Flex plate deflection question
08-05-2014, 06:41 PM
#1
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Flex plate deflection question
Hi guys, I'm considering a 928 and have been doing a fair amount of reading here; great resource.
Are there any conditions where it would be possible to determine that flex plate bow is present on a given car without conducting a visual inspection.
Looking for a go/no-go test, actually more of a no-go test. That is, can a flex plate that is already bowing to a significant extent, and therefore the crankshaft has already eroded (partially or more fully) the thrust bearing or even started to contact the internal block web be identified via an indirect test/observation. If this were possible it'd make it easier to walk away from a potential purchase without having to invest on a complete PPI.
I apologize if this has already been addressed but couldn't find it upon searching. Thanks in advance.
Are there any conditions where it would be possible to determine that flex plate bow is present on a given car without conducting a visual inspection.
Looking for a go/no-go test, actually more of a no-go test. That is, can a flex plate that is already bowing to a significant extent, and therefore the crankshaft has already eroded (partially or more fully) the thrust bearing or even started to contact the internal block web be identified via an indirect test/observation. If this were possible it'd make it easier to walk away from a potential purchase without having to invest on a complete PPI.
I apologize if this has already been addressed but couldn't find it upon searching. Thanks in advance.
08-05-2014, 07:35 PM
#2
Just my thoughts but I guess you could ask the owner when it was last checked/released. They could of course lie. Also watch carefully when the car is hot and check it idles well without stalling. Neither would rule out issues but maybe give you the confidence to pay to get a PPI done.
08-05-2014, 08:12 PM
#3
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There's a pretty good sized hole in the top of the upper bellhousing where the clutch release arm would live if you were buying a 5-speed. Given a cheap USB endoscope
http://www.ebay.com/itm/2-5-7-10M-US...item2a365fafdf
you might be able to snake it in there and get a sense of how flat the flex plate is and whether there are any marks or indicators that the flex plate clamp has been looked at.
The more important part of checking the flex plate is actually to release it so you can check the crank end play, that's the real number you want to know. Kind of hard to check the end play without dropping the lower bellhousing and releasing the clamp....
http://www.ebay.com/itm/2-5-7-10M-US...item2a365fafdf
you might be able to snake it in there and get a sense of how flat the flex plate is and whether there are any marks or indicators that the flex plate clamp has been looked at.
The more important part of checking the flex plate is actually to release it so you can check the crank end play, that's the real number you want to know. Kind of hard to check the end play without dropping the lower bellhousing and releasing the clamp....
08-06-2014, 06:08 AM
#4
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Agree with Rob.
For such an important check, and one that can potentially cost you more than the initial purchase price to fix, the crankshaft end play should be measured carefully. No easy way around it, but to raise the car and do it properly.
A PPI done by a knowledgeable mechanic on any used car, especially a high end exotic, is a must.
Sorry Luis, no quick way to get it done.
Good luck with your hunt.
For such an important check, and one that can potentially cost you more than the initial purchase price to fix, the crankshaft end play should be measured carefully. No easy way around it, but to raise the car and do it properly.
A PPI done by a knowledgeable mechanic on any used car, especially a high end exotic, is a must.
Sorry Luis, no quick way to get it done.
Good luck with your hunt.
08-09-2014, 02:59 AM
#5
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if you hear a growling sound from under ther car, it's probably the TT bearings, and if they are bad then the flex plate probably has some pressure on it. The flex plate may have cracked.
at minimum, 1K DIY cheap temporary fix.
at minimum, 1K DIY cheap temporary fix.
08-09-2014, 10:12 AM
#6
+10 to Constantine post #4.
I'm going on 15 years of 928 ownership and I check mine at every 12 month service. No real shorts cuts, however initially painted splines adjacent to clamp and have checked migration via inserting a small light through the plug hole in the bell housing. You could use an endscope, however you cannot check the crankshaft bump clearance of the thrust bearing, as the lower half of the bell housing needs to be removed. When you have your first inspection done also check the aft flexplate clamp and its allen headed bolt. I would suggest that you fit new bolts front and rear initially with initially tightening the aft clamp first and then the forward clamp.
I'm going on 15 years of 928 ownership and I check mine at every 12 month service. No real shorts cuts, however initially painted splines adjacent to clamp and have checked migration via inserting a small light through the plug hole in the bell housing. You could use an endscope, however you cannot check the crankshaft bump clearance of the thrust bearing, as the lower half of the bell housing needs to be removed. When you have your first inspection done also check the aft flexplate clamp and its allen headed bolt. I would suggest that you fit new bolts front and rear initially with initially tightening the aft clamp first and then the forward clamp.
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08-09-2014, 12:52 PM
#8
Drifting
Just to explain Bertrand's picture further. The clamp will only migrate to the left in the picture (towards the engine). So if your flex plate gets additional force on it the clamp and the paint on the shaft splines will show a non painted section, thereby letting you know that the clamp has migrated and you need to release it.
08-09-2014, 06:48 PM
#9
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To the OP, it is important to note that when you look at Bertrand's photo, he has the aftermarket "P-Klamp" installed (adjacent to the left side of the stock pinch clamp) to prevent drive shaft migration.
When checking other 928's, it is likely that you will see only the stock pinch clamp without having the "P-Klamp" installed or having a Constantine Super Clamp installed instead of the stock clamp.
Bilal's description of seeing a non-painted section of the splines after migration is excellent and a relatively simple way of checking for migration after applying the paint during your first inspection.
When checking other 928's, it is likely that you will see only the stock pinch clamp without having the "P-Klamp" installed or having a Constantine Super Clamp installed instead of the stock clamp.
Bilal's description of seeing a non-painted section of the splines after migration is excellent and a relatively simple way of checking for migration after applying the paint during your first inspection.
08-09-2014, 09:07 PM
#11
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I haven't checked it this year but I did put a super clamp on so I feel I have a better handle on it than stock.