BMS Forged Crankshafts

[Mike E]

I've searched and found a lot of info on the BMS cranks here, but there really isn't a thread devoted to talking about them.

There are pleny of reports of failures, and a few people that make good power with them. There is usually very little info posted about the condition of the crank before the breakage. There is no way to put a definite limit on one, but having real world experience can help people make a better judgement about how far to push one.

For the guys who have had one break.
What was the condition of the crank when you put your motor together? Freshly machine forging.
-Used drag only.
-Used good condition round track.
-Repaired (welded, hardchromed).
When did it break? street cruising, burnout box, top end of the track.
How much power?
What stroke?
What Rod Journal Diameters? Standard, undercut buick sizes,2.200bbc, 2.100 sbc
Wide Journal or not?
If you suspect it broke becuase of an issue outside the strength of the crank, then what? Can the breakage be attributed to a bad tune, hydrolocking, detonation, spun bearing, oiling etc.
If you have pictures of the crank after broken that would be nice. A picture of the fracture surface can tell a lot about how and why it failed.

Same questions for the guys that have had success with one?

 

[Mike E]

Even though my motor is still being built, I'll start.

I've got a 3.59 stroke wide journal crank.
The main and rod journals were said to be standard. But putting my good calipers to them, they measure ~2.2465 on the rods and 2.4975 on the mains.
I was told it was a used Busch piece from one of Ernie Irvan's motors. No idea if it was a dyno part or if it went through a race.
There are no grooves, heat marks, checking or visible cracks. Without hearing the previous history, there is no way to know it was used.
It's going to be magged before pistons get ordered, so I'm not stuck with that stroke should it have issues.
The balance info is scribed onto the front counterweight showing it was balanced 3/6/90. I'm not sure when they stopped using V6's in the busch series, but I don't think it was too long after that.

I'll be running a peterson external single stage oil pump and the enginer builder thinks based on those journal diameters it may be ok to run with that much clearance. I'm hoping to make up to 1200hp flywheel with a larger turbo for local ultimate/ 275/ mean street races.

 

[WHITE T]

I wonder how many have nice standard cranks (by eye) and run them without magging.

I have a beautiful billet std/std 3.59 that has a nice crack it in... good thing I checked!

 

[750H.P.V6]

Mike,

I've had some bad luck with 2nd hand cranks lately. The last 3 I bought were cracked. 1 was a billet and 2 were BMS forgings. No clue on the history of them since day 1. Conversely I had a BMS crank in my Stage II street car going back 10-12 years or so. It has been thru a couple of owners, been blown up a couple of times and the crank is still fine. I don't think there is an underlying problem with the BMS forgings just what the cranks themselves were subjected to over the years.

Neal

 

[Mike E]

I'm trying to convince myself that my crank is good enough for my goals. You guys aren't helping.

The crank is the weakpoint in my motor and if it goes it's going to take a couple very expensive rods and probably the excellent condition block I have. I'm starting to think it may be best to just break down and spend the money for a new billet so I can push the motor as hard as I want without worry. But what will it snowball into next. Decisions.

 

[turbobitt]

I'm trying to convince myself that my crank is good enough for my goals. You guys aren't helping.

The crank is the weakpoint in my motor and if it goes it's going to take a couple very expensive rods and probably the excellent condition block I have. I'm starting to think it may be best to just break down and spend the money for a new billet so I can push the motor as hard as I want without worry. But what will it snowball into next. Decisions.

I was in the same boat your in. Had a nice BMS crank but decided to protect my block and rods with a new Crower billet crank.
Allan G.

 

[Mike E]

I was in the same boat your in. Had a nice BMS crank but decided to protect my block and rods with a new Crower billet crank.
Allan G.

Did you ever run the BMS crank? If so what power was it making at the time? Did you know any previous history?

I talked with the engine builder a little about this just a little while ago. He says we should wait and make a decision based on what the wet-mag inspection finds. If the crank is close to end of life there will be micro-cracks that will show up. If it turns out to be crack free, I'll run it and just keep the power limited to what a 71 and 76 might make.

 

[Nick Micale]

Did you ever run the BMS crank? If so what power was it making at the time? Did you know any previous history?........

When I was working on the Gallina NHRA SS GN years ago, it was developing over 1300 HP on a BMS crank at 9000 RPM and never had a crank problem,

As far as I know, Kenny only used virgin cranks in John's Super Stock engine builds.

