Hi all.

About 40 000km ago my A12 engine was opened due to overheating.Me and my dad did it.We replaced rings on the pistons and bearing caps on the conrods.The head was also totally overhauled.Now I want to open up the engine again in the future to balance it and put some sidedrafts on after that.
My question.The car is still running the standard bore and there was no wear on the sleaves.It actually still had the honing marks from the factory and no reach at the top.The pistons also had no play.
I just want to know if I must replace the conrods even if they do not have wear.I will take them in for measurements to make sure about it. Have they not weaken due to hot cold hot cold in it's livetime. I am going to ring it's neck when balanced aiming for 8000rpm.
The engine currently has 140 000km on the clock. +- 40 000km of this was after the head gasket blew and we needed to do the stuff as mentioned above.

The rods are forged from the factory..I wouldnt replace them...

Rods are not normally replaced, even in a major rebuild.

The only time that you would even think of replacing con rods is if they were mechanicly damaged in some way, like a spun bearing in the rod [fixable] or it's badly bent [hydraulic lock?] or failed a crack test.

Some of the fastest engines around have been remanufactured using servicable but definately ""used" con rods as these are probably the toughest part of an infernal conbustion engine, Well,... in a Datsun they are.

thanks for the replies guys.
I got hold of a place here that crack test engine parts.Will take them to them to test.

I have also interesting news of racing in South Africa in the 70's.
I went to a mechanic that I know well to find out if he knows where I can get sidedrafts.He send me to a guy nearby.I went to him and saw quite alot of Alfas.Obviously he is a Alfa mechanic.
I talked a bit to him and we got talking about the past.He was a mechanic in the 70's for a Datsun racing team.Great!!!!
I asked as much as possible.
He mentioned that in the class they competed those days were a standard production class.No changes were allowed to the cars mechanically and also with brakes, etc.
He said they balanced the internals, lightened the flywheel,used the standard GX cam as they were not allowed to change it and made some kind of box effect in the sump to prevent the oil from flowing to one side when cornering hard and fitted a freeflow exhaust.
Even the Hitachi SU's weren't allowed to be removed.
They replaced the diff with a Datsun utility diff to get higher revs for better torque.
He said they went with one engine for a whole season and to this day that same engine is still driving in that same Datsun as someone's wife's daily driver.Can you believe that.
He says he has more respect for a A12 engine than a A14 due to the internals.
(Sorry A14 guys).
He said they revved to 8000rpm and if on the dyno at 7000 he said the engine was not vibrating if looked at.
One of the events he also mentioned they could not compete in their own class due to twin carburation and they needed to compete in the 1600 class.They did not win the race but he said they could keep up nicely with the 1600 cars.He also mentioned that they once took on a Datsun 510 SSS with the 1600 engine and twin Hitachi SU's.
They managed to pull a small gap on it.Nice for a 1200 hey?

This is what I plan to do.Build a car to the specs of the 70's racing class.

you probably don't want to hear this, but there is no sense balancing an otherwise standard GX engine for street use. It simply will not make power to 7000 or 8000rpm. I wouldn't bother crack testing the rods either.

What has been done to your engine so far? I think you already have the GX head and carbs? thats a decent start. Headers and exhaust next, if you don't already have them. Then the "Three C's" - Compression, Cam and Carbs is the way to go.

I think you would be dissapointed with the results for the time, effort, and expense of removing the engine just to have the flywheel lightened and engine blanced. Those are good ideas if you are taking measures to make the engine develop power higher in the rev range, but a waste of money on a stock engine - the money could be better spent elsewhere with far greater gains - like a cam grind, compression, and carbs. Leave the balancing until you are building a serious engine.

L18_B110

Thanks for the reply and yes you are 100% correct.
By I think something is not right with my 1200GX engine at the moment.When I hit 5000rpm it is fine.Go over it, and it starts to vibrate up to 6000rpm.It's redline is at 6400rpm. At the moment I am not thinking of even touching 6400.The reason I want to balance the internals is to get more reliable high revs.As it is at the moment, I don't think the vibrating is good for reliability.

My idea is actually to build a higher performer A12GX engine. I just thought of crack testing my conrods before I push it hard and one of them decide to break.
But I will first find out how much it costs.
The cam I am also going to replace with a 270. Actually I am still doing research on what precise grind to get.As I want the torque and power to rise evenly from low to high rpm and not be only at the top of the rev range. It must also give more power aswell.But I don't want a cam that gives the car a rough idle.My friend has such a cam in his opel.It will soon start to work on my nerves.Later I will fit 40 sidedraft webers.

I like to plan desently and do research before doing something.
It currently is a stock standard GX engine.
GX head, GX exhaust manifold, 256 GX cam and twin Hitachi SU's.

Unless you go massive port job and massive cam twin webbers wont to sh-it. You onle need the webbers if your building a race engine for extreme rpm. The twin 1.5" hitachi su's will do fine to 8000rpm and probably more. The fuel/air system alone does not boost power. You only need to upgrade air/fuel system to accomodate other things like cam, porting and compression. Take this advice and save yourself alot of money that could be spent elseware on making the car faster. Brakes, suspension etc.

That is why I am going to do the carbs last.Maybe.

The GX head I do not want to port or anything as they are very rare.
I just want to balance and put in a different cam and see what happens.If I am happy I will keep it that way.

Freak, I think you are right about the carbs.If reading my reply about the guy that raced them in the 70's in the standard production class, he mentioned it could rev 8000 with ease using the Hitachi SU's as they were not allowed to change it.
That is what I want to do.
I want it the same as the specs of the 70's racing production class of South Africa.
I will replace only the cam to get better power at the high rpm.

guys correct me if i'm wrong but if you change the cam what you gain here you lose there, if you know what i mean. if you want go top end power you will loose torque,and if you want more torque you will loose power. dont be a girl port your head, 270-280 cam, branch and free flow. if you go too much on the head you can weld it. do mods that are worth the time and effot.

my a-14 with a 270 cam and blah blah blah revved to 7200rpm, no funny noises or vibrations, and that motor wasn't balanced

good luck