blown engine
09-11-2015, 05:11 PM
#391
Drifting
I wonder how many M96 rebuilders replace rings because that used to be the standard procedure with other ,older engines ?
The problem would be not just the sealing of the round rings in an oval bore but the ring gap?
Ahsai has a good tip -measure the delta of the bore directly.Do not calculate it like Jafromobile does in the video.
The problem would be not just the sealing of the round rings in an oval bore but the ring gap?
Ahsai has a good tip -measure the delta of the bore directly.Do not calculate it like Jafromobile does in the video.
09-11-2015, 05:12 PM
#392
Would you mind sharing with me the wear data for the Cayenne? Was it for the V8 or the VR6? I've never seen any limits published anywhere. I've always gone with the limits from the aircooled cylinders of max .002" ovality and taper in the cylinders. Unless a block is new or very low mileage, they always are out of spec - most are a minimum of .005" ovaled - the worst we found had .015" ovality.
That is why we instruct shops that are doing repairs not to re-ring the pistons if they aren't re-doing the bores. They are better re-using the original rings per position since they have already worn to match the bores. New rings will never seat otherwise.
That is why we instruct shops that are doing repairs not to re-ring the pistons if they aren't re-doing the bores. They are better re-using the original rings per position since they have already worn to match the bores. New rings will never seat otherwise.
Come to think about the spec, they spec that the wear on all 6 measurement points shall be < 0.08mm (~3 thou). I think that automatically implies implicitly both ovality and taper shall also be < 0.08mm (~3 thou). So I think your 2 thou sounds very good and conservative.
They also list the ring specs and the piston specs
09-11-2015, 05:19 PM
#393
Schnell, grab that pdf before it's gone and I know what you'll be busy with this weekend 
I plan to measure the used ring as well to see if they wear evening in all radial directions. I still keep the original orientation of them when I removed the pistons. It would be interesting to see if the thrust side will wear more and if the rings are round or oval.
Even though fitting new rings on used bores is not a good practice, there seems to be plenty of ppl doing that w/o much problem.
I plan to measure the used ring as well to see if they wear evening in all radial directions. I still keep the original orientation of them when I removed the pistons. It would be interesting to see if the thrust side will wear more and if the rings are round or oval.
Even though fitting new rings on used bores is not a good practice, there seems to be plenty of ppl doing that w/o much problem.
09-12-2015, 12:16 AM
#394
Former Vendor
Note the second ring is pinned......
New rings in a bore thats not round, and isn't straight, doesn't work well at all. Old rings have a better chance of sealing.
New rings in a bore thats not round, and isn't straight, doesn't work well at all. Old rings have a better chance of sealing.
09-12-2015, 01:16 AM
#395
Right and I think the ring gap will grow beyond spec too as it starts to wear to conform to the oval.
09-12-2015, 01:23 AM
#396
BTW, I measured the diameters of piston #1 and here are the measurements:
Top (non-thrust side): 3.7549"
Top (thrust side): 3.7581"
10mm from bottom of skirt (thrust side): 3.7794"
Skirt bottom (thrust size): 3.7783"
Combined this with the cylinder #1 measurements, I think the piston to cylinder gap (total gap, not divided by 2) is 2.4 thou.
Note the top of the piston is about 25 thou smaller to allow for extreme thermal expansion.
Top (non-thrust side): 3.7549"
Top (thrust side): 3.7581"
10mm from bottom of skirt (thrust side): 3.7794"
Skirt bottom (thrust size): 3.7783"
Combined this with the cylinder #1 measurements, I think the piston to cylinder gap (total gap, not divided by 2) is 2.4 thou.
Note the top of the piston is about 25 thou smaller to allow for extreme thermal expansion.
09-12-2015, 10:00 PM
#397
Former Vendor
BTW, I measured the diameters of piston #1 and here are the measurements:
Top (non-thrust side): 3.7549"
Top (thrust side): 3.7581"
10mm from bottom of skirt (thrust side): 3.7794"
Skirt bottom (thrust size): 3.7783"
Combined this with the cylinder #1 measurements, I think the piston to cylinder gap (total gap, not divided by 2) is 2.4 thou.
Note the top of the piston is about 25 thou smaller to allow for extreme thermal expansion.
Top (non-thrust side): 3.7549"
Top (thrust side): 3.7581"
10mm from bottom of skirt (thrust side): 3.7794"
Skirt bottom (thrust size): 3.7783"
Combined this with the cylinder #1 measurements, I think the piston to cylinder gap (total gap, not divided by 2) is 2.4 thou.
Note the top of the piston is about 25 thou smaller to allow for extreme thermal expansion.
09-13-2015, 09:48 AM
#399
Rennlist Member
09-13-2015, 03:49 PM
#400
I"ll be happy to do that if anyone sends me a garage freezer
Btw, I found the spec for 997 pistons for pistons in the "X" group. 95.985mm to 95.995mm when new. Wear limit is 0.1mm
Btw, I found the spec for 997 pistons for pistons in the "X" group. 95.985mm to 95.995mm when new. Wear limit is 0.1mm
09-29-2015, 10:03 PM
#403
09-30-2015, 06:19 AM
#405
Asaih, calling yourself a 'tree-shade' mechanic sounds very modest. I personally think otherwise and I don't think I'm alone here. All your posts and write ups have been extremely informative and show that you are having a great understanding and in depth knowledge of these cars and I have learned a lot from them. Thank you!
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