The BMS crank I personally had in my first Alum build was a used one and ran fine for 2 years. After it was freshened we found the crank needed a little straightening. When we started this engine on the dyno to run it in, the crank broke at the no. 1/2 journal when we reached 3000 RPM?

Moral of this story is I will NEVER put used parts in a rotating assembly for any high RPM engine.

In my case, after about 500 passes or so, which is usually 2 years, the rotating assembly is completely replaced with new parts.

 

[Alky V6]

When I was working on the Gallina NHRA SS GN years ago, it was developing over 1300 HP on a BMS crank at 9000 RPM and never had a crank problem,

As far as I know, Kenny only used virgin cranks in John's Super Stock engine builds.

The BMS crank I personally had in my first Alum build was a used one and ran fine for 2 years. After it was freshened we found the crank needed a little straightening. When we started this engine on the dyno to run it in, the crank broke at the no. 1/2 journal when we reached 3000 RPM?

Moral of this story is I will NEVER put used parts in a rotating assembly for any high RPM engine.

In my case, after about 500 passes or so, which is usually 2 years, the rotating assembly is completely replaced with new parts.

Nick, what was the stroke on Gallina's engine? If I remember correctly, wasn't he running a short stroke? Even fire or odd fire?

 

[turbobitt]

Did you ever run the BMS crank? If so what power was it making at the time? Did you know any previous history?

I talked with the engine builder a little about this just a little while ago. He says we should wait and make a decision based on what the wet-mag inspection finds. If the crank is close to end of life there will be micro-cracks that will show up. If it turns out to be crack free, I'll run it and just keep the power limited to what a 71 and 76 might make.

I had a BMS crank nd I bought it used with unknown history. At the time, my goal was just to have a reliable 9 second car and was able to easily achieve that. Car was heavy with an old T76 turbo. Probably could have made it run a lot better if I tuned it and turned up the boos. I only ran it a few times at the strip and street drove it for the last 10 years.
For my new build, decided to step it up a little but still want to retain some durability. All out performance was comprimised with long term valve train reliability. Ultimatly want to make about 1100-1200 at the tire and sure I can do it with my combination. Turbo is back with a new compressor wheel and also played with the cam.

Allan G.

 

[750H.P.V6]

Nick,

Wasn't the BMS crank you had that broke ground with SBC rod journals? That's what I seem to remember but I'm not sure I trust my memory these days.

Neal

 

[Mike E]

Turns out that the crank I payed good money for that was supposed to be standard/ standard and I was told was in great shape is not only not standard/ standard, but it's cracked. Now I'm out $900 and I still have to buy a billet, this really sucks and sets me back on my car quite a bit.

 

[750H.P.V6]

Mike,

I've been down that road before, I feel for you. I know Rick Elam is working on getting some new cranks made by Moldex. That will probably be a few months away. I might have something you can work with. Shoot me a PM.

Neal

 

[tsm3089]

Mike,

I've been down that road before, I feel for you. I know Rick Elam is working on getting some new cranks made by Moldex. That will probably be a few months away. I might have something you can work with. Shoot me a PM.

Neal

Is rick doing a billet. Or bms forgings.

 

[Mike E]

Pm sent neal.

I'm gonna bite the bu...billet and get a new one from crower. I already have their rods. Thats the only way I'll have piece of mind and no weak link in my motor. The problem now is I have no excuse not to put an 88 on it to run tso and x275.

 

[750H.P.V6]

Is rick doing a billet. Or bms forgings.

Rick is having 4 BMS forgings machined. I believe 2 are his and 2 belong to his friend Garret.

Neal

 

[Mike E]

It had a crack on the outside (main journal side) fillet on the #5 rod journal. I wasn't there to see it with the magnet still on it, but they circled the crack with sharpie.

 

[750H.P.V6]

Mike,

Did you machine shop mag the crank for you? The only reason I ask is that most crank shops use a wet mag rather than a dry mag process. Bummer about the crack but it's a really common place to find cracks.

Neal

 

[Mike E]

They were going to send it to another crank shop for a wet mag, but they decided to dry mag it there first just to check for obvious big cracks.

 

[750H.P.V6]

This was a billet crank I got that had longitudinal cracks in the #3 main journal.