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Post by Deleted on Jun 14, 2020 4:58:57 GMT
My toy trawler has a pair of BMC 1.5D engines. When I bought the boat I was aware that the starboard engine was a bit "funny". Same engines same hours (1600h) but the starboard unit has a slightly "poppy" or "crackly) sounding exhaust and it has now got a very loud knock. So my first thought was rod bearing failure, which is possible, but could this knocking be detonation? I'm wondering if that odd sounding exhaust would be caused by a failed big end, it seems improbable but I don't know. It's intriguing me now. Engine starts and runs ok a little bit more smoke than the other one but this knock is now very loud. It does sound a bit like detonation but I'm not quite sure how to work out if it's that. Oil pressure is ok so maybe not a bearing? Engine mount is a possibility but I'm mainly intrigued about the crackly exhaust tone which is something the engine has exhibited since I got it. It's curious. Any advice from people like TonyDunkley will be appreciated here.
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Post by TonyDunkley on Jun 14, 2020 6:02:52 GMT
My toy trawler has a pair of BMC 1.5D engines. When I bought the boat I was aware that the starboard engine was a bit "funny". Same engines same hours (1600h) but the starboard unit has a slightly "poppy" or "crackly) sounding exhaust and it has now got a very loud knock. So my first thought was rod bearing failure, which is possible, but could this knocking be detonation? I'm wondering if that odd sounding exhaust would be caused by a failed big end, it seems improbable but I don't know. It's intriguing me now. Engine starts and runs ok a little bit more smoke than the other one but this knock is now very loud. It does sound a bit like detonation but I'm not quite sure how to work out if it's that. Oil pressure is ok so maybe not a bearing? Engine mount is a possibility but I'm mainly intrigued about the crackly exhaust tone which is something the engine has exhibited since I got it. It's curious. Any advice from people like TonyDunkley will be appreciated here. There is a fairly broad scope of possible causes, Andrew, . . anything from a faulty injector nozzle, to bent or sticking valves, broken valve springs, or even a broken crank. The first stage in diagnosing what's wrong is to establish whether it's a combustion knock or a mechanical one. Does the intensity/loudness of the knock change or disappear on or off load, at different speeds, when picking up speed or on the overrun, . . and does it change at all if you crack and then re-tighten each injector pipe in turn with the engine at a fast idle and off load ?
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Post by Deleted on Jun 14, 2020 6:46:30 GMT
Thanks Tony I will do these tests later this morning.
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Post by Deleted on Jun 14, 2020 7:36:23 GMT
My toy trawler has a pair of BMC 1.5D engines. When I bought the boat I was aware that the starboard engine was a bit "funny". Same engines same hours (1600h) but the starboard unit has a slightly "poppy" or "crackly) sounding exhaust and it has now got a very loud knock. So my first thought was rod bearing failure, which is possible, but could this knocking be detonation? I'm wondering if that odd sounding exhaust would be caused by a failed big end, it seems improbable but I don't know. It's intriguing me now. Engine starts and runs ok a little bit more smoke than the other one but this knock is now very loud. It does sound a bit like detonation but I'm not quite sure how to work out if it's that. Oil pressure is ok so maybe not a bearing? Engine mount is a possibility but I'm mainly intrigued about the crackly exhaust tone which is something the engine has exhibited since I got it. It's curious. Any advice from people like TonyDunkley will be appreciated here. There is a fairly broad scope of possible causes, Andrew, . . anything from a faulty injector nozzle, to bent or sticking valves, broken valve springs, or even a broken crank. The first stage in diagnosing what's wrong is to establish whether it's a combustion knock or a mechanical one. Does the intensity/loudness of the knock change or disappear on or off load, at different speeds, when picking up speed or on the overrun, . . and does it change at all if you crack and then re-tighten each injector pipe in turn with the engine at a fast idle and off load ? Tried the injectors they did vary the sound a bit and one of them resulted in engine stopping. The noise really sounds like explosions and it is coming straight out of the air intake . Wrapping a sock around the air intake (it's ok it won't get drawn in) quietens it down enormously. No exhaust coming out of air inlet and the valve train seems to be operating normally. I'll do a recording a bit later of both engines one after the other. I should correct the point about the oil pressure. No gauges but the red lights which do work are not coming on even at tickover. Could be low pressure I suppose. The crackling exhaust note has always intrigued me. Completely differeny sound to the other engine.
