Newly rebuilt 350, top o bottom. fully balanced, bearings plasti gauged, everything "by the book."
We have been chasing this for a while
Replaced all the new rockers, balls, push rods, lifters and still there, remeasured the cam to check for signs of bad bedding in...all ok.
We did have 2 taps...found that early...with the higher lift cam, one of the rockers was just touching the tappet cover, we ground a little off the inside and thats gone....at the same time we ground a little off in the spot where a rocker could possibly touch.

The tapping is just like a loose rocker adjustment...
There is no pulling of studs or nuts backing off
There are no leaks on the manifolds
It is not in the water pump, pullieys, alternater or anything like that
There is no missing, power loose or a sparks jumping.
No pinging and plugs are txt book.
Oil pressure and temps are excellent.

It only taps when under light to full load on the road
It sounds (from inside the car) to be drivers side

Fuel Pump Pushrod?

OK, if it only does it under load then it's not your valve train. Hmmm, is this a test?
Not a incorrect/wrong bearing in your kit,,, you plastigauged it. Hmmm. Under Load,,,,,.
Are you positive it's not an exhaust leak?

Fuel Pump Pushrod?
MARK! I was going to say that! But it's on the drivers side. Diagnosing a fuel pump broken return spring when I was a kid brings back 40 year old memories.:) It made me 'one of the guys' at the local hangout.
And that kind of noise should happen with no-load too.

Under load???? Are you sure it can't be made to knock by reving the engine in neutral? Piston touching head maybe???

No it is not fuel pump...it doesnt have a fuel pump, doesnt even have a petrol line or pertrol tank lol

Piston touching head, no...everything was dumied up for clearances before assembly ...without head gaskets

And will not do it in neutral and rev unless 1st starting in the morning, disappears after about 100 yrds.

Absolutly positive is not exhaust leak...2x new gaskets, running cast rams horns, checked flat surfaces, checked for leaks, retorqued more times than I can remember now

Summer is here, Xmas holidays, club runs, show season...

I had something similar, yrs ago on an engine, eventually stripped it right down and found a cracked piston!!! just hoping Dont have to strip down again...means not just replacing the pistion but rebalancing etc etc

Oh great! Now I'm going to lay awake all night thinking about it!
Don't fret about the balance. Just duplicate the old piston weight, if it comes to that.:sad:
Hmmm, maybe it's time for a leakdown test,,,,

Compressions are all good...Engine has now done about 500 miles, loaded it but havnt opened her full up thru the gears yet...its bedding in nice and the idle screw has had to be turned down a turn.
Compressions are good...radiator coolant clean and no HC. oil is good...been changed a couple times now...
I think I know its a piston and just dont want to admit it cause I have so much work on at the moment

Dont have to strip down again...means not just replacing the pistion but rebalancing etc etcIf you have to replace a piston, the shop can rebalance the piston by itself to match the engine balance. They get the weight from the balance card listing.

You still have the balance card? All the weights of the components are listed.

And as Fred suggested, I'd either do a leakdown test or at least shove shop air into each cylinder and feel the oil fill for amount of blow-by on each cylinder.

Summer is here, Xmas holidays, club runs, show season...


Cheer up. We had record winter ugly weather last month. There's still snow on the ground from LAST MONTH. And winter is two weeks away. Feel better?:angry:

I warned you! As I laid awake most of the night, it dawned on me. You're driving FROM THE WRONG SIDE OF THE ROAD. Your car is probably a right hand driver. Right? So the drivers side is the starboard side?
OK, still no fuel pump. But no matter what's wrong you've gotta pull off the drivers side exhaust manifold. DO THAT FIRST. Let everything else wait. Inspect the hell out of it. Look under every corner and bend for a small crack. You know, the kind that gets bigger when heated-up under load. If there's one, it should be evident by now.
Also, are you running a heat valve? That's the flapper valve on the exit of one of the exhaust manifolds. If so, it's worth a look. Good Luck.

More cheery news for you. That snow from two weeks ago is still here. Melting like crazy but there's still some virgin stuff, and it's raining again like crazy! Not even the birds can/will fly! Cheered up?

Thats a possiblity...cracked manifold...
Yep will crack test this week, thu its still a long shot.

We had record winter ugly weather last month

There is something wrong with the weather, Summer here and we have had a hudge temp drop and out od season hail yesterday

Tapping? Like valve clatter? Timing?

Yes I do have the balance sheets...still have the ones from back in 86 rebuild
Exhust manifolds has no cracks
Did have a lifter type tap...1 was just touching the Al cover ..thats fixed..
Its hard to describe...a deep tapping or a tapping type of knock???
It is not the valve train... the new valve train been fully replaced...did find a faulty lifter...

Im coming back to a cracked piston,,,,someone drop the box of pistons someware between the factory and shelf here in NZ???

A cracked flywheel or bad torque converter will make a racket under a load.

Its hard to describe...a deep tapping or a tapping type of knock???If you remove one spark plug wire at a time, does the knock go away from the crankcase?

I dont know...its only under load....I tried but it was a tight squeeze under the bonnet going up the road...and it was dark...Im scared of the dark...lol

Not being sacastic...just got passed the stage of pissed of and to keep sane need a but of twisted humour lol

Seriouly thu, I know most of the tricks of the trade...pulling the plugs can u explain the reasoning to me? I can see it would locate the piston/cylinder but as to ID ing a cracked piston Im not sure...
If one doesnt ask one doesnt learn...and there is always something to learn.

