Rod Bearings #'s 2 and 6.... Better Check Them All
09-17-2010, 08:28 PM
#31
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Yes, have a very accurate bearing micrometer.
__________________
greg brown
714 879 9072
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Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
09-17-2010, 08:38 PM
#32
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09-17-2010, 09:29 PM
#33
A few points I have gathered over many years dealing with and mantaining internal cumbustion engines.
1. The failure rate in any piece of equipment is proportional to the number of its moving parts.
2. More damage is done by opening up good operating engines to inspect parts for wear etc.
3. Industry moved from maintenance and repair based on running hours (time-predictive) maintenance to
4. Condition monitoring. That is regular inspection and if it operating within the vibration and wear limits as prescribed by the manufacturer and if the oil analysis is satisfactory, leave well enough alone.
I have read many threads on this forum regarding the type of engine oil to be used and and lubricating oil analysis. I stick to the grade recommended by Porsche (based on their building experience, operating experince and racing experience) and relate this to the temperature profile that the car will be operated in. We need to be mindful that the engines within our cars were initially developed over 40 years ago and by todays technology they would be classified a classic engines, as internal combustion technology has come a long way since these engine were installed.
With regards to the condition of the bottom end bearings my impression/suggestion is to box them up and use the correct viscosity and grade of oil as recommended by Porsche. (Note: Doug Hillyard, IIRC his name correctly, has written lots on oil viscosity and grades of oil for our car and lub oil analysis, to which I agree).
I read a lot about "refresh" parts etc., hoever I also suscribe to the philosophy of 'if it ain't broke don't fix it". If you really want to know what is happening inside your engine get a lub oil analysis done.
With regards to the wear pattens on the bottom end bearing, I have assumed that the low bearing shells are the tops? and they show the most wear. In other threads in this forum I have mentioned the art or discipline of "Tribology", which is the engineering discipline of lubrication and wear of moving parts. This can adequatley describe the condition of these bearing shells from an operating engine.
On the compression stroke and subsequent driving stroke the greatest downward force is exerted on the bottom end bearing, which can cause wear on the top beaing shells if the oil film breaks down and allows boundary lubrication. The rest of the time the crank can mearly be said (for the sake of simplicity) to be whirling, that is rotating with the mass of the rod and the piston with not much load on the bearing shells.
The areas of the bearing surfaces within a internal combustion engine usually have a safety margin and are designed for film lubrication by the lube oil being delivered to the bearing under pressure. If the lubricating oil pressure is being maintained above the minimum level, the lubricating oil film within the bearing should be maintained and all should we well.
My thought for what they are worth.
Tails 1990 928S4 Auto
1. The failure rate in any piece of equipment is proportional to the number of its moving parts.
2. More damage is done by opening up good operating engines to inspect parts for wear etc.
3. Industry moved from maintenance and repair based on running hours (time-predictive) maintenance to
4. Condition monitoring. That is regular inspection and if it operating within the vibration and wear limits as prescribed by the manufacturer and if the oil analysis is satisfactory, leave well enough alone.
I have read many threads on this forum regarding the type of engine oil to be used and and lubricating oil analysis. I stick to the grade recommended by Porsche (based on their building experience, operating experince and racing experience) and relate this to the temperature profile that the car will be operated in. We need to be mindful that the engines within our cars were initially developed over 40 years ago and by todays technology they would be classified a classic engines, as internal combustion technology has come a long way since these engine were installed.
With regards to the condition of the bottom end bearings my impression/suggestion is to box them up and use the correct viscosity and grade of oil as recommended by Porsche. (Note: Doug Hillyard, IIRC his name correctly, has written lots on oil viscosity and grades of oil for our car and lub oil analysis, to which I agree).
I read a lot about "refresh" parts etc., hoever I also suscribe to the philosophy of 'if it ain't broke don't fix it". If you really want to know what is happening inside your engine get a lub oil analysis done.
With regards to the wear pattens on the bottom end bearing, I have assumed that the low bearing shells are the tops? and they show the most wear. In other threads in this forum I have mentioned the art or discipline of "Tribology", which is the engineering discipline of lubrication and wear of moving parts. This can adequatley describe the condition of these bearing shells from an operating engine.
On the compression stroke and subsequent driving stroke the greatest downward force is exerted on the bottom end bearing, which can cause wear on the top beaing shells if the oil film breaks down and allows boundary lubrication. The rest of the time the crank can mearly be said (for the sake of simplicity) to be whirling, that is rotating with the mass of the rod and the piston with not much load on the bearing shells.
