scat crank failure

[dieseldummy]

Since I've seen alot of talk about scat cranks in the past I thought I'd share my experience with them. I will preface this story with the fact that this short block came to me second hand from a core dealer so it's full history is unknown. The whole thing consists of all aftermarket parts, block, crank, rods, & pistons. When I bought it I tore it apart & had it all checked out @ a machine shop. It all looked good so after a thorough cleaning, light hone job, new rings, & bearings it went back together. I toped it off with a new set of Chinese heads to match the rest and dropped it in my'93 crew cab. I figured it would be a good test to see how good this off shore junk is. Well 7 months and 9000 miles later it broke the shiny scat crankshaft... it still ran but made a hell of a racket so I parked it and built a new short block for it. I'm in the process of swapping them and came across the point of failure. The crank broke between the #1 main & #1 rod which is odd since only the accessories put a load on that area. Luckily the block looks salvageable so that's a plus.

[Liftgate]

:(From what I can see, it looks like a new break. No old cracks. Bummer

[Robyn]

Are you sure that this is a scat crank, and not one of the offshore ones.

A friend of mine ordered an off shore block/crank combo "kit" and the crank came in a large cardboard box, which had been dropped, and upon opening the box revealed a 4 piece crank.

I have a scat crank in my fresh Dahoooley engine (as yet unfired) and there are no markings on it.

The only way I know its a scat is that I ordered it directly from scat.

Just curious, as this is the first time I have heard of a Scat crank breaking.
I have heard of the offshore ones, as I mentioned above.

Another question I have, it looks like the sides of the counter weights are a rough finish, is this how they are ( pictures do not always show the real deal) ?????

The Scat cranks do not have a rough sandy finish, they are a shiny machined surface, at least the sides of the counterweights are as are the outer diameters of the weights too.

I am suspect that you have a Chinese copy there and not a Scat unit.

More info please

Missy

[Robyn]

OOOOOOOOOK

I went back through a mountain of old posts on the discussion of the Scat cranks for the 6.5

Seems that the diesel crank is cast in China and then machined in the California machine shop.

Now, as I mentioned, the scat crank I have has all counterweight surfaces machined, and the ones being sold from other sources are not. or are sand blasted.

There is so much crap out there, it is hard to tell whats what any more.


Missy

[Liftgate]

Was the crankshaft thrust in spec? :confused:

[dieseldummy]

This is definately a real scat crank. It is engraved with the scat part number just like it should be. I am pretty disappointed it failed because the machine work looked great on it and it seemed to be a quality piece.

All bearing clearances and end play were right on the money when I re-assembled it. Since it came to me as an unknow I took alot of time and double checked everything.

Fortunately with a good crank the short block is salvagable so it wasn't a total loss. I hate to say it but I'm actually fairly impressed with the chinese block, it took a beating and took it. I put the aftermarket heads on the old 599 block that I rebuilt and it's up and running, hopefully it stays that way for a long time!

[john8662]

Thanks for sharing this occurance.

I had deep reservations about all the claim that SCAT offered up over this 9000 series cast crank.

You've spared me an engine failure showing this inferior part's ways. I'll stick to good used GM cranks and AMG Forgings.

J

[OIL BURN]

It never seems to end when it comes to crankshafts and these 6.2/6.5 diesels.Iv'e seen stock cranks where a rod journal has failed and chewed away an 1/8 inch ,total 1/4 and the crank never broke. Also examples of motors going 400,000 miles NO problems. Reground cranks, against advice of nitriding being ground away performing flawlessly.And not to mention replacing stock dampners with fluid dampners where after two to three thousand milkes broken crank.
Iv'e called scat cranks,talked to a sales rep.played dumb and asked what the the 6.5 was made of?. His response was he did not know! WHAT? So I tried to help him along with hints is it cast nodular iron?,cast steel?, threw in forged steel just for kicks, his response was ALL our cranks are cast/forged in china and machined here in our facilities.As Robyn may have said, the machining is usally kind of shiney not bead blasted.
This was a chinese block that this allegedly Scat crank broke ,and yet the block had survived!
I've recently talked to Bill Heath and he uses Scat cranks with a fluid dampner, although from what I've read Scat does not recommend the use of fluid dampners on these 6.5 cranks. Although Bill did mention that he's never seen a 6.5 stock crank break, but has heard of cases of this happening. So if anyone can test the durability of a Scat crant I think Bill Heath can.
What to do? If I had the money Peninsulars forged steel crank would fit the bill,$1000.00 so maybe if possible I would try saving up for it. But A build has to consider your budget,quality of parts on hand. and of main importance a crack free block,which you I assume you magnafluxed. I know Robyn has good success with outer main bolt hole repair on g.m. blocks, don't know about chinese blocks.If you say your block is good,thats a major part of the battle won.
On the build I am working on,6.2 with 2 piece crank,I had the crank checked for straightness,magnafluxed,journals miked, all stock sizes except for 7/8 rod journal ground .0005 undersize,common on stock g.m. cranks and bearings are available,polished and oil holes elongated. Rotating mass balanced for less than the price of a fluid dampner with a new pioneer dampner. Robyn has an excellant post on bearing fitting and assembly,explaines the crazy sizes.
If you stay stock, check everything,bore size to main bore alignment and squareness,main bore may be tweaked,g.m.'s sometimes are ,can't see why the chinese blocks would be any different.Also rod lengths and small pin bushing,rod alignment and big end size.All this checking may cost a couple of bucks,but its cheap insurance and a confidence builder. Have the replacement crank checked as I did above,even if you were told the crank is o.k.,and balance the assemble with a new dampner.

