Cross-drilling (Borra extra oljeutsläpp i veven)
Posted: 2006-01-11 09:24:32
Hallå alla som river/har rivit sina motorer!
944:an lider ju av ngn okänd anledning tendenser till att slita ned 2:ans vevstakslager betydligt fortare än andra vevstakslager.
Gissningsvis har det med oljetillförseln att göra och det har väl något med vevens interna utformning att göra.
Mitt vevstakslager var nerkört men det var inte dom andra.
På amerikanska forum är detta ganska hett diskuterat. Har läst att de rejsinteam som prep-drillat (borrat nytt oljehål 90 grader från orginalhålet) säger sig blivit av med problemet.
Ni som kör hårt och framför allt ni som kör turbo, har ni gjort ngt åt detta?
Eftarenheter?
Finns en del mumbojumbo i ämnet om att man ska ha extra mycket olja i tråget osv. Har hittat lite som jag anser vara ganska sakligt:
Here's a picture I drew up years ago on the 'perp-drill' mod:
At low-RPMs, the centripedal force from the crank rotation isn't that great and oil-pressure can force oil back towards the crank to make it out the side hole on the rod journal. However, as RPMs increase, this centripedal force will overcome oil-pressure and you'll have oil trapped at the outermost reaches of the journal. HOwever, new oil that's flowing out that hasn't traveled past the hole can still get out. I appears the best scenario is to drill a hole at the outermost end of the rod-journal so that oil-pressure will be enhanced by the centripedal force of the spinning crank.
One thing I didn't bring up about this situation is oil clearances in the bearings. As a bearing wears, it will have larger clearances than new bearings. If the #2 were to wear out faster somehow, it will have larger clerances than the other. The result of larger clearance? MORE OIL FLOW! That's why your oil-pressure goes down when yor bearings are worn out. So there's a feedback self-correcting loop here of sorts. Assuming all oil-feeds to all journals are even, then a bearing that wears out sooner than the others will get extra lubrication to slow down its wear. This drains oil-pressure from all of the other bearings which will wear faster. At some point, those other bearings will catch up to the wear of that 1st one and and they'll all be even again. That's why I suspect a differential in the oil-supply between the bearings.
Now, a quick lesson on the infamous 944 #2 rod bearing failure
A spun #2 rod bearing is the most common cause of 944 engine failures by a long shot. This is the same thing that happened to my non-turbo in the summer of 2000. Do some sustained high-g cornering (all too common problem with those darn 944s ), oil gathers on one side of the pan, pickup sucks air, good bye #2 bearing. I've read and heard a number of theories as to why is specifically #2, but regardless of that outcome, I'm going to work on preventing the cause.
1) Installing oil pan baffle(s) to keep the oil from sloshing too far away from the pickup
2) Weld a "collar" around the pickup to encourage it to draw the oil "up" from the bottom of the pans, rather than sucking air at the edges.
3) Install a crank scraper to strip oil from the crank, actually helping the oil situation, and making a few hp at the same time! Repeated tests show 3-5% "gain" (or more accurately, "reduced loss") in hp/tq. I'll take that all day long, especially for a whopping $69.95 shipped!
4) "Perp drill" the #2 and #3 rod bearing journals in the crank. "Perp" rather than cross, as the hole is drilled perpendicular to the original, facing radially outward. Centripital force (or lack thereof) helps draw the oil out into the bearing. Its done to #2 and #3 only, as its been proven #1 and #4 are almost never starved for oil, while #2 always goes first, and #3 is usually following about 50% behind it.
944:an lider ju av ngn okänd anledning tendenser till att slita ned 2:ans vevstakslager betydligt fortare än andra vevstakslager.
Gissningsvis har det med oljetillförseln att göra och det har väl något med vevens interna utformning att göra.
Mitt vevstakslager var nerkört men det var inte dom andra.
På amerikanska forum är detta ganska hett diskuterat. Har läst att de rejsinteam som prep-drillat (borrat nytt oljehål 90 grader från orginalhålet) säger sig blivit av med problemet.
Ni som kör hårt och framför allt ni som kör turbo, har ni gjort ngt åt detta?
Eftarenheter?
Finns en del mumbojumbo i ämnet om att man ska ha extra mycket olja i tråget osv. Har hittat lite som jag anser vara ganska sakligt:
Here's a picture I drew up years ago on the 'perp-drill' mod:
At low-RPMs, the centripedal force from the crank rotation isn't that great and oil-pressure can force oil back towards the crank to make it out the side hole on the rod journal. However, as RPMs increase, this centripedal force will overcome oil-pressure and you'll have oil trapped at the outermost reaches of the journal. HOwever, new oil that's flowing out that hasn't traveled past the hole can still get out. I appears the best scenario is to drill a hole at the outermost end of the rod-journal so that oil-pressure will be enhanced by the centripedal force of the spinning crank.
One thing I didn't bring up about this situation is oil clearances in the bearings. As a bearing wears, it will have larger clearances than new bearings. If the #2 were to wear out faster somehow, it will have larger clerances than the other. The result of larger clearance? MORE OIL FLOW! That's why your oil-pressure goes down when yor bearings are worn out. So there's a feedback self-correcting loop here of sorts. Assuming all oil-feeds to all journals are even, then a bearing that wears out sooner than the others will get extra lubrication to slow down its wear. This drains oil-pressure from all of the other bearings which will wear faster. At some point, those other bearings will catch up to the wear of that 1st one and and they'll all be even again. That's why I suspect a differential in the oil-supply between the bearings.
Now, a quick lesson on the infamous 944 #2 rod bearing failure
A spun #2 rod bearing is the most common cause of 944 engine failures by a long shot. This is the same thing that happened to my non-turbo in the summer of 2000. Do some sustained high-g cornering (all too common problem with those darn 944s ), oil gathers on one side of the pan, pickup sucks air, good bye #2 bearing. I've read and heard a number of theories as to why is specifically #2, but regardless of that outcome, I'm going to work on preventing the cause.
1) Installing oil pan baffle(s) to keep the oil from sloshing too far away from the pickup
2) Weld a "collar" around the pickup to encourage it to draw the oil "up" from the bottom of the pans, rather than sucking air at the edges.
3) Install a crank scraper to strip oil from the crank, actually helping the oil situation, and making a few hp at the same time! Repeated tests show 3-5% "gain" (or more accurately, "reduced loss") in hp/tq. I'll take that all day long, especially for a whopping $69.95 shipped!
4) "Perp drill" the #2 and #3 rod bearing journals in the crank. "Perp" rather than cross, as the hole is drilled perpendicular to the original, facing radially outward. Centripital force (or lack thereof) helps draw the oil out into the bearing. Its done to #2 and #3 only, as its been proven #1 and #4 are almost never starved for oil, while #2 always goes first, and #3 is usually following about 50% behind it.
som kör turbo, har ni inte hört talas om detta?