M28.22 Compatibility With M28.12
11-30-2023, 07:28 PM
#1
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M28.22 Compatibility With M28.12
Hi I have a 1985 euro 310 hp car with the M28.22 engine and L-H Jetronic that is showing symptoms of TBF and I am looking at an 1982 M28.12 300 hp engine with the K-Jetronic.
I want to retain my original intake, injection and twin dizzies etc and wondering if it is simply a matter of putting it all on the new engine.
Should I swap the heads or are they the same? the 84 car has a bit more compression 10.4 opposed to 10.0
Are the pistons the same
I think my 84 is an interference engine and wondering if the 82 is
If anyone knows the answers to any of these it will be very much appreciated
I want to retain my original intake, injection and twin dizzies etc and wondering if it is simply a matter of putting it all on the new engine.
Should I swap the heads or are they the same? the 84 car has a bit more compression 10.4 opposed to 10.0
Are the pistons the same
I think my 84 is an interference engine and wondering if the 82 is
If anyone knows the answers to any of these it will be very much appreciated
11-30-2023, 07:37 PM
#2
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First order of business is to measure the crank end play.
I had an '89 with TBF, could not find another 89 block. I split the block, cleaned it, replaced the crankshaft and bearings and used Constantine's Super Clamp to prevent future migration.
Customer has been driving it for over a year with no issues.
Kevin
I had an '89 with TBF, could not find another 89 block. I split the block, cleaned it, replaced the crankshaft and bearings and used Constantine's Super Clamp to prevent future migration.
Customer has been driving it for over a year with no issues.
Kevin
11-30-2023, 08:08 PM
#3
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Second what Kevin said.
Blocks should be the same - both are interference engines.
Blocks should be the same - both are interference engines.
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Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
12-01-2023, 03:46 AM
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First order of business is to measure the crank end play.
I had an '89 with TBF, could not find another 89 block. I split the block, cleaned it, replaced the crankshaft and bearings and used Constantine's Super Clamp to prevent future migration.
Customer has been driving it for over a year with no issues.
Kevin
I had an '89 with TBF, could not find another 89 block. I split the block, cleaned it, replaced the crankshaft and bearings and used Constantine's Super Clamp to prevent future migration.
Customer has been driving it for over a year with no issues.
Kevin
How did you go about cleaning it out, did you disassemble it? that's probably my main concern.
I measured the crank movement at 0.84mm
12-01-2023, 08:38 AM
#5
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I have access to a very large parts washer at my machine shop. I split the block and placed it there overnight. My shop cleaned out the dirt traps of the replacement crankshaft.
To quote another member: The specification for later engines is .0024" to .0076". Wear limit is .016". If your end play is more than .016", then you are experiencing Thrust Bearing Failure.
.084mm is .033" so you are past the wear limit. The '89 I referred to above was so bad the crank could be heard clanging against the block.
I don't think your wear is enough for the crankshaft to interfere with the block. Only inspection will confirm that.
Whether you elect to replace the block or not is up to you. Sometimes it's about the 'devil you know'.
You seem to have the proper training and tools to address the issue either way.
Good luck.
To quote another member: The specification for later engines is .0024" to .0076". Wear limit is .016". If your end play is more than .016", then you are experiencing Thrust Bearing Failure.
.084mm is .033" so you are past the wear limit. The '89 I referred to above was so bad the crank could be heard clanging against the block.
I don't think your wear is enough for the crankshaft to interfere with the block. Only inspection will confirm that.
Whether you elect to replace the block or not is up to you. Sometimes it's about the 'devil you know'.
You seem to have the proper training and tools to address the issue either way.
Good luck.
12-01-2023, 08:42 AM
#6
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TBF is not common on the 16v cars like it is on the 32v ones.
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GregBBRD (12-01-2023)
12-01-2023, 03:31 PM
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This is a true statement, with a bit of something added, if I may:
I believe that the major difference is that all the 3 speed cars came with the torque tube shaft, with the circlip groove, with the shims, the special washer, and the circlip, to absolutely prevent the flex plate from migrating.
And, as far as I know, none of the 4 speeds came with the shims, the special washer, and the circlip, although Porsche continued to provide the torque tube shafts, with the snap ring groove, well into the very late 1980's. (And PET still lists the pieces, as if they were used.)
In my theory of this failure, the higher the torque/horsepower, the more the torque tube shaft twists and "pulls itself" out of the front flexplate.
It is very rare to see any torque tube shaft migration out of the flexplate on the early US cars with 4 speeds ('83/'84)....as they didn't make very much torque.
More common to see some failures on the 5 liter '85/'86 engines, although Porsche significantly increased the "thrust bearing surface" on the 5.0 engines...presumably for this reason.
