Hello all, first post in this section (though I read through them almost daily) I am in the process of rebuilding a 1986 6.9 I got from a junk yard, so I have not heard it run, or know the history of it. Everything looks new on it when i took it apart bored .030 over. Question 1 The bottom side of the piston says
+
oil 20 Mahle
U1 A2
T241

I can't find any Info on these. Is it an old part#, Are they forged or cast? I've seen both looking through the forums none of these #'s match whats in there current catalog. Bores still have crosshatching visible Piston to cylinder clearances are .007 at the tightest to .0088 at the biggest (using dial bore gauge and mic) witch is just out of tolerance. Would you hone and keep the .030 pistons or do i Need to step up to .040? This is not my first engine rebuild, but it is my first Diesel thanks for all the help.

 

I can tell you that theyre cast, and that maybe the mahle 20 means theyre shaved .20 but other than that im of no help to you.

 

If the bores still show crosshatching all the way up and down the cylinder I would not bore it. I (personally) wouldn't even hone it. I would put put the pistons back in as is, unless the the ring grooves are packed with carbon. Then you could clean the ring grooves, put new rings on it and run a deglazing hone down it (bead type) which won't remove as much material as a finish hone (stone type). .005-.008 is the spec. for clearance when assembling new. Not for when it needs bored or honed.

 

There isn't any carbon on the rings at all, so i'll probably line the ring gaps back up and reinstall them. I'll get a measurement on the pin height to see if anything was taken off. Anyone know the stock pin height? Motor was in a truck at the junkyard didn't have any turbo stuff on it. Had all the stock exhaust in place yet, so i hope the pin height is stock. Bearings all look really good also. If I had know that it looked like this inside I wouldn't have taken it apart, Thanks

 

Unless im misunderstanding you, definately dont line the ring gaps up...

 

factory pistons were available in factory bore and a tiny bit bigger A and B when for when engines are freshened up, if I am not mistaken

 

if it has been bored 30 over. someone may have burnt it down, and had to bore it. or a rebuilder soaked some duffus hard to say, slip some rings on it put back to together

 

Get some new piston rings, Hone and GO....Don't line up the ring gaps....I put the top ring towards the front of the engine. The second ring towards the rear. The oil ring gap should go towards the valley of the engine... This is to keep it from unloading its oil down the cylinder wall at shutdown. If you have any questions about how to seal up the engine....Just ask there are a lot of people that will answer your questions.

 

Ok thanks for the info. My bad, by line up i ment put where the shop manual said to put the gaps. I got a used standard 3.995 piston from my storage unit at supper tonight it is also a mahle piston but the bottom side doesn't look the same. I got to get the two side by side now and really look at them.

 

After market pistons benefit from newer technology. Just use the same pistons.. Just clean and Install new rings....The last bore job is most likely better than the stock piston fit anyway....

 

Thanks for the info people. Ofter measuring and having them side by side they appear to be standard replacement .030 over pistons. I think i'll go with racer30 and clean them up and put knew rings on. Maybe I'll make a small build thread as i get a little farther along (type4 cam, banks wastegated sidewinder, headstuds, Powerstroke intercooler, ZF-5, Going in my 1978 F-250 supercab 4x4) Have all the parts gathered up got to start putting it all together