Thermostat Replacement
02-03-2011, 07:14 AM
#62
Should I stand in dread of the "professors response"?
Sorry didn't realise this thread had been hacked by IMS issues (about which I have written plenty in the UK) and I don't have time right now to read back - but from a quick skip through it seems that many of you have missed a couple of important points.
Bearings are indeed manufactured with different clearances that can be specified on purchase and this largely depends on the useage and interference fits planned.
Different failures have been noticed by us - some just burned out while others running OK have split the cage due to excessive expansion and insufficient clearance - others have run rough and broken the weak spindle (what an awfull design that is! breaking all the rules about sharp edges and undercut diameters).
The IMS shaft by its design has a heavy interference fit to the bearing and the inner sleeve is a tight fit also which can run the bearing so tight that it rubs off more than usual small wear particles in the first few thousand miles of use. Grease lubrication is OK for the speed and application but the heat is a different matter.
When the seal on the bearing starts to wear (speeded up by those metallic particles trying to escape) - hot thin oil penetrates the bearing and mixes with the grease and metallic particles inside (which we have observed looking like grinding paste in some bearings if we catch them at the right mileage).
After that oil seeps in and grease disperses out until it is running with hot old trapped oil mixed with metal particles that cannot easily escape.
If the fits allow the bearing to survive this early trauma and the seals are worn enough to allow some ingress and exit of oil and exit of metal particles - it may then be worn enough and the oil refreshed enough - to last forevermore.
The standard single row bearing bought in with the correct clearance (and therefore the correct fit) but fitted without a seal (so it both allows the metallic particles worn off during running in to circulate and be collected by the filter and magnets while the oil spray from the chains close by (that run up to 40mph in effectively an oil bath) refreshes the bearing with clean cool oil) is perfectly reliable and we have never had any problem with it (although we do upgrade the spindle etc and can fit new bearings to the old double row IMS as well as the new ones) .
We are now in the process of manufacturing replacement end gears (to rebuild damaged IMS shafts) since the price has gone up and we are making them with both sprockets and HIVO gears to suit both types of crankshaft.
Also I accept the point made previously that many manufacturers are conning us over readings on instruments. This is a worrying outcome (smacking of 1984 and all that mind control) because it takes away the customers awareness that they should look into a worrying reading and our ability to analyse problems at an early stage until we understand what the true situation is following proper expensive testing that should not be neccessary.
The 3.8 997 I was testing yeasterday (fitted with our oversized pistons following scored bores) was very slow to respond to temperature differences and oil pressure fluctuations - as if the process has been taken a step further and a huge amount of time based damping planned in.
Pretty soon there will be a guage that lights up when the cylinders get scored, the IMS fails or the liner cracks - that says your engine is perfectly OK because we made it - if it stops running it is your fault and you must therefore pay us for a new one.
Baz
Sorry didn't realise this thread had been hacked by IMS issues (about which I have written plenty in the UK) and I don't have time right now to read back - but from a quick skip through it seems that many of you have missed a couple of important points.
Bearings are indeed manufactured with different clearances that can be specified on purchase and this largely depends on the useage and interference fits planned.
Different failures have been noticed by us - some just burned out while others running OK have split the cage due to excessive expansion and insufficient clearance - others have run rough and broken the weak spindle (what an awfull design that is! breaking all the rules about sharp edges and undercut diameters).
The IMS shaft by its design has a heavy interference fit to the bearing and the inner sleeve is a tight fit also which can run the bearing so tight that it rubs off more than usual small wear particles in the first few thousand miles of use. Grease lubrication is OK for the speed and application but the heat is a different matter.
When the seal on the bearing starts to wear (speeded up by those metallic particles trying to escape) - hot thin oil penetrates the bearing and mixes with the grease and metallic particles inside (which we have observed looking like grinding paste in some bearings if we catch them at the right mileage).
After that oil seeps in and grease disperses out until it is running with hot old trapped oil mixed with metal particles that cannot easily escape.