Therefore, it makes sense, to me, that 4 speed automatic S3 cars (which are 4.7 blocks, with the narrow thrust bearing) need to be monitored for torque tube migration and probably need some "preventative measures" done to prevent TBF. (I have seen TBF failure on automatic S3 vehicles.)
Again, just my theory, from decades of seeing 928's and analyzing damage.
I apologize if this post offends anyone.
Just trying to add some possible assistance.
I believe that the major difference is that all the 3 speed cars came with the torque tube shaft, with the circlip groove, with the shims, the special washer, and the circlip, to absolutely prevent the flex plate from migrating.
And, as far as I know, none of the 4 speeds came with the shims, the special washer, and the circlip, although Porsche continued to provide the torque tube shafts, with the snap ring groove, well into the very late 1980's. (And PET still lists the pieces, as if they were used.)
In my theory of this failure, the higher the torque/horsepower, the more the torque tube shaft twists and "pulls itself" out of the front flexplate.
It is very rare to see any torque tube shaft migration out of the flexplate on the early US cars with 4 speeds ('83/'84)....as they didn't make very much torque.
More common to see some failures on the 5 liter '85/'86 engines, although Porsche significantly increased the "thrust bearing surface" on the 5.0 engines...presumably for this reason.
Therefore, it makes sense, to me, that 4 speed automatic S3 cars (which are 4.7 blocks, with the narrow thrust bearing) need to be monitored for torque tube migration and probably need some "preventative measures" done to prevent TBF. (I have seen TBF failure on automatic S3 vehicles.)
Again, just my theory, from decades of seeing 928's and analyzing damage.
I apologize if this post offends anyone.
Just trying to add some possible assistance.
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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!
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12-01-2023, 08:31 PM
#10
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12-01-2023, 08:32 PM
#11
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This is a true statement, with a bit of something added, if I may:
I believe that the major difference is that all the 3 speed cars came with the torque tube shaft, with the circlip groove, with the shims, the special washer, and the circlip, to absolutely prevent the flex plate from migrating.
And, as far as I know, none of the 4 speeds came with the shims, the special washer, and the circlip, although Porsche continued to provide the torque tube shafts, with the snap ring groove, well into the very late 1980's. (And PET still lists the pieces, as if they were used.)
In my theory of this failure, the higher the torque/horsepower, the more the torque tube shaft twists and "pulls itself" out of the front flexplate.
It is very rare to see any torque tube shaft migration out of the flexplate on the early US cars with 4 speeds ('83/'84)....as they didn't make very much torque.
More common to see some failures on the 5 liter '85/'86 engines, although Porsche significantly increased the "thrust bearing surface" on the 5.0 engines...presumably for this reason.
Therefore, it makes sense, to me, that 4 speed automatic S3 cars (which are 4.7 blocks, with the narrow thrust bearing) need to be monitored for torque tube migration and probably need some "preventative measures" done to prevent TBF. (I have seen TBF failure on automatic S3 vehicles.)
Again, just my theory, from decades of seeing 928's and analyzing damage.
I apologize if this post offends anyone.
Just trying to add some possible assistance.
I believe that the major difference is that all the 3 speed cars came with the torque tube shaft, with the circlip groove, with the shims, the special washer, and the circlip, to absolutely prevent the flex plate from migrating.
And, as far as I know, none of the 4 speeds came with the shims, the special washer, and the circlip, although Porsche continued to provide the torque tube shafts, with the snap ring groove, well into the very late 1980's. (And PET still lists the pieces, as if they were used.)
In my theory of this failure, the higher the torque/horsepower, the more the torque tube shaft twists and "pulls itself" out of the front flexplate.
It is very rare to see any torque tube shaft migration out of the flexplate on the early US cars with 4 speeds ('83/'84)....as they didn't make very much torque.
More common to see some failures on the 5 liter '85/'86 engines, although Porsche significantly increased the "thrust bearing surface" on the 5.0 engines...presumably for this reason.
Therefore, it makes sense, to me, that 4 speed automatic S3 cars (which are 4.7 blocks, with the narrow thrust bearing) need to be monitored for torque tube migration and probably need some "preventative measures" done to prevent TBF. (I have seen TBF failure on automatic S3 vehicles.)
Again, just my theory, from decades of seeing 928's and analyzing damage.
I apologize if this post offends anyone.
Just trying to add some possible assistance.
12-01-2023, 11:18 PM
#12
Rennlist Member
I have here a 85 S 2 automatic with TBF. The failure occurs after 100.000 miles.
Bought the car for 2.250 € 15 years ago, the good old days.
This car has the short gearbox, maybe the long 2.20 final drive reduce the risk of failure.
Bought the car for 2.250 € 15 years ago, the good old days.
This car has the short gearbox, maybe the long 2.20 final drive reduce the risk of failure.
12-02-2023, 12:02 AM
#13
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