1989 351W Engine Knock |
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Greg_SA
Senior Member Joined: April-19-2007 Location: South Africa Status: Offline Points: 172 |
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Posted: September-14-2024 at 6:44am |
Hi Guys, Its been a long time, but my engine/boat problems aren't over My previous thread where I replaced the engine is here: Since fitting the "new/used" engine and getting it running last year, I only used the boat for 3 days and everything was great. Then
a week later (still in December 2023) the boat was running great, but
then while cruising for about 10 minutes at ~2500 rpm I heard a knocking
sound. It was a deep knocking sound, at a rate
of about 2 knocks per second. I slowed the boat down, and it idled
fine, and the knock slowed down to about 1 knock per second. I sounded
like it was coming from the back of the engine (transmission side) but
it is hard to be sure as the cover was closed. I
shut the boat down, but couldn't see anything wrong. I tried to
restart, but it puffed and spluttered and would not start. So I towed
the boat in. I am not sure if the starting problem is directly related
or maybe it was totally heat soaked? I have been so busy this year that I haven't had much time to diagnose. - Plugs look fine - Oil looks good - no metal shavings I have pulled all the plugs, disconnect ignition and raw water pump, and cranked the engine. It turns over smoothly, no noises. I then did a compression test, and all cylinders were around 140 psi, but what was strange is than during the compression test of cylinder 4, it made a puffing sound (almost like a backfire) at the intake area. None of the other cylinders did that. Any suggestions or ideas? Greg |
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1989 Ski Nautique (SN2001)
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11030 |
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it's coming from the rear, #4 cylinder is in the rear and it did funny things.
As a starting point, maybe pull the valve cover off and look at the rocker arms and springs for #4 especially the intake because of your description. |
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Fl Inboards
Grand Poobah Joined: January-20-2008 Location: United States Status: Offline Points: 2092 |
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leak down test on number 4. and maybe the rest. i had one do that a number of years ago. turned out exhaust valve stem retainer was not installed correctly and it dropped the valve on top of the piston.
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Hobby Boats can be expensive when the hobbyist is limited on their own skill and expertise.
1993 Shamrock "fat" 20. 2008 Nautique 196 5.0 |
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Greg_SA
Senior Member Joined: April-19-2007 Location: South Africa Status: Offline Points: 172 |
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Managed to remove the valve cover, and this is what I found. No. 4 exhaust rocket bolt has sheared off. - Is it possible to pull the stud and replace without removing the head? - I believe the studs are press fit? - Could this have caused the knock sound? I would expect a tick not knock? I saw a video of someone that tapped the broken thread on the stud a bit longer and use a nut and washers to extract it. Fitting a new one would probably require a press? Or tap the hole and use a threaded stud to replace? I do have my previous engine's heads as spares, but it is a bit different (newer style with bolt down rocket gear). I assume mixing different heads is a bad idea? These are the spares I have. |
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1989 Ski Nautique (SN2001)
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