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Old 07-11-2008, 19:12   #1
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Angry Bent Con Rod

I'm pretty sure I bent a con rod when I hydrolocked my yanmar 3gm30f the other day(that's another embarrassing story....I know better). I get a louder knock between 1800 and 2400 rpm while in gear at dock. Is it remotely possible to replace a rod while the engine is still in the boat. Instinct is telling me "NO" but again, I am obviously no mechanic.
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Old 07-11-2008, 20:01   #2
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I know nothing about diesels but it would seem like a bent con rod would affect engine operation at all RPMs. Since the more it bent the easier it would be to bend further it seems like once started it would bend until there was a mechanical interference, like the the bent rod hitting the bottom of the cylinder, in which case the engine would just lock up. But I'm just guessing here....

Maybe you lucked out and just spun a bearing...!
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Old 07-11-2008, 21:50   #3
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I would think that if you really bent a rod that it would be noticeable at all RPM's. I assume you were cranking the engine trying to start it and raw water entered the cyls? You might have bent a rod if this is the case but more likely you damaged/fouled an injector. I would try cracking open each inj. line while running and see if you have one cyl. that is weak (makes very little difference when you open the line). If one is bad pull the inj. and have it tested or rebuilt. Changing the rod more than likely means pulling the engine, start with the easy stuff.

Good luck. John
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Old 08-11-2008, 06:50   #4
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Instincts are great, facts are better. For a bent rod I'd pull the engine. I've never seen a 3gm that you could get to that didn't have to be pulled to work the bottom. About the best you can do is pull the head and use a depth micrometer to possibly determine if and which rod might be bent by measuring TDC on each of the three pistons. If I hydrolocked an engine and got a rod knock right after, I'd pull it.
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Old 08-11-2008, 07:24   #5
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Pull the engine. It may be more than a bent con rod. Quite often with a hydrolock bolts on the crankshaft can be sheared. I've seen this on a 3GM.
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Old 08-11-2008, 08:52   #6
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Pull the engine, you especially need to check the runout on the crankshaft, for starters pull the head it should be obvious to see any indentation on the piston, hopefully you won't have damaged the block. If I was looking at this I would try to rig a frame to lift the engine high enough to remove the oil pan first and check the lower end bearings, the few times I have seen such a case usually the head bolts crack or stretch and I always look over head bolts for any pits or stretch, I usually replace diesel head bolts when I do overhauls.
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Old 08-11-2008, 09:33   #7
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ya'll are causing way to much work.....
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Old 08-11-2008, 11:45   #8
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Occam's Razor

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ya'll are causing way to much work.....
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Old 08-11-2008, 17:06   #9
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Occam's Razor
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Originally Posted by never monday
ya'll are causing way to much work.....


That'll help Toddt a whole lot. Heck with those golden tidbits of wisdom how could he go wrong.
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Old 08-11-2008, 17:29   #10
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Heck with those golden tidbits of wisdom how could he go wrong.
because no one here has any idea what boat the engine is in and what access he has. Yet everyone tells him to pull it out, IMHO unnecessarily.
Todd and I have been emailing and speaking on the phone. He has a task list and will report his findings.
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Old 08-11-2008, 19:20   #11
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because no one here has any idea what boat the engine is in and what access he has. Yet everyone tells him to pull it out, IMHO unnecessarily.
Todd and I have been emailing and speaking on the phone. He has a task list and will report his findings.

Oooooo a mystery! Can we have a clue?
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Old 09-11-2008, 05:11   #12
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Occam's Razor
hee-hee


Quote:
Originally Posted by never monday
ya'll are causing way to much work.....


That'll help Toddt a whole lot. Heck with those golden tidbits of wisdom how could he go wrong.
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Oooooo a mystery! Can we have a clue?
Tellie,
you might just be a genius in your world. I'm putting you in my troll file.
Your comments so far have been less useful than mine.

It just amazes me that the first thing you guys want to do is pull it out....there are less invasive ways to determine if there's a bent rod. Then he can make a decision on his terms if he needs to pull it or not.
Replacing a rod and in-framing a GM series is easy in the boat IF you have the room. The OP has a Hunter 34. There is a ton of room to do this operation.
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Old 09-11-2008, 05:47   #13
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Put me in any file you like. I believe this to be an open forum for any member to respond without giggles and smarmy one liners from others that can't take the same. But thanks for the mechanical update and perhaps the OP will post pics of his efforts so all interested respondents can be enlightened to this procedure.
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Old 09-11-2008, 05:58   #14
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Put me in any file you like. I believe this to be an open forum for any member to respond without giggles and smarmy one liners from others that can't take the same. But thanks for the mechanical update and perhaps the OP will post pics of his efforts so all interested respondents can be enlightened to this procedure.
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Old 09-11-2008, 07:10   #15
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What precipitated

What caused the hydrolock? I'm sure many others would like to know so they could possibly learn from your mishap and not do the same someday..
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