The areas of the bearing surfaces within a internal combustion engine usually have a safety margin and are designed for film lubrication by the lube oil being delivered to the bearing under pressure. If the lubricating oil pressure is being maintained above the minimum level, the lubricating oil film within the bearing should be maintained and all should we well.
My thought for what they are worth.
Tails 1990 928S4 Auto
09-17-2010, 10:02 PM
#34
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A few points I have gathered over many years dealing with and mantaining internal cumbustion engines.
1. The failure rate in any piece of equipment is proportional to the number of its moving parts.
2. More damage is done by opening up good operating engines to inspect parts for wear etc.
3. Industry moved from maintenance and repair based on running hours (time-predictive) maintenance to
4. Condition monitoring. That is regular inspection and if it operating within the vibration and wear limits as prescribed by the manufacturer and if the oil analysis is satisfactory, leave well enough alone.
I have read many threads on this forum regarding the type of engine oil to be used and and lubricating oil analysis. I stick to the grade recommended by Porsche (based on their building experience, operating experince and racing experience) and relate this to the temperature profile that the car will be operated in. We need to be mindful that the engines within our cars were initially developed over 40 years ago and by todays technology they would be classified a classic engines, as internal combustion technology has come a long way since these engine were installed.
With regards to the condition of the bottom end bearings my impression/suggestion is to box them up and use the correct viscosity and grade of oil as recommended by Porsche. (Note: Doug Hillyard, IIRC his name correctly, has written lots on oil viscosity and grades of oil for our car and lub oil analysis, to which I agree).
I read a lot about "refresh" parts etc., hoever I also suscribe to the philosophy of 'if it ain't broke don't fix it". If you really want to know what is happening inside your engine get a lub oil analysis done.
With regards to the wear pattens on the bottom end bearing, I have assumed that the low bearing shells are the tops? and they show the most wear. In other threads in this forum I have mentioned the art or discipline of "Tribology", which is the engineering discipline of lubrication and wear of moving parts. This can adequatley describe the condition of these bearing shells from an operating engine.
On the compression stroke and subsequent driving stroke the greatest downward force is exerted on the bottom end bearing, which can cause wear on the top beaing shells if the oil film breaks down and allows boundary lubrication. The rest of the time the crank can mearly be said (for the sake of simplicity) to be whirling, that is rotating with the mass of the rod and the piston with not much load on the bearing shells.
The areas of the bearing surfaces within a internal combustion engine usually have a safety margin and are designed for film lubrication by the lube oil being delivered to the bearing under pressure. If the lubricating oil pressure is being maintained above the minimum level, the lubricating oil film within the bearing should be maintained and all should we well.
My thought for what they are worth.
Tails 1990 928S4 Auto
1. The failure rate in any piece of equipment is proportional to the number of its moving parts.
2. More damage is done by opening up good operating engines to inspect parts for wear etc.
3. Industry moved from maintenance and repair based on running hours (time-predictive) maintenance to
4. Condition monitoring. That is regular inspection and if it operating within the vibration and wear limits as prescribed by the manufacturer and if the oil analysis is satisfactory, leave well enough alone.
I have read many threads on this forum regarding the type of engine oil to be used and and lubricating oil analysis. I stick to the grade recommended by Porsche (based on their building experience, operating experince and racing experience) and relate this to the temperature profile that the car will be operated in. We need to be mindful that the engines within our cars were initially developed over 40 years ago and by todays technology they would be classified a classic engines, as internal combustion technology has come a long way since these engine were installed.
With regards to the condition of the bottom end bearings my impression/suggestion is to box them up and use the correct viscosity and grade of oil as recommended by Porsche. (Note: Doug Hillyard, IIRC his name correctly, has written lots on oil viscosity and grades of oil for our car and lub oil analysis, to which I agree).
I read a lot about "refresh" parts etc., hoever I also suscribe to the philosophy of 'if it ain't broke don't fix it". If you really want to know what is happening inside your engine get a lub oil analysis done.
With regards to the wear pattens on the bottom end bearing, I have assumed that the low bearing shells are the tops? and they show the most wear. In other threads in this forum I have mentioned the art or discipline of "Tribology", which is the engineering discipline of lubrication and wear of moving parts. This can adequatley describe the condition of these bearing shells from an operating engine.
On the compression stroke and subsequent driving stroke the greatest downward force is exerted on the bottom end bearing, which can cause wear on the top beaing shells if the oil film breaks down and allows boundary lubrication. The rest of the time the crank can mearly be said (for the sake of simplicity) to be whirling, that is rotating with the mass of the rod and the piston with not much load on the bearing shells.
