Is it true that water/coolant in the oil could cause cam lobe pitting? I was told that once by a mechanic when I asked him to look at the pits on a couple of cam lobes in a small Mitsubishi turbo-diesel I had apart for rebuild. The engine had blown a head gasket at least once shortly before I got it, so his story seemed credible given that I knew coolant had been in there. Any truth to that tale?
Camshaft pitting!
- Thread starter Solo2driver
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Hi,
Bruce - you said;
"IMHO Doug do not insult my intelligence or my expertise I've been doing this for 32 years."
There was nothing I said to justify your comments above - I actually endorsed what you had previously said. I made the one priviso that these Porsche engines DO suffer from corrosion based pitting and NOT wear. I do NOT know of any cam shaft wear problems in the 924,944,968,928 family of Porsche engines at all
Your previous comments were correct and I also said;
"If excessive wear is associated with the pitting your comments are most valid IMHO"
And they are - in this engine as in most of these Porsche engine families NO excessive wear is evident and in 99% of instances with them this is so Internationally
You have perhaps simply misunderstood what I meant
Perhaps you are slightly younger than I - I've been doing it for nearly 50 years!
Keep smiling Bruce and keep posting your excellent material!
Regards
Doug
Bruce - you said;
"IMHO Doug do not insult my intelligence or my expertise I've been doing this for 32 years."
There was nothing I said to justify your comments above - I actually endorsed what you had previously said. I made the one priviso that these Porsche engines DO suffer from corrosion based pitting and NOT wear. I do NOT know of any cam shaft wear problems in the 924,944,968,928 family of Porsche engines at all
Your previous comments were correct and I also said;
"If excessive wear is associated with the pitting your comments are most valid IMHO"
And they are - in this engine as in most of these Porsche engine families NO excessive wear is evident and in 99% of instances with them this is so Internationally
You have perhaps simply misunderstood what I meant
Perhaps you are slightly younger than I - I've been doing it for nearly 50 years!
Keep smiling Bruce and keep posting your excellent material!
Regards
Doug
Doug 32 years at blending and formulating and trouble shooting lubes of all kinds not 50 years of turning wrenches which is a very valuble tool and is to be respected but in this case is not the same thing.
I took you post with a condensending attitude perhaps it was not ment that way if so SORRY.
But unless this guy says car sits for a long time in a salty air garage I stand by my post about pitting/wear.
bruce
I took you post with a condensending attitude perhaps it was not ment that way if so SORRY.
But unless this guy says car sits for a long time in a salty air garage I stand by my post about pitting/wear.
bruce
Kestas
Staff member
It could just be from corrosion, but if the engine uses roller followers, your cam could be experiencing what is called "Hertzian stresses" which results in a unique phenomenon called "microstructure decomposition". I've documented dozens of such cases in bearings. In layman's terms, the repeated cyclic stresses on the surface alters the material microstructure making it more prone to subsurface cracking and spalling.
What is the camshaft material?... cast iron?... powder metal?... then don't worry too much about it. The nature of cast iron or PM would lend itself to a small amount of spalling without too much worry. But if the camshaft is made of steel, then the spalls may tend to continually progress without checking.
What is the camshaft material?... cast iron?... powder metal?... then don't worry too much about it. The nature of cast iron or PM would lend itself to a small amount of spalling without too much worry. But if the camshaft is made of steel, then the spalls may tend to continually progress without checking.
Might be a different problem, but I recall an article on gear wear noting increased levels of 'micro pitting' due to higher levels of an anti-scuff agent being used. There were trade offs on the types of wear vs additives being used address them.
Cams typically aren't considered gears, but they do share common attributes like high, cyclic loads, tight tolerances for surface finishes, specific hardening requirements, etc., and they exhibit some similar failure and wear mechanisms:
http://www.mt-online.com/articles/01-00mpt.cfm
Failure Analysis for Gearing
Corrosive wear (Fig. 3) is visible as surface deterioration, caused by the chemical action of active ingredients in the lubricant. These may include acid, moisture, foreign materials, and extreme-pressure additives. During operation, the oil breaks down and allows corrosive elements present in the oil to attack the gear contact surfaces. This action may affect the grain boundaries and cause fine, evenly distributed pitting. Checking the oil for breakdown and changing it at regular intervals can help minimize corrosive wear. Lubricants with high antiscuff, antiwear additive content must be observed even more carefully because they are chemically active. Gear units that are exposed to salt water, liquid chemicals, or other foreign materials should be sealed from their environment
Pitting failures depend on surface contact stress and the number of stress cycles. Initial pitting (Fig. 5), with areas of small pits from 0.015 in. to 0.030 in. in diameter, occurs in localized parts of the gear teeth that are over-stressed. It is sometimes called corrective pitting because it tends to redistribute the load by progressively removing high contact spots, and often stops once the load has been redistributed. Continued operation may polish or burnish the pitted surface and improve its appearance. Pitting can be monitored by periodically putting some bluing on the affected area, then applying some cellophane tape to lift the pattern and put it in a notebook. Comparing the impressions over time will tell whether the pitting has stopped. While accurate manufacturing control of involute profiles is the best method of preventing pitting, a careful break-in at reduced loads and speeds once the unit is installed also will help minimize pitting by improving gear tooth contact.
