So blew up my #3 rod. wondering what caused this. lack of oil, due to rpm? poor return? oil pump sucking air?

last time it was #2 rod. I really don't want to live with this again.

Motor specs,
Dual oil coolers with full flow plumbing
102 bore by 80mm stroke
long rods,
ham heads and valve train.
Running to 6800 rpm
g loads to 1.5
windage tray modified at pushrod tubes for oil flow
tuna can with 1/2 extra oil

Pics of horror below. First are this failure, then old failure.
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What kind of rod is that? Looks aftermarket?

Odd that it's snapped in half and the cap bolts are snapped

Man that sucks!
I think the rod bearing seized on the crank. I see micro-welding on the journal. That happened before the rod broke.
Any warning? Weird vibration, change in engine tone? Anything?

Is the oil pressure stable in corners?

State of tune? Detonation can cause bearing failures. Bearing failures can break con rods.

I did get some warning (that I ignored) running hotter than normal, low oil pressure at idle, knock, etc.

I heard something happen part way through a run. but nothing visible outside. I knew better than to run it, but only 2 runs to finish the season....No detonation, running 100+ octane at 12:1 afr. this was a really fast motor. revved quick and put the power down. I figure close to 200hp and also 180ish torque.

Not trying to be a jackass . . . but sometimes it is what I do.

And we're discussing how/why this happened?

It does suck but when playing at those power levels and racing, this sort of failure shouldn't be a surprise. Especially when combined with ignoring the warning signs.

You have my utmost sympathy though. This is an expensive failure. But . . . racing is an expensive hobby. Ask me how I know.

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On a more constructive note.

Play with this centripedal force calculator.

https://www.engineersedge.com/physics/centrifugal_force.htm

In this specific case, RPM's have increased from 5500 rpm to 6800 rpm. RPM is directly related to the velocity term.

The force on the rod bearings is going up as the SQUARE of velocity. Said differently, the force increase isn't linearly proportional to the crank journal velocity, it is increasing exponentially.

Double the velocity term in the calculator and watch what happens to Force, it goes up by way more than double.

Bottom line, although the top end was likely beefed up to control the valve float, the stock lower end rod bearing journals are getting overloaded. This squeezed out the very thin oil film that separates the rod bearing from the journal and prevents metal on metal contact.

First part of this occurs as dramatically increased bearing material wear. Eventually it results in steel on steel contact and the micro-welding Lew mentioned.

If you are going to run this type of engine at these elevated power levels I'd recommend that you do professional oil analysis after every race. If you establish a baseline immediately after engine break in, you WILL be able to tell when the bearing material is being shredded off into the oil more rapidly than usual.

At that point, you need to stop running the engine and replace the bearings at predetermined intervals. Ultimately you will likely get a crank failure in the long term after some unknown number of bearing replacements.

With the stroker crank, do a really thorough inspection/magnaflux of the crank, especially if it's a DPR or other built up then machined OE one. If it's a new forging it might have survived, but I'd be wary of a reworked OE. Had two DPR's fail on me due to the resulting closeness of the oil channel to the web after offset grinding. Went with FAT performance new forging crank after that.

I can't think of a motor with nearly a 4" bore that turns more than 6k.

Pushing an engine with low oil pressure and knocking sounds. Sorry but thats just dumb. As for what caused the failure I think Superhawk is onto a good lead. Sure a T4 can push 200 hp with some reliability but it will always need alot more attention and preventive maintenance than a less high strung engine. Changing the oil after every race with an oil analysis is a good start. Measuring is knowing. To me this isnt as much an engine failure as an maintenance/owner failure, the signs were there and you saw them and chose to ignore them.

I accept the responsibility for the failure. No need to run it in.
What I would like to generate is what to do to have a high rev engine live more than 20 hours? Bearing coating? Super secret windage tray mods? Better balance? Lots of folks build big bore motors, hopefully we can help them with longevity.

Regarding bearings, I’m curious why 6800 is high revs on a 4 and normal for a six. Are the bearings loads or stresses different! I always thought valve train was more the limiting factor to revving a four.

Exactly what I thought also. That the valve train was the weak point. I did address that. Let the high revers chime in.

Herb..

