KM intervals for changing of piston and rings on original engine.

think itsa a chain on this engine but cannot remember as i work on so many different cars ,if its a chain then leave it alone unless its noisey .

Three sizes of pistons are available:
1. Std.
2. Over size 0.010 in (0.25 mm).
3. Over size 0.020 in (0.50 mm).
Over sized pistons and rings are widely used in all automobiles with no trouble at all. They last for more than 200,000 km, provided if the engine oil, oil filter and air filters are replaced at the recommended intervals.
The most important point to consider here is to maintain the oil clearances between the various parts during the machining process.
For example piston to cylinder clearance, crankshaft to main journals and big ends clearance, valve to guide clearance, at room temperature. Then comes cleaning process and the engine assembling process.

Oil change intervals for motorcycles depend a great deal on your riding conditions and riding style. For lower-revving street bikes, I often change my oil about every 2000 miles (~3200 km). However, someone with a sport bike who regularly revs their engine closer to the redline, I would suggest a more frequent change interval. Off-road / dirt bikes should have their oil changed sooner because of the dusty conditions. The oil is still full of lubricants, but it is contaminated with dust and dirt that clogs the filter and eventually goes right into the engine, increasing wear. I can't offer much guidance for dirt bike oil change intervals.

60,000 miles is the typical recommended interval for timing belt replacement. The belt can become worn and skip a tooth or even break. In that event, the pistons can collide with the valves and cause a considerable (and expensive) amount of damage. Changing the timing belt at recommended intervals is good insurance to protect against valvetrain and piston damage due to belt failure.

Have a compression test run on the engine.

In my view if you are burning this much oil and the plugs are fouling then the piston rings are quite worn and need to be replaced. If this is a high mileage 88 model running on the original engine you must expect this kind of wear especially if the engine oil has not been replaced at optimum intervals during the vehicle's life. Typically owners do not change the engine oil in their vehicles often enough for the type of driving they do.

The required engine work (or rebuilt engine change over) will be expensive. If you have an average vehicle its low retail market value (and very low dealer trade in value) would mean you are much better off spending the money on a newer replacement vehicle in much better condition.

The transmission consists chain sprocket assembly, with the smaller sprocket on the engine & a larger one at the rear wheel. The chain stretches and the sprocket teeh keeps getting worn whenever you accellerate or use the engine as a brake to slow down. This play can increase up to 2 inch,. thus on lower gear, higher mechanical advantage, looses since the sprocket of the engine transfers power after that play/gap/time required to tranfer the same power to the rear sprocket result of metal on metal hammer.
Tighten chain at regular intervals and change the chain sprocket if its still the original one. If the bike runs 50+ km in a day and/or at high speed, change the engine oil every 500 to 750 km running i.e. once a month. Whichever comes first. The oil becomes darker & looses it