Destructive pitting (Fig. 6) appears as much larger pits than initial pitting, often in the dedendum section of the gear teeth. These larger craters usually are caused by more severe overload conditions that cannot be relieved by initial pitting. As stress cycles build up, pitting will continue until the tooth profile is destroyed. To correct the cause of destructive pitting, the load on the surface of the gear needs to be reduced below the material’s endurance limit, or the material hardness needs to be increased to raise the endurance limit to where pitting will not occur.
Spalling (Fig. 7) resembles destructive pitting, except that the pits may be larger, quite shallow, and irregularly shaped. The edges of the pits break away rapidly, forming large, irregular voids that may join together. Spalling is caused by excessively high contact stress levels. Remedies include reducing contact stress on the gear surface or hardening the material to increase its surface strength.
Both spalling and destructive pitting are indications that the gears do not have sufficient surface capacity and should probably be redesigned if possible.
Micropitting is a type of contact fatigue that appears as frosting or gray staining under thin film conditions (Fig. 8). The surface acquires an etch-like finish, with a pattern that sometimes follows the slightly higher ridges left by cutter marks or other surface irregularities. It usually shows up first on the dedendum section of the driving gear, although it may begin on the addendum section as well. When viewed under magnification (Fig. 9), the surface is seen as a field of very fine micropits under 0.0001 in. deep. Causes include high surface loads and heat generation, which thins the lubrication film and leads to marginal lubrication. Improving the surface finish is an effective remedy, through either manufacturing techniques such as hard honing and grinding or a careful break-in cycle. These techniques help lower heat generation by improving conformity of tooth contact and equalizing load distribution. Reducing the lubricant temperature and surface loading will also minimize frosting. Sometimes, frosted areas that appear initially will slowly be polished away during subsequent operation if loads and temperatures are not excessive
http://www.mt-online.com/articles/01-00mpt.cfm
Failure Analysis for Gearing
Corrosive wear (Fig. 3) is visible as surface deterioration, caused by the chemical action of active ingredients in the lubricant. These may include acid, moisture, foreign materials, and extreme-pressure additives. During operation, the oil breaks down and allows corrosive elements present in the oil to attack the gear contact surfaces. This action may affect the grain boundaries and cause fine, evenly distributed pitting. Checking the oil for breakdown and changing it at regular intervals can help minimize corrosive wear. Lubricants with high antiscuff, antiwear additive content must be observed even more carefully because they are chemically active. Gear units that are exposed to salt water, liquid chemicals, or other foreign materials should be sealed from their environment
Pitting failures depend on surface contact stress and the number of stress cycles. Initial pitting (Fig. 5), with areas of small pits from 0.015 in. to 0.030 in. in diameter, occurs in localized parts of the gear teeth that are over-stressed. It is sometimes called corrective pitting because it tends to redistribute the load by progressively removing high contact spots, and often stops once the load has been redistributed. Continued operation may polish or burnish the pitted surface and improve its appearance. Pitting can be monitored by periodically putting some bluing on the affected area, then applying some cellophane tape to lift the pattern and put it in a notebook. Comparing the impressions over time will tell whether the pitting has stopped. While accurate manufacturing control of involute profiles is the best method of preventing pitting, a careful break-in at reduced loads and speeds once the unit is installed also will help minimize pitting by improving gear tooth contact.
Destructive pitting (Fig. 6) appears as much larger pits than initial pitting, often in the dedendum section of the gear teeth. These larger craters usually are caused by more severe overload conditions that cannot be relieved by initial pitting. As stress cycles build up, pitting will continue until the tooth profile is destroyed. To correct the cause of destructive pitting, the load on the surface of the gear needs to be reduced below the material’s endurance limit, or the material hardness needs to be increased to raise the endurance limit to where pitting will not occur.
