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Old 02-16-2010, 05:46 PM   #1
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Default Datalog shows 15,000rpm: crank pulley shears and...

I find all this magic pixie dust in my oil pan haha

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I guess I get to do a full rebuild rather than just a new top end

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Atleast the top end looked good (brown/black buildup wipes right off)
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So enlighten me as to why/how because I'm no engine builder and I don't want to do this every winter lol.


-Dean
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Old 02-16-2010, 06:01 PM   #2
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Why/how on which... why there's crap in your oil pan or how you managed to spin it 15k?

For the latter I'd hazard you shifted into a gear a bit lower than intended or the datalog is wrong...

The former, if a little metal in the pan is all you got out of 15k I'd say you were really lucky. I've seen Carillos come apart lower than that by far (like 12k on an engine that normally runs to 9k regularly).

Now throw away your old rods and start over...
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Old 02-16-2010, 06:06 PM   #3
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Well the spinning to 15k happened in a 4th gear pull at 21psi and the crank pulley sheared all 4 bolts in half...

So rods are junk now or can they be checked out or something?

Replace them and the main bearings, and likely get the crank checked I'm assuming?
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Old 02-16-2010, 06:07 PM   #4
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Well the spinning to 15k happened in a 4th gear pull at 21psi and the cranl pulley sheared all 4 bolts in half...
Screenshot of datalog? Or just the datalog?
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Old 02-16-2010, 06:07 PM   #5
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I'll get the screen shot when I get home sure.
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Old 02-16-2010, 06:10 PM   #6
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I still dont understand why the **** you turned 15k...
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Old 02-16-2010, 06:18 PM   #7
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I still dont understand why the **** you turned 15k...
I was setting a miata record? haha
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Old 02-16-2010, 06:20 PM   #8
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So rods are junk now or can they be checked out or something?
If it were my engine, and assuming that it actually was turning at 15k (and it wasn't just a sensor glitch) then rods would be going in the trash. So would the pistons, the crankshaft, heck, I'd even be a little afraid of the flywheel at this point.

The block will definitely need inspection, to make sure that the main bearing journals and their caps are still straight. At a minimum I'd be buying new main cap bolts.

I still want to know how you accidentally get the motor up to that speed without botching a shift. Hath thou no rev limiter?
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Old 02-16-2010, 06:33 PM   #9
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A few things come to mind...like the actual flow rate needed for the motor to spin at that rate, and if the head would support this, much less the compressor, and even if you botched a shift, if traction would break before it spun the motor that high.

I've heard of people hitting 10K rpm when missing a shift, but 15K seems excessive. Compression braking would be ridiculous at that engine speed.
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Old 02-16-2010, 06:44 PM   #10
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The datalog shows 15k, but in all seriousness it probably wasn't even close to that.

What happened was I was driving along in 4th in boost, getting close to 7k (IIRC) and the I heard a clank and shut it down, felt like another busted tranny actually.

Pulled over and saw my crank pulley laying on my undertray and 4 bolt heads beside it.

So, bolts sheared, I guess I lost acessory load (tranny might have busted to, haven't driven it since) and the datalog shows 15807rpm or something retarded, but theres no way engine speed went from 7400 to 15k in 0.1 of a second...

Everything else looks fine, no valve contact, no piston to head contact, ect

I'm starting to think that something (crank) maybe be off balance or the mains were done shitty and have been shaking themselves apart all summer. Maybe this could explain the two trannies I cooked, vibration cause by bearing wear?

Again I highly doubt the motor saw 15k (datalog shows it goes from 7k to 15k in .01 of a second with sounds like bullshit to me), also I do have a mbsp, crower rods, wisecos, arps studs, and a balanced crank (although I do want to get that checked out now for sure as it could be off)
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Old 02-16-2010, 06:55 PM   #11
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Wanna buy your rods back?

Is this on the 1.9l built motor you bought last year? I thought you sold the turbo kit off?

Don't take this the wrong way, but you need to get into a different kind of car. A Miata just can't handle your mad driving skillz. How many diffs, transmissions and motors have you killed? I really don't think the Miata can stand up to your style of driving.
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Old 02-16-2010, 07:07 PM   #12
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Wanna buy your rods back?