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Post by Deleted on Jun 14, 2020 9:50:43 GMT
Both engines started one after the other. Tickover no heat starting fine.
Second one is the loud one.
Exhaust is very crackly on the loud one and hadls been since I bought boat
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Post by JohnV on Jun 14, 2020 11:27:09 GMT
I'm wondering if you've got a sticky or broken valve. Best to wait till Tony has had a listen but it sounds like a BMC 1.8 I came across, years back that had a damaged exhaust valve
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Post by Deleted on Jun 14, 2020 11:44:14 GMT
Exactly what happened to mine, a sort of chuffing knock sound through the air intake. I've been putting a bit of acetone in with the diesel, 100ml. This has resulted in almost eradicating the issue, slowly but surely. So I'm assuming a bit of gum between valve and seat, or gummed up injector.
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Post by TonyDunkley on Jun 14, 2020 12:14:45 GMT
There is a fairly broad scope of possible causes, Andrew, . . anything from a faulty injector nozzle, to bent or sticking valves, broken valve springs, or even a broken crank. The first stage in diagnosing what's wrong is to establish whether it's a combustion knock or a mechanical one. Does the intensity/loudness of the knock change or disappear on or off load, at different speeds, when picking up speed or on the overrun, . . and does it change at all if you crack and then re-tighten each injector pipe in turn with the engine at a fast idle and off load ? Tried the injectors they did vary the sound a bit and one of them resulted in engine stopping. The noise really sounds like explosions and it is coming straight out of the air intake . Wrapping a sock around the air intake (it's ok it won't get drawn in) quietens it down enormously. No exhaust coming out of air inlet and the valve train seems to be operating normally. Having listened to the sound recording, and from what you've said above, it's not pointing to any crank or bottom end bearing woes. The engine stalling when one particular injector pipe is slackened off, together with the lesser effects of slackening the other three, does mean that cylinder is doing the lions share of the work when the engine's running, . . with very much less coming from the other three. If your luck's in, this could be nothing more than tight tappets. Start by checking the clearances on the noisy engine - 0.015" (cold) inlet and exhaust. You might find that the cylinder that caused the engine to stop with the injector pipe slackened is the only one with the tappet clearances anywhere near correct.
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Post by Deleted on Jun 14, 2020 12:33:08 GMT
I've tried turning it over with a spanner. It seems to turn over ok but I didn't actually check all the tappets so thanks for that I will do that.
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Post by Deleted on Jun 14, 2020 12:56:19 GMT
If your luck's in, this could be nothing more than tight tappets. Start by checking the clearances on the noisy engine - 0.015" (cold) inlet and exhaust. . Oops!! Just a quick check shows you are spot on here Sir. I can already see two tappets with about 1/8 inch clearance or more. Obvious question is how did they get that far out?? Strange
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Post by Deleted on Jun 14, 2020 13:05:23 GMT
Tony I owe you a beer. Or several. Tappets adjusted now engine runs like new. Happy man is me
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Post by Deleted on Jun 14, 2020 13:12:10 GMT
Exactly what happened to mine, a sort of chuffing knock sound through the air intake. I've been putting a bit of acetone in with the diesel, 100ml. This has resulted in almost eradicating the issue, slowly but surely. So I'm assuming a bit of gum between valve and seat, or gummed up injector. It's interesting as the boat has some little bottles of diesel treatment but I never added any out of laziness. Adjusting the tappets just now has completely eradicated the noise problem. I guess previous adjustment may have seen the tappet adjusters left a bit loose. I haven't touched them since buying the boat. / 100 hours.
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Post by naughtyfox on Jun 14, 2020 13:44:51 GMT
Isn't 'adjusting the tappets' wrong speak for 'valve clearances'?
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Post by Isambard Kingdom Brunel on Jun 14, 2020 13:50:07 GMT
May be worth setting the tappets on the other engine too...................................................... It is part of the routine service on a BMC, along with re-torquing the heads down.......................................
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Post by Deleted on Jun 14, 2020 13:56:16 GMT
May be worth setting the tappets on the other engine too...................................................... It is part of the routine service on a BMC, along with re-torquing the heads down....................................... I'm reluctant to touch the other unit as it is 100% and no smoke once running. Remarkably good unit actually all I want to do is be naughtyfox on that one.
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