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Marine BBC has squeek in valve terain and minor backfire

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Old 02-29-2012, 09:45 PM
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Default Marine BBC has squeek in valve terain and minor backfire

I have a 454 Chevy in a jet boat. I have been chasing all kinds of problems since a local auto store did a crappy job on a rebuild many years ago. Being that it is in a boat has taken longer than usual to comb through everything. However, I have a high pitch squeak and exhaust backfire/poping coming from the valve terain on the right side of the motor.

I do not know how to begin to tackle diagnosing the problem so I can fix it. It is running hudraulic lifters and roller rockers on aluminum heads. I don't know weather it is a valve or a lifter or what cylinder it is coming from. Could the valves need readjustment? I imagine for some reason something is causing a exhaust valve to be out of adjustment and causing a backfire... If anybody has any experience or ideas dealing with this I could use some help.



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Old 02-29-2012, 10:12 PM
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Exhaust valve hanging in the guide possibly. Need to get the valve cover off first and see if anything looks unusual. If you can run it with the cover off you might see something or at least be able to pin point which one it is. Pull the plugs on that side and see if one is noticebly different than the others. Check to see if it is adjusted correctly.
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Old 02-29-2012, 10:26 PM
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you might have a broken valve spring,or a flat cam lobe.do a compression check to locate the bad cylinder,then remove valve cover&inspect fot broken parts.let us know what you find please.
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Old 02-29-2012, 11:08 PM
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Default Observing the valves

I would have tried to pull the valve cover a while ago but the motor has over the transom headers. Besides oil spraying over the motor and cooking on the headers it is a mess. Maybe I need to remove the header completely so it is out of the way and I don't have to worry about burning my arm trying to hunch over a hot header. Anyway, thanks for the ideas. I'll see what I can find.
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Old 03-01-2012, 12:05 AM
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Last time I heard a motor do that it was a roller lifter that had broken it's retainer and twisted in the bore. This caused the roller to scuff against the cam and make the noise. You can do a compression test without taking off the covers, then when you find a cylinder low you can pull that cover and start getting deeper into it.
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Old 03-01-2012, 03:08 AM
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that head is coming off, though.
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Old 03-01-2012, 11:20 AM
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Removing the head is what I'm worried about having to do. I'm sure it will have to be done but wish it didn't have to be such a pain do. I'm heading to get a compression tester today and I'll check it out and post my findings.
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Old 03-01-2012, 12:34 PM
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If it is a flat tappet cam I would say the most likely culprit is that you've lost a lobe on the cam.
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Old 03-01-2012, 04:19 PM
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a stuck open valve can sometimes cheep or squeak as the exhaust gasses blow out when lit, instead of waiting for exhaust valve to open. do comp test. it won't be right. take off header and valve cover and crank on starter. i just can't see a cam lobe. that is wear. very few boat motors live long enough to wear.
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Old 03-01-2012, 04:29 PM
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I made the leap and spent $42 on a compression tester. I went and tested the compression and all cylinders read too little to register the gauge. I assume they were nowhere they should have been. I literally just noted it as a few psi. The number one cylinder has no compression at all. Cylinder 7 reads about 107 psi.

I imagine I need to re-adjust all the valves because it appears they are not adjusted correctly. We had pulled the heads and had to set the valve lash and we followed a set of instructions I found online. Guess it isn't quite right. Odd how I can still get it to run though.

I wondered why I couldn't get it to start and I thought it was a ignigion problem because I could get it to run on occasion it was just really hard to start. Just thought the ignition was weak. Well I got the new ignition and it must really work well because it is lots easier to start this low compression beast than what it was before I replaced it.

I guess I need to set the valves correctly so I can tell what if any cylinder it is or if the valves being set incorrectly is causing my problem. What is the best and proven method to set my valves properly? What compression range am I looking to achieve for a mildly modified BBC?
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