Spalling (Fig. 7) resembles destructive pitting, except that the pits may be larger, quite shallow, and irregularly shaped. The edges of the pits break away rapidly, forming large, irregular voids that may join together. Spalling is caused by excessively high contact stress levels. Remedies include reducing contact stress on the gear surface or hardening the material to increase its surface strength.
Both spalling and destructive pitting are indications that the gears do not have sufficient surface capacity and should probably be redesigned if possible.
Micropitting is a type of contact fatigue that appears as frosting or gray staining under thin film conditions (Fig. 8). The surface acquires an etch-like finish, with a pattern that sometimes follows the slightly higher ridges left by cutter marks or other surface irregularities. It usually shows up first on the dedendum section of the driving gear, although it may begin on the addendum section as well. When viewed under magnification (Fig. 9), the surface is seen as a field of very fine micropits under 0.0001 in. deep. Causes include high surface loads and heat generation, which thins the lubrication film and leads to marginal lubrication. Improving the surface finish is an effective remedy, through either manufacturing techniques such as hard honing and grinding or a careful break-in cycle. These techniques help lower heat generation by improving conformity of tooth contact and equalizing load distribution. Reducing the lubricant temperature and surface loading will also minimize frosting. Sometimes, frosted areas that appear initially will slowly be polished away during subsequent operation if loads and temperatures are not excessive
Hello Bruce - firstly I have never been a "wrench man" - well except during part of my Engineering Studies in NZ in the 1950s!!
And perhaps sometimes on development work with prototype vehicles and equipment
I have had Senior Engineering Positions with Motor Manufacturers (in NZ, Europe and Australia), Government/Industry Bodies and Fleets. I have formulated Standard Policy and Practice in Servicing and Maintenance within the Automotive and Transport Industries and at Federal/State Government levels.
My time with an Oil Company (Caltex-Chevron) was spent in NZ and Denmark where I conducted research, development and training in conjunction with Bosch, MB and VW
I have had my own Transport Consultancy and Training Business in this field since 1988 and operate a trucking business as well! I do NOT and have NEVER had my own workshop - all work is done by OEM and/or outside contractors (well, except my own cars)
My Company's name is Road Transport & Training Resources Pty Limited and was incorporated in 1989!
Through my Fleet and my Customer's Fleets (including some with 250t road trains) I still (until virtual retirement last year) do some contract work for Castrol and Mobil. One project has just commenced!
My first development job with Castrol involved 10w-60 synthetic in 1979-80
Bruce, the cam lobe corrosion pitting issue is quite well known in Porsche circles and has never translated into excessive wear to my knowledge!
Paul who started the post said:
"This car is daily driven, but saw intermittant use before I had owned it."
This is very typical for Porsche cars and Paul states that the engine ('82) only has 62k on it - this is less than 3k per annum. Again many Porsche cars get this sort of "low use" life!
This type of use causes many specific problems like, cam belt failure, tyre failure, radiator & block corrosion, intercooler oil leaks, brake system seizures, electrical gremlins and etc etc.
Paul knows that the 924 Turbo is not always an easy engine to live with and is harder on its engine oil than most!
The main thing is that he should monitor the camshaft pitting and enjoy his car - it is premature to do anything else
Regards
Doug
And perhaps sometimes on development work with prototype vehicles and equipment
I have had Senior Engineering Positions with Motor Manufacturers (in NZ, Europe and Australia), Government/Industry Bodies and Fleets. I have formulated Standard Policy and Practice in Servicing and Maintenance within the Automotive and Transport Industries and at Federal/State Government levels.
My time with an Oil Company (Caltex-Chevron) was spent in NZ and Denmark where I conducted research, development and training in conjunction with Bosch, MB and VW
I have had my own Transport Consultancy and Training Business in this field since 1988 and operate a trucking business as well! I do NOT and have NEVER had my own workshop - all work is done by OEM and/or outside contractors (well, except my own cars)
My Company's name is Road Transport & Training Resources Pty Limited and was incorporated in 1989!
Through my Fleet and my Customer's Fleets (including some with 250t road trains) I still (until virtual retirement last year) do some contract work for Castrol and Mobil. One project has just commenced!
My first development job with Castrol involved 10w-60 synthetic in 1979-80
Bruce, the cam lobe corrosion pitting issue is quite well known in Porsche circles and has never translated into excessive wear to my knowledge!
