View Single Post
Old 08-06-2006, 07:57 AM   #7
bugeyes
Scooby Specialist
 
Member#: 64494
Join Date: Jun 2004
Location: Australia
Vehicle:
2001 V7 sti

Default

Interesting points you make. One thing you touched on I want to take further.

The oem cross drilled crank.
It was always my understanding that the requirement for a cross drilled crank was on engines that only had half groove main bearings. I think an example of this would be some straight six engines. In these engines the lower half of the bearing cap had no groove. This was to provide maximum bearing surface area against the combustion load pressing on it from above. The top half of the bearing had a groove and in order to keep oil supply to the rod journals the crank had to be cross drilled.
Now on our subaru engines we dont use half groove bearings due to the boxer layout, however even though we have virtually full groove bearings (the rear thrust bearing is in fact a full groove all the way around), we also have a cross drilled crank.
When I mentioned this to my hard core "I'll never run anything but a chevy" friend he thought it was a peculiar setup.

I just did an internet search and found numerous accounts and several tech articles on how cross drilling has great potential to damage rod bearings. After reading several of these I'm and pretty much convinced this is our problem. Subaru's tend to kill rod bearings, not main bearings. We have an odd setup that is ok whilst the engine runs at reasonable speeds but will starve the rod journals at high rpms.
The typical solution is high oil pressure but this has other downfalls, what we really need is a 2 stage oil pump. A pump that runs at oem oil pressure at revs less than 5500 and boosts the pressure up over 5500 so it ensures we overcome the centrifugal force that work against our oil flow at high rpms through the crank.
* Registered users of the site do not see these ads.

Last edited by bugeyes; 08-06-2006 at 09:29 AM.
bugeyes is offline   Reply With Quote