So I snapped a crank in my 311 memorial day weekend !
 

Sunday of memorial day weekend I snapped my crank in the starboard motor. The boat is an 88 311 with 420 TRS. I am gonna take this as an oppurtunity to upgrade to roller cams. I was running 69.8 gps @ 4950 with my 25 pitch mirage props. Any guesses on where I will be with a little massaging... Marine Kinetics is helping me with camshaft selection. Oh.. and the new crank will be from Callies.

You should gain a couple of mph with the correct cam,intake and carb. It takes a lot to do so little.good luck.

Not really looking for overall top speed on this one, just a little more reliability. I would like to spin my 25 pitch mirages at 5200 like I use to be able to with my 23 pitch props. I think that would gain me a few. The goal is to make 1 hp per cubic inch with the roller cam upgrade.

Post a pic of the crank when you pull it. It will be interesting to see where it came apart. I come from a family of metallurgist and we are always discussing dynamic failures in castings and the causes of. This sounds like an original flaw in the casting. Spinning that engine at 5000 rpm with good lubrication and cooling with no significant vibration shouldn't have caused that failure. I'm guessing it is a cast piece as opposed to a forged unit? I would wonder about the starboard engine as well.

A roller cam with some heavier springs ad a bit more lift should give you the power to put you reliably where you want to be.

Good luck with this.

The crank snapped across the counterweight ... Clean break and no pieces in the pan. My machinist said it was due to the previous engine builder taking all the radius out of the crank when they turned it down. It was a 4340 eagle crank.

On another note ... Does anybody have any input on the stage 1 teague cams ?

Had a great weekend on the lake with the new setup. Teague stage 1 cams seem to be right on the money for these motors. Still stock bore 454 but with merlin III's in aluminum. I spun my 25's to 5100 rpm for just a second and the dream o meter was buried solid. Boat feels a little loose up on top now! I need to get a gps so I can lay down some accurate numbers.

This is now sounding better!!

For future reference...how far down was the broken crank turned?

Sprink ... I will measure the crank up when I get a chance but I am pretty sure my machinist told me it was only .010".

I'f 454Captiva's doesn't work out let me know. I have a 4340 crank turned .010 with new rods and bearing I'd like to make somebody a deal on to get it out of my hair.

Snapped Crank