20 hours is pretty good for MTTF
were both engine failures at the 20 hr mark?
I see a sheared rod bolt...that is definitely a failure point on a high rev engine.

Dry sump with a few suction points...

It would be interesting to measure and log gallery oil pressures at high speed and see what happens in relation to lat./long. acceleration. As noted, there is likely a story on the bearing overload side which is related to oil pressure.

I will know more after the post. Engine is ready to drop. I should have it apart Saturday. Small thin bearing material in the sump. Correct on 1 sheared rod bolt. The other is ok, I haven't found the rod cap yet

Use a 1.7L crank and bigger bore to increase the displacement. Shorter stroke/bigger bore allows more usable RPM with the same displacement.

For example... a 76 930 engine with a 70 911S counter-weighted crank and 906 cams gives you a motor with about 2.5L, but will rev to 10K. AS explained above, it lowers the stress on the rod bearings. It is a screamer of an engine, but not very streetable.

So get a 1.7L crank with counterweights, and bore it as big as possible. you can probably get 7K out of the motor.

I would suggest asking Jake Raby about this. He knows more about it than I do.

Clay

Clay that's a 66x95 2.8....76 911 66x90 2.5+...but get your point...

HEY!! Give me a break. I am doing this from memory.

All I Know is; Type Four Sale

Herb, you can't assume that because you have a fat AFR that you aren't experiencing detonation. Indeed, because a fat tune takes extra time to react completely in the combustion chamber it's common to have elevated temps around the exhaust valve and higher egt's since the fuel burned at the end of the cycle does so around the valve. That concentrated heat can definitely contribute to detonation.

You said it was running hotter than normal. CHT's, EGT"S, oil. . . what was running hotter?

You may need an accusump. Your rod failures might be a combo of state of tune and inadequate oiling. Could just be oiling alone.

oil temp was elevated due to the rod bearing failure. symptom of low oil pressure at idle and temps of 220 oil temp.

normally I run around 180 degree oil temp and 30 psi pressure at idle.
Also running 100+ octane race fuel at 12:1 full throttle and about 9:1 compression.

Thinking out loud here...Why are you running high octane fuel with a mild CR? With such low hours are your rings totally seated or are you pushing some fuel into the oil?

I had to rebuild two motors before switching to a dry sump due to rod knock. The CB Performance pump has pretty poor idle pressure, but is fine at anything about 1200 RPM. I did do a bit of work to open the ports in it...

Evan and I beat the piss out of the motor now (7000-7250 RPM) and it doesn't bat an eye.

actually my CR is higher, more like 10:1. I hate fuel knock. I would get some with running 93 so I just used 100 in this motor from the start.

How does the dry sump perform better if the oil is trapped in the heads and the issue is return flow? I guess you could tap a port in each head to help the return?

Don't vent the heads. Oil pools in vented T4 heads. The higher the revs the more pooling.
https://newsite.hamheads.com/2016/12/10/typ...tests-analysis/

Good read. Thanks Len.

For things to note, I did see my dip stick extend after runs. Seems to indicate excessive crank case pressure.
I did have the heads vented to a breather box that drains back. The dry sump and no vents sounds promising.

I employed Lens and Jakes work on the current motor. Heads are not vented and a -10 AN welded to the chimney that leads to a breather tank.

There used to be pictures of the test engine with modified valve covers with glass windows where you could see the oil pooling. Those pics were very convincing and had me pulling my head breathers out.

Zach

Herb, if you're just AXing then a dry sump system would probably be overkill. A lot goes into converting a wet-sump engine into a properly designed dry sump engine.

Keep the tuna can. Dump the head vents and add an Accusump.

As for the possibility of detonation, one easy tell-tale sign you can look for during disassembly is if top and second ring gaps have lined up. That's a classic sign of detonation.

Len, just so I am clear, plug the head vents, don't cross connect?

Totally taking this off-topic a bit further...last few races I experienced unhappiness with my 914 regarding vented rockers.

Last summer with my 2L I was taking a nice long left-hander at Thompson (under the bridge) and the pressed vent tube in the right head came out. Dumped shad-ton of oil all around the bend, causing a couple cars to spin and one to hit the wall (I strongly apologized and ensured he did not buy beer or dinner that night). Field-fixed it by slightly swaging the tube, tapping it back in tightly, and gooping it with silicon. Held for the weekend.

