2G 420a crankshaft

[Myjr]

Well, after rebuilding the entire motor with eagle claw rods and JE pistons, it seems like we have broke a crankshaft. We were in the 500 mile break in period (during which the motor never saw rpms over 4k. All of a sudden the motor had a problem keeping up idle then suddenly stopped. We can turn the starter freely but the camshafts don't turn. We havent taken the motor back out of the car yet, but I am guessing a snapped crank?

Any where to buy a new one? or do I have to start searching Junk yards. I guess if we are able to buy one, i would like forged , right?

I am new to all of this, so any advice would be well taken. Thanks

 

[BLACK'98DSM]

There's no need for a forged crankshaft, unless you're making serious power levels. Like 500+.

You don't seem to have any objective evidence that the crankshaft is broken, and that's very unlikely at such low RPM. Try rotating the engine via the crankshaft pulley bolt and see what happens.

With this information I could guess that the timing has jumped, or the timing belt is broken. The crankshaft spinning without camshaft spinning doesn't make a ton of sense though, since these are interference engines.

 

[Myjr]

After pulling the 420a motor out my mechanic said it snapped one of the main tensioner bolts and of course bent the valves, ect., ect., ect. Waiting for the head to comeback from the machine shop and parts to show up on Monday to finish putting back together.

I just wonder how in the world you could snap one of those bolts? (Any thoughts?)

I will have pictures tomorrow and upload. Anything I should ask when I go see him?

 

[BLACK'98DSM]

Those bolts don't just snap naturally. They must have been cross threaded, over torqued, or the tensioner is not properly installed. Perhaps the OE bolts were not used and something lower grade had been installed. Pictures would be helpful to determine this.

 

[Myjr]

There's no need for a forged crankshaft, unless you're making serious power levels. Like 500+.

You don't seem to have any objective evidence that the crankshaft is broken, and that's very unlikely at such low RPM. Try rotating the engine via the crankshaft pulley bolt and see what happens.

With this information I could guess that the timing has jumped, or the timing belt is broken. The crankshaft spinning without camshaft spinning doesn't make a ton of sense though, since these are interference engines.

The tensioner bolt just broke. No idea how this happened. One of the theories is that the hydraulic tensioner (not pictured here) that we replaced was stuck in the down position for who knows how long where it bounced on it for possibly years and the bolt finally gave out. The one pictured here is new so that would have prevented any bouncing around like before. Luckily he was at an idle in the parking lot when it decided to go. So it only bent the 2 exhaust valves of cylinder number 4 and we already have the head back from the machine shop. We are just waiting on the new bolt ordered from mitsubishi (hard to believe he found it) then we can put it back together. I have 2 questions.

1. Does anyone have any other ideas on what may have happened?
2. Does anyone have any suggestions on anything else to check to make sure this can't happen again?

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