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I'm not new to M88/ S38 scene...I recently completed a 1985 E24 M635 engine rebuild (M88/3 engine), so I know my way around the motor pretty good. I replaced ALL (24) of the valves on that rebuild, because the previous owner had buried all 4 of the #5 cylinder's valves into the piston...which I still have, and can see daylight through....Different circumstances, so I wondered if I could get away with re-using the valves in this case. Their condition doesnt appear to be too bad.
Exhaust valves-and seats have a hard time in any S38/M88 and therefore I concider them as consumables. Therefore IMHO, it is wise to replace all (12) of them. The intake valves run rather cold and can be reused.

During my M88/3 rebuild, I replaced all 24 valves as well. The exhaust valves for the above mentioned reason; the intake valves because of their relative low cost, @30 Euro/pc (ex VAT) it didn't make sense to cut cost in an 8k (Ex VAT) project. That was my simple reasoning. I also specified the replacement of the valve-seats by sintered types.
 

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The machinist is supposed to grind in the intake valves in...they looked fine after I wire wheeled them clean, and I'm going to get a new set of exhaust valves.
That already is an excellent approach; the intake valves aren't highly stressed. Will you replace the valve sprins and collets as well ?

you have any thoughts on piston rings? I did a leakdown test, but since I was not able to get the exhaust valves on the #'s 5 and 6 to seal, there really was no way to check the ring condition. The bottom end has 129k miles on it, and cylinder condition looks good(block still in the car).
The only method to determine actual wear and thus condition is by measuring the cylinder-to piston clearances. When I dropped my short block at the machinist, his first analysis was that the cylinder walls looked fine and no new pistons were needed. However, that changed after he performed his measurements, forcing me to leave my original plan of just replacing the bearings and piston rings combined of a rehone of the cylinders. I could have insisted on a second measurement of the pistons but that would not have changed anything as I already had decided to buy a new set of pistons (first oversize). These come with a new wrist-pin and a new set of piston rings.

At 129k miles, the short-block usually is still within the first halve of its expected life. It's the head that needs major work first. However, I wouldn't feel myself safe without inspecting the bearings and piston rings before making such decisions. This also applies to the waterpump
If you hadnt discovered it, BigCoupe.com is a great site for 6 series stuff, but there are alot of M5 owners there, since the engines are the same, and there is alot of valuable technical info there.
Thanks, I wasn't aware of that site. I will take a look at it later this week.
 

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Thanks for the links; I have took a quick glance at your pictures and story today, will read it thouroughly this weekend, but from what I have seen, you have performed a quality rebuild. My compliments.

BTW: It seems that your new pistons are from the same batch as mine (0797).
 
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