302 knock (AGAIN!!!)

simonjrwinter · #1 (**permalink**) 02-28-2003, 10:11 AM

Right. This is a 400 mile old engine. It was rebuilt with all new parts and developed a knock at 300 miles. I've changed the big end bearings, I've replaced the camshaft and it STILL KNOCKS!!
It sounds like it's coming from the camshaft-ish area, ie not one side or another, its a definate knock not a rumble (so I don't supect the mains) It was rebored +30 with new pistons and rings and the noise DOES sound a bit like piston knock, but surely not at 400 miles? If there had been a problem with the re-bore (I couldn't see any) surely it would have knocked from new?
HELP!!!
Thanks

wilf leek · #2 (**permalink**) 02-28-2003, 10:21 AM

Simon - you just have to let an engine guru listen to that d*mn thing!
Where are you in the UK?

simonjrwinter · #3 (**permalink**) 02-28-2003, 11:27 AM

Hi Wilf,

Well I did! I asked Cheng Lim to come around to have a listen, (I'm in Essex) and he was sure it was the camshaft making the noise. He's as suprised as I am that it's not the problem!
Simon

GUMBALL UK · #4 (**permalink**) 02-28-2003, 12:08 PM

Simon,

I think the only thing to do now is to pull that motor out and rip it apart to find the problem. It would appear to be a problem other than cam or big ends as you have said - could it be some sort of contact inside (Distributor drive??) ??? An improper sized bearing (mains??) ??? As you said before, and as shown in the photos you sent, the cam wasn't badly worn, and that has now been replaced.
Did you have the crank reground??? - could be an issue here???, and could still be big ends???

I'll keep my brain ticking over for a while longer, and see if it comes up with some other ideas!!!

GUMBALL UK

Clois Harlan · #5 (**permalink**) 02-28-2003, 01:38 PM

Excuse me gents for the interruption but Simon are you running a mechanical fuel pump? If so have you checked to see if the knock is coming from there? How about the timing chain and spocket. Do you have a stethoscope that you can place on different parts of your engine while it is running? Could your rods be bumping the bottom of the oil pan?

Good luck!

Clois Harlan-Tulsa, OK (USA)

simonjrwinter · #6 (**permalink**) 02-28-2003, 04:07 PM

It's an electric fuel pump, the sump clears everything swinging around underneath, and I have tried with a stethescope (well..a piece of tube) to locate the sound but it seems to be coming from right in the middle of the engine (hence the new cam)

wilf leek · #7 (**permalink**) 02-28-2003, 05:26 PM

Simon - have all the lifters pumped up?

Excaliber · #8 (**permalink**) 02-28-2003, 05:34 PM

Like I said in an earlier post:

Engine noises is one of the most difficult areas to diagnose. Not surprising that even a veteran mechanic with years of experience could be mis-led.

The rubber hose is good, sometimes better than a stethoscope, I like both.

Center front is the location? At least that helps narrow down the suspects. Sound "travels" though, it's tricky stuff.

Ernie

simonjrwinter · #9 (**permalink**) 03-01-2003, 01:01 AM

Wilf,

How would I check if the lifters have pumped up? The lifters I took out all seemd fine.

boxhead · #10 (**permalink**) 03-01-2003, 01:25 AM

lifter noise is more like a ticking sound and it is at half engine speed as they are driven via the camshaft.
is the noise there at idle? or is it only at a certain rpm range?
does the noise only come when driveing the vehicle? ie under load
it could be camshaft or crank end float?
just tossing ideas around as it is very very difficult to diagnose engine noise with out hearing it.
if the noise is there at idle try droping the box out and run the engine, atleast if the noise is still there it is deffinatley in the engine

dscott · #11 (**permalink**) 03-01-2003, 08:02 AM

I had this problem one time and it was a mind teaser. What I finally found out was the bore size was about .010 over what it should be. It made a hard knock that came from the center of the engine so I tried everything you have. The machine shop screwed up and I learned a good lesson, always check clearances!
Don

ScottieR · #12 (**permalink**) 03-02-2003, 11:31 AM

look at the piston wrist pin boss bottoms, we has an engine that knocked after 5 min. we found the chrank shaft counter weights just touched the piston bottoms once the pistons were warm and expanded.

GREENSNAKE · #13 (**permalink**) 03-02-2003, 12:11 PM

Hey Simon! I had the Same Problem in a 351w Had it apart twice Had that Knock in it Finially found out what it was The mains were good ,Rod bearings were good , Cam was good ,Lifters all adusted right, Finially i Noticed what it was. It Was the Conecting Rod the Piston Skirt sat so far over the rod that you couldnt see it It was bent but really couldnt tell till it was off the piston but sure enough bought a newone put it back together and ran perfect Hope this helps (greensnake)