Paul who started the post said:
"This car is daily driven, but saw intermittant use before I had owned it."
This is very typical for Porsche cars and Paul states that the engine ('82) only has 62k on it - this is less than 3k per annum. Again many Porsche cars get this sort of "low use" life!
This type of use causes many specific problems like, cam belt failure, tyre failure, radiator & block corrosion, intercooler oil leaks, brake system seizures, electrical gremlins and etc etc.
Paul knows that the 924 Turbo is not always an easy engine to live with and is harder on its engine oil than most!
The main thing is that he should monitor the camshaft pitting and enjoy his car - it is premature to do anything else
Regards
Doug
I realize that, but I just can't help wanting to see your response. Besides, until now, I didn't know Ted wore a bra.
Actually the far right censored my joke on the far left.quote:
Originally posted by Doug Hillary:
Has Texas become more Democratic?
All kidding aside, I continue to believe HDEOs will only provide very marginal additional corrosion protection in sporadically used vehicles. At least that's what I've been told by my engineering contacts at the larger car and truck manufacturers and from my personal experience wrenching on engines.
Hi, I'm Paul, and I'm an Oil-a-holic.
-James W
Porsche 924 Turbo
-James W
Porsche 924 Turbo
If the pitting is caused as has been mentioned, then said pitting may or may not also be related to the surface hardening applied during the mfg. process. Perhaps the cam lobes can be tested to see if they are within the hardness spec. I know of one specific case where the cam lobes were short of the hardness spec. (too soft) and prematurely failed, not a Porche though, but a Japanese brand beginning with "T".
Hi Paul!
My '86 XR was an automatic, which also led to its final demise.....heat exchanger leak filled the tranny with anti-freeze. Always wanted a Scorpio, reclining rear seats were just TOO hard to resist!
Ted,
you are very perceptive - sorry for my error but you were no doubt referring to the components in
Werner von Braun's text book "A Real Blast" too
Born in Texas well before Gottlieb Daimler and Karl Benz of course he was truely a great guy
You should re-read the parts on excessive camshaft wear in TATA turboprops, V1 V2 and V3 pulsejets and reverse turbocharging even if you already do know everything!
You could also refer to the excellent 1900 text book in Russian titled "0w-40 oils - a cold start in Stalingrad". It provides excellent reference data on flow rates, desmodromic valve actuation and high wear metal levels (iron especially)when using a product called "Amsoilski". It also covers camshaft pitting causes during cold starts and was written by Pablo Zabrinski who started Amway in 1775 I believe
Such is age Ted - such is maturity (or a lack of it) - such is life!
Regards
Doug
you are very perceptive - sorry for my error but you were no doubt referring to the components in
Werner von Braun's text book "A Real Blast" too
Born in Texas well before Gottlieb Daimler and Karl Benz of course he was truely a great guy
You should re-read the parts on excessive camshaft wear in TATA turboprops, V1 V2 and V3 pulsejets and reverse turbocharging even if you already do know everything!
You could also refer to the excellent 1900 text book in Russian titled "0w-40 oils - a cold start in Stalingrad". It provides excellent reference data on flow rates, desmodromic valve actuation and high wear metal levels (iron especially)when using a product called "Amsoilski". It also covers camshaft pitting causes during cold starts and was written by Pablo Zabrinski who started Amway in 1775 I believe
Such is age Ted - such is maturity (or a lack of it) - such is life!
Regards
Doug
HDEO's are much better for protection of engines used on a seasonal basis, like farm equipment and Marine inboards. It stands to reason they would be better for intermittant use in car/truck engines. I think the UOA data bears this out....
Doug,
Very funny!
Ted
Doug,
Very funny!
Ted
An article on corrosion/wear in aircraft that I've posted a few times before. In addition to having more additives designed to address corrosion, HDEOs should do better for low use rates as they're thicker.
http://www.eaa49.av.org/techart/str_oil.htm
Our own experience (based on incoming calls to our engine hotline) tends to confirm that lubrication-related problemsespecially involving the camshaftare generally much less among users of straight-weight oils than among users of multigrade oils. There is nothing scientific about our sampling method, admittedly. But we do routinely ask callers what kind of oil they are using, and how often they fly. The people with serious engine problems (scuffed cam lobes, spalled lifters, etc.) we've noticed, are virtually always using a multigrade oil and/ flying less than 100 hours per year. (The number of people calling our hot line who scuff a cam while using straight-weight oil is negligible.) There could be many reasond for the apparent better performance of single-weight oils. It may be for instance, that operators who use straight-weight oils are more careful about preheating in cold weather (or tend not to live in cold areas at all) and therefore have less exposure to cold-start damage. Or it may be that operators who fly very little are more likely than most to buy "fancy" oils, in hopes that this will better protect their engines against the inevitable consequences of inactivity. (We have noticed that the multigrades do seem to have achived a very high market share among inactive or barely-active owner-operators.)