This September at the Lime Rock Labor Day historics, using a borrowed 1.8L. The valve covers have welded 1/2" tubes coming off the valve covers with oil hose secured by hose clamps. First session out, driving through Big Bend and the left hose came off the tube....dumping a shad-ton of oil all around the bend, causing myself and several other cars to spin (no contact, thank goodness). Field-fixed by cleaning it all up, screwing it on as tight as I could, then drilling a hole across the hose, clamp, and tube and putting in a cotter pin, sealing it with silicon. Held for the rest of the weekend.

I'm also running a CB Performance dry sump pump.

I'm really getting tired of that. If I don't need these rocker vents then I'll just drill/tap/plug the holes on the 2L engine I'm building now and be done with it.

Curious...could unbalanced components accelerate the bearing wear and lead to this sooner?

Yes. Just plug them.

Basic engine theory: Place the oil sump pick up at the engines lowest point in the crankcase and vent the crankcase at its highest point. Keep it simple.

Greg you don't need anymore oil incidents! Your last one ought to hold you for the rest of your driving career.

Greg,

Just make sure that you increase the chimney vent some. I went with a -10 AN weld-in bung and a catch can to ensure good breathing.

-Aaron

Jeebus! That's not even considering that one!!! Toss in the "putting the Super Touring car on its lid" in early 2018 and it's been an "interesting" 18 months...I really do need a boring hobby...

Fantastic meeting you and your dad at VIR. Hope that happens again soon.

I think I'm'a gonna plug those head holes.

That shouldn't be a hassle. I've modified the "stack" there to both vent and accept drainback from the can (kinda see it in this photo); it would be easy to toss in a larger vent tube on that block-off plate.

Damn Greg! You've had a hell of a year and a half. That VIR shit was scary and such a suck ass way to end up considering how hard you guys worked to make the race.
The NOLA "Jackie Stewart" commentary is gold! I have to ask, how did you handle the post race de-brief with the dive-bomber? Was a jack handle involved?

Dad and I had a really good time at VIR. We sure did appreciate the passes and we enjoyed meeting your guys. Wish we could have socialized more. Maybe next time you won't have to work so hard!

Oh, it did not go well AT ALL. The short version is I was tossing paper as I was climbing out of the meat wagon, and when the SOM decision went against him, he and his dad yelled and cursed at the stewards and flipped them the bird. Then started yelling at us, claiming we were damaging his chances for his future racing career. At the time it was kinda surprising; in hindsight it's freaking hilarious.

I DO NOT like thrashing at the track (or, really, at home). But I seem to surround myself with people that are all like, "dude, we're here, let's fix that s**t" and it makes for good stories. I need more less-motivated friends.

But last weekend at NJMP was nice: good weather, 914 ran all weekend without a hitch, boring video, pretty car goes back on trailer as pretty as it was when it arrived. Need more of those.

Now to decide what to do in 2020. I am becoming more attracted to that limited prep HProd 1.8L option...know anyone that could build a Micro/Megasquirt using the stock throttle body...?

Back to our regularly-scheduled "toss a rod" discussion. In that vein, here's what happened to me the weekend before the Lime Rock Historics 2019 (remember what I said about needing to be more boring...?)

Knitting. That's the ticket. Or crochet or quilting. Though they get pretty serious about that stuff...

check your connecting rod ratio to assist in cakculating you approximate RPM range. The long rods should allow for higher RPMs but the size of the Piston may be causing the inertia to jerk the bolts apart.

My BMW 2002 had a con rod ratio of 1.6875 which translates to 6875 RPM's at an extended 7200 the harmonics and piston inertia would pull the rod bolts apart. Ok for short bursts but really a grenade waiting to happen.

Did I miss something in this thread, or did the OP note that he ran the car despite a noticeable rod knock and low oil pressure?

Seems a pretty easy answer...no?

I did run it to failure. Before this last event there was no indication of potential problems. I also had a couple of runs that were normal. From first indication, it was a quick failure.

