The first factory light weight crank shaft that has been full circle machined available to the general GEO METRO public. Lets face it there is simply no crank choice available for a G10 engine. I looked at building a full CNC billet crank and we now have the ability to manufacture the part. There were more upsides to just making the factory crank better.
First off a full billet crank at our low demand numbers estimated out to be worth about $1500.00 each. I told myself I wouldn't even spend that much money so why would any one else.
I would right to lathe with 6 cranks and started in with the basics. Knife edging, counter weight removal, cross drill weight dropping and even did a heavier crank by welding on weights just to make sure some thing odd on a 3 cylinder didn't get past the dyno. Heavier does nothing good by the way.
After running all 6 cranks I decided to follow the direction of the Atlantic open wheel Indy race teams. They have crank weight rule and they have to use a stock crank. there allowed to go .020 on the bearings I believe. The crank has to weigh 26 lbs. It just helps keep the money out of the part because you cant go to titanium or run a super light weight crank. Plus a stock crank is only so strong so it helps keep the over all HP all fairly even. They could build more power but then they would fail the stock size bearings is the idea.
We have no rules or limits except common sense. Even in turbo land 100 hp is way up there so 75 hp is fairly realistic. That's only 25 hp on each cylinder under boost if its turbo charged. Its not even very much load at full power is my point. So we can do what ever we can afford to the crank and virtually never see a geo bottom end go away. Which never happens by the way.
To keep the cost down I modeled the new crank shaft off of the factory crank. Starting with this as our core to build takes out a few hundred dollars of billet we would have ad to turn into chips to get a crank shape out of. Next I chucked it into the lathe and went with a full circle lightening job. The crank is centered and zero'd in on the lathe and the rod end of the crank arm is machined to the bearings surface. This removes about 9 mm of material off the crank counter weights or the over all diameter of the crank. It also drops about 1lb of weight off the crank which is simply amazing considering the original crank is in the 12 lb range. To remove 1/12 of the reciprocating weight right at the source is amazing. Plus we get the diameter of the shaft down by almost 10 mm which is almost 1/3 more than the INDY car engines when compared.
Between this and light weight fly wheel the only thing better and I recommend this with it is a turbo charger system on propane so you can get the cheap fuel and the high octane. Its like having $15.00 a gallon race fuel for half the price of cheap unleaded fuel.
The crank is cut down to size, de burred and then rebalanced or like I like to say balanced for the first time.