The areas of the bearing surfaces within a internal combustion engine usually have a safety margin and are designed for film lubrication by the lube oil being delivered to the bearing under pressure. If the lubricating oil pressure is being maintained above the minimum level, the lubricating oil film within the bearing should be maintained and all should we well.
My thought for what they are worth.
Tails 1990 928S4 Auto
BTW..the lower row of bearings are from the caps. The ones marked with the number and a "U" are the uppers....which is the upper row.
09-17-2010, 10:47 PM
#35
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Do you use a mic with a ball end on one end for bearing shells?
Mine is a Jap brand for the shells.
It is hard to find good mics anymore, so much junk out there.
Some one helped them self to most of my mics a few years back and the newer ones just do not seem to have the quality of the older ones.
Mine is a Jap brand for the shells.
It is hard to find good mics anymore, so much junk out there.
Some one helped them self to most of my mics a few years back and the newer ones just do not seem to have the quality of the older ones.
09-17-2010, 10:52 PM
#36
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09-18-2010, 12:19 AM
#37
Captain Obvious
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We have found that the oil temperature in the oil pan gets very, very high in the cars that have the cooler below the radiator. The temperature will quickly go over 270 degrees when sitting in traffic with the A/C on.
This might have been a great design change, in Europe, where there isn't as much traffic, but was certainly not a good idea in warmer climates with traffic.
We have built up line sets that allow us to use both a cooler in the radiator and the original cooler. Note that this also requires a change in the radiator, to get an oil cooler in the left tank.
This modification allows the oil to be cooled in traffic, by the radiator, and still allows heat to escape (when the car is moving) from the stock cooler. An interesting side effect is that this also allows the oil temperatures to warm-up quicker in cold weather, which further reduces engine wear. This is the best of all worlds and virtually all of these cars need to be modified.
BTW....Carl, no doubt, will steal this idea in about 2 minutes and then claim that he had no idea we were doing this and it was totally his idea.
This might have been a great design change, in Europe, where there isn't as much traffic, but was certainly not a good idea in warmer climates with traffic.
We have built up line sets that allow us to use both a cooler in the radiator and the original cooler. Note that this also requires a change in the radiator, to get an oil cooler in the left tank.
This modification allows the oil to be cooled in traffic, by the radiator, and still allows heat to escape (when the car is moving) from the stock cooler. An interesting side effect is that this also allows the oil temperatures to warm-up quicker in cold weather, which further reduces engine wear. This is the best of all worlds and virtually all of these cars need to be modified.
BTW....Carl, no doubt, will steal this idea in about 2 minutes and then claim that he had no idea we were doing this and it was totally his idea.
I've ony had about a couple dozen engines apart like this over the years and to me those bearings don't look that bad. I've seen some worn down to the copper layer.
09-18-2010, 12:34 AM
#38
Nordschleife Master
Since the bearings were measured can't that measurement be compared to a new bearing giving the exact amount of wear and showing any variation over the surface?
09-18-2010, 01:07 AM
#39
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Greg - Let's say someone put Glycos in about 4 years and 8K miles ago. Should they be worried???
Thanks in advance - JW
Thanks in advance - JW
09-18-2010, 02:03 AM
#40
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What gets me is many will look at those and think they are fine, some will say they are wore out, and many from both groups will have enough end play in the crank that absolutely means there is copper showing through and rationalize how it is ok to run a thrust bearing that looks like that.
09-18-2010, 03:36 AM
#41
Captain Obvious
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What gets me is many will look at those and think they are fine, some will say they are wore out, and many from both groups will have enough end play in the crank that absolutely means there is copper showing through and rationalize how it is ok to run a thrust bearing that looks like that.
09-18-2010, 10:16 AM
#42
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Dan,
I seem to recall that there is a thermostat in the oil line for the '89+ cars that sometimes fails, which may result in the oil not being circulated to the heat exchanger. Not 100% sure of that, but if my memory is correct, and that thermostat failed on the Zyclamrot car, that could be another reason for the possible overheating of the oil.
Greg has probably checked that as well, however.
Gary
I seem to recall that there is a thermostat in the oil line for the '89+ cars that sometimes fails, which may result in the oil not being circulated to the heat exchanger. Not 100% sure of that, but if my memory is correct, and that thermostat failed on the Zyclamrot car, that could be another reason for the possible overheating of the oil.
Greg has probably checked that as well, however.
Gary
09-18-2010, 12:35 PM
#44
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Been through this a few times, but here's the highlights.
The bearings are supplied by Porsche in three separate dimension "groups", which vary by about .0002, from size to size. These sizes are blue, yellow, and red...with blue being the "smallest/tightest" bearing. Porsche originally picked rod bearings that were sized to the particular crank...to get the correct oil clearance. The cranks were marked, when they were made with a paint mark and the assembler simply matched up colors. The colors washed off instantly.
