Author Topic: Motor Guru Question.... (Read 296 times)

NUTTZ · « **on:** April 18, 2005, 10:08:51 PM »

My GTO engine went.

Symptoms: Sounds like I threw a rod, But the sound is the Harmonic balancer/pully on the crank shaft Going In and out about a 1/4 to a half inch.

belts off the pully STILL goes in and out and clanks.
Fires up, not missing, Just the pully going in and out and clanking.

If the crank shaft broke at any point could it still run? motor still gets power to the tranny, and timing chain.

dropping the pan and checking the crank is inevitable.

But this is boggling.

My brother said the single center bolt ( harmonic balancer ) could be loose. It's Tight.

Neigbor rebuilds engine for trucks and says " If the crank shaft broke at ANY point It either wouldn't get power to the trans or the timing chain, Or not even fire up. So he is stumped.

Lets see who can call this one, before I rip the oil pan off.

It's a 455HO.

NUTTZ

GtoRA2 · « **Reply #1 on:** April 18, 2005, 10:21:12 PM »

You sure the rubber in the harmonic balancer didnt go, so part of it can move?

GtoRA2 · « **Reply #2 on:** April 18, 2005, 10:24:37 PM »

Also if the guys here can't this site has a great though clunky board.

http://www.classicalpontiac.com/

Maverick · « **Reply #3 on:** April 18, 2005, 10:55:16 PM »

Sounds like you lost the shims or spacers regulating end play of the crankshaft.

GtoRA2 · « **Reply #4 on:** April 18, 2005, 10:57:06 PM »

Mav
I didnt think Pontiacs used shims like that... hehe but its been some time since I had one apart so I could be wrong.

rpm · « **Reply #5 on:** April 18, 2005, 11:10:21 PM »

Yes, you may have a broken crank. If it broke in one of the journals, the rod bearing could be holding it together. I've seen it happen and the engine still run.

Thorns · « **Reply #6 on:** April 18, 2005, 11:58:26 PM »

It's been a long time since I saw the inside of a ponyack engine, but you might want to pull the pan, and check the crankshaft thrust bearings. If it's been clanging and banging very long, you might want to pull the engine, and check the damage to the block and crankshaft.

Thorns

Roscoroo · « **Reply #7 on:** April 19, 2005, 01:25:52 AM »

broken crank is a posibility and it will still run but it will make one hell of a noise.

(pull the plugs and put a breaker bar on the balancer bolt and rock it )

Could be a worn thrust bearing if its a 4 speed behind it ... ive never seen the trust wear out in a auto pontiac.

the balancer could be cracked also

the 455 crank is a fairly stout peice and it takes a hell of a lot or a very bad harmonic to crack one , A main bearing may have spun but a rod bearing always goes out 1st when that happens .. (or ir ya buzz a stock cast rod 455 past 5600 rpm)

if i could hear it i could tell ya exactly what it is .. ( Pro Pontiac eng wrecker here)

Im gunna guess that you have worn bearings and one of the rod bearings let go ..your getting the eccessive end play because its a 4 speed

Nunzi still makes the peened and polished cast rods that will hang in a 455 if you dont have alot of cash .
I raced 3 yrs on a set in a 455 running mid 11's in a 72 gto and daily drove it .

Captain Virgil Hilts · « **Reply #8 on:** April 19, 2005, 07:26:37 AM »

I'd GUESS the crank is broken, at the #1 rod journal. A crank that fails on its own (as opposed to failing because of the failure of another component) will almost always break at the #1 journal or the #8 journal.

lazs2 · « **Reply #9 on:** April 19, 2005, 08:10:35 AM »

If the thrust bearing, or thrust surface on the rear main went away completely... you wouldn't even get an eighth of an inch play... might look like more... if it is a stick, what does it do with the clutch in? I have run cranks with 15 thou play and they looked like a lot more.

if it were a crank broken anywhere past the balancer... you wouldn't have a functional cam chain. if broke past the chain the pulleys wouldn't turn .

If the balancer is gone then the center would stay put as the ring moved when running.

crank broken at the rear wouldn't have that much play in the mains to make quarter inch plus... flywheel wouldn't turn.

ya got me. do an autopsy.

lazs

stantond · « **Reply #10 on:** April 19, 2005, 09:21:19 AM »

Since you are still diagnosing here are some simple things to try. Try moving the harmonic balancer by hand in the crank axis. I suspect the 1/4 to 1/2 inch of motion you are seeing is an amplification of the movement. Also try pulling the harmonic balancer and check how much you can move the crankshaft using a longer bolt in the harmonic puller threads. You can also run the engine with the harmonic balancer off and look at the crank movement. Check if the harmonic balancer is bent. I have a hard time seeing the engine run with 1/4 to 1/2 inch axial (thrust) movement in the crankshaft. Maybe it's really 1/8 inch but seems more while in motion? When you drain the engine oil, bits of metal from bearings will be in the oil if they are gone.

Regards,

Malta

Roscoroo · « **Reply #11 on:** April 19, 2005, 11:41:39 AM »

... duh ... Drain the oil Nuttz
look for bearing / iron in it that will tell ya right now .. Pontiacs always toss a hell of a lot of metals in the oil when they wear out.

rpm · « **Reply #12 on:** April 19, 2005, 12:09:32 PM »

Let me explain my broken crank scenario a bit more. The crank broke and the break is diagonal. The rod bearing is holding the 2 pieces together. It will run, and make a little noise, but eventually fail completely.

I saw it happen to a 238 Detroit Diesel in a truck. We had trouble getting it to start, but once running it was fine. We assumed it was a flywheel problem. We drove it loaded from Houston to Dallas then dropped the pan and it was clear what the problem was when we saw the play only on 1 end of the crank.

Granted this is a rare thing, but it is possible. Drop the pan and see where the play is happening internally. Rosco is right about finding metal in the oil, but it may not be as much as you might think in this situation.

eddiek · « **Reply #13 on:** April 19, 2005, 12:17:30 PM »

I've seen a dragster run with the crank broken. Started missing a bit, no knocking noises, just a miss.
We pulled the engine out of the frame and tore it down, the crank came out in two pieces.
That was a small block Chevy though, not sure how a Poncho motor would react.
Funny thing was, the engine had just been built two races prior to the incident, and the crank had been magnafluxed.......the machine shop ate that one, cause the metal was really dark where the crack was and you could see the shiny metal of the rest of the crank where it completely broke.
But the engine did run, broke crank and all. Thank God the driver decided to shut her off at the starting line.

NUTTZ · « **Reply #14 on:** April 19, 2005, 12:35:29 PM »

Sorry I didn't mention It's an Automatic, Thanx for all the input. Laz, Kinda nailed it, if the crank was broke at any point It wouldn't cause the problem it is having ( or could it?)

I need to order a Chiltons book, I can't find mine. I can move the pully/balancer by hand with the engine off ( of course) and as it comes out about it turns slightly at the same time. I wonder if the crank could be cracked but on a slightly vertical angle to the shaft. That would explain why it still runs. Well until i pull the pan and check physically we'll never know, But I posted the problem here cause alot of mechanics are baffled and have different opinions.

I did mention the sound it is making is LOUD, like i threw a piston, but it's not miss firing and the sound IS coming fron the pully banging in and out ( with and without the belts on)

Once again thanx for the input,

NUTTZ