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Author Topic: Significant vibration STW3 - any experiences or suggestions  (Read 228 times)

RestlessII

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Significant vibration STW3 - any experiences or suggestions
« on: February 23, 2021, 10:32:20 AM »
Hi all, we have a Lister Marine STW3 engine, around 1981-85 vintage fitted to our sailboat. Over the past 4-5 months it has started vibrating, particularly in the 1200-1800 rpm range. It is mounted on 4 PolyFlex mounts that historically have lasted between 3 to 4 years. No other obvious signs from the engine of any problems.

So we have replaced the engine mounts, checked and rechecked. Realigned the prop shaft twice. Checked valve clearances and all good. The one thing I haven't done is to remove and service the injectors.

Because the injectors are under the rocker covers, close to the moving valve rockers it isn't obvious to me how to check the injector operation without removal.

Is there any advice on how to check the injectors; perhaps other possible sources of the vibrations...appreciate any assistance...Im not a mechanic unfortunately but keen to learn.

Many thanks

cobbadog

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Re: Significant vibration STW3 - any experiences or suggestions
« Reply #1 on: February 23, 2021, 10:56:49 AM »
To check the injectors they need to be removed. Then you can reconnect them to the fuel line and wind the engine over and watch the fuel spray. It must be a very fine spray. DO NOT put ypur hands in front of the spray as it can piece the skin and make you very unwell.
As for other possible causes you would need to check tension on the flywheel bolts. Are your filters clean because if it is starving for fuel or air this can upset the apple cart. Is there anything hanging off the prop underwater or a piece mising off it? Is there a bend in the prop shaft.
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dieselgman

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Re: Significant vibration STW3 - any experiences or suggestions
« Reply #2 on: February 23, 2021, 02:11:11 PM »
Injectors are routinely bench tested and serviced off the machinery. If you have access to a reputable local shop then the costs will be low and results usually good. If no local shop, you can get replacement spares and/or send out your used parts for servicing. Usually advisable to service all 3 cylinders together. Your fuel system is likely the weak link to allow gradual degradation of performance. In our shop we use an IR laser thermometer to check individual cylinder performance. If they are running within 10 to 15 F to each other, then you are running within spec. Are you running with a lift-pump? Those are often the cause of much difficulty. Of course the obvious stuff is to inspect exhaust color and condition under load to see any obvious combustion issues. Inspection inside the exhaust manifold will also tell you a lot about what is going on with your engine and can pinpoint an individual cylinder malfunction. In a pinch, you can engage the decompressors - one at a time - to see how much load an individual cylinder is pulling. They should all be even. CAUTION, your decompressors must be adjusted properly or this option can allow exhaust valve damage if it were to contact the piston.
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RestlessII

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Re: Significant vibration STW3 - any experiences or suggestions
« Reply #3 on: February 24, 2021, 09:56:44 AM »
Thank you for the info/advice. The prop shaft has been disconnected in order to isolate the vibration source and it is the engine.
There is a local injector servicing facility, so we will be removing them this week and having them serviced.
Hopefully that fixes the problem. I will update on the outcome for the info of all.
Many thanks 🙏

cobbadog

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Re: Significant vibration STW3 - any experiences or suggestions
« Reply #4 on: February 24, 2021, 10:19:36 AM »
At least if they are serviced you know then that they are good. Talk to them first and also consider doing the pumps too.
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