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I think alot of people on this site have come to know me to be a bit of a worrier even though I have a complete spare GX engine savely wrapped in a garbage bag in my garage.

I just have that thinking of "if this can happen to someone else, what prevents my engine from the same".

Just shows how much punishment ours Datsuns must take before they break, and only breaking when they have a defect.

Ahhh dodgeman you got me there So drawn in by the picture, didn't look at the date!!
If you see the boss over the weekend - give him our best. Hope he can fly the Datto flag on the dias as usual
Cheers

Ahhhh Hendrik, you might be a worrier, but you love your Datsun dearly & care for it well. If every Datsun owner was as good to his car as you are to yours then we would have a lot more Datsuns to love. Don't ever stop caring.

I won't get to see the 'Boss' untill about Tuesday or so, but I called into the workshop this afternoon & Mrs Boss came straight out & told me the news. The wet track & a locked diff quite understandably caused some problems with traction in the corners this morning, but the track improved in the afternoon & he aparrently gave it a bootfull with a rewarding result.
The last minute tweak on his dyno produced an extra HP or two, so there is still more in the old girl yet.

Datgo, thanks for bringing this one to the fore again as it has given rise to some worthwhile thought & discussion.
The current engine was built with some proper attention to rod prep this time. It looks like it will pay off.
The little pushrod A series engines may have more technological comonality with a mid 20's Chev than with some of the twin cam, four valve exotica, but the last victory that these engines will take is still a long way off.
A very long way off.

Given the time for the crack to propagate, this thing would have eventually gons so far that it would have separated at a fast idle, but it just happened to separate when the car was downshifted after the end of the race, during the slowdown lap. The engine had been wrung out to the max during the race & the crack was growing. Just lucky that it didn't happen at racing speed as the oil on the track would have made it hazardous for following cars.

Thats sucks Dodgeman, im dreading things like this when i start, so you have the 1000 on the track now? Got any good pics of it fanging around?

OK. The busted parts are from someone elses A15 race engine. I can't afford this kind of stuff, so I remain 'strictly street'

The photo is the other half of the deal. The damage to the piston is confined to a small chunk out of the skirt & a matching, slightly bigger chunk from the bottom of the bore, so the rod seems to have done the damage very near the bottom of the stroke. Since the piston was found at the top of the bore, it can be reasonably assumed that it was probably on its way up at the time of separation.
This engine has race EFI, but I guess that it was possible that the piston was 'sucked' back up from the bottom of the intake stroke, but it's not the conclusion that I came to.

The rod went round & round a few times smashing everything it could find & this would be the cause of the appearance of 'necking' This view would be supported by the condition of the top section. This has clearly suffered from the propagation of a crack across the rod.

The cam lobe in the picture was found in the bottom of what was left of the sump & was taken out by one good hit from the rod in its circular path of destruction. Both sides of the block were also holed, so with all this damage being done by the end of the rod, it's no wonder that it looks 'necked'


This is a related picture link.


WhiteSedan
If you are concerned about rod failure, & what racer isn't, then the factory offered some help in their race buletins. This particular rod was used without any prep other than balancing.

Looks like someone will have to get a wiggle on with the CA16
Good to see you back on line Dodgey!
Cheers

Ok guys, I'm starting to worry now.
My A12GX is thrashed over weekends and it is stock standard without a aftermarket balance job. I frequently rev it to 5500rpm and 6000rpm.
Now, because mine does'nt have a tidy balance job, what is the chance of this happening to my engine?

I know that this was caused by fatugue but are Datsun conrods proun to brake when put under stresses?
Why I am asking, it is a 28 year old design and engine that I am handling like a 2006 designed car.

Your a12 will be fine. I frequent 7000rpm in my a14. Been in for years now and quite alot of punished K's. Lots of others will say the same about the A-series. Not many break.

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I can assure you that your Datsun conrods will take far more punishment than 6000rpm.

