Thread: Thrown Rod???

Tweet

Well I just recently bought an '85 Trans Am. It has a freshly rebuilt engine (I saw the paperwork) it has a Python alarm system, a new interior, brand new tires and rims. Everything on it worked except the tach (easy fix).
I test drove it 3 times, even had my dad test drive it before I bough it. The engine ran completly smooth, the idle was perfect no excessive engine noise or anything.
Drove it around town for a day (picking up family members and dropping them off places).
Next day going to school i fired it up and now its knocking like it has a bad rod.
I can't figure it out, I drove it with decency, kept my foot out of it and only 1 day later it has a bad rod. I didn't redline it once.

Does anyone know if there are other explanations? Only thing I know is if you redline em once to much you can throw the rods.. but I didnt red line, not once...

bad machine work some one did not tq the rod bolts bad rod bolts someone over rev it and more

Took a 302 apart for someone because of a knock. It had spun the bearings previously and somebody cut a mountain dew can and shimmed the rod bearing on one of the cyl. Stoped the knock long enough for them to sell it.
Loose flywheel bolts or broken flywheel can also sound like a rod knocking.

Originally posted by chevydrivin
Took a 302 apart for someone because of a knock. It had spun the bearings previously and somebody cut a mountain dew can and shimmed the rod bearing on one of the cyl. Stoped the knock long enough for them to sell it.
Loose flywheel bolts or broken flywheel can also sound like a rod knocking.

how about a tobacco can or a belt strap. I NEVER HAVE DONE THIS .but it hase been done

Originally posted by DennyW
You got it on the strange things for repairs.

I would check it over and make sure no bolts are loose on like the flywheel area.

Your tach isn't off is it ?

them pop cans make nice shim stock cut some up to level my mill coast less than $1.50

Originally posted by DennyW
You got it on the strange things for repairs.

I would check it over and make sure no bolts are loose on like the flywheel area.

Your tach isn't off is it ?

All the bolts on the flywheel are good, its definantly the engine itself lol.
My tach don't even work, I think the conection is bad I'll just rewire it to the distributor later on.

that happened to me, but my van woudnt kick over. turns out the guy i bought the van from threw a big cam in and didnt upgrade the rest, so the rod snapped inside the block, it was bent into a ''L" shape, and everytime i tried to kick it over it would bang around. now i cant even use the block, big chunks missing out of the block at the the bootmom of the cylinder wall. so if i were you be carefull. it also might be a fly wheel bolt got loose it is banging aroung in the pan, that also happened to me, check it to be sure.

Originally posted by weylinthedirty
All the bolts on the flywheel are good, its definantly the engine itself lol.
My tach don't even work, I think the conection is bad I'll just rewire it to the distributor later on.

Well It doesn't have a stereo + whenever I get into a car im not familiar with i listen to the engine, the way it shifts, how it takes off ect...

The transmission did shit a little weird, probably only because im used to riding on a hard shitting transmission with a B&M shift kit in it. This tranny didnt, it shifted very smooth and sometimes I was unsure.

But i listened good to the engine, and it didnt rev very high at all (right around 2,500-3,000 was the shifting points)

How "fresh" is it? I notice that you said "I saw the paperwork". Do you have the paperwork, like shop ticket or receipts? Maybe you can find out if it is under warranty.

It has just alittle over 15,000 miles on the rebuilt engine. But the warranty expired because it only had a 1 year and he rebuilt it almost 2 years ago...

If it were mine, I would pull the oil pan, and check to see if there is any freeplay between the connecting rods and the crankshaft. If there is, it's a spun rod bearing, and it will need to be re-built. Others have offered some good ideas as to what might have caused it. So, now it's time to get dirty and see if you can get it fixed.

Good Luck,
Dutch

Are you sure its a rod?
When I was 16 i got a 400 small block inmy 66 chevy truck with my dads help (ford guy) (never worked on a chevy) One night I put it to the floor for about 4 miles. Man I was moving, when i clutched it it died DIED. finally recrunck and hada rod knocking. Drove straight to the shop Pulled pan and it took about 1/4" off two of the rods. Put crank kit and rebroke the motor in. 50 miles later I ran it real hard again and knock, knock, knock. Sounded like a rod again. Stoped and bought some rod bearings, went to shop replaced all (tight???) bearings. Crunk up and still knocked. Dam cut the belt and it turned out to be the water pump.
Later I found out the six cylinder flywheel does not work well with the 400. very unbalanced, I always thought the vibration was from my homeade drivesaft.

The ol’ loose flywheel syndrome. I have experienced that and took me way too long to figure out what the noise was. But now I know and I can tell you that if your flywheel is loose, you will only notice/hear it at idle when the motor is loping (the cranks angular velocity is rapidly increasing and decreasing causing the flywheel to slam from side to side on the bolts, thus causing the knock). When you accelerate the motor (in neutral) of course the flywheel is pressed up against bolts and your noise goes away. Rod knocks only get louder as RPMs increase, flywheels get quieter.

Sounds like it is time pull the pan and get dirty. If you spun a bearing you will most likely see the blue rod cap immediately.

Funny how that works huh! It is always the day after the warranty expires or right after you pay cash for something, that it breaks!

Keep us posted

Brian