The idea is, because it's happening under load, to reduce or eliminate the load. If with a plug pulled, that cylinder can't produce load and if the knock stops, that's a major clue. Great way to diagnose bad bearings.

If your car has a large-body HEI distributor, you might want to check the firewall clearance. I chased a similar problem with my 69 RS shortly after I purchased it - a tapping that sounded like an exhaust manifold leak. It turned out the distributor cap was wedged up against the firewall enough that the rotor was actually striking the cap. It usually showed up under load, which I suspect was forcing the cap toward the firewall a tad more.

Worth a look...

Yep will do so tomorrow
Ihave a GM HEI been installed for about 15yrs
The cap clears, the HT lead holder part is to big to fit so I have shaved the back of it..That was a long time ago. With the rebuild, possibly the motor is sitting back a couple mm more????

Nope not the Dizzy...missed a suggestion above re torque converter...no it not that either the sound in more engine than bellhousing...Stetoscope

I think will leave till after Xmas....had a hard out 4 weeks of work, 1 day started 7am thru to 3:30am next morning worked straight thu, then started again 7:30am thru to 7pm!!
These young guys just cant hack the pace of us old guys lol
Some weeks I have 2 or 3 hrs a day then everything is all on lol

Piston pin comes to my mind.

Yeah that what we have also thought, I described the sound as a cross between a knock and tap...sort of between a tappet/cracked piston or gudgen.
Either way we are going to strip the engine down in the new yr

sounds like what I had happen to me with a 87 s/10 blazer, after the motor was rebuilted,at idle and low speeds it sounded great then once I ran it on the highway, the tapping started,it turned out to be a semi clogged cat which caused the piston skirt to heat up and expand and scuff some of the the piston skirts maybe you have a clog in your exhaust (mouse)








































i

Hmmm looked for a Cat...couldnt find one on the 69, so cant be that.

had a hairline crack in my flywheel. professional engine builder swore up and down it wasnt the flywheel. So I checked neway, small hairline crack...worth a check...

Have a flexiplate, and this was crack tested, along with other stuff, before the crank was balanced...Crank balancing done with flex plate, Harmonic balance and bolts in place and marked/labeled.

Worn distributor bushings will make the very same noise...

What cam are you running?

Had a very similar problem with the tapping under a load.
Tried almost everything to find out the cause.
Turned out to be a leak in the header gasket.
Sounded just like a valve tap.
You never know!

Before you tear the engine down I would try backing the timing off 10 degs or so and drive it again just to be sure you don't have a spark knock problem.
Pulling the plug wires one at a time and test driving it with one wire shorted to grd is a very good idea. This may help you narrow down what cly it is before you have to take it apart.

Worn distributor bushings will make the very same noise...
What cam are you running?
Nope, rebuilt shaft, cold metal spray, Al/Bronze/Co with new reemed to fit bronze bushes
Cam is a custom billet high lift (yeah a couple rockers where touching the tappet covers)

Turned out to be a leak in the header gasket.
Already cover in previous posts

try backing the timing off 10 degs or so
Done, thu not for the knock reason, to establish opitum curve..and it is not a ping.
Pulling the plug wires one at a time and test driving it with one wire shorted to grd is a very good idea. This may help you narrow down what cly it is before you have to take it apart.
Yep a previous post, naroowed down to 1 of 2 cylinders on the left bank

Love the feedback! We're rooting for ya! I suspect that each reader is hoping his guess will be the right one. I sure am. Did you check your manifold even closer?;)

Im not going to do anything this side of New Yrs, then I HAVE to get the new engine for the Bradford put together and reconed Diff/gearbox in for a couple shows in late Jan and Feb...
The camaro is running fine in the mean time, not going to open her up thu, it just the tapping annoys the crap out of me ....turn the radio up lol

Love the feedback! We're rooting for ya! I suspect that each reader is hoping his guess will be the right one.
Run a sweeps stakes huh? lol

I still say cracked flywheel or torque converter.

Well have pulled the engine down last week...and the bad news didnt find anything...
So took all the heads etc down to a good friend who specialises in heads...
He picked it up straight away....
The skirt on the pistons have collasped...on #5 piston there is a 24/1000 diff between dia below the bottom ring and the dia at the bottom of the piston skirt...
And all the rest also have colapsed to a lesser deg..
This all happened during intial cam break in...
This is caused by heat..not over heating but normal heat on crap pistons

What brand and type of pistons was it ??

wristpin play too...i just revently had a "mystery" noise in my truck that sounded like a lifter...the
front pump in the trans i just installed was cavitating!!!1 quart of dex3 later it was gone...lol...wow, did i get in late in the game...didnt realize the other 2 pages of posts...lmao...

wow, did i get in late in the game...didnt realize the other 2 pages of posts...lmao...
U will notice there is quite a while before my update lol
I will come back to on the brand...It wasnt a performace high rpm engine so didnt use a top brand.. They are ex States...the details are down the workshop...Will make sure the details are 100% right before mention a name.
Be a few days before I get down there.

Seal Pro...and in the fine print made in Mexico
Im contintuing this thread in a new thread here
http://www.camaros.net/forums/showthread.php?p=734317#post734317
as I need comments on these pistons...any troubles etc