Cam lobe to Lifter misalignment

[A2000RICH]

I worked in the V6 base engine group at the BOC V6 center of expertise at what was 902 E.Hamilton Ave, Flint Mich 48550 with the turbo group as a test /applications engineer. I have never seen an as released Turbo V6 valve geometry which looked so sick. The allowable tolerances which I reviewed as compared to the pictures do not make sense. The factory 36 ( engine plant ) checking gage / fixture would not allow a cam to be off the push rod/ lifter c/L so badly as to not be detected. These pictures look like possibly the wrong cam, or the cam thrust face (block bulkhead) was milled significantly (for whatever reason), or the cam collar was turned down. I can only imagine what the front cover looked like with "0.070" thrust clearance even with the old plastic thrust button. I was fortunate to have needle bearings laying around which I could use for cam thrust in the "80's". Sorry to sound disgusted but the product was better than that. Have a great day.

rather than start with an explanation of my post which you seem to have such a problem with i will take a little time to explain where those numbers came from. a little over ten years ago i put a team of rather gifted engineers on a project to define why there were so many cam failures in the GN v6's. as a base i took a brand new SG 109 short block and reverse engineered the measurements that i am showing in my last post. if you look carefully you will see that the measurements of the block are actually precise and symmetrical. the variations are due to cam lobe spacing not of the block. everyone knows that a couple of the lifters actually turn in reverse due to the design of the block. this can easily be seen in each of these drawings. it is the cam lobe spacing that is all over the place both on the GM cam (brand new stock cam never used) and the aftermarket one as well. i did several GM cams and they were similar. i did at least two cams from each of the more popular cam suppliers and the variations in alignment were very great. there was NO wear on the block and the cams were all new out of the box. before i continue i will post tomorrow night pics of the original blueprints of the 109 block which i have a complete 22 page set of every single dimension of the block spec. The Buick V6 was well known as a engine that was somewhat problematic with cam wear. Thats the reason it was chosen by the API for the ASTM D 5533 sequence III-E wear test. Cam wear tests were done with several different types of engines. One engine (i think it was a Nissan inline 6) was chosen just to sit and idle for a lot of hours since it had a particular cam issue with prolonged idling. The Buick V-6 was chosen for a much more strenuous test that consisted of a continuous run of 64 hours at 3000 rpm with an oil temp of 149 C degrees. The 109 block was used for this test well into the early 2000's and GM apparently continued to supply the API with these blocks long after they were no longer available to the public. This info is available in the 1061 page book titled "Fuels and lubricants Handbook : technology, properties, performance, and testing" published by the ASTM and was current in the latest edition i have dated 11/1/07. Cost to download this book is in excess of a thousand dollars. And worth every penny since it is a fabulous study !!



I assure you that i am not making this stuff up and that i know what i am talking about.

 

[TTipe]

rather than start with an explanation of my post which you seem to have such a problem with i will take a little time to explain where those numbers came from. a little over ten years ago i put a team of rather gifted engineers on a project to define why there were so many cam failures in the GN v6's. as a base i took a brand new SG 109 short block and reverse engineered the measurements that i am showing in my last post. if you look carefully you will see that the measurements of the block are actually precise and symmetrical. the variations are due to cam lobe spacing not of the block. everyone knows that a couple of the lifters actually turn in reverse due to the design of the block. this can easily be seen in each of these drawings. it is the cam lobe spacing that is all over the place both on the GM cam (brand new stock cam never used) and the aftermarket one as well. i did several GM cams and they were similar. i did at least two cams from each of the more popular cam suppliers and the variations in alignment were very great. there was NO wear on the block and the cams were all new out of the box. before i continue i will post tomorrow night pics of the original blueprints of the 109 block which i have a complete 22 page set of every single dimension of the block spec. The Buick V6 was well known as a engine that was somewhat problematic with cam wear. Thats the reason it was chosen by the API for the ASTM D 5533 sequence III-E wear test. Cam wear tests were done with several different types of engines. One engine (i think it was a Nissan inline 6) was chosen just to sit and idle for a lot of hours since it had a particular cam issue with prolonged idling. The Buick V-6 was chosen for a much more strenuous test that consisted of a continuous run of 64 hours at 3000 rpm with an oil temp of 149 C degrees. The 109 block was used for this test well into the early 2000's and GM apparently continued to supply the API with these blocks long after they were no longer available to the public. This info is available in the 1061 page book titled "Fuels and lubricants Handbook : technology, properties, performance, and testing" published by the ASTM and was current in the latest edition i have dated 11/1/07. Cost to download this book is in excess of a thousand dollars. And worth every penny since it is a fabulous study !!



