ExceSSive

iTrader: (13)

an internet diagnosis...

I helped my buddy install a forged 347 into his car, with a high lift turbo cam, low compression pistions and some ported LS1 heads. The engine block was honed, deck flattened and pistons installed with rings gapped for a FI.

During the break in period it has started to make a high pitched noise that we can not pinpoint what is causing it. It starts when the car has warmed up for about 5-10 minutes and goes away when uder a load. We changed the starter, took out the trans, clutch, all belts removed and the noise comes back.It is definitely louder when under the car. It is not a steady noise but a wavering tone that seems to me something is out of balance and rubbing something it should not be.

Anybody have an idea of what this might be before we tear the engine out and rip into the bottom end again?

Thanks
Jon

ExceSSive

iTrader: (13)

23 views and nobody has any idea what could be causing this noise?

I think it must be a crank bearing or something.

DaddySS

Why do you think a crank bearing noise would go away under load?

Almost sounds like a vacuum leak if it goes away under load. Can you get a vid? Can you get some more info - how's the oil pressure? When you say under load, you mean accelerating, just revving in neutral, pulling hard?

oange ss

iTrader: (50)

how's oil pressure ?

ExceSSive

iTrader: (13)

Oil pressure is fine on the guage. When I say under a load I mean in gear accelerating...in neutral it makes the noise, does not get better or worse when giving it gas. Sounds like nails on a chalk board only louder. I will try to get video of it on Wednesday and I will check it for codes with my HPTuners.

ExceSSive

iTrader: (13)

Just a guess, but it seems to loud to be a vacuum leak...when I get the video maybe you guys can give me more of an educated guess. I know this is hard on the internet without hearing for your self.

Gold Z

iTrader: (3)

Is this Mark's engine?

John02SS

iTrader: (47)

I've heard the noise and it is REALLY loud! All accessories, clutch, throw out bearing, and tranny have been ruled out. It is something internal, but with the oil pressure not dropping I wouldn't think it would be a bearing. Just unsure as to what the hell it is.

Irocss85

iTrader: (1)

have you changed the oil? if its someinng inside thats rubbing metal to metal it will be in the oil you'd think. and I have heard a vacuum leak make a wicked loud high pitch noise. almost like letting the air out of a balloon really slow. you know, when you stretch the balloon nipple while letting the air out? anyways, that turned out to be a vacuum leak that leaked into the crankcase, not out to the atmosphere. and it would pull air around the front/rear main seals into the engine. it changed with load like you said. pull the oil cap off while the eng. is running and if thats the case, it'll go away with the cap removed and you can feel the suction at the cap.
another idea is Ive heard on here people who get bad cams make a loud whining noise. possibly a bad cam surface? how bout the roller rockers? any of them not getting oil? maybe caused by a bad lifter or clogged pushrod? guess it could be a bad roller on a lifter too.

does it make a diff. if the eng. is hot or cold? noise same, louder, not as loud?

good luck

SPRAYED 01

iTrader: (22)

I had the same problem a few months ago. This might sound weird but remove the oil cap while its making the noise and see if it goes away. Let me know if that fixes it. You could have a massive vacum pull on the crankcase. This would cause the vacum to try and suck from any possible spot,dip stick mainly. Do you still have the vacum line from the throttle body to the pass valve cover hooked up?

ExceSSive

iTrader: (13)

unfortunately...it is

ExceSSive

iTrader: (13)

Actually it does not start until the car has been running for at least 5 - 10 minutes. I will give the oil cap a try.

Irocss85

iTrader: (1)

that sounds more like the problem i encountered. Im not sure how you could get that leak on an LS1, mine was on a customers grand prix with the 3.8. the pcv valve is in the intake plenum, and there's an oring around it to seal the vacuum from goin around the valve. someone changed the valve, and didnt put in the oring so the vacuum went right around the valve. are the pcv/vent hoses possibly crossed up somehow?

P Mack

iTrader: (6)

I would say take off the timing cover and see if the timing chain is hitting the oil pump if you have a double roller, or if the cam bolts have backed out and are rubbing against the timing cover. Also check the oil for metal.

ExceSSive

iTrader: (13)

Well Mark changed the oil and went from regular to synthetic, but he does not have a magnetic plug...so it was obviously clean. I told him he need to get one soon.

I agree with you that the timing cover should come off because maybe something is loose in there and rubbing. It is really strange though.

DaddySS

Well the only thing I can think of if it goes away under load and in gear, not acceleration in neutral is crankshaft endplay causing rubbing somewhere. Can you narrow down where it's coming from with a mechanic's stethoscope?

SPRAYED 01

iTrader: (22)

You try taking the oil cap off? I was ready to take my trans out and spend hundreds of dollars fixing it. Already had an oppointment and every thing. It ended up being a huge vacum noise. I fix cars for a living and it stumped me and about 5 other Mercedes Techs. Dont over look the small and weird things.

ExceSSive

iTrader: (13)

we will do that this week.

ExceSSive

iTrader: (13)

you wouldn't believe me if I told you what it was, but the sound is gone

Irocss85

iTrader: (1)

no no no. do tell.