Is this on the 1.9l built motor you bought last year? I thought you sold the turbo kit off?

Don't take this the wrong way, but you need to get into a different kind of car. A Miata just can't handle your mad driving skillz. How many diffs, transmissions and motors have you killed? I really don't think the Miata can stand up to your style of driving.
Ya but I didn't build this motor, I bought it built, so who knows how competent they were..

Turbo kit is sold off I'm building a new one centered around a holset hy35 and new manifold (going for 21psi on the holset)

I haven't killed any motors, short nose crank on the first broke 2 days after I bought the car, second motor had 200k on it and it was just worn out so it was replaced with this one.

Trannies and diffs are a different story. (i now have a 6speed thank you.)
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Old 02-16-2010, 07:09 PM   #13
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So which turbo was on the car? I'd inspect it for sure, who knows what might have come out the other end.
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Old 02-16-2010, 07:14 PM   #14
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When you lost the pulley the cams stopped spinning. Intake cam stopped with lobe on top of lifters on one cylinder, pushed it backwards quarter turn, causing sensor output that MS interpreted as really high rpm.

Cams have a low moment of inertia, and stop quickly when the belt goes, and as anyone whose done a TB change knows, the springs/lifters can put a lot of force on the lobes when in the duration for that cylinder.

Only plausible theory (until JP shows me up that is).
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Old 02-16-2010, 07:16 PM   #15
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I would be willing to bet $100 the 15k number is an sensor glitch. For the amount of damage you're showing I don't think you got anywhere near even 10k rpm. 11-12k rpm in a k20 motor broke valves and lodged them in the exhaust ports (completely awesome) among other death and destruction.
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Old 02-16-2010, 07:18 PM   #16
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When you lost the pulley the cams stopped spinning. Intake cam stopped with lobe on top of lifters on one cylinder, pushed it backwards quarter turn, causing sensor output that MS interpreted as really high rpm.

Cams have a low moment of inertia, and stop quickly when the belt goes, and as anyone whose done a TB change knows, the springs/lifters can put a lot of force on the lobes when in the duration for that cylinder.

Only plausible theory (until JP shows me up that is).
Didn't lose the timing belt, just the harmonic damper, so the timing belt was still on and intact.

I remember I didn't even hit rev limit (7800) I shut it down fast, it definately didn't rev that high, but the datalog shows it for some wierd reason.
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Old 02-16-2010, 07:21 PM   #17
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Didn't lose the timing belt, just the harmonic damper, so the timing belt was still on and intact.

I remember I didn't even hit rev limit (7800) I shut it down fast, it definately didn't rev that high, but the datalog shows it for some wierd reason.
Random unexplainable sensor glitch then.

Stop refuting my scientific explanations and start looking at your tach occasionally.
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Old 02-16-2010, 07:21 PM   #18
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I would be willing to bet $100 the 15k number is an sensor glitch. For the amount of damage you're showing I don't think you got anywhere near even 10k rpm. 11-12k rpm in a k20 motor broke valves and lodged them in the exhaust ports (completely awesome) among other death and destruction.
Completely agree.

No to the more important issue of why I have 10lbs of bearing material in my oil pan. Obviously this just didn't happen when the pulley came off.

I'm thinking either my crank is off balance (and it has been machined) or the bearings were done incompetently.
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Old 02-16-2010, 07:23 PM   #19
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Only plausible theory (until JP shows me up that is).
No, that's pretty much what I was thinking as well.

I'd been doing some reading up on his past posts to see if he was running a crank trigger or still using the CAS. With the crank trigger, it would have been a no-brainer that his ECU got bogus data as it was coming off.

I'm having sort of a hard time picturing the timing belt pulley coming free of the crankshaft. I suppose that if the woodruff key managed to work its way out then maybe the pulley could have freewheeled.

Either way- the front of that crankshaft needs a pretty thorough inspection at this point.


This is the sort of thread where the OP would save us all a lot of frustration by just posting a damn picture of the front of the engine, or at minimum, a through description of what actually happened...
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Old 02-16-2010, 07:26 PM   #20
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I bet that even if the belt is still on there, the timing is off.
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