roscobbc

Warning - This is going to be a long-winded post as I am really stumped with this issue. Have an engine noise on my '68 Coupe which I am at a loss to explain. A bit of background - Engine is a 454 4 bolt with stroker kit giving 489 cu ins. Heads are Brodix Race Rite oval ports. Inlet is Edelbrock RPM Air Gap with 950 Pro Form DP carb. Cam is a Howard flat tappet hydraulic. Rockers are roller. Distributor/ignition is MSD. Timed at 21 degrees static/38 degees total. Gas used is Super Unleaded. Fuel pump is mechanical similar to OEM. Oil pressure is as good as its always been (70 psi at idle - more or less off the clock at cruise) water temperature goes up as far as 180/190 degrees. I'm getting a clattering/knocking noise which seems to be at half engine speed when accelerating from perhaps 1500 rpm through 3000 rpm where it is at its worse. Decelerate at these revs and it quietens down. I have 'sounded-off' all over the engine using an 'old school' metal rod to the ear and at idle I can hear a slight noise held against no. 3 inlet port. It is definately not valve gear or rockers. Its not low enough in the engine to be big ends (and oil pressure says otherwise anyway) small ends perhaps? - the noise seems to be from the centre of the engine - camshaft area.
Over the winter I removed the inlet off the engine - checked out roller rockers, push rods - pulled lifters, cam have perfect wear patterns etc - all seemed OK. I had the engine built and installed 4 or 5 years ago and have done less than 2000 miles. Got it all back together today and thinking it may have been something simple like rocker adjustment issue, I carefully did did lifter preload - timed it - took it out to test run and noise is still there. My laddo said he could actually feel the vibration through the floor pan. I know some guys have had issues with the Centerforce clutches - its not that. The fact that it seem to be at 1/2 engine speed indicates perhaps that its a cam related issue? The noise is certainly towards the front of the engine - around 1/2, 3/4 cylinder positions.
So - could fuel pump pushrod/cam eccentric be responsible? - don't seem to have any fueling issues. Have a small in-line fuel pressure gauge on the carb fuel log that indicates a regular pressure of 5 psi (the needle does fluctuate which I presume is normal and due to eccentric on cam operating pump). If camshaft bearings had 'run' and the camshaft was effectively 'flapping about' in worn bearings I would have thought there would have been timing chain 'slap' ?
I trained-out as a mechanical engineer many years ago and have (IMHO) had a good 'ear' for issues such as this but this has really got me. Hoping some of you long served 'guru's' on here may have experienced this problems and perhaps direct me?

FireballXL5

Any chance for a vid? Any chance for motor/trans mount allowing play and getting a knock/rattle at lower Rpms where it may be less 'smooth ' overall? I've got a few clearances such as my trans mount after installing the new 700r4, that if the rubber mount ever went I'd hear it there first... And I could see lower Rpms causing a hit , where higher Rpms and smoother firing of the engine may not ... Just helping to trouble shoot, could be waaay off base here...

Indiancreek

Cam bearings would have caused a drop in oil pressure. Could you put a timing light on one plug at a time and see if the noise matches the light pulse with one particular cylinder?

Super6

Half engine speed and very high oil pressure. Could it be connected to the distributor/oil pump drive shaft? Do you run a heavy duty drive shaft with a metal collar? What's your oil pressure at idle with hot oil? Flat tappet cams have slight taper on cam lobe to keep cam from walking. I wonder how strong that centering force is versus the back and forth load an oil pump could put on the cam through the distributor gear.

Did you pull the timing cover? Could a cam bolt be backing out?

Did you look at fuel pump push rod?

Full floating pin pistons?

As mentioned above, a video would help.

roscobbc

Definitely not engine mount related - have good poly mounts

roscobbc

good point re. oil pressure vs can bearings. Good idea re. timing light

roscobbc

Oil pressure at idle hot is 70 psi.
Haven't pulled timing cover as yet.
Ditto fuel pump pushrod.
Full floating pin pistons - can't recall - can check later.
Can't say I noticed an irregular wear pattern on cam.
Car still performs as well as ever.
I took a video late Autumn before laying car up for a few months - can't find it - phone records in HD but audio struggles with this kind of sound.

Super6

I have a high volume pump in mine and I'm over 70 at idle on cold start, but when hot I've got able 35-38 psig at idle. You must have a high pressure high volume pump, the pressure is a stronger relief spring(?). Don't know. What shape is your distributor gear in, must be a pretty good load between the distributor and cam gears.