If the fits allow the bearing to survive this early trauma and the seals are worn enough to allow some ingress and exit of oil and exit of metal particles - it may then be worn enough and the oil refreshed enough - to last forevermore.
The standard single row bearing bought in with the correct clearance (and therefore the correct fit) but fitted without a seal (so it both allows the metallic particles worn off during running in to circulate and be collected by the filter and magnets while the oil spray from the chains close by (that run up to 40mph in effectively an oil bath) refreshes the bearing with clean cool oil) is perfectly reliable and we have never had any problem with it (although we do upgrade the spindle etc and can fit new bearings to the old double row IMS as well as the new ones) .
We are now in the process of manufacturing replacement end gears (to rebuild damaged IMS shafts) since the price has gone up and we are making them with both sprockets and HIVO gears to suit both types of crankshaft.
Also I accept the point made previously that many manufacturers are conning us over readings on instruments. This is a worrying outcome (smacking of 1984 and all that mind control) because it takes away the customers awareness that they should look into a worrying reading and our ability to analyse problems at an early stage until we understand what the true situation is following proper expensive testing that should not be neccessary.
The 3.8 997 I was testing yeasterday (fitted with our oversized pistons following scored bores) was very slow to respond to temperature differences and oil pressure fluctuations - as if the process has been taken a step further and a huge amount of time based damping planned in.
Pretty soon there will be a guage that lights up when the cylinders get scored, the IMS fails or the liner cracks - that says your engine is perfectly OK because we made it - if it stops running it is your fault and you must therefore pay us for a new one.
Baz
02-03-2011, 10:58 AM
#63
Banned
Join Date: Oct 2009
Posts: 731
Likes: 0
Received 0 Likes
on
0 Posts
No, because your responses are factual, and you are not an ignoramus making laughably assinine assertions that bearings are not designed with clearances reflective of the proposed choice of lubricant.
I still maintain however, that a thermostat's function is to hold back coolant in order to allow the engine to come to operating temperature. None that I know of function like A/C thermostats to actually regulate temperature. The temperature setting of a coolant thermostat represents the temperature at which it opens to allow coolant flow. From that point, it is purely the function of the pre-designed efficiency of the cooling system that is responsible for keeping the engine from over heating. As a practical experiment, anyone can simply remove the valve from the thermostat, thereby effectively rendering it a "zero degree" thermostat...and see what the operating temperature of the engine comes to. $5 says it won't maintain the engine in the cold zone
...any more than a 160-degree thermostat will alter the operating temp of an M96 other than during warm-up.
I still maintain however, that a thermostat's function is to hold back coolant in order to allow the engine to come to operating temperature. None that I know of function like A/C thermostats to actually regulate temperature. The temperature setting of a coolant thermostat represents the temperature at which it opens to allow coolant flow. From that point, it is purely the function of the pre-designed efficiency of the cooling system that is responsible for keeping the engine from over heating. As a practical experiment, anyone can simply remove the valve from the thermostat, thereby effectively rendering it a "zero degree" thermostat...and see what the operating temperature of the engine comes to. $5 says it won't maintain the engine in the cold zone
...any more than a 160-degree thermostat will alter the operating temp of an M96 other than during warm-up.
02-03-2011, 03:11 PM
#64
I think you have forgotten that the thermostat controls the colant flow rate.
So a thermostat does control the temperature that the engine runs at when it is warmed up (as long as the capacity of the cooling system is greater than the requirement).
It does this by opening slowly - if the thermostat opens quickly too much coolant will circulate to the radiators and be overcooled and then shut the thermostat again, but if the thermostat is slow there is a gradual classic control system feedback loop in which the amount it opens controls the flow rate and with that the amount of cooling - it is not an open and shut valve - except when the system cannot cool the coolant below the thermostat setting - when it simply stays open while the temperature continues to rise until the fans switch in.
A lower temperature thermostat will run the engine coolant at a lower temperature than a higher temperature thermostat.