I assure you that i am not making this stuff up and that i know what i am talking about.

Mr. Clark. Please understand that I do not have a problem with your post, but rather the pictures used as compared to the allowable tolerance to lifter c/L (which I could barely read) that I could see (ie ~ 0.070"; +/- 0.035"). SG parts may not have been qualified (go /no go testing) for LC2 use at factory 36. I can be more specific in regards to at least one critical SG asm that was not qualified for LC2 use per the service engineer who released these asms and the vendor (but would not speak to this in a public forum). The default use was for LD5 (231 NA carb). The #3 exhaust lifter bore is off ~ 0.030 to 0.050" (I think) and the cost to retool was not justified based on durability results. The study of an SG short block/ SG cam may (undertaken in 2007/8) not provide as production representative result as one would hope / depend on. I don't think an SG short block would have included the cam but I could be wrong. I believe the 109 block & cam were chosen to study because of the lifter to cam lubrication relationship (zinc). Perhaps aftermarket valve spring pressures played a part in these failures. Premature valve seat "pound out" should be expected as well. I would also expect to see chain destruction, lifter bore side loading & timing cover witness of excessive cam button wear. A stellyte lifter foot was used to promote durability. This "babbling" is based on the pictures, not any math or anyone's capability as an engineer. I just think you had to use what you could acquire through a normal effort. The Comp folks replicated what they were given. If I can locate my old stock cam (which came out of a measured engine) I would gladly send it to you if wish to look at it. I know that mine was correct & performed as expected. I think I still have actual cam prints (Van Dykes-brownlines). The government pressure on the oil companies to remove zinc may have been a factor in cam failures but not in the 80's and maybe beginning in the early 90's. My only thought was I have never seen lifters so far off the lobes & I did not think the pictures represented the measurements you & your team had taken. I tried to expand the drawings & their measurements / tolerances?? but the resolution did not allow. I may be a victim of what I thought were lousy pictures? I wonder what sample size ASTM used for their testing? I remember talking with the rod & piston engineer about the fears we had of people bringing rollers & higher lifts and spring loading to the table. The system was purposed designed (and archaic) but met the torque requirements for LC2 horsepower. I thank you for the professional response & I enjoy the development that you have fostered to further the Turbo Buick legend.

 

[MG8T7GN]

OP. do you still have the cam that came out? Put it in and see where the lifters line up. If all is well with the old cam, problem is with the new cam.

 

[A2000RICH]

How's this compare to my drawing?

 

[A2000RICH]

Mr. Clark. Please understand that I do not have a problem with your post, but rather the pictures used as compared to the allowable tolerance to lifter c/L (which I could barely read) that I could see (ie ~ 0.070"; +/- 0.035"). SG parts may not have been qualified (go /no go testing) for LC2 use at factory 36. I can be more specific in regards to at least one critical SG asm that was not qualified for LC2 use per the service engineer who released these asms and the vendor (but would not speak to this in a public forum). The default use was for LD5 (231 NA carb). The #3 exhaust lifter bore is off ~ 0.030 to 0.050" (I think) and the cost to retool was not justified based on durability results. The study of an SG short block/ SG cam may (undertaken in 2007/8) not provide as production representative result as one would hope / depend on. I don't think an SG short block would have included the cam but I could be wrong. I believe the 109 block & cam were chosen to study because of the lifter to cam lubrication relationship (zinc). Perhaps aftermarket valve spring pressures played a part in these failures. Premature valve seat "pound out" should be expected as well. I would also expect to see chain destruction, lifter bore side loading & timing cover witness of excessive cam button wear. A stellyte lifter foot was used to promote durability. This "babbling" is based on the pictures, not any math or anyone's capability as an engineer. I just think you had to use what you could acquire through a normal effort. The Comp folks replicated what they were given. If I can locate my old stock cam (which came out of a measured engine) I would gladly send it to you if wish to look at it. I know that mine was correct & performed as expected. I think I still have actual cam prints (Van Dykes-brownlines). The government pressure on the oil companies to remove zinc may have been a factor in cam failures but not in the 80's and maybe beginning in the early 90's. My only thought was I have never seen lifters so far off the lobes & I did not think the pictures represented the measurements you & your team had taken. I tried to expand the drawings & their measurements / tolerances?? but the resolution did not allow. I may be a victim of what I thought were lousy pictures? I wonder what sample size ASTM used for their testing? I remember talking with the rod & piston engineer about the fears we had of people bringing rollers & higher lifts and spring loading to the table. The system was purposed designed (and archaic) but met the torque requirements for LC2 horsepower. I thank you for the professional response & I enjoy the development that you have fostered to further the Turbo Buick legend.

