Engine Problem discovered...

[jadams]

I pulled the engine out of my jalopy of a car, and found out what the problem with my engine at the Watkins Glen event. I know....it was over a month ago, but I am just getting around to it now. The problem was that I had two crankshafts. One main one, its little baby that broke off of the main one. So I am not sure what caused the crankshaft to break. At this point I am kind of leaning towards a manufacturing defect in the crankshaft. But who knows. I guess it doesn't really matter anyway. I just need to fix it with a new engine. Maybe I was just making too much power for it! O well....back to the drawing board. Is there any way to post pictures on here? I have a couple of cool pictures out of it anyway.[/img]

[grovefromnh]

If you are currently running a 350, put in a STEEL 400ci crank. It will give you the strength that you need plus bump the engine to 383ci.

[jlwhorf]

Crankshaft failure is usually either from a stress crack (from previous dammage), not running or having the wrong dampener, or severe detonation. If you ran a cast crank in your old motor, shame on you. They are totally unsuitable for a race engine. A GM steel crank is marginal at best. For a chevy race engine, you really should run a 4340 crank. Good luck on you new engine.

Jonathan
900 Monte Carlo PA

[rajito]

Current RWHP: 0
Current Torque:-5 ft-lbs

Joel, how'd you get -5 ft-lbs torque with 0 rwhp? That's pretty cool!

Raj

[jadams]

It is a phenomenon that is only technically possible when you have two independent counterrotating crankshafts. It is so rare that most people overlook the obvious.

[jadams]

If I had severe detonation to cause the crankshaft to break, wouldn't I have probably have other visible signs of detonation? Like broken ring lands, or pistons, or screwed up aluminum heads. Everything on the top side of the pistons looks perfect, this is why I have basically ruled out detonation as a cause. Yes, my crank was cast instead of forged, but the engine builder told me that I would not need a forged crank unless I was planning on supercharging, turbo charging, or running nitrous. I guess he was wrong.

[grovefromnh]

You need a new engine builder if he gave you bullshit advice like that.

[jadams]

Well I am bringing the block back to him this weekend. Sure am curious to hear what he is going to say. The block has a three year warrantee on it, so I can't wait to hear the excuses.

[dinoracer]

Joel

I also broke a crank at the Glen, maybe it's something in the gas...

Mine broke at the #2 main bearing, I think due to lack of oil. I was seeing low oil pressure during the event until it finally failed. Taking it apart, it looks like that bearing overheated (black staining), couasing it to spin in the bore, after which it REALLY overheated until the crank snapped at that overheated point. Are you seeing any heat damage?

[jadams]

Nope, no heat damage at all. In fact all the bearings look fine. The cranks just snapped at the first throw. Certainly looks like a casting defect to me. The material grains looks kind of suspect to me. I guess it is still possible that my engine had detonation, but I would expect to see other damage and I don't see it. Like you said, maybe the fuel up there was not really 93 octane?!?!?

[grovefromnh]

Oilpans on American cars are not suited for hard cornering. With limited or NO baffeling the oil slides up the side of the block away from the pickup, resulting in low pressure then bearing failure. A good baffeled oil pan will give you added capacity plus engine longivity.

[chaos4NH]

Oilpans on American cars are not suited for hard cornering. With limited or NO baffeling the oil slides up the side of the block away from the pickup, resulting in low pressure then bearing failure. A good baffeled oil pan will give you added capacity plus engine longivity.

Having "cooked" the engine in that 1970 Javelin due to loss of oil pressure in turn 8 of Bryar Motorsport Park, I can attest to the problems caused by lack of oil pan baffles!

[enjoythemusic]

I can attest to the problems caused by lack of oil pan baffles!

Ditto, and btw the oil pan in some cars might be good for one direction, but not the other. EXAMPLE: Had to mod the oil pan in the red car as there is a known oil starvation problem when taking long/hard right turns. Why they had a proper baffle for left turns and not right is a thing only Italians could conjure up at night while wearing a hat with moon and stars on it.

One of the many reasons the red car is semi-retired.

[turtlevette]

Does anyone run dry sump?

I think that's the real solution.

[jlwhorf]

Does anyone run dry sump?

Yes. I run a dry sump now. it is nice having the oil pressure stay contant throughout the RPM ranges. Oil pressure does not fluxuate with throtte like in wet sump conditions. They quite a bit of work to install. I had to cut the front clip to fit the pump, there is a fair amount of plumbing, and finding a good place for the tank. Good used stuff is pretty available and affordable at the Thompson swap meet in October.

Back to the broken crank discussion: A spun bearing should not be the cause a crank to break. It usually is caused by stress from harmonic vibration due to going on and off the throttle. A good balancer is a must. I have seen broken cranks often in short (oval) track racing when people run a hub instead of balancer.

Jonathan
900 Monte Carlo PA