924Board.org

[CorsePerVita]

Alright so I'm at that point where I've found a good machine shop to do my engine.

So I have decided for the first season I'll probably just replace my pistons since the old ones were "whoa there turbo... you're crazy" in condition.

However, I am not sure what all will need done. If you were going to race the crap out of a nearly stock engine (maybe a little head work done) what would you:

A. Have replaced.
B. Double check?

My primary concerns would be:

- Main bearings? Do I need to replace these with new ones no matter what? The crank looks like it is in absolutely fabulous shape.

- Head work - the valves look fine. Head is dirty, but nothing is rusted, gnarly or looks to be in bad shape. In fact, quite the opposite, it's just a bit dirt but all looks fine, no pitting, etc.

- Block work - now the block i'm using did have a blown head gasket. If need be, I can always tear MY engine apart as it blew as well but I have only ran it a handful of times in and out of my driveway to work on it, however, has almost no contamination. But I've posted pictures of the cylinders below, I'm assuming I can probably hone or bore it and do new rings and be happy, yes?

I guess a better question to ask would be: For those that have rebuild these engines, what are the crucial things to look out for? This is my first rebuild. What are the things that you'd check, update, be absolutely sure to check, etc.

I've got 2 engines to work with if need be. So I'm sure between the two of them things will work out fine.

I'm not worried about CIS - i am converting to megasquirt, so I'm mostly only concerned about the rebuild between the head and the block.

Here are pictures of each cylinder




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- 1977 Porsche 924 2.0 N/A (Trackday Project)
- 1979 Porsche 924 2.0 N/A (The other daily)
- 1980 Porsche 931 (Daily)
- 1987 Lamborghini Jalpa
- 1999 Ducati 900SS

[daniel]

Cant give you specific 924 info, but in general if you are building a race engine, these are the things I would do, in order of importance:

- Reliability is king, so make sure you crank tunnel is checked, journals are ground. Also check the rods for big end size and twist as well as little end size. Don't forget the cam, check that it isnt bent and that the journals are atleast reasonable.
Next get flywheel to pully balanced and also get the rods dynamically balanced, i.e. all little ends the same and all big ends the same. Balance the pressure plate seperatly incase you need to change it later. Dont forget to balance pistons, you can do this your self with kitchen scales and a die grinder. Easy job
Get a good quality hone job using progressive stones, ring seal = hp so dont scrimp.

Before I forget, some form of windage try will keep your oil pressure in check, also I added an oil cooler - made a big difference.
Also use new bearings and rings regardless of how yours look.

The next step is to make sure that the surface of the block and head is true and flat. Your machine shop will do this. While were on the head, I always chuck valves, springs, collets and retainers. Some may disagree but unless you know the exact history of the engine your building, why risk it. Have the head blasted and inspected for cracks around the valve seats. If you have done head gaskets, might be an idea to get the head pressure tested, with hot water.
Finally when you put it together, be patient. Do it as many times as it takes to get it 100%. I often put a race motor together and pull it down 5 or 6 time before im happy. A few things to watch:
1) Crank should spin easily with your little finger. If it dosn't take it to a shop to be checked, dont accept it until its right. There should be no tight spots in the rods at all. I often assemble them and torque them up with the crank out of the engine.
2) Get all four piston deck heights the same, if there different either machine piston tops or swap rods.
3) all combustion chambers (even if its just valve releifs in a NA head should be within 1cc of each other
4) check your cam timing, even if its a standard cam. Get the max out of what Porsche has given you.

- SO you've done all that and probably made 5-10hp more than stock. A lot of work for not a lot of gain, but the good new is you now have a good reliable base for future rebuilds. Next step would be a small compression increase, say to 10:1 on a 924 motor, a port and polish job and take some weight of the flywheel. Get a big valve kit to if your budget streaches to it.

- Finally you could bump the compression up a bit more and install and mild to hot cam. You would want to get the motor spinning a bit quicker at this point, so consider some light weight valves and retainers and also a HD set of valve springs.

Any more than this and you need to start incrementing in small steps trying one thing at a time to see what works.

Remember, be clean, be througher and be patient and you should have a good motor.
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Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet