I'm rebuliding my 1968 Mustang Ford 302 V8 engine. I need to replace my crankshaft, beacuse the engine was shaking and i think crankshaft was the problem.

But i have problem to figure out which crankshaft would be exactly right? I know i need 2MA one for 2 piece rear main seal. I already have 28oz flywheel and a flexplate for the other side (3 speed automatic trans). I'm searching Rockauto for parts but i can't findout for which flywheel their crankshafts are made?

Any help would be great.

 

sure you dont have a bad harmonic balancer or the wrong balancer??

 

It was replaced with new one. Problem was still there.
The engine was shaking and underperformed. Top speed around 65mph. We changed harmonic balanser and completly isolated the engine. It was a litle bit better but far from good.

The engine was opened and everything looks ok, new pistons and everything. So mechanic thinks it must be the crankshaft. Nothing else looks wrong.

 

In what way could it be the crankshaft? Bent, maybe?

 

ok

Keep
It
Simple
Silly (used a G rated adjective here)

KISS... always look at everything.
Underperferformance and vibration can come from many places. Misfiring can cause shimmy and shake.
Do you have good igintion at all 8 cylinders? do you have a flat cam lobe or 3?

Try this simple test. get a spark tester (looks like a spark plug that clips on a ground.)
Put it on the #1 spark plug wire. Start the engine. If the engine DOES NOT RUN WORSE
Then that cylinder has issues, either spark, fuel or compression related. Repeat on all other cylinders and record the results.

Now has the engine always vibrated badly? if not what happened when it started vibrating?

 

More likely the rotating assembly was never balanced. I wouldn't go through the effort of simply replacing the crankshaft - you may end up with the exact same problem you already have. A true out of balance issue will require that you disassemble everything and send the entire rotating assembly off to the machine shop to get it balanced.

That said, I'm still not entirely convinced that's your problem. How bad is it shaking? At what rpm do you start to notice it? Is it all the time, or just under load?

 

If your problem is, in fact, the crankshaft, and you are having that big of a shaking and performance problem, you should be able to verify by looking at your main and rod bearings. They surely would be pounded to death and would indicate the imbalance. I strongly suspect you will find the problem elsewhere, as in the ignition system, the harmonic balancer, the flywheel, or a basic engine assembly problem.
Best,
Al

 

I had this problem back when I was a kid.I built my first motor a 69 302 and I installed the pistons in the wrong order. If the rod caps are numbered 1-2 on the first cylinders they are wrong. I hadn't noticed when I pulled the rods and put it back wrong when it first started I knew it had to be pulled back out..