Built Motor Reliability

[McRat]

Why does the crank break in the front?

Random thought:

If you do the trig, the bending force imparted on a crank by an externally balanced engine weight gets larger the smaller the dia of the counterweight is, and how close it is to the main journals. Our rear weight is on a large dia and close to the main, and the front is on a really small dia far from the main.

The answer might be as simple as a new design front weight, that moves the mass as close to main journal, and as far out radially as is possible. This could perhaps even be done to a factory harmonic balancer.

 

[Dirtymaxx03]

Why does the crank break in the front?

Random thought:

If you do the trig, the bending force imparted on a crank by an externally balanced engine weight gets larger the smaller the dia of the counterweight is. Our rear weight is on a large dia, and the front is on a really small dia.

The answer might be as simple as a new design front weight, that moves the mass as close to main journal, and as far out radially as is possible. This could perhaps even be done to a factory harmonic balancer.

i lost you at trig lol

 

[hondarider552]

Think Newlys motor has just over 50k miles on it. :thumb:

 

[McRat]

i lost you at trig lol

It's like this. Take a hoe (not a ho') and spin it in your hands near the handle. You can't keep straight when spinning.

Now move your hands right up near blade and do it again. You can keep it straighter.

All internally balancing does is to move the weight closer to the blade, and that's the best way. But getting the weight as close as possible helps if you can't internally balance.

Now getting enough weight close enough to the front main might be a PITA. This is where radius of where the weight sits comes in. You need less metal to make the same weight when you move outwards radially, so you can get the weight closer to the main, simply because there's less metal. And trig comes into it.

 

[Dirtymaxx03]

that makes a shit ton more sense

 

[paint94979]

Also look to built motor longevity in a Drag Racing application vs. a Sled Pulling application... my bet is sled pullers get many more season's out of a max effort setup vs. drag racers.

 

[McRat]

Another theory why they might always break near the front could be the process sequence used to form them.

IIRC, the Dmax crank is rotation forged. In other words, they first forge the crank flat, then they bend (forge) the throws offset on a rotation. The order in which they do the secondary forging could make one area weaker than another. I don't buy "accessory drive" issues. Why? Full engine output is attached to the rear of the engine, and only partial load goes through the nose. If anything, the rear should break.

 

[LWATSON]

Another thing people arent taking into account is the fact that most guys that have built engines are attempting to get every ounce of power they can. Its a different type of person that ususlly has a built engine, if you gave built engines to 50 average Joe's they would last a very long time. 50 hard core racers will not sleep until they have gotten every possible ounce of power out of the engine. Then He'll come up with another idea.

 

[blk smoke lb7]

Also look to built motor longevity in a Drag Racing application vs. a Sled Pulling application... my bet is sled pullers get many more season's out of a max effort setup vs. drag racers.

I thought the sled pulling would be worse not much air moving thru there and and dont they run 1 speed or a 2 speed trans now,holding a high rpm for a longer time?

 

[dmaxvaz]

Another theory why they might always break near the front could be the process sequence used to form them.

IIRC, the Dmax crank is rotation forged. In other words, they first forge the crank flat, then they bend (forge) the throws offset on a rotation. The order in which they do the secondary forging could make one area weaker than another. I don't buy "accessory drive" issues. Why? Full engine output is attached to the rear of the engine, and only partial load goes through the nose. If anything, the rear should break.

I wonder if thats why Banks uses 2 fluid dampeners on the front of the engine, maybe to balance the heavy weight from the other end

 

[Stingpuller]

Motors

Sledpulling is not nearly as hard on the motors. They are never loaded like you are drag racing. Has anyone ever looked a a Big Block Ford and how they balance them? They are external and have a big weight about 5" from the main bearing. There crank snout if about half as big as a duramax. The rod throw on the crank is smaller and the main is smaller. That would make the crank weaker. The more overlap you have from the main to the rod the stronger the crank will be. I sure don't have the answers but sometimes I think there is more to breaking these motors than some tell. Maybe spun keyways on crank dampner, sudden stop of motor or broken driveline and the motor get's instant rpm or maybe spinning the tires and a sudden jolt. It's odd that some break and some don't that's for sure. I wish someone had the answer so alot of us would stop wasting money. Jeff

 

[Mike L.]

Has anyone broke a crank with a concrete fill block? These blocks are at the end of the line. Too much shifting.

 

[GMC_2002_Dmax]

What about the stroker kits that have broke cranks? Is there enough running to prove that they will hold up better? I know they havent proven more power yet... And i would also say, while crank breakage happens with these, pistons are more common.

I didn't know trucks broke with Strokers, were they stock cranks cut down like TTS did ? Or were they true Stroker's ??

If you know who busted a crank spill the beans.

 

[Rhall]

I didn't know trucks broke with Strokers, were they stock cranks cut down like TTS did ? Or were they true Stroker's ??

If you know who busted a crank spill the beans.

I know of one personally, ive only heard of others. Im not at liberty to say, just like you wouldnt tell me stuff about your customers trucks without permission. But it was a billet stroker.

 

[Rhall]

Im not saying anything bad about the cranks, it just goes to show everything breaks when your running high horsepower, do the stroker cranks decrease the chance of breakage? Who knows, the ratio of stock crank built motor trucks to stroker crank built motor trucks is probably 10 to 1 or more, so of course more stock cranks are going to break.

 

[ChevyDieselLLY]

I look at it like this. If I run less hp with my built motor then I did with my stock motor my truck should last for a very long time. If you have a race truck and push it to its limits every time out you have to expect to break something. I don't think we will ever know what is the cause for cranks to break because people will never come out and say what happened to their truck. Either they aren't on the forums or they just don't want their business out there. Maybe they aren't even sure why it broke. and if my stock cut and coated piston fail then I know they had a good life due to being in a built motor that broke a crank (Ed Wayne's motor I believe broke the crank and that's where these came from)

 

[Subman]

Like I said in the DPC thread we have scatter three engines, none had a broken crank, one did have a crack but more likely caused when the block cracked. We fill the blocks about half way although that one wasn't filled The one where we cracked the block had been hydro locked due to a cracked head. Also had bent rods. As I said we hoped to get 20 minutes out of an engine at WOT, only one of the three made it. I truely believe the key is build the hell out of them and turn down the power 10-15%:thumb:

 

[Rhall]

Like I said in the DPC thread we have scatter three engines, none had a broken crank, one did have a crack but more likely caused when the block cracked. We fill the blocks about half way although that one wasn't filled The one where we cracked the block had been hydro locked due to a cracked head. Also had bent rods. As I said we hoped to get 20 minutes out of an engine at WOT, only one of the three made it. I truely believe the key is build the hell out of them and turn down the power 10-15%:thumb:

The turn them down 10-15% doesnt apply in sled pulling unless you want to loose. I gaurantee you that.

 

[wes06dmax]

The turn them down 10-15% doesnt apply in sled pulling unless you want to loose. I gaurantee you that.

Sled pulling is very serious around here aint it Rob,

It is hard enough to win a brush pull around here let alone a big event like Ts or Schieds you have to run all out if you wanna win or hope like hell the other 20+ trucks you are pulling agents breaks

 

[hondarider552]

I thought the sled pulling would be worse not much air moving thru there and and dont they run 1 speed or a 2 speed trans now,holding a high rpm for a longer time?

umm no.