It works on warm up by staying shut until the opening temperature is reached at which point it opens a little and allows some coolant to flow around the system. but this slow flow rate does not cool it enough so shortly afterwards it opens a little bit more. This goes on until a balance is found.
Driving faster increases the cooling air flow rate so the temperature falls and the thermostat slowly closes until it is in balance again.
If you are stuck in traffic it gets hotter so opens some more and if it is insifficient when fully open (and a low coolant speed because the engine (and therefore water pump) is running slowly - then the radiator fans help increase airflow to maintain temperatures.
Baz
So a thermostat does control the temperature that the engine runs at when it is warmed up (as long as the capacity of the cooling system is greater than the requirement).
It does this by opening slowly - if the thermostat opens quickly too much coolant will circulate to the radiators and be overcooled and then shut the thermostat again, but if the thermostat is slow there is a gradual classic control system feedback loop in which the amount it opens controls the flow rate and with that the amount of cooling - it is not an open and shut valve - except when the system cannot cool the coolant below the thermostat setting - when it simply stays open while the temperature continues to rise until the fans switch in.
A lower temperature thermostat will run the engine coolant at a lower temperature than a higher temperature thermostat.
It works on warm up by staying shut until the opening temperature is reached at which point it opens a little and allows some coolant to flow around the system. but this slow flow rate does not cool it enough so shortly afterwards it opens a little bit more. This goes on until a balance is found.
Driving faster increases the cooling air flow rate so the temperature falls and the thermostat slowly closes until it is in balance again.
If you are stuck in traffic it gets hotter so opens some more and if it is insifficient when fully open (and a low coolant speed because the engine (and therefore water pump) is running slowly - then the radiator fans help increase airflow to maintain temperatures.
Baz
02-03-2011, 05:36 PM
#65
Advanced
Thread Starter
Join Date: Nov 2010
Posts: 93
Likes: 0
Received 0 Likes
on
0 Posts
You will note Prof, that I never said bearings do not have different clearances as Baz has stated. Just that the different clearances that one selects for application are not selected on the basis of how the bearing will be lubricated, but on the "usage and interference fits as planned." In fact, he just backed up my argument about grease and oil lubricated bearings in his post. You need to read what Baz said, not what you erroneously believe, which in both cases, thermostats and bearings, has been shown to be rather academic.
02-05-2011, 05:38 PM
#68
Banned
Join Date: Oct 2009
Posts: 731
Likes: 0
Received 0 Likes
on
0 Posts
I've dealt with this type of thing now in two careers. Mechanics, like the various medical technicians sometimes like to pretend they are educated professionals like engineers and physicians, instead of the trained tradesmen they are, doling out advice to their friends and neighbors, peppering their misinformation with the technical vocabulary they've read and heard. At least when mechanics do it, nobody dies as a result, so I more laugh at it than worry 
02-05-2011, 08:16 PM
#69
Poseur
Rennlist Member
Rennlist Member
When doctors make a mistake, they have to bury their mistakes. When architects make a mistake, their clients are advised to plant vines. I don't know what you do when your mechanic screws up! Although I know that they are usually stuck to make things right!
02-08-2011, 05:27 PM
#70
Advanced
Thread Starter
Join Date: Nov 2010
Posts: 93
Likes: 0
Received 0 Likes
on
0 Posts
I can't speak for Baz, but I would guess his 1st hand experience would trump the classroom every time.
As far as I am concerned, I'll put my 44 years in the field of lubrication and my stint a Chief Engineer with Mobil Oil, up against any two careers in academia, especially if those two careers produced the level of knowledge and understanding, or lack thereof, of thermostats and bearing lubrication as displayed here.
As far as I am concerned, I'll put my 44 years in the field of lubrication and my stint a Chief Engineer with Mobil Oil, up against any two careers in academia, especially if those two careers produced the level of knowledge and understanding, or lack thereof, of thermostats and bearing lubrication as displayed here.
