Engine quit, no compression?
Printed From: Laser 28 International Class Association
Category: Laser 28 General
Forum Name: Maintenance
Forum Description: All the things to care for your boat
URL: http://www.laser28.org/forum/forum_posts.asp?TID=720
Printed Date: 23 November 2024 at 10:16am
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Topic: Engine quit, no compression?
Posted By: Cayuga
Subject: Engine quit, no compression?
Date Posted: 02 September 2015 at 9:44pm
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Hi All, My DV10 developed a problem tonight and I hoped some of you might have an idea where to start. We were motoring away from our mooring when the engine abruptly stopped. We had been running for about 10 minutes at half throttle. I checked that we hadn’t run out of fuel and when we tried restarting the engine a few minutes later the flywheel was spinning freely as if there were almost no compression. I was able to turn the flywheel by hand with not much resistance. The oil level looked fine and there was no water in it. Does this sound like a symptom of anything obvious?
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Replies:
Posted By: Bill Layton
Date Posted: 03 September 2015 at 9:23am
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Yes I've had this and found the valve adjustment was too tight causing the valve(s) not to close causing no compression. This has happened on a number of boats. It's unusual because normally at least on car engines valve lash gets loose not tighter. I suspect this is because the head and cylinder are cast iron while the block is aluminium. Anyways reset your valve lash properly and you'll likely be ok.
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Posted By: Cayuga
Date Posted: 03 September 2015 at 9:52am
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Thanks Bill, I'll try adjusting the valves this weekend and see if that does the trick. I've never even had the valve cover off so it wouldn't surprise me that they're out of adjustment.
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Posted By: Bill Layton
Date Posted: 03 September 2015 at 9:55am
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You'll need a #10 metric boxed end wrench and a very small adjustable wrench.. like a 4" one.
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Posted By: Cayuga
Date Posted: 03 September 2015 at 10:16am
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Is there are mark on the flywheel to indicate TDC?
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Posted By: bal149
Date Posted: 04 September 2015 at 7:40pm
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Actually Bill and I acknowledge your long relationship with the Bukh , but typically valve lash Decreases and this is due to the valve pounding into the seat. That this event happened suddenly is not typical-hard starting would generally be the first symptom. I would adjust the valves and make sure they go up and down as I hand turned the engine. The compression release can also be a source of a lack of compression. In a diesel, a hole in the piston would be very unlikely.
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Posted By: Cayuga
Date Posted: 05 September 2015 at 7:32am
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I removed the valve cover and found that the exhaust valve was stuck partially open. Turning the engine by hand I was able to free it but it's still sticky. Good news is that compression has returned. Now the exhaust valve opens ok but hangs up momentarily when closing. I assume the valve stem is sticking in the guide. We haven't run the engine hard all season and I think there's a lot of carbon built up in the head. I'm going to see if I can get the valve moving smoothly before I resort to pulling the head.
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Posted By: Cayuga
Date Posted: 06 September 2015 at 8:00pm
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Just to follow up on this, I sprayed penetrant (PB blaster) on the exhaust valve, both from the valve cover side and through the exhaust opening on the cylinder head, rotated the flywheel by hand a bunch of times, let it sit overnight, and it was freed up the next day. Adjusted the valves and it's running great again.
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Posted By: frfletch
Date Posted: 07 September 2015 at 2:37pm
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That is a great story with a great ending! Still, why did it happen in the first place? I would check the valve adjustments on the rocker arm contacts with the push rods. This area is oiled and should not get sticky. Insufficient gap on the exhaust side logically could cause carbon build-up on the valve or valve seat, but not between the valve shaft and the valve guide through which it reciprocates. Bit of a mystery to me?????
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Posted By: bal149
Date Posted: 07 September 2015 at 4:24pm
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Heat usually- no water in head, or exhaust back pressure too high- have a look at the outlet and I agree it is a happy story
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Posted By: Cayuga
Date Posted: 18 November 2015 at 12:22pm
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Following up on this again in case anyone runs into something similar down the line. My exhaust valve was sticking open causing the engine to quit. I was able to get it moving again enough to run the engine by removing the exhaust elbow and spraying with a lubricant, then turning the engine by hand, but it got sticky again if the engine sat for a few days. I pulled the head and found a small crack in the exhaust valve guide that was preventing the valve from sliding freely. I sent the head to Keith at Crinmar and he was able to get it reconditioned, replaced the guide and the valves, and ground in the valve seats. I wasn't sure I wanted to trust anyone locally with an exotic and difficult to replace cylinder head. Keith was great to deal with.
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