5 ms·

"Since cylinder bores are bored exactly parallel to each other and at exact right angles to the cylinder head surface, multimachine accuracy begins at the facto

"Since cylinder bores are bored exactly parallel to each other and at exact right angles to the cylinder head surface, multimachine accuracy begins at the factory where the engine block was built." My understanding is that this isn't entirely right. The block deforms under the combination of temperature and head bolt tension when fully assembled and in operation, and this is taken into consideration when machining the block. When cylinders are re-bored there's supposed to at least be a mock head attached and fully torqued to spec to ensure correct results when assembled.

serf 8y ago
>When cylinders are re-bored there's supposed to at least be a mock head attached and fully torqued to spec to ensure correct results when assembled. that's not usually true, and it'd be pretty difficult to achieve without a different jig for every engine. When I spent time in the engine shop, we used a mag-table/mag-chuck for steel parts, and we used table vices/clamps for the rest of it. We would start with inspection and disassembly, move on to parts-holding, and then finally we'd bore/hone/surface, in that order. There is a 'mock head' installed in that the piece is being held to the work surface, but other than that it's not typical to add more structure when machining -- it makes things much more difficult to move around. For (very) high performance engines, some manufacturing processes require the engine to wear an external girdle before finish; but it's not too common elsewhere or in the aftermarket world. For flow-benching head I've have seen the head bolted down like you're talking about, but for that they're trying to approximate an engine's flow.
- newnewpdro 8y ago
  Are Cummins B series diesel engines considered "very high performance" [1]? While use of the torque plate in re-boring is apparently more optional than I thought, the point stands; these things aren't ncessarily square when unassembled and the original manufacturer of warrantied engines is going to take distortion into consideration when machining the new parts. On an unrelated note; EVs can't take over fast enough, good riddance of all this archaic ICE junk. [1] http://www.engineprofessional.com/TB/TB031516-2.pdf http://www.engineprofessional.com/TB/TB031516-2.pdf
- justtopost 8y ago
  I have rebuilt tons of engines. Reboring requires torque fixtures. Period.
paddy_m 8y ago
From what I can see the largest source of inaccuracy with this machine would be in the bed rails. Angle iron has wild tolerances. Still impressive work, more than I can do.

serf 8y ago

>When cylinders are re-bored there's supposed to at least be a mock head attached and fully torqued to spec to ensure correct results when assembled. that's not usually true, and it'd be pretty difficult to achieve without a different jig for every engine. When I spent time in the engine shop, we used a mag-table/mag-chuck for steel parts, and we used table vices/clamps for the rest of it. We would start with inspection and disassembly, move on to parts-holding, and then finally we'd bore/hone/surface, in that order. There is a 'mock head' installed in that the piece is being held to the work surface, but other than that it's not typical to add more structure when machining -- it makes things much more difficult to move around. For (very) high performance engines, some manufacturing processes require the engine to wear an external girdle before finish; but it's not too common elsewhere or in the aftermarket world. For flow-benching head I've have seen the head bolted down like you're talking about, but for that they're trying to approximate an engine's flow.

newnewpdro 8y ago
Are Cummins B series diesel engines considered "very high performance" [1]? While use of the torque plate in re-boring is apparently more optional than I thought, the point stands; these things aren't ncessarily square when unassembled and the original manufacturer of warrantied engines is going to take distortion into consideration when machining the new parts. On an unrelated note; EVs can't take over fast enough, good riddance of all this archaic ICE junk. [1] http://www.engineprofessional.com/TB/TB031516-2.pdf http://www.engineprofessional.com/TB/TB031516-2.pdf
justtopost 8y ago
I have rebuilt tons of engines. Reboring requires torque fixtures. Period.

paddy_m 8y ago

From what I can see the largest source of inaccuracy with this machine would be in the bed rails. Angle iron has wild tolerances. Still impressive work, more than I can do.