I think I bent a push rod

sailor26

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Hi All, took my boat out for first trip on the lake yesterday. Ran like a top all afternoon (at 2500 and below, including idle). On the way back to the dock I stepped it up to about 3k and felt like there was a little hesitation occasionally. When I powered down it started idling rough. So, I thought I would take one blast around to see if I could clear a possible carb block. I gave it 3/4 throttle right off and all of a sudden got very loud clanking and banging, then stalled and wouldn't start again. I first thought I snapped the timing chain because it had a rattley sound at first. When I got the boat back in my yard it started right up again, but with a lot of clanking and knocking, both at 1500 and idle.

My boat is a 82 Cobalt with a Mercruiser 305.

My question is, since the noise includes a clanky (like something broken) and knock, at both 1500 and idle, does this sound like it may be a bent or broken push rod and possible broken valve spring?

If so, is this a common occurrence or more likely a sign that my 30 yr old engine is not to be trusted anymore?

I really broke the bank last summer getting this new project going. Can't afford to send it back to the mechanic. I have fixed a broken push rod before in my old 69 Doge van so I feel I could tackle that OK.

Appreciate your thoughts.
Dana
 

jtrasap

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Re: I think I bent a push rod

A "Clanky" sound would be more likely to be a rod knocking. If you rev the engine then let off does it get louder on let off?
 

sailor26

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Re: I think I bent a push rod

I will have to check that again. Seemed to me it was pretty loud both ways but did seem to be relative to RPM.


A "Clanky" sound would be more likely to be a rod knocking. If you rev the engine then let off does it get louder on let off?
 

Don S

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Re: I think I bent a push rod

Pull the valve cover and have a look, it will be really obvious.
 

Watermann

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Re: I think I bent a push rod

That doesn't sound like a bent push rod, for it to do that normally it would have had a lifter freeze up which would be a noticeable ticking or tapping sound to begin with. Not a timing chain broken or it wouldn't even start. The rod knocking from a spun bearing with no oil now or it nuked the bearing which could cause the clanking sound with the piston skirt slapping the cylinder. No telling for sure as it is, the motor needs pulled and torn down to find the cause.
 

sailor26

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Re: I think I bent a push rod

Ok, thanks, this doesn't sound good. Looks like the canoe for the rest of the summer.
 

Watermann

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Re: I think I bent a push rod

Ok, thanks, this doesn't sound good. Looks like the canoe for the rest of the summer.

Oh man that's a real bummer for sure. Start shopping around for a 305 long block and when you find one sell the canoe.
 

Don S

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Re: I think I bent a push rod

Did you pull the valve cover and look ????? I have seen rockers crack open and the studs pull out. Not a big deal to fix. Couple hours and back on the water.

Hard to troubleshoot a sound when you can't hear it.
 

gm280

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Re: I think I bent a push rod

First of all DON"T crank it up again until you figure out what is wrong! Every time you run it, it is doing more damage... Like Don S suggested, pull the valve cover(s) off and see what is going on. And also like Don S stated, can't determine what it could be without hearing it. Could be something simple as a rocker arm stud pulled out or as serious as a broken connecting rod. But don't keep cranking it and doing more damage... Time for some disassembly now... :eek: But certainly not the end of the world either.
 

sailor26

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Re: I think I bent a push rod

Ha, going to take more than the price I will get for my old canoe. Should have kept my sail boat though.

Unfortunately I am a real sucker for a fixer-upper. At 61 you would have thought I would have learned by now. When I bought this old Cobalt last summer I saw the quality that was put into it when build. All the old, grey, teak came right back to life with a little cleaning and oil. Very heavy rugged boat. Great quality on the chrome work. Last summer I spent 3x the purchase price just getting it to run right. Included all new wiring from the dash to the motor, all new dash gauges, carb, fuel pump. Shampooed the carpet before going out last weekend. looked pretty good (other than the upholstery, that's another story). Ran like a champ until I gunned it and screwed it up. Oh well, time to start saving up.
 

sailor26

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Re: I think I bent a push rod

As soon as this heat wave breaks I will do this. I haven't given up on the possibility of a bent push rod and or broken valve spring. I had this happen on an old 69 Dodge van many years ago, sounded very similar. Hopefully this weekend I will get to pull the valve covers.
thanks
 

sailor26

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Re: I think I bent a push rod

Oil pressure was running at about 30lbs most the time. I didn't notice what it was when idling before I opened it up.
 

sailor26

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Re: I think I bent a push rod

thanks for the advice. I was going to start it up again and record the sounds, but now I won't do that.
 

Watermann

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Re: I think I bent a push rod

Yeah it wouldn't help much anyway, 2 dimensional sound without direction from a video is going to get you the same amount of "it could be's." Just be sure to let us know what you find.
 

H2Onut

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Re: I think I bent a push rod

As other have said you need to pull the valve covers. Broken valve springs typically don't make noise they just don't seat the valve and engine doesn't run right. It sounds like a stud pulled out or the rocker arm adjusting nut backed off and and the rocker arm is clattering. You should be able to bump the motor over (remove coil wire so it don't start) and watch as soon as a valve closes (the lifter is on the base circle of the cam). At this point you can spin the pushrod to see if it is bent. You should also be able to wiggle the rocker arm but it should not have clearance between the pushrod or valve. Repeat this for all 16 valves. Sounds like a valve train issue. I have had my share on at the drag strip.

If you are holding 30 PSI of oil pressure I don't thing you have a rod bearing loose. Good luck!
 

sailor26

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Re: I think I bent a push rod

I'm starting to feel better already. Hopefully this weekend I can get the valve covers off. Will keep you posted. Thanks
As other have said you need to pull the valve covers. Broken valve springs typically don't make noise they just don't seat the valve and engine doesn't run right. It sounds like a stud pulled out or the rocker arm adjusting nut backed off and and the rocker arm is clattering. You should be able to bump the motor over (remove coil wire so it don't start) and watch as soon as a valve closes (the lifter is on the base circle of the cam). At this point you can spin the pushrod to see if it is bent. You should also be able to wiggle the rocker arm but it should not have clearance between the pushrod or valve. Repeat this for all 16 valves. Sounds like a valve train issue. I have had my share on at the drag strip.

If you are holding 30 PSI of oil pressure I don't thing you have a rod bearing loose. Good luck!
 

sailor26

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Re: I think I bent a push rod

Thanks, will let you know.

Yeah it wouldn't help much anyway, 2 dimensional sound without direction from a video is going to get you the same amount of "it could be's." Just be sure to let us know what you find.
 

sailor26

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Re: I think I bent a push rod

Well, everything looks in order under both valve covers. I turned the engine over and rotated all the rods. All looks good. Must be a deeper problem. Have to start saving up for a re-man block.
 
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