if you look at the post i did earlier tonight you can see that the lifter bore relationship to cam thrust surface is the same on the blueprints (these are original 109 prints dated end of 1985) as they are on my drawings derived from actual block measurements. I cannot really find any difference in the 109 SG blocks to the production 109 blocks. lifter bore spacing is exactly the same in all the blocks that i have ever measured to within a couple tenths. i have numerous GM production cams as well as GM replacement cams.....last part number digits are 80 vs 81. they vary little from my drawing marked "GM cam 2". Simply put the lifter to lobe alignment in these blocks is really poor. in case you can't make out the drawings clearly enough to read them here are the bore spacings on my drawings for driver side. 1.520-2.720-1.620-2.720-1.520. and on the GM blueprints re: the datum line they are 13.225-11.705-8.985-7.365-4.645-3.125. there is no getting around the fact that these blocks had very poor bore to lifter spacing and it doesn't matter whose cam blanks you compare them to. If you have a cam that lines up with these bore spacings i would really like to see it. If such a cam exists then why have i never seen one in the hundreds of cams that i have installed in the last 25 years?

 

[TTipe]

How's this compare to my drawing?

How's this compare to my drawing?

I don't think your drawing was so bad, I just couldn't see it clearly. The extra distance between cylinder 3 exhaust & intake c/L's are obvious. It would be easy to do the study if the block & cam were machine finish parametric models. The cam could be placed into the block. A slice of the block finished view (front to back) through the driver side lifter bore would provide a true view of the cam to lifter bore based on the cam shoulder to bulkhead extreme thrust position. Ain't going to happen. Thanks for going to the trouble of posting that view. Maybe I will have opportunity to bring you a cam drawing if I can get away to your event.

 

[TTipe]

if you look at the post i did earlier tonight you can see that the lifter bore relationship to cam thrust surface is the same on the blueprints (these are original 109 prints dated end of 1985) as they are on my drawings derived from actual block measurements. I cannot really find any difference in the 109 SG blocks to the production 109 blocks. lifter bore spacing is exactly the same in all the blocks that i have ever measured to within a couple tenths. i have numerous GM production cams as well as GM replacement cams.....last part number digits are 80 vs 81. they vary little from my drawing marked "GM cam 2". Simply put the lifter to lobe alignment in these blocks is really poor. in case you can't make out the drawings clearly enough to read them here are the bore spacings on my drawings for driver side. 1.520-2.720-1.620-2.720-1.520. and on the GM blueprints re: the datum line they are 13.225-11.705-8.985-7.365-4.645-3.125. there is no getting around the fact that these blocks had very poor bore to lifter spacing and it doesn't matter whose cam blanks you compare them to. If you have a cam that lines up with these bore spacings i would really like to see it. If such a cam exists then why have i never seen one in the hundreds of cams that i have installed in the last 25 years?

Richard I had previously stated that I had no issue with the study you / your crew had performed. The lifter on lobe pictures are very "humbling" to say the least. I have seen tear downs / engines in build with the same bore spacing less your lighting. I have reduced confidence in some "service" components based on prior knowledge and release practices. I apologize if I led you to believe that I knew of a cam that used a different casting to change the bore spacing. I was referring to front cover asm's (LD5) which were being sold as LC2 front covers. When you had indicated the use of an SG part in your study, the warning light went on. Sorry to not be more specific in my prior comment.When I saw your pictures I thought something was terribly wrong (it was by today's technology) like a turned down collar or cam thrust bulkhead. All front cover asms for the 3.8L were qualified by pressure at RPM in a test stand. If min pressure was not observed, the cover went to the carb motor.

 

[bison]

You will notice the #3 ex lobe is more central and is the most common failure point on a flat cam. It’s position reduces its spinning.


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