This is one of many threads associated to a Metro 1275 Engine that I have salvaged from a car that has been sitting around outside a barn for about 15 years. I am planning to refurbish the engine and have been doing lots of research and have obtained several quotes for machine work.
I managed to speak to another local machine shop yesterday, this guy has been around for ages and has done plenty of A series Engines. He was recommended to me by one of my other Mini acquaintances.
Following lots of peoples advice on here I am going for a rebore to 1293, which is stated as being +20.
Am I correct in my thinking that +20 means +20 thousandth of an Inch, written as 0.020 inches? And that these would be the correct pistons?
To help what is the bore diameter of:
On speaking to my machinist I said I am looking for a +20 Thou rebore to 1293 to which he replied that +20 was not 1293?? 1293 being more like 100 Thou?? Not sure if I asked or phrased the question incorrectly?
As I will be doing all of the build work myself I have confirmed the following plan with the machine shop:
After stripping everything apart from the Crank.
1. Rebore to 1293 - this will be done with pistons / rods removed but the crank still in place to avoid having to strip and refit (which will be done after the dry build).
2. Dry fit new pistons and measure piston to deck height.
3. Strip Crankshaft.
4. Hone bores and skim block face to deck the pistons.
5. Build short engine.
6. Refurb head (to include trimming Inlet Valve Guide Bosses and Valve Guide Bases).
7. Calculate chamber capacity to calculate CR.
8. Skim head as required to gain correct CR.
One of the bores has suffered some rusting as a result of coolant being left sitting in the bore, I cleaned it up with some W&D but I can still feel a roughish area (The pistons are still in and the crank rotates smoothly and any lubricant is forced out on the upstroke).
20 thousandth of an inch is 0.5mm and my concern is that a rebore to 1293 may not be sufficient (can't quite picture exactly what 0.5mm would look like on the bores) and so I guess I shouldn't order the pistons until after the rebore in case we need to take it out to 1310?
Thanks for taking the time and bearing with my dumb questions
Edited by JonnyAlpha, 05 March 2019 - 09:08 PM.