Thread: knock noise

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Sorry I read a comment wrong so I deleted my post.

Em

DO NOT START OR CRANK THE MOTOR OVER until you determine wether or not the rod is bent. If the rod is bent and stuck up onto the cam, starting or cranking the motor could damage the cam.
On the SBC the fuel pump bolts to a plate that is bolted to the block with 4 bolts, the rod will not come out without taking this plate off. Sometimes the rod drops down and wedges between the plate and the block and can not be moved through the small elongated hole in the pump plate. Remove the plate and the rod should come free easily.

Hit it with some penetrating fluid and let it sit for a few hours and it came right out. It's got a flat spot on it about center possibly where someone ran the bolt to tight to hold it in place while replacing the fuel pump. Goona try a new rod and see where that gets me.

Originally Posted by milogreen

Hit it with some penetrating fluid and let it sit for a few hours and it came right out. It's got a flat spot on it about center possibly where someone ran the bolt to tight to hold it in place while replacing the fuel pump. Goona try a new rod and see where that gets me.

That's the right thing to do, but I'd be wondering about the cam lobe if the rod was that tight. Maybe you'll get lucky and the new rod is all you need and the lobe is fine. Next oil change check for fine metallic dust in the old oil.

Originally Posted by rspears

That's the right thing to do, but I'd be wondering about the cam lobe if the rod was that tight. Maybe you'll get lucky and the new rod is all you need and the lobe is fine. Next oil change check for fine metallic dust in the old oil.

Closely inspect the cam end of the rod for galling at the cam. If the cam lobe has started to go away, there is no saving it. Only fix at that point is to bolt a plate over the pump mount and install an electric pump.
If the rod end looks shiny with no galling, you may have gotten lucky.

.

As a side note;
I've had bad luck with the rubber diagrams in mechanical pumps and todays ethanol laced fuels. After changing two mechanicals a year apart, I switched to an electric. Ethanol doesn't seem to bother the vanes used in electric pumps.

The end looks to be in pretty shiny and apparently the lobe is not worn down so much that it wasnt operating the fuel pump. Only problem was the knock noise. I have a few more hours for the RTV to fully cure and then I will fire it up and see where I am at.

Thanks one and all for the help.

Milo

Originally Posted by milogreen

The end looks to be in pretty shiny and apparently the lobe is not worn down so much that it wasnt operating the fuel pump. Only problem was the knock noise. I have a few more hours for the RTV to fully cure and then I will fire it up and see where I am at.
Thanks one and all for the help.
Milo

Milo,
So how did it sound?

You're right that the lobe isn't worn down enough to keep the pump from working, but is it worn away 10%? 20%? The problem is that once the wear starts it's likely to continue, even with a new rod, because you will have worn through the surface hardened profile, exposing the softer substrate of the lobe. It would be prudent to check your oil drain pan like Tech described above, if for nothing else but peace of mind. It'd be a shame to trash the whole engine and learn of it when your fuel pump quits pumping enough to fill the carb. Just my $0.02, yours to consider as you see fit.

Ok update here, I dont know if I solved the knock noise or I was hallucinating, but now I have more of a metallic rattle, If I goose the engine as it come back down to idle I get the rattle noise as best as I can tell it is loudest at the water pump, but this is with the fan belt disconnected. Is it possible there is a broken part in the water pump just rattling around?

Impeller could be a little loose on the shaft or have a broken vane rattling around inside...

Go back and read post #8----------short out cylinders one at a time to isolate which ones are making the noise--------If it makes rattle noise on decal, it could be timing chain/gear links-------


Any chance this has a gear drive?

I agree with Jerry, the timing chain might very well be the issue, too. You say it's a '68 truck with '76 (you think) engine. Any idea how many miles on the engine? Just wondering if it's a very high miles survivor that still has good compression?

It could be a high miles survivor, but I thinking that it has had some work done on it although maybe its just window dressing. Anyway I pulled off the plug wires one by one still had the rattle, pulled the water pump all look good. It appears my harmonic balancer is dinging against my timing chain cover. Is it possible for these to go bad?

As a side note when I looked up the engine # ( dont have it infront of me right now) I tracked it down to a engine built in Flint and assembled in a truck at the NUMI plant in Fremont CA in 76.
Pulling of the valve covers the number on the head, The number was 8 or 6 917290 GM2 L? 27. The design on the outside of the head is a square block with a rounded hump in the center. When I looked that up it said 327 68-70 or 307/327/350 68-79.

Your harmonic balancer is delaminated and needs to be replaced.

I hate when my harmonics become delaminated!