When you've done everything you can do within your financial means,and yes this can get pricey, thats as good as it gets at this point in time. Remember there are a lot of these 6.2/6.5's that have gone hundreds of thousands of miles without a major problem just good old fashioned maintenance.Search the Page, there's a volumn of build information to help you with your situtation. GOOD LUCK.

OIL BURN

[Robyn]

I had hoped that the Scat crank was going to be a really good deal.

Can you take some more close up high res pix of that crank from various angles and post them please.

This is the first one of these that I have heard of that failed.

Bill Heath has been selling the $#@! out of these, plus running one in his race truck, spinning it 5000 RPM

I am very currious as to why this failed.

Thanks

Missy

[Robyn]

Been doing some serious thinking about that busted crank.

Did the engine come to you with the ballancer and the serp pulley ????

Research on my part has turned up nothing in the way of a track record of failures on the scat 9000 cranks

The ballancer and serp pulley issues are still very important to maintaining engine integrity.

If there was no history on the unit, it makes it tough to really come up with any theories on this.

I just read an article on the 6.5 that had input from Bill Heath.
The mainline was mentioned, and the that many blocks will "move" after the machining is complete, and during the first many duty cycles.(hot and cold)

This issues causes the mainline to literally go out of alignment, which places undo stress on the crank.

Over time this misalignment causes the crank to flex where it should not and then snap.

Another tid bit that has crept into my little pea brain is the possibility that the engine you have, could have been in a rig that was involved in a frontal crash.

A smack to the crank snout, even one that seemingly did zero damage to anything, could have serious degrogatory effects inside the engine.


Looking at the amount of material in the area of the crank that broke, it becomes easy to see that there is little metal there.

The comment was made that the front of the crank drives only the accesories, not quite true.

The crank snout runs the entire valve train and the injection pump.
There is a buttload of pulsing loads that effect the crank from this area.

Normally, this is inconsequential, but, there are factors that could have been at work here that nobody knows about.

Core dealers, by the simple nature of the business, rarely have any inside info on any particular engine.


The wrecking yards yank the rigs apart and then market the stuff off to either private buyers or the rebuilders.

My question would be, why did a core buyer get that unit, rather than it being sold as a runner ???/

This question may have little merrit, as many yards sell their engines directly to the core buyers instead of the general traffic.


The fact that this was a relatively fresh build would suggest that the vehicle met with a bad end.

I am not convinced as yet that the Scat crank is a bad piece, but always currious.

Had you purchased the crank new from Scat, and done the build, then had a failure, this would be a far different story.


Just some thoughts.

Missy

[dieseldummy]

I took a couple more pics, hopefully they are better quality. Not sure what else there is to say about the subject... I had a one piece scat crank that's now one of the rare two piece varieties. It had a good balancer & got a clean bill of health from the machine shop so it stands to reason that the crank was faulty.

I made this post to share my first hand experience with this crankshaft so that maybe it might save somebody so trouble someday if they were considering buying one of these things. Good rule of thumb is that if something seems to good to be true it probably is. $400 is cheap for a diesel crank so it's got to be cheap for a reason... and as far as I'm concerned if Bill Heath promotes them that's a big black mark against them.

This build was done because I picked the parts up cheap so I figured it would be a good test of all the aftermarket parts on the market. Stage 1 is complete since the crank broke, stage 2 will start after a GM crank is installed then it will go back on the road and see what happens next.

[Robyn]

Well, all the dealings with Bill Heath have been positive from my end.

Any casting is suspect, no matter who made it.

The GM units scare me to death, especially after a lot of duty cycles.

I have seen several that magged fine and broke soon after they were put back in service.

The only sure bet is the forged unit from AMG for $1000

The last GM crank I saw break was in a 96 2 DOOR Tahoe 4x4
It belonged to an old fella who used it for a town rig and never ever worked it at all hard.

It was sitting idling after a cold start in July and BANG :eek:

He shut it right off after it broke.
There was no indications in the break that it had been broken a long time, just looked like your pics.

Sad deal for sure. Hope your new unit works out well.

Missy