Broken Crankshaft Count?

[Burn Down]

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 wouldn't say its a weak design when kept within the designers original max power output... The problem is that many of todays diesel engines are easy to turn up, far exceeding the original design limits. I'm sure if Isuzu was told the crank needs to withstand 2000hp and 3000tq they would have built it slightly beefier:rofl:

 

[Burn Down]

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.

Any proof of this or just what you heard secondhand?

 

[mike diesel]

I think at this point if no one has figured out why they break and has been able to resolve the issue, (if these stories about broken cranks with AF cams are true) it is never going to be figured out atleast not without spending insane amounts of money.

We all know what we are getting ourselves into when we decide to build an engine. Have fun while it lasts and don't be scared to redo the engine if it happens to you

 

[Cknight199]

Any proof of this or just what you heard secondhand?

I heard it talking with Joe at HSP. I figured he is credible enough

 

[mike diesel]

Any proof of this or just what you heard secondhand?

It's all second hand in my opinion. No one steps up to prove it when you hear about it. You would think people would want this put out there so further testing can be done to try and combat the issues even more..

 

[Burn Down]

It's all second hand in my opinion. No one steps up to prove it when you hear about it. You would think people would want this put out there so further testing can be done to try and combat the issues even more..

Agreed.

 

[S Phinney]

It's all second hand in my opinion. No one steps up to prove it when you hear about it. You would think people would want this put out there so further testing can be done to try and combat the issues even more..

Except that some of the guys manufacturing the AF cams and having broken cranks couldn't sell their cams for a few hundred extra dollars. Just remember nothing we do is failure proof.

 

[Stingpuller]

Cranks

I totally agree its well past what it was designed for. With the bore spacing what it is there is only so much you can do. You could narrow the rods and have a crank made with a .140 radius and a wider counter weight on the crank.

 

[Slowmax]

It's all second hand in my opinion. No one steps up to prove it when you hear about it. You would think people would want this put out there so further testing can be done to try and combat the issues even more..

You mean it is not all about just selling you parts....? :woott:

 

[Lance LB7]

To me it still goes back to balance because they all break in nearly the same place. We all know about the firing order being 3-1-2 and that makes me think that throws the harmonics off. If it was an inherent design flaw of the crank itself they should break in any and every spot. It would be interesting to see how many guys have actually broken cranks with AF cams and where they broke.


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[MarkBroviak]

It's all second hand in my opinion. No one steps up to prove it when you hear about it. You would think people would want this put out there so further testing can be done to try and combat the issues even more..

Exactly, I will be the first to say it will not fix all the broken cranks but after all the engine dynoing between the designs and in field testing I can say very confidently that it is a big step in the right direction. We have a built lly customer that has broken two cranks back to back that were internally balance with a stock firing order and both broke in the less than 3,000miles range and he was not beating on the truck at all cause he was scared of the truck. Bearings and everything looked like brand new but the crank was broken. On the third time of rebuilding it we did an external no frills balance and changed the cam to an AF cam of the same profile grind and he has already doubled the mileage without issue and is actually driving the truck pretty hard now that he isn't as afraid of it since it is still in one piece. It truely was the perfect storm of the parts combo to bring this issue to the surface. It is an S468-87 1.0ar with 100%inj and Dual fuel at the 900hp mark and he loves to drive it a lot. With his 5sp and 3.42 gears it put the motor cruising right at the same rpm that we see all the vibration on our engine dyno so it only makes sense. I have not seen a broken crank yet with my own eyes that has an AF cam but I have seen plenty of stock firing order ones broken. Time will always tell and it will always come out in the end. In my business I am always looking for a better way to build these things to last longer and produce more sustainable hp without these kinda issues.

 

[andy-stevenson]

What rpm are you seeing the most vibration at?

 

[MarkBroviak]

What rpm are you seeing the most vibration at?

1600-1900rpms and then again around 2850rpms but the lower range is the worse on the engine dyno.

 

[PACougar]

1600-1900rpms and then again around 2850rpms but the lower range is the worse on the engine dyno.

I'm going to remove that rpm range from my tune

 

[adeso]

I would love to see actual vibration readings on both cams on an engine dyno and in a truck on a dyno both under full load and a load you would expect to see driving at 70 MPH. And hold each 25 RPM or so for a good 60 seconds to let a harmonic situation develop

 

[adeso]

1600-1900rpms and then again around 2850rpms but the lower range is the worse on the engine dyno.

Is this a trend with different tunning and internals or do you see different ranges with different tunes and parts??

 

[MarkBroviak]

https://www.youtube.com/watch?v=QVhx1yxc9MQ&list=UUV6Kphz6imzjrc9kM2sCV6A

Here is a perfect example of it, watch the intercooler water box in front of the motor and watch the water dance just off idle area. When it gets loaded down, you will notice the vibration settles down. I haven't seen where tuning makes any different in it at all, load and rpms seems to be the biggest factor.

 

[adeso]

makes sense, I would be curious to see some actual data off of it, and see if you can put it into a harmonic event holding it at a set power level and RPM.

 

[MarkBroviak]

https://www.youtube.com/watch?v=pPnGPrhfctg&feature=youtu.be

Here is the video of the coupler as it was failing due to the vibration from the motor, I was just bringing it up through the rpm of the vibration. This was the video we sent the dyno company trying to figure out why we had this god awful noise at low rpms.

 

[adeso]

watching it the event seems to be really pronounced for the short duration that it is there. I would be curious to see what the crank is doing during that time, although I'm guessing being in a truck hooked to a driveline will take a lot of the stability out that is required for a serous event to fully develop. But still it makes you wonder what going in and out of that range while on cruise control is really doing. Or if it is modified by the alt fire cam