'69 427-400HP knocking
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
All the valve train looks good? Nothing loose, no broken springs, no really blue looking rockers, all the pushrods nice and straight not rubbing on the guideplates.
Before you pull the pan, just for fun, start it and reach down and grab the fuel pump. I've seen a couple start going bad and cause a knock. (Watch the moving parts- fan/belts and stuff) Better than that, stick a long screwdriver or a broom handle on the pump and hold it to your ear.
Timing chain ever been replaced? Chain could be sloppy and hitting the cover. IF the cam timing is all over the map that could be part of your performance problem.
If you end up dropping the pan, look for any discoloration on the rods or trash in the bottom of the pan.
Before you pull the pan, just for fun, start it and reach down and grab the fuel pump. I've seen a couple start going bad and cause a knock. (Watch the moving parts- fan/belts and stuff) Better than that, stick a long screwdriver or a broom handle on the pump and hold it to your ear.
Timing chain ever been replaced? Chain could be sloppy and hitting the cover. IF the cam timing is all over the map that could be part of your performance problem.
If you end up dropping the pan, look for any discoloration on the rods or trash in the bottom of the pan.
Advanced
Joined: Feb 2006
Posts: 50
Likes: 0
From: Mississippi
Have you checked your ballist resistor?
If you are still running a ballast resistor,and have the stock ignition system
or an after market that requires one,they will go out intermittently.When the ballast resistor goes out the engine will miss like!@@# and develops no power(and then sometimes work fine).The purpose of these is to keep voltage the same when cranking etc... thus not burn up points/condenser.
Engine detonation knock sounds different than rod/valve knock.Had an engine once that knocked whenever it warmed up.It was a cracked cylinder,and when thermostat open it put water in the cylinder,and the oil.
Pressure tested block and couldn't find it til engine completely disassembled and vatted.Coils also are known to short when hot and be fine when cool.
1st step is to be sure what kind of
knock and from where it is from.
or an after market that requires one,they will go out intermittently.When the ballast resistor goes out the engine will miss like!@@# and develops no power(and then sometimes work fine).The purpose of these is to keep voltage the same when cranking etc... thus not burn up points/condenser.
Engine detonation knock sounds different than rod/valve knock.Had an engine once that knocked whenever it warmed up.It was a cracked cylinder,and when thermostat open it put water in the cylinder,and the oil.
Pressure tested block and couldn't find it til engine completely disassembled and vatted.Coils also are known to short when hot and be fine when cool.
1st step is to be sure what kind of
knock and from where it is from.
Melting Slicks
Joined: Sep 2011
Posts: 3,372
Likes: 215
From: Peoria Arizona
Is it possible what you're hearing is detonation? Maybe you have a fuel pressure issue of some sort? Just trying to think of more simplistic things before you dive into a teardown.
Hope it all works out the best it can.
Adam
Hope it all works out the best it can.
Adam
Thread Starter
Drifting
Joined: Feb 2001
Posts: 1,539
Likes: 63
From: new ulm mn
Noticed one of the plug wires was loose. thought that might be the problem. Put valve covers back on and started her up. Ran great for about 1-2 minutes, then, weird rattle and motor starts missing and knocking again. Hmm. Seems when I let it cool off it starts great and runs great and then shortly thereafter it goes to hell. Checked vacuum advance and it works. Going to try and get it to the mechanic as soon as I can get a trailer lined up.
Last edited by loflite; Sep 4, 2012 at 10:29 PM.
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
The suspence here is interesting.
Can't explain the smooth startup and then knocking after 2 mins. Sounds alot like a timing chain. Put 40 psi at idle is high - at least for a small block. Yea bad rod bearings get louder as the engine warms up. But from your posts the knocking can go away also.
Well if only one rod then why the power loss (first post) - V8 still pushes the car with 7 or even 6 cyl?
Yea my money is on the timing chain that sometimes flops back to original location.
Good luck and please let us know what u find,
cardo0
Well if only one rod then why the power loss (first post) - V8 still pushes the car with 7 or even 6 cyl?
Yea my money is on the timing chain that sometimes flops back to original location.
Good luck and please let us know what u find,
cardo0
Thread Starter
Drifting
Joined: Feb 2001
Posts: 1,539
Likes: 63
From: new ulm mn
Found the problem. Apparantley someone had at some point put a small brass spacer between the lower air cleaner cover and the carburetor. I must have knocked it into the carburetor and it got sucked into the #6 cylinder, at least that's where the pieces were. Gonna have the other head pulled right of way and check for any damage. The intake valves are pretty dirty with build up for only a 6-7 thousand mile engine, so it will be an opportunity to check for any bent parts and do a clean up right of way. Good news is there is no damage to cylinder walls or pistons on passenger side. will see drivers side later today. Could have been alot worse. Should have been more careful when I pulled the air cleaner off last time. I don't think that brass spacer was factory as it does not show up on any parts catalogs. Another plus, was able to take pictures of all part numbers and build dates to verify numbers matching. Too bad it had to happen though.
Thread Starter
Drifting
Joined: Feb 2001
Posts: 1,539
Likes: 63
From: new ulm mn
Drivers side is good. Looks like one of the cylinders had some parts bouncing around on this side too as the carbon is knocked off here and there. Got lucky. Now going to have the heads checked and clean the intake real well and hopefully get back on the road soon. Thanks for all the info. from those who contributed.
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