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IMS failure in a 996 turbo
- Thread starter melodasi
- Start date
orangecurry
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I didn't think the GT block engine had an IMS?
GT4
Nordschleife
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By a stretch of the imagination
It doesn't.
But one in 300,000 (after lack of care and/or bad oil and bad luck) Mezger layshafts fail.
The slightly less rare event on Turbos is stretching or breakage of the timing chains (they go long before the shaft does), this is torque dependent - ie more likely on very heavily tuned blocks.
It doesn't.
But one in 300,000 (after lack of care and/or bad oil and bad luck) Mezger layshafts fail.
The slightly less rare event on Turbos is stretching or breakage of the timing chains (they go long before the shaft does), this is torque dependent - ie more likely on very heavily tuned blocks.
Tony the Chief Porsche guy at Dovehouse, said to me he's done loads of IMS's on 996's & Engine re-builds on 997's but never on the turbo variant of these.
GT4
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Erm, please no more "evidence" of the non-existence of fairies.
It isn't required.
PS - the Turbo block is NOT a variant of the Carrera engine (they are completely different), not unless you mean upto and including 993.
Of course 997.2 onwards Turbos are again a variant of the Carrera engine, but using the totally new design DFI MA1.01 block and doesn't have an IMS to go wrong; and runs cool enough and with closed deck block to avoid bore scoring and ovalisation too (so just like the early days again!)
It isn't required.
PS - the Turbo block is NOT a variant of the Carrera engine (they are completely different), not unless you mean upto and including 993.
Of course 997.2 onwards Turbos are again a variant of the Carrera engine, but using the totally new design DFI MA1.01 block and doesn't have an IMS to go wrong; and runs cool enough and with closed deck block to avoid bore scoring and ovalisation too (so just like the early days again!)
NineExcellence
Albert Park
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Just to be clear there is an IMS, but the seal is an o-ring. The IMS has white metal bearings, and does not suffer from the same issue.
I have heard, but not seen where the bolt can "loosen" which results in a full rebuild.
Nothing to worry about.
I have heard, but not seen where the bolt can "loosen" which results in a full rebuild.
Nothing to worry about.
GT4
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Not sure that helps.
You are using IMS as a generic term, blocks with chain or gear driven cams will often have an intermediate shaft (in fact technically the phrase intermediate shaft is not even specific to engines, by definition it is simply the shaft between!)
But the specific use of the phrase or acronym IMS when applied to Porsche ls invariably means the notorious M96/M97 cam drive shaft).
Going back to generics, technically the Turbo has a layshaft, not an intermediate shaft to down gear the crank speed to cam speed.
Therefore the Turbo does not have an IMS (intermediate shaft), if anything it is an gear driven layshaft (performing some on the same functions).
However, it is neither technically an IMS (intermediate shaft), nor does it have ISB (intermediate shaft bearing) nor ISS (intermediate shaft seals).
It certainly does not exhibit the issues the "IMS" does as it is a completely different design.
The Turbo layshaft is gear driven vs. chain driven in the NA 996 engine and doesn't have the ball race bearings of the NA 996. This doesn't make the layshaft in the Turbo engine indestructible but given the number of these cars around and the age and number of miles they're racking up and for some the engine hp mods they receive the usage they're subjected to it doesn't appear to be a weak link in the Turbo engine.
The layshaft is not a full length shaft. It is gear driven by the crank and in turn provides chain drive to the exhaust and intake camshafts. The layshaft is short, roughly a 3rd the length of the engine,'and resides in the rear of the engine under the crankshaft.
The layshaft has plain bearings which are pressure fed oil (not encapsulated and sealed as the NA ball race). The lack of fresh cool oil is the main reason for true IMS bearing failure on the NA Carrera.
You are using IMS as a generic term, blocks with chain or gear driven cams will often have an intermediate shaft (in fact technically the phrase intermediate shaft is not even specific to engines, by definition it is simply the shaft between!)
But the specific use of the phrase or acronym IMS when applied to Porsche ls invariably means the notorious M96/M97 cam drive shaft).
Going back to generics, technically the Turbo has a layshaft, not an intermediate shaft to down gear the crank speed to cam speed.
Therefore the Turbo does not have an IMS (intermediate shaft), if anything it is an gear driven layshaft (performing some on the same functions).
However, it is neither technically an IMS (intermediate shaft), nor does it have ISB (intermediate shaft bearing) nor ISS (intermediate shaft seals).
It certainly does not exhibit the issues the "IMS" does as it is a completely different design.
The Turbo layshaft is gear driven vs. chain driven in the NA 996 engine and doesn't have the ball race bearings of the NA 996. This doesn't make the layshaft in the Turbo engine indestructible but given the number of these cars around and the age and number of miles they're racking up and for some the engine hp mods they receive the usage they're subjected to it doesn't appear to be a weak link in the Turbo engine.
The layshaft is not a full length shaft. It is gear driven by the crank and in turn provides chain drive to the exhaust and intake camshafts. The layshaft is short, roughly a 3rd the length of the engine,'and resides in the rear of the engine under the crankshaft.
The layshaft has plain bearings which are pressure fed oil (not encapsulated and sealed as the NA ball race). The lack of fresh cool oil is the main reason for true IMS bearing failure on the NA Carrera.
NineExcellence
Albert Park
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GT4 said:
A good summary :thumb:
I did think of posting something similar but thought it might confuse further. The bottom line is that is it a non issue and that is what matters.
Ken
GT4
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Thanks
I appreciate my original black and white: "the Turbo has no IMS" was a simplification for the purposes of answering the spirit of the questioning about the IMS bogeyman, rather than diving straight in with a much more detailed reply.
On balance, I would still categorise the Mezger blocks as without "IMS" in the informal shorthand sense that the term has become used for on forums with respect to the M96/M97 blocked 986/987/996/997 vehicles.
As generally, people just mean will it blow up like I've heard rumours about.
I wouldn't want to give the impression they are in anyway physically equivalent and hence allow an interpretation that either an M96/M97 could use a Turbo IMS, or that the Turbo could have an "IMS replacement" in the M96/M97 sense.
But that is a judgement call on the original purpose of the question, if the question was about the detailed internal composition of the engines, then that is the point at which a full description becomes relevant.
I appreciate my original black and white: "the Turbo has no IMS" was a simplification for the purposes of answering the spirit of the questioning about the IMS bogeyman, rather than diving straight in with a much more detailed reply.
On balance, I would still categorise the Mezger blocks as without "IMS" in the informal shorthand sense that the term has become used for on forums with respect to the M96/M97 blocked 986/987/996/997 vehicles.
As generally, people just mean will it blow up like I've heard rumours about.
I wouldn't want to give the impression they are in anyway physically equivalent and hence allow an interpretation that either an M96/M97 could use a Turbo IMS, or that the Turbo could have an "IMS replacement" in the M96/M97 sense.
But that is a judgement call on the original purpose of the question, if the question was about the detailed internal composition of the engines, then that is the point at which a full description becomes relevant.
NineExcellence
Albert Park
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- 21 Sep 2009
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- 1,587
We don't want to be pushing prices down on Mezger blocks, especially when I own a couple 
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