Did you happen to look at the journal walls around the cam bearings to see if a lobe is riding on the web there. Don't know how much forth and aft movement of the cam it would take to actually cause an interference. Could the cam and cam gear be pulled toward the back of the engine by the resistance to rotation exerted by the oil pump. With the result the cam gear is grinding on the block around the front cam journal. Just a rookie/amateur builder asking these questions.

cardo0

U could try and pull 1 plug wire at a time to see if it unloads a knocking rod.

Did u pull all the lifters for inspection? Did u make sure all the lifters go back in the same hole they cam out of?? Cannot swap lifters on different cam lobes (unless brand new).

Any loose rockers now? Have u ever set lifter pre-load before?? Amazing number of owners have never set lifter preload before and are influenced by others that it is easy. If maybe easy if u know what your looking for but the consequences of incorrect preload are not just ruined cam but can be the entire engine.

So how did u identify "zero lash". How much preload did u use? How did u lock your poly locks?

It reads here like something happened due to your inspection.
cardo0

roscobbc

Lifters and pushrods were all pulled for inspection and replaced in same locations
As you say preload can be a tricky thing to do. Used 'Lars' method. Find tdc - do no.1 inlet and exhaust - rotate engine 90 degrees - do next in firing order etc etc. Pre-load set at 1/2 turn.
Noise was there before inspection (and afterwards) so no change here.

May try taking car out and 'pulling' plug leads one a a time to see if I can pin it down to a specific cylinder.

KRUST

What is your compression ratio? If it is high, like 10:1, it might be engine pre-detonation (knocking). What octane gas are you using? Just something to look at.

roscobbc

10.5 c/r. Only ever use Premium Super UnLeaded. It isn't 'knocking' from pre-ignition (if it is I'm in really deep **** as the noise is a single source rather than multiple cylinders - thanks for response and thoughts!

Jig A Low

has this sound been there since the engine was built or did it just start?

I built my 350 into a 383, had my block clearance using the actual parts going in the engine, I ended up with a tap that only showed up with the car in gear (never at idle), turned out that while the block was clearanced the oil pan had not and there was just enough side movement on the crank it was barely touching the oil pan each time that rod came around, took a while to find that one.

roscobbc

Noise appeared last year - not from when built. It crossed my mild - doubt if an issue would show itself now - unless of course a big end was bad, causing end of conrod to hit block. Keep 'em coming guys! - I was hoping someone may have had a fuel pump rodrod issue and could comment.
I'll try and get car out for video in the next day or so - started raining now so not today!

hugie82

Does engine temp make a difference? A lifter noise would usually change from cold to hot but a fuel pump wouldn't. Don't forget hormonic balancer, dent in the oil pan, cracked fly wheel, broken valve spring, ect....

I had a friend with a knock that was loud but no drop in oil pressure and it ran great. When we finally got into the motor, it was a bend connecting rod from water getting into the motor. It bend it just enough that the counter weight would come around and bump the bottom of the piston.
I'm not saying this is your problem but it just goes to show, ya never know and don't give up!

DaveL82

I chased a problem in my car which I thought was engine related. Seem to come in when torque was highest. seems crazy but it was a motor mount that caused the engine to allow the fan to hit the shroud.

May not be your problem but thought I'd throw that strange one out there.

roscobbc

Been there with that one in the past - still have the chewed-up fan shroud as a reminder!

gkull

This right here is wrong. In any motor you adjust oil pressure with the weight of the oil hot. Period. 25 - 30 ish is fine and it should climb and top out lets say just at your oil bypass oil spring shimmed regulated pressure. which is generally 10 psi per 1000 rpm. In a blocked bypass motor which is the preferred setup you are not limited to the 70 psi which you might have.

You are putting a terrific load on the cam dizzy gear and timing chain. 21 degrees initial is a bit high. Because you have to think about the added vac advance causing super high cylinder pressures. You use ported vac advance (not full port Vacuum) and limit it to like 10 degrees with an adjustable vacuum advance can. All in timing should be 3000 ish

Your main and rod bearing will love you for that.

I just rebuilt a HP 427 and the bearings were down to copper. It is only caused by excessive cylinder pressure, heat, lack of oil pressure.

higher octane can only save a motor so much.

roscobbc

Thanks for coming on and commenting George - so are we saying that irrespective of gauge showing what appears to be good oil pressure - this may be hiding the fact that I have a shot big end bearing (or two)?

gkull

First I would verify that your gauge is correct.

Second I would turn the timing down and see if the noise goes away

I have experience and been around motors that come into the pits with rod knock. It is easy to identify. just blip the throttle and you can hear the death rattle or even a squealing sound.

When you had the intake off did you actually pull the roller lifters and inspect the wheels? I've had failed roller wheel barrings back when I used cheap SR lifters and a failed aluminum rocker.