wana Camaro

There is a '87 firebird formula 350 that I could buy that a has a engine knock. He said it's coming from the back of the engine. He also told me that not the previous owner, but the owner before that didn't change the spark plug in the rear on the passanger side. So what I need to know is what is the knock probably caused by?

sofakingdom

iTrader: (1)

Spark plugs don't knock.

That's all you need to know.

"He said", when buying a car with an engine that's said to "have a knock", isn't good enough. That probably means "engine sounds like it will scatter itself all over the pavement any second now". If a seller says that, that means it's SO BAD there's no hope of bamboozling even the most ignorant buyer into a profitable sale.

Most likely, the crank is trashed, and at least one rod. Which means, it's tear-down and rebuild time. Certainly not something you're going to fix by changing out the right rear spark plug, you can believe that. If that's all it REALLY needed, he (a) wouldn't be selling it at all, or (b) he'd have done it himself.

If it sounds to good to be true, it is. (too good to be true, that is)

If you're not prepared to deal with a car that needs its engine rebuilt, it's probably not a good deal. On the other hand, if TO YOU an engine rebuild is nothing but a minor scheduled maintenance like it is to some of us, you might have a great score there.

Think of it as a car with no motor, and price it accordingly. If you can get it for that, then it's OK; if he wants more than that for it, walk.

wana Camaro

Let me clairify myself. I know spark plugs don't knock, i'm not retarded. He said the old owner never changed it and then the next owner did and then it started to knock. "He Said" other than the knock the engine runs great with steady idle, and a ton of power. It spins the tires very easily. And I think I could rebuild it pretty easily with my dad witch is a mechanic and raced with a 350 in his car. What I wanted to know what the knock exactly was so I would roughly know how much parts would cost, so I could figure if it is actually worth it.

lzjr88

I just had that same issue with my 86 IROC. It sat for about 6 years because my brother-in-law couldn't figure out what the engine noise was. He said it had plenty of power and would burn the tires, but it had a bad noise. He just sold it to me, and I got it running on Wednesday. As soon as it started up, you could tell it was a rod knock sound. I took the oil pan off to discover that the #8 connecting rod was bent, and the noise was the sound of the crank shaft counter balance hitting the bottom of the piston. I took the Intake, head and piston/connecting rod out today and am in the procces of getting parts for it. The crank shaft and the bearing all checked out OK, and the remaining 7 connecting rods were all good-to-go. I'm keeping this totaly low budget due to I'm going overseas with the Marine Corps for 3 years and won't be home to drive it. I'm planning on building a 350 for it when I get back. In the mean time, I'll let my brother-in-law drive it. I'm estimating that I'll have about $300 into fixing it.

sogabe

Ignition knock stands for
gasoline not burning in the correct timing,
thus will give u rough ride and could possibly damage the engine.
newer cars(i think most 3rd gens?) has whats called a Knock Sensor,
which retards or boosts the ignition timing to conpensate for this situation.
Ignition knock is caused by low octane fuel,
ignition problem etc.

now if an engine has a KNOCK,
it means that internal part of the engine has broken.
this could be the main/rod bearings, connecting rods, crankshaft, pistons etcetc, you never know until u open up the engine what you will have to
buy caz it could be one piece thats broken or the entire assembly that went trash.

sofakingdom

iTrader: (1)

Forget about the spark plug. It's a typical used-car-seller's lame excuse for trying to explain away something that's an indicator that they're asking too much for the car. Just leave that whole line of thought OUT of your evaluation of this car.

You'll find out in a BIG HURRY how serious it REALLY is, if you tell the seller that you're not interested until AFTER this supposedly knocking spark plug is replaced. In other words, remove the lame excuse, and bring it back to reality. Then take it from there.

If it still knocks (99.9999% probability it will) then the engine has an issue, and all the spark plug talk was just a smokescreen to draw attention away from the real matter of concern.

wana Camaro

Well he told me that he thought it was a crank bearing or a connecting rod, but I don't know why he made the spark plug excuse. And I don't think that $600 is too much for the car, so I might buy it and fix the knock. Thanks for the help everyone. I guess the only real way to do it is to take it apart.

sofakingdom

iTrader: (1)

It's amazing sometimes how a little truth and logic can penetrate even the densest layer of that a used car salesman can throw down.

In this case, the motor is blown up, but the seller is trying to convince you that it has something to do with a PO not changing the one spark plug. Suuurrrre. And I bet he's looking for someone else to buy his "rare" and "genuine" share of the Brooklyn Bridge, too.

So yeah, if the rest of the car is all there and in good shape, then it's probably worth $600.

I'd suggest pulling the motor out and turning it over, and just pop the crank out; leave the heads on, the pistons in, and so forth; and if there's no damage to the rod(s), but rather all it is, is the bearing is wiped out on the crank without spinning in the rod and there's no metal shed everywhere in the oil system, then just get the crank ground and put new bearings in it; and drive it.

wana Camaro