the engine mounts to the beds are tight and also check the nuts holding the fee to the mount are tight. If one is loose tighten the bottom nut up to the top but never the other way around or you will mess up the engine alignment. The fact it does this in neutral rather rules out a shaft alignment problem. I might be a faulty injector although I would expect that to cause at least some exhaust smoke. I suppose its possible the drive plate may be breaking up, that can give some very odd symptoms but as the gearbox has to come off to check it would be some way down my check list. No smoke, good cold starting and no overheating or coolant loss (the last not mentioned) also tends to rule out a head gasket problem. It is always worth changing the fuel filters and inspecting what they have caught, even to the extent of opening them up. Partially blocked filters can also cause poor running but I would also expect loss of maximum power and speed. I am afraid that is about all I can think of at present.

BrandonC
BrandonC

Posted: Wed Sep 19, 2018 11:03am

Post Subject: Yanmar engine vibration

Thanks Tony. Yes, it starts ok with no excessive smoke. There is no coolant loss (although during the very hot weather the expansion bottle ejected a little into the drip tray). The engine indications, coolant temperature and oil pressure are all normal, 80degs C, 50 psi. Oil and fuel filters were changed recently and the fuel is clean. I will check the valve clearances asap and the engine mount security. I found one of the machine screw heads securing the engine to the mounting frame fractured off two or three years ago and the group of three was replaced. Because of their position they are very difficult to torque. John

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