Cross-drilling crankshaft?
03-04-2016, 03:16 PM
#1
Pro
Thread Starter
Cross-drilling crankshaft?
I know there are other discussions regarding this recently and that some have done this. My previous engine had #2 bearing failure in the setting of a cross-drilled crank but probably had low oil level at the time. My current builder is recommending cross-drilling all 4 rod journals and I have talked to a reputable builder who says not to cross-drill at all, and Michael Mount mentions in a post that his race-prep involves drilling #2 and #3. I'm leaning towards doing what my builder recommends because he is my builder but I really don't want to go through this again soon and so am inclined to try to do the smartest thing. I don't know how to set up a poll but since #2 is always the problem why not just drill #2 if it helps, and if it doesn't help and might hurt maybe I'm best off just leaving it. Looking for informed answers if there are any - this is for track cars that will see sustained high G loads. My understanding of oiling is pretty limited so I am at the mercy of those that understand these things better. I am not going to exceed stock redline (ever if I can help it) and will probably try to shift more at 6000 rpm. This is a sleeved 2.5L block with a new 3L crank. Thanks
Pauter machine would do the drilling if I decide to do it FWIW
Pauter machine would do the drilling if I decide to do it FWIW
03-05-2016, 02:22 AM
#2
Hi, I am in a engine rebuild process myself and have spent many hours reading about this issues. There are a lot of threads regarding this topic in this forum.
This is a good post by Rennlist Member who was/is building 944 and 928 race engines for more than 20 years:
https://rennlist.com/forums/924-931-...ng-fail-7.html
Realistically, drilling the crank isn't going to do anything if the engine is turning less than 6,500 rpms. In some approaches to drilling, drilling the crank will "hurt" more than help. However, drilling #3 main and sending that oil to #2 and #3 rod isn't going to do anything, but help. You need to modify the #3 main bearing to provide an oil path, if this is done. It can be full grooved, but will work better if it looks like the "other bearings".
Cool oil is essential. 260- 300 degree pan temperatures are common. This has to be lower for oil to work properly. My "target oil temperatures" are 215 minimum and 240 maximum. I won't run an engine with 260 degree oil. It got "turned off" at 250.
Never run the engine above 2,000 rpms with oil colder than 215 degrees. Allow the oil to warm up. Your oil thermostat should be open, before you put the car on the track.
The proper bearing clearance will help. I always "shot" for .003" (minimum) clearance on #2. You can run .002" on all the rest, but .0025" would be better.
Coat the bearings. It will help, when the bearing "touches" the crank. Cold start, etc. You need to maintain the proper clearances, however. "Scotch brite" the surface of the bearing and remove the "shipping" layer, before coating, if the coater doesn't do this. Ask them.
Run 20/50 oil. Brad Penn or Torco. Anything that has a minimum of 1200ppm of zinc and phosphorus. Ansoil might be a good alternative to consider. Stay away from the "grocery store" oils....for a track car. Use that stuff in your street car.
Improve crankcase ventilation. Not head ventilation. Crankcase ventilation. The cam carriers get completely filled with oil, at higher rpms. you need this oil to get back to the crankcase, without restriction.
Confirm that the pick-up has enough "room" to get oil to it. Many times, in the 944 engines, I'd have to machine on the inside of the oil pan to get enough room between the pick-up and the pan. 1/16" isn't enough.
You really need a screen/baffle in the oil pan to help "control" the crank picking the oil up, out of the sump.
__________________
This is a good post by Rennlist Member who was/is building 944 and 928 race engines for more than 20 years:
https://rennlist.com/forums/924-931-...ng-fail-7.html
Realistically, drilling the crank isn't going to do anything if the engine is turning less than 6,500 rpms. In some approaches to drilling, drilling the crank will "hurt" more than help. However, drilling #3 main and sending that oil to #2 and #3 rod isn't going to do anything, but help. You need to modify the #3 main bearing to provide an oil path, if this is done. It can be full grooved, but will work better if it looks like the "other bearings".
Cool oil is essential. 260- 300 degree pan temperatures are common. This has to be lower for oil to work properly. My "target oil temperatures" are 215 minimum and 240 maximum. I won't run an engine with 260 degree oil. It got "turned off" at 250.
Never run the engine above 2,000 rpms with oil colder than 215 degrees. Allow the oil to warm up. Your oil thermostat should be open, before you put the car on the track.
The proper bearing clearance will help. I always "shot" for .003" (minimum) clearance on #2. You can run .002" on all the rest, but .0025" would be better.
Coat the bearings. It will help, when the bearing "touches" the crank. Cold start, etc. You need to maintain the proper clearances, however. "Scotch brite" the surface of the bearing and remove the "shipping" layer, before coating, if the coater doesn't do this. Ask them.
Run 20/50 oil. Brad Penn or Torco. Anything that has a minimum of 1200ppm of zinc and phosphorus. Ansoil might be a good alternative to consider. Stay away from the "grocery store" oils....for a track car. Use that stuff in your street car.
Improve crankcase ventilation. Not head ventilation. Crankcase ventilation. The cam carriers get completely filled with oil, at higher rpms. you need this oil to get back to the crankcase, without restriction.
Confirm that the pick-up has enough "room" to get oil to it. Many times, in the 944 engines, I'd have to machine on the inside of the oil pan to get enough room between the pick-up and the pan. 1/16" isn't enough.
You really need a screen/baffle in the oil pan to help "control" the crank picking the oil up, out of the sump.
__________________
Last edited by Smudo; 03-05-2016 at 02:34 PM.
03-05-2016, 12:42 PM
#3
Drifting
Here is something to think about for everyone. The rod journal may be to big in diameter. Causing the oil to heat up that much fast at high RPM's along with the compression on the rod onto the surface of the rod journal. I want to know if there has been any failures on SID's biuld using an offset grind and Mitsubishi rods from eagle. I would think the smaller journal size would help cut down on friction at higher RPM's. Like an under drive pully set. That's how Honda hanlded there rod bearing problems. Also the oil has to travel a shorter distance to the rod bearing. Just food for though. This would go along with a few other mods that should be addressed for oiling issues on these engines.
03-05-2016, 02:37 PM
#4
Has anyone pictures or more detailed description of this mod?
Drilling #3 main and sending that oil to #2 and #3 rod isn't going to do anything, but help. You need to modify the #3 main bearing to provide an oil path, if this is done. It can be full grooved, but will work better if it looks like the "other bearings".
Drilling #3 main and sending that oil to #2 and #3 rod isn't going to do anything, but help. You need to modify the #3 main bearing to provide an oil path, if this is done. It can be full grooved, but will work better if it looks like the "other bearings".