Broken Crankshaft Count?
- Thread starter EDP
- Start date
Sounds identical to when mine went except I was cruising at 80mph. Started to vibrate a bit like I was driving on the side of the road rumble strips then coast to a stop.
Hi Steve. Sorry to hear that, that sucks!! Just wondering if you had the stock cam keyed when you built the motor? That motor was putting out some power,
I think u said your weight was 6900 ish and 133 trap speed. That's like 1100 hp
Crazy! Keep us in the loop on what u find.
Just curious what Pistons?
And sorry to hear Steve, I am sure it will be running better than ever when it gets back together. Hopefully some of the internals are salvageable, you have swayed my decision for an AF cam in my build.
I am currently running the delipped stock LLY pistons in my truck. Chris(DuramaxRacer8) machined them himself while he was building the motor and they have held up to all the abuse I have thrown at them. When the motor was built I think I told him I wanted a reliable 700hp. The goal went up and the motor didn't bat an eye lash. Since the power goals went up we had discussed a possible switch to Fingers oval pistons. I didn't want to tear the motor down since it was running so well. Now the motor has to be taken out anyways so we will be discussing a few different options.
We've replaced 4 cranks this year alone & out of those 4 only 1 got into the block. There's a good chance your block & caps are ok. That said I have #5 in the driveway.... but this one's different. This crank broke after some yahoos couldn't fix a wiring issue & sprayed enough starting fluid in it to keep it running at high rpm for a few minutes. Some of these oil patch mechanics need to stick to mechanical engines.
If you shut it down right away the block should be salvageable. My cousin drove his 60 miles after it broke and it trashed the block.
I think we will probably make the change to a set of fingers cast ovals but will definitely check the skirts out of curiosity. I spoke with Chris this morning and the motor probably won't be coming out of the truck for at least a month or two. I really hadn't budgeted for another rebuild. Going to use that time to research and come up with a plan to keep her in 1 piece.
I'm definitely no expert but these are just my thoughts on it. I did some research on the old 6.5's a while back on why they break cranks and the best I could come up with was balance. I don't think it has any correlation to power because the 6.5's didn't have enough power to get out of their own way and yet they still snapped cranks. I also don't think it has much to do with manufacturing flaws. To me it all shows to be balance issues. The late 6.5's had updates to the harmonic balancers to and they're still no powerhouses but they apparently do not break crankshafts. we've all seen fat ladies sing at a certain pitch and break a glass. everything I read tells me metal does the same thing at certain frequencies. so if the engine isn't balanced right, the vibration will weaken the crankshaft over time, eventually leading to a failure. I was surprised to see one duramax with an aftermarket balancer break a crank, but I've yet to hear of one with an AF cam do so.
AF cams have broken a crank. The ratio may be less than normal cams, but they have still broken a crank. I know of a billet crank and alt firing cam that broke.
I think it is horsepower mixed with certain rpm's. Most full race builds don't break cranks unless they are daily driven. And most race builds don't see the rpm's that DD's see.
Crankshaft
I think its just a very weak design. If you look at the crank and the overlap from the rod journal to the main journal there just isn't enough metal there. Banks I think made a new crank with a bigger rod journal to help with that. Harmonics plays a rule and I think a hard shift or harsh lockup also plays a rule. I really don't think the AF cams do a lot but if your buying a cam it can't hurt.
I think its just a very weak design. If you look at the crank and the overlap from the rod journal to the main journal there just isn't enough metal there. Banks I think made a new crank with a bigger rod journal to help with that. Harmonics plays a rule and I think a hard shift or harsh lockup also plays a rule. I really don't think the AF cams do a lot but if your buying a cam it can't hurt.
Banks designed that crank since they were breaking cranks left and right in their marine motors. I heard rumors that their new crank has been broken as well.