I think my rod ratio was good, but will review my that was one of the changes with this motor. I had shorter rods previously.

To me 6800 rpm is really pushing the limits of a stroker T4.
You have a number of fail points that can be happening all at the same time, below I'm only addressing crank flex.

Crank flex the crank actually bending at/near the center main journal, as well the 2" "chevy" rod journals. Having 2 throws without support in between the rod journals is another weak point. the higher the RPM the more flex.
This flex is why a 1.7/1.8 case is a better choice over a 2.0 case, as the crank flexes even in a stock engine and it's hard on the center main case bearing saddle. VW knew this, basically stating a 2.0 couldn't be done reliably and it was Porsche that designed/modified the 2.0 crank for the '73 914. VW didn't use the 2.0 engine in the bus, till the 914 proved it was satisfactory reliable enough, for the 1976 model year.
With a longer stroke, in this case a 80mm, at high rpm you are amplifying all the bad, the crank flexes, causing bending stress on the rods, points of the bearings begin touching the crank journals, side loading, heat begins to spike, add into the mix events high RPM downshifting causing mechanical over rev, etc.
All of these stress points begin to cascade as RPM increases until the weakest point fails, in this case the rod.


I'd choose the 78mm crank with T1 rod journals just because the bigger T1 journal has more strength. I'd also lower my redline to no more than 6500rpm.

Hope this makes sense, I've got a L5 herniated disc back issues and I'm whacked out on pain meds.

Thanks Mark, I was hoping to get your insite.
Try whiskey? It helped with the pain of losing this engine.

Hope you get well soon..

When I had my heads reworked the machine shop closed/weld the breather vents is that a good or bad idea?? Click to view attachment

It sounds like it was a good idea.

Pretty funny the guy accused the racer he dumped of ruining his career. If he keeps driving like that he'll get more than paper thrown at him eventually.

I don't think you'll have too much trouble finding someone to build your MSquirt. What about DIY in Atl? I'll bet a post on the Sandbox would flesh out sources fast.

Greg your broken crank is kind of unusual for a stock crank. They're actually nice chilled forged German steel. I think case flex and or shuffling may have something to do with your failure. I have heard of them breaking in the center main before, but like I said it's not common.

I broke a 1.8 crank on the FP 914 at the #1 journal, just in front of the flywheel. But we had lightened the shit out of that crank and I was turning around 8k at W.O.T. in turn 9 at Roebling. Caused a momentary rear wheel lock up. It was exciting.

For our race engines I used to drill the 6 main bolt bores for 1/2" bolts. They fit snug in the case and that totally eliminated shuffling. I torqued them down good and that eliminated any separation of case halves. I line-bored the case with the new big bolts. This process was waaaaay cheaper and easier than installing shuffle pins and buying ARP case hardware.

I would spend in the neighborhood of a 100 hours prepping our dry sump race cases.Click to view attachment Click to view attachment Click to view attachment

@HAM Inc

Love the fact that you're using the 1/2" bolts to effectively shuffle pin it without all the work and machining associated with shuffle pins. Colin Chapman would be proud.

“…simplicate, and add…lightness" has been attributed to Colin Chapman. To paraphrase his lightweight philosophy, each part should serve multiple functions. Your creative solution achieves that goal. Nice way to work smarter not harder.

Great job Len!

Dat's purdy work up there...if you're bored and want to do another one...

Not sure that I want to pursue the Limited Prep HProd route. I already have the chassis at LP (it's an ex-ITA/ITB car) but the induction regs require using the stock, unmodified throttle body. That's a lot of development that has to be done around that one piece.

Colin Chapman was a genius. He would have gun drilled those bolts. I did at leat lop off the extra threads I considered using Jet Nuts to save some more weight, but didn't want to spend the money.

Greg, you ought to talk to Blake Meredith. He ran a ITB 914 and considered switching it over to HP. IMO it would be an expensive exercise in

The case work was a labor of love. And it worked great. That bottom end never gave a minute of trouble and ran 11 double weekends plus test days. Oil samples always came back perfect and hot idle oil pressures never changed one bit from new.

When I sold the car that engine was in it. Kip sold it to a guy in CA. I'd love to be a fly on the wall when he tears into it.