When my dad used to do oval track racing, they used Ford Kent engines, for some unknown reason, probably because they are dirt cheap to rebuild. How ever, they modified a 1600 Datsun crankshaft and conrods to be used in the Kent. The last 2 years he raced, they went out with a bang, and had it "professionally" balanced, and got the Kent to rev up to 10k Rpm plus. They sold the car with the engine, and it still ran for sometime afterwards before puking it's insides out.

They used the Datsun stuff, because it's forged and not cast like the Ford's...

I can still remember how they went to the local grocer to borrow his scale, when they did the "balancing" themselves...

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Glad to be back. I was working away again & had no access to the net for a few weeks.

Now if everyone looks at the date under the picture, it will be noticed that this happened over two years ago & this is an old thread that has been resurected by datgo a few days ago.

This engine was replaced by the backup engine while a new & improved race engine was built. The new race engine was then installed & the backup engine was upgraded to the new engines spec's. It now sits in storage just growing old.

This new engine, now about two years old, has just today [Fri.3/11/06] powered the 'Boss' up the course at the Bathurst hillclimb in a time that is lower than the class record, & that's just in practice.
This is the same engine that lowered the class record at Wakefield Park twice in one afternoon at a recent raceday.

How many would be rushing to replace a winning car with an unknown/untried replacement.
When this one stops winning, then I guess that the 'Secret Weapon' will get a priority. This might take a while.

Hendric, you must be the biggest worrier in the club.
This rod had a forging imperfection that would have caused no problem in normal service, but would likely have been picked up during race prep of the rod, but it was used basicly untouched in a race engine that saw a great deal of stress at very high RPM. A lot more than the 5,500 to 6,000 rpm that we all rev our 1200's out to on a regular basis.
It was just a bit of bad luck as much as anything &, if anything, 'A' series Datsun rods are known for their strength, so you would need to be extremely unlucky to have a problem in your engine. Very unlucky indeed.

Do you think high RPMs caused this?

commonly known as a 'fuel delivery problem'...

(The rod knocked the fuel pump off the block)

Ddgonzal
This damage "occured" at moderately high rpm, but wasn't "caused" by the high rpm.

It would appear that the rod had developed a fatigue crack that had been propagating for a while. It had grown to the point where the rod was seriously weakened & the extra revs from a downshift at the end of a race during the slowdown lap were enough to overstress the remaining, uncracked, part.

I believe that the rod separated as it was begining it's upward journey on the exhaust stroke. The rod took out a part of the piston skirt, as well as the bottom of the bore, yet the relatively undamaged piston was found at the top of the bore.

The fracture face of the top part of the rod was not touched after separation, indicating that the piston separated near the bottom of an upward stroke, went up & stayed there.

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Not at the top of the stroke with a low pressure (closed carby) situation? I thought most of the rod faliures that happen in closed throttle situation are tensile faliure rather than compression faliure, and occur at the change of direction at the top of the stroke- (the piston keeps going up after the rod has started to come down.)

I'd have to agree with Grunterhunter. You can see where the rod has "necked". this happens when things are in tension??? If it buckled, the rod would have bent sideways???

My first year mech eng material science tells me that you are never going to get failure during a compression cycle for something like this. the "necking" is obviously a tension failure. Albeit there may be stresses in the compression cycle that may have reduced the elastic life of the metal. An 8-10K rpm down shift stress is going to reduce the life of a piston rod but will probly not cause a failure, once in a blue moon. But, every other weekend at the track or at your favourite hairpin to/from work will reduce the life. Everything is built with a set amount of "out of elastic range" scenario "engineered" into the design, but unless you are running with an F1 budget you are not going to have facilities to measure, test and account for these. The mushrooming and necking evident in this pic tell me that it was a tension failure and it was battered a bit after the failure. I am guessing it was a fatigue failure and it was not under "extreme" circumstances at the death of it. If it was an extreme failure there would be more catastrophic failure instances, like fragments and complimentary failure from other cracks or crack-like-inclusions within the rod.

just an opinion.

Hey Jack.......between every compression cycle is...what kind of a cycle????When the piston is going up on the exhaust stroke..there would be minimal pressure acting on the piston????
If this rod broke comin down it would have buckled???