On the other hand, it may well be that straight-weight oils provide better protection against wear than multigradesa hypothesis that many in the oil industry seem reluctant to consider, but that may have to be reconsidered in the light of a new study published by the prestigious Society of Automotive Engineers.
http://www.eaa49.av.org/techart/str_oil.htm
Our own experience (based on incoming calls to our engine hotline) tends to confirm that lubrication-related problemsespecially involving the camshaftare generally much less among users of straight-weight oils than among users of multigrade oils. There is nothing scientific about our sampling method, admittedly. But we do routinely ask callers what kind of oil they are using, and how often they fly. The people with serious engine problems (scuffed cam lobes, spalled lifters, etc.) we've noticed, are virtually always using a multigrade oil and/ flying less than 100 hours per year. (The number of people calling our hot line who scuff a cam while using straight-weight oil is negligible.) There could be many reasond for the apparent better performance of single-weight oils. It may be for instance, that operators who use straight-weight oils are more careful about preheating in cold weather (or tend not to live in cold areas at all) and therefore have less exposure to cold-start damage. Or it may be that operators who fly very little are more likely than most to buy "fancy" oils, in hopes that this will better protect their engines against the inevitable consequences of inactivity. (We have noticed that the multigrades do seem to have achived a very high market share among inactive or barely-active owner-operators.)
On the other hand, it may well be that straight-weight oils provide better protection against wear than multigradesa hypothesis that many in the oil industry seem reluctant to consider, but that may have to be reconsidered in the light of a new study published by the prestigious Society of Automotive Engineers.
Ahh the memories. 1987 Merkur XR4Ti. Red, gray interior, sunroof and a 5 speed tranny. Could whip 944's all day long. Great car until the engine went belly up on me. Had to sell it for parts 5 years later. Fun while it lasted though. I loved the double wing on the back.
The "T9"? wasn't that a crashbox trans for larger trucks???????
Yeah, T9...that's what it said. I doubt it was the truck gearbox, as it was VERY TINY and frail-looking, and traditionally only good for about 250 wheel hp and prone to catastrophic failure in higher-boosted cars.
Yes, the XR4Ti was one of my favorite cars. Could out-launch a WRX (in the dry) and run 18(stock) to 24psi all day long on pump gas, no intercooler. Wasn't really that hard on oil either. Parts are still plentiful if you know where to look.
Still haven't changed the oil in the Porsche, been driving the Suzuki to save gas. That thing needs a change, Royal Purple Racing 21 for about 7K miles including long desert trips to out-of-state races. I'll be driving it out to Kansas (3115 miles RT) next month, whoopee!
-JamesW
-JamesW
Yes, the XR4Ti was one of my favorite cars. Could out-launch a WRX (in the dry) and run 18(stock) to 24psi all day long on pump gas, no intercooler. Wasn't really that hard on oil either. Parts are still plentiful if you know where to look.
Still haven't changed the oil in the Porsche, been driving the Suzuki to save gas. That thing needs a change, Royal Purple Racing 21 for about 7K miles including long desert trips to out-of-state races. I'll be driving it out to Kansas (3115 miles RT) next month, whoopee!
-JamesW
-JamesW
Seems like if it was a corrosion issue there would be pits on the entire lobe. I have examined cams that have had corrosion issues and they generally had pitting all the way around the lobe. From the descriptionquote:
Originally posted by Doug Hillary:
Hi,
James - cam pitting is not "normal" but is quite common in low use engines. It is caused by corrosion and metal fatigue and occurs "regardless" of the oil used
Pitting is considered to be "damage" but minor pitting without excessive wear across the lobe is "acceptable" but should be monitored
It is lessoned in most cases by using HDEOs of a suitable viscosity. This is why I always advise using HDEOs in low use engines and have done for decades
None of the oils you mention will be better than another - it is significantly "use" related but a modern HDEO will moderate it!
UOAs will NOT "show" a pitting trace!
Regards
Doug
It sounds more like a wear issue because it is in the highest load pressure area of the lobe. This would be particularly true if pitting was on the opening side of the cam lobe centerline of the cam lobe.
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