One piston has a different letter stamped on the top, is this a problem???

[Brad S.]

Doing some cleaning on the passenger side of the engine, heads are still off but have been rebuilt.
I noticed that my no. 3 cylinder piston has a "B" stamped on the top of it with some other numbers.
All of the other pistons have "A" stamped on them.
To the best of my knowledge this engine has the factory pistons in yet.
Is this a problem or did they run out of letter A pistons and started using B's???
What do you guys think or have run into this.

 

[chris142]

The A,B and C corolates to the bore size. Not all bores are the same size and they needed a B piston to fit that hole. Its normal.

 

[icanfixall]

This is a common practice from th factory. Every cylinder is bored a differant size. Now don't go run off with just that statement from me. Heres what it means. A 7.3 bore is 4.10425" + or - 0.00025. Now knowing this when cylinders are bored they get close to that and then fit a piston thats close with the piston to cylinder clearances. The factory had 5 differant size pistons to fit the individual bores. It starts with the letter U. Then its B,A,C,D. Why it went in that order is a mystry to me but thats from my shop manual from international. Hers the sizes again from smallest to largest...
u 4.10325" +-0.00025
B 4.10375 +-0.00025
A 4.10425 +-0.00025
C 4.10475 +-0.00025
D 4.10525 +-0.00025
Want more demensions of the bore sizes. Guess what.. The rear cylinders on both banks are bore larger than the front 6 cylinders. The piston to cylinder clearances in 1 thru 6 is 0.0055 to 0.0085 and the rear two cylinder called 7 & 8 are 0.0060 to 0.0085. Not much of a differance and nobody bores like this any longer. It felt the reason for this is the slant the engine sits in the frame. Any CDR oil sucked into the intake manifold runs to the back two cylinders and is burned as extra heat producing fuel. So thats the news for today. Is all this needed... I don't think so . The demensions are in the one hundred thousands. Most can measure down to one thousands easily. down to a tenth of a thousands depends on the temp of your micrometer. Down to a hundred thousands depends on a climate controlled room. Your stock engine is just fine with those differant lettered pistons in it. Jag did this same thing in their V12 engines as does Rolls Royce. Custom fit a piston to a particular bore. Or spend the time on the bore machine doing it exact.. Well we all know the factory wont spend the money doing that...

 

[Brad S.]

Thanks guys, it looked like everything was still from the factory.(was hoping as much)
Just wanted some confirmation. Lotta good info here on the OB.

 

[Knuckledragger]

The engines were bored and honed by machine automatically. Even though the machines always followed programs, they did not always end up with the same hole size. U is the smallest undersized hole (get it? U is for undersize!) that would not require the block to go back for more honing to an acceptable size. A is nominal size, all the other designations just rotate around, like a head bolt torquing pattern.

 

[93 RHD]

I learn something every time im on here