253 V8 rebuild
In 2004, I acquired a 253 V8 engine block that was cast on 26 September 1972 with an engine number very close to that of my original engine. My original engine may have even been cast on the same day!! The replacement engine was acquired “just in case” I ever wanted to take the car back to its factory drive train configuration.
In December 2016, I decided to rebuild the 253 V8 and an M21 with the aim taking my GTS back to its original factory configuration. The engine was machined by Blackburn Crankshaft Rebuilders (as was my LS 350 engine). I did not realise that 253 V8 engine parts are becoming hard to obtain – even though the engine had its original bore, the smallest oversize piston obtainable was 30 thou oversize. Heads and block were first crack tested – all ok. The block was decked just enough to ensure flatness and squareness whilst maintaining visibility of the original engine number. The crankshaft was ground for 10 thou oversize bearings. The block tunnels were line bored. The orginal crank rods were re-sized to fit the re-ground crank. The heads were prepared for unleaded, 91 octane fuel. New inlet and exhaust valves were used. A near standard profile camshaft was installed, new lifters and the original rocker gear re-used because you just can’t get new or replacement rocker gear. The standard points distributor was used. The WW 2 barrel stromberg was rebuilt by MLP Carburettors. I would normally rebuild a carb but the throttle shaft was badly worn and needed to be replaced and the throttle body rebushed.
The finished engine. For more pictures of the engine rebuild click here.
Optioning an M21 “High Performance” 4 speed manual behind a 253 V8 was a very rarely chosen HQ option but combined nicely with the other options chosen including a 3.36 LSD and dual exhausts to provide a reasonable performance package on a seriously constrained budget.
Obtaining replacement M21 parts is becoming more difficult. I managed to source a NOS Holden cluster gear (part No. 2813487), NOS input gear (9930924), genuine holden NOS bearings and seals and aftermarket 2nd (2813490) and 3rd gears (2813492). I had the 2nd gear circlip slot on the mainshaft enlarged to take a thicker circlip. For more pictures of the M21 rebuild click here.