Stroker thrust bearing groove
09-08-2005, 06:09 PM
#31
Rennlist Member
The stock crank has two oil ports in each journal except no. 3 (thrust bearing). The main journals are cross drilled so if you stick something in one oiling hole it comes out the hole on the opposite side. I believe each main journal feeds both rods on a single rod journal, ie Main 1 feeds rod 1/5, Main 2 feeds 2/6; Main 4 feeds 3/7, and Main 5 feeds 4/8.
On the stroker crank, the oil ports in the main journals are not connected, and instead each oiling port is dedicated to a single rod, and in so doing Main no. 3 (thrust bearing) does have oil ports and is used to supply oil to the two inboard connected rods closest to it.
So: Main 1 has one oil port that feeds rod 1; Main 2 has two oil ports, one feeds rod 2 and one feeds rod 5; Main 3(TB) has two oil ports, one feeds Rod 3 and feeds rod 6, Main 4 has two oil ports, one feeds rod 7 and one feeds 4, Main 5 has one oil port that feeds rod 8.
The stock Porsche main bearings are channeled half way around, meaning at all times one of the cross drilled oil ports is receiving oil from the block and is feed the dedicated rod pair. With the stroker, it would appear if you only have half the bearing channeled, than you have one rod going for half a stroke without pressurized oil. True?
I think this is an interesting (non?) issue. I'm going to check with my local machinest who does mainly Chevy work and see how the "real" chevys
deal with the oiling situation.
On the stroker crank, the oil ports in the main journals are not connected, and instead each oiling port is dedicated to a single rod, and in so doing Main no. 3 (thrust bearing) does have oil ports and is used to supply oil to the two inboard connected rods closest to it.
So: Main 1 has one oil port that feeds rod 1; Main 2 has two oil ports, one feeds rod 2 and one feeds rod 5; Main 3(TB) has two oil ports, one feeds Rod 3 and feeds rod 6, Main 4 has two oil ports, one feeds rod 7 and one feeds 4, Main 5 has one oil port that feeds rod 8.
The stock Porsche main bearings are channeled half way around, meaning at all times one of the cross drilled oil ports is receiving oil from the block and is feed the dedicated rod pair. With the stroker, it would appear if you only have half the bearing channeled, than you have one rod going for half a stroke without pressurized oil. True?
I think this is an interesting (non?) issue. I'm going to check with my local machinest who does mainly Chevy work and see how the "real" chevys
deal with the oiling situation.
09-09-2005, 01:26 AM
#33
Rennlist Member
Hi Guys.
Everyone brings good information to the floor. I have to say that Marc Thomas has built more engines with his stroked cranks than anyone, however there are a couple of issues that people have not addressed. One of the critical issues on the thrust bearing is to provide oil pressure to both surfaces of the thrust journal. Make the area of the cut too wide , or too deep and and it can readily deliver oil to the rods, but reduces the pressure being exuded to the thrust sections. Make it too small and it offers no real benefits to 2/6 oiling.
Porsche made sets of factory racing bearings for the 944 series cars in the late 1980's and early 1990's. These sets were very similar to thier early factory bearings with a full cut bearing surface. It does provide less oil pressure, but provides more oil flow. Not the best thing for a factory warranty engine, but seemed to be just what they were looking for in their racing engines.
I have used the pressure fed mains in 944s with straight shot oiling on numerous occassions with great luck.
We all have our ideas, but I think that the factory race program probably spent more on engineering and trial and error than we have.
I like their ideas and will keep giving them a try until there is a better product out there.....like 928 cranks with honda rod journals!!!!
Good luck.
Everyone brings good information to the floor. I have to say that Marc Thomas has built more engines with his stroked cranks than anyone, however there are a couple of issues that people have not addressed. One of the critical issues on the thrust bearing is to provide oil pressure to both surfaces of the thrust journal. Make the area of the cut too wide , or too deep and and it can readily deliver oil to the rods, but reduces the pressure being exuded to the thrust sections. Make it too small and it offers no real benefits to 2/6 oiling.
Porsche made sets of factory racing bearings for the 944 series cars in the late 1980's and early 1990's. These sets were very similar to thier early factory bearings with a full cut bearing surface. It does provide less oil pressure, but provides more oil flow. Not the best thing for a factory warranty engine, but seemed to be just what they were looking for in their racing engines.
I have used the pressure fed mains in 944s with straight shot oiling on numerous occassions with great luck.
We all have our ideas, but I think that the factory race program probably spent more on engineering and trial and error than we have.
I like their ideas and will keep giving them a try until there is a better product out there.....like 928 cranks with honda rod journals!!!!
Good luck.
09-09-2005, 07:08 AM
#34
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Thanks Adam, that clears up a bit. Yet, shouldn't all bottom halves have these grooves or 6 rods will only get oil 1/2 of the rotation? Instead of grooving them all I would drill the crank and use stock version on bottom.
09-09-2005, 11:42 AM
#35
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I find it interesting that you can buy Chevy main bearing sets w/ 180 groove, 220 grove and a 360 groove.
Also find it interesting that there are as many engine builders who believe in 360 groove as do a 180 groove.
Doesn't appear to be a "right" answer, at least in the "Chevy" world.
Also find it interesting that there are as many engine builders who believe in 360 groove as do a 180 groove.
Doesn't appear to be a "right" answer, at least in the "Chevy" world.
09-11-2005, 06:50 PM
#37
Rennlist Member
So I took another look at the center main (thrust bearing) webbing after Vilhuer questioned about both halves of the thrust bearing having oiling holes.
The stock thrust bearing for my motor had no channels, but did have holes that matched oiling holes in both the crank saddle for the upper thrust bearing, and was the only lower bearing that had oiling holes which match up with oiling holes in the crank girdle.
So what is happening at the thrust bearing journal with the stock crank? Is it receiving pressurized oil both down through the block and up through the cradle? Or are the holes in the lower bearing an oil return?
The stock thrust bearing for my motor had no channels, but did have holes that matched oiling holes in both the crank saddle for the upper thrust bearing, and was the only lower bearing that had oiling holes which match up with oiling holes in the crank girdle.
So what is happening at the thrust bearing journal with the stock crank? Is it receiving pressurized oil both down through the block and up through the cradle? Or are the holes in the lower bearing an oil return?
09-12-2005, 12:07 AM
#38
Rennlist Member
Adam,
Find the "feed" to the mains and follow the feed. The prosche designed bearing clearences are set up to build and hold oil pressure under many conditions.
Unlike racing engines whose bearings are replaced often, and run under very controlled conditions, as an example, rarely does a race engine overheat or get started in sub zero weather. We all know about 928 engines and overheat dont we!
Anyway, use whatever you think is the right center main for your application.
Find the "feed" to the mains and follow the feed. The prosche designed bearing clearences are set up to build and hold oil pressure under many conditions.
Unlike racing engines whose bearings are replaced often, and run under very controlled conditions, as an example, rarely does a race engine overheat or get started in sub zero weather. We all know about 928 engines and overheat dont we!
Anyway, use whatever you think is the right center main for your application.
