Post by enigmas on Oct 17, 2016 10:01:17 GMT
For the Tech heads:
I've been wanting to build up a spare P76 engine for some time now. I've also been collecting parts for a number of years. The block needed some repairs and this was done expertly by 'Crankshaft Rebuilders' several years ago. The centre bearing support and its integral thrust face seatings was damaged. Some fettler had also shimmed the bearing insert. The bores were in good condition and I had a stock of second hand pistons (about 16) from which I selected 8 and matched them for weight and size. I'd also during my scavenging, managed to locate a .020" oversize new set (specially cast non Factory) from an ex racer who had them in a stash.
The gist of all this, is that I decided to stay with the standard bores for several reasons. The primary reason, is that the matched set of second hand (Factory) pistons provide an exact 9:1 compression ratio. Most aftermarket/speciality or Rover pistons don't when used in a P76 engine. There's several other options (including early OZ Holden pistons) but most require modification to some major components, e.g. Crankshaft.
The OEM P76 pistons were often found with cracked skirts. The causes were usually down to detonation and engine knock from erratic ignition timing. A Leyland P76 points distributor can produce firing variations of over 6 degrees. Not exactly accurate! (If your Rover still runs a points distributor and you can rock the points cam back and forth with hand pressure...that's bad news.)
The set of pistons I chose were deburred, sharp edges radiused, top ring land machined for custom rings, matched for weight and then sent off to HPC Coatings in Leongatha, a country town in Victoria. A 3hr return trip.
Two coatings were applied. A full skirt coating (blue) in colour, and a piston crown coating. The skirt coat can build the piston diameter up to either .001" or .003". It's also a super slippery coating used for race engines (and turbo/supercharged engines)
The second coating on the piston top both contains the heat of combustion in the chamber and resists/rejects carbon build-up. The cost is $35 - $38 per piston. I intend to build the engine up on a purpose built stand, complete with radiator, mufflers, gauges and pushbutton starter.
NB. The dark spots on the piston crown are my thumb prints...from handling the old damaged piston beside the reconditioned one.
I've been wanting to build up a spare P76 engine for some time now. I've also been collecting parts for a number of years. The block needed some repairs and this was done expertly by 'Crankshaft Rebuilders' several years ago. The centre bearing support and its integral thrust face seatings was damaged. Some fettler had also shimmed the bearing insert. The bores were in good condition and I had a stock of second hand pistons (about 16) from which I selected 8 and matched them for weight and size. I'd also during my scavenging, managed to locate a .020" oversize new set (specially cast non Factory) from an ex racer who had them in a stash.
The gist of all this, is that I decided to stay with the standard bores for several reasons. The primary reason, is that the matched set of second hand (Factory) pistons provide an exact 9:1 compression ratio. Most aftermarket/speciality or Rover pistons don't when used in a P76 engine. There's several other options (including early OZ Holden pistons) but most require modification to some major components, e.g. Crankshaft.
The OEM P76 pistons were often found with cracked skirts. The causes were usually down to detonation and engine knock from erratic ignition timing. A Leyland P76 points distributor can produce firing variations of over 6 degrees. Not exactly accurate! (If your Rover still runs a points distributor and you can rock the points cam back and forth with hand pressure...that's bad news.)
The set of pistons I chose were deburred, sharp edges radiused, top ring land machined for custom rings, matched for weight and then sent off to HPC Coatings in Leongatha, a country town in Victoria. A 3hr return trip.
Two coatings were applied. A full skirt coating (blue) in colour, and a piston crown coating. The skirt coat can build the piston diameter up to either .001" or .003". It's also a super slippery coating used for race engines (and turbo/supercharged engines)
The second coating on the piston top both contains the heat of combustion in the chamber and resists/rejects carbon build-up. The cost is $35 - $38 per piston. I intend to build the engine up on a purpose built stand, complete with radiator, mufflers, gauges and pushbutton starter.
NB. The dark spots on the piston crown are my thumb prints...from handling the old damaged piston beside the reconditioned one.