Porsche replacement bearings are supplied two to a box and they are also marked with a color code, although you can not specify which color you want, any longer. They will always come with two yellows (mid size clearance), or one blue mixed with one red (tightest bearing with biggest bearing...I guess they think this equals two yellows?) You will see no other variations, unless someone has mixed things up, after they were boxed. We go through these bearings, confirm their sizes, and will actually pick sizes to get optimum oil clearance. (We would never put a blue with a red...makes no sense.)
The aftermarket replacement bearings, made by Glyco, don't come supplied with any colors. They generally come very tight. I think they plan on the cranks wearing slightly and intentionally build the bearings tight to compensate for any wear. However, the cranks are very hard and do not seem to wear...so it is very possible to get bearings that are too tight and not provide enough bearing clearance. Many engines have failed, immediately after a bearing change...possibly from this.
There is also some that think the bearings are constructed differently, of which I was one of. However, after weighing many of these bearings to try and compare, they all seem to weigh very very close to each other...which might indicate they are built from the same materials. I simply don't know.
I am currently running a test engine that has a "mixture" of factory rod bearings and Glyco aftermarket bearings, for a study. They were carefully selected to be all sized the same. We will run this engine for 6 months or a year and check the bearings for wear and compare them. There are also several other "developmental" pieces that we will be reviewing, when that "inspection" occurs.
Here's my ideas....measure very carefully and make sure that you have adequate rod bearing clearance. Compare the replacement bearings with the original bearings, for size purposes.
You've got to take this all with a grain of salt, however....I'm not an SAE member....so that magazine has not made me an expert.
The bearings are supplied by Porsche in three separate dimension "groups", which vary by about .0002, from size to size. These sizes are blue, yellow, and red...with blue being the "smallest/tightest" bearing. Porsche originally picked rod bearings that were sized to the particular crank...to get the correct oil clearance. The cranks were marked, when they were made with a paint mark and the assembler simply matched up colors. The colors washed off instantly.
Porsche replacement bearings are supplied two to a box and they are also marked with a color code, although you can not specify which color you want, any longer. They will always come with two yellows (mid size clearance), or one blue mixed with one red (tightest bearing with biggest bearing...I guess they think this equals two yellows?) You will see no other variations, unless someone has mixed things up, after they were boxed. We go through these bearings, confirm their sizes, and will actually pick sizes to get optimum oil clearance. (We would never put a blue with a red...makes no sense.)
The aftermarket replacement bearings, made by Glyco, don't come supplied with any colors. They generally come very tight. I think they plan on the cranks wearing slightly and intentionally build the bearings tight to compensate for any wear. However, the cranks are very hard and do not seem to wear...so it is very possible to get bearings that are too tight and not provide enough bearing clearance. Many engines have failed, immediately after a bearing change...possibly from this.
There is also some that think the bearings are constructed differently, of which I was one of. However, after weighing many of these bearings to try and compare, they all seem to weigh very very close to each other...which might indicate they are built from the same materials. I simply don't know.
I am currently running a test engine that has a "mixture" of factory rod bearings and Glyco aftermarket bearings, for a study. They were carefully selected to be all sized the same. We will run this engine for 6 months or a year and check the bearings for wear and compare them. There are also several other "developmental" pieces that we will be reviewing, when that "inspection" occurs.
Here's my ideas....measure very carefully and make sure that you have adequate rod bearing clearance. Compare the replacement bearings with the original bearings, for size purposes.
You've got to take this all with a grain of salt, however....I'm not an SAE member....so that magazine has not made me an expert.
If you would prefer this be in a different thread just let me know and I'll open one.
09-18-2010, 03:47 PM
#45
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Thanks for the reply Greg. Great information as usual. With the Glycos, how tight are we talking? If the Glycos are a little tight, would it not be possible to have the crank polished to regain this lost tolerance? Is this not feasable? The reason I ask is that I am in the process of building a 4.5L . I don't know what brand of bearings were quoted to me but I'm assuming they were probably not Porsche NOS bearings.
If you would prefer this be in a different thread just let me know and I'll open one.
If you would prefer this be in a different thread just let me know and I'll open one.
Unless....
You happen to be an SAE member, with a nasally little voice.
"Another thread hijacked!"
Then you get your own thread...all to yourself.
Anyway, yes, if the crank is out, you can certainly have it micropolished to slightly open up the bearing clearance. When I first started writing about this problem, all the bearings from Glyco measured very tight. The last ones I was sent had a bit more clearance. I'm sure they have a production tolerance, too. Just make sure you measure things.