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Discussion Starter #1
Boat ran fine at Big River all weekend until the end of the day. It started knocking hard, then we killed it. Floated to a random house and picked it up with the trailer. I'm trying to figure what caused the knocking because we started it quickly after that and the knocking went away. We only had it idled for about 15 sec but no knocking. The boat has 60 lbs oil pressure, oil is clean ( no flakes or chunks), pulled the valve covers off and turned the motor all the rocker arms were going up and down properly. It did not overheat. Did a compression check (note that the gauge is does not go to 0 but stays at 20 psi, so maybe +20 to my numbers)
Cylinder
1) 155
2) 150
3) 154
4) 150
5) 135
6) 125
7) 130
8) 154

My only guess is one of the lifters went out to cause the knocking and then somehow started working again. The variance in the compression, because 5 and 7 are next to each other, may be from a leaking head gasket?

My buddy is suggesting to pull the heads, get them milled down, and checked out. Get a new cam and lifter while I'm at it. Easy for him to say because he's not the one paying the bill. The guy at the machine shop said if the noise went away it is most likely top end.
I almost wish I found something broken. Now everything seems fine, but I do not want to chance it.
Its a BBC 454 with 049 heads.
Any hints on further diagnostics?
 

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E-7 Sheepdog (ret)
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Repeat teh compression test afte a squirt of motor oil in each cylinder, see if that seals up a ring in #6 or if that leaves valves suspect.

A leakdown would be next.

In leu of a leak-down tester, a pressure fitting (to permit valve spring changes without removing heads) would let you pressurize #5 6, and 7 (one at a time) and search the exhaust ports and intake for leakage noise (hissing). Find a bad valve THAT way. (back off all the valve rocker adjustments first). Also would bleed to an ajacent cyl. if gasket is leaking.

Good luck.

Either that or pull the heads (only certain expense is $100 in gaskets), clean them and check them for warpage, BEFORE possibly wasting money having them milled. Don't bother milling a flat surface, mill a bent one flat. Then pull the valves to look at the wear patern on the seats, and for straightnesss on a flat surface (large plate steel or glass). Also looking for burned gasket.
 

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Sounds like probably a collapsed lifter. You are running hydraulic I bet.
 

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Discussion Starter #6
Sounds like probably a collapsed lifter. You are running hydraulic I bet.
Are hydraulic lifters bad? What kind should I look for? Will I be able to tell if there is a collapsed lifter when I take it out?

After reviewing my Summit catalog, my intake looks more like a dual plane.
 

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Discussion Starter #7
I think that gauge is not accurate, but should be a good indication of variance. How many PSI should I see in each cylinder for it to be normal?
 

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That wrench in the lifter valley could have been making the noise too:)sphss. That does suck. I broke the top of a piston off before

Cy
 

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thats # 7! i did that a few times running too lean! the knocking could have been detonation. did your fuel system (fIlter /tank) get plugged ? did you make sure you had enough fuel for the new motor . the right octaine/timing . slap a piston in it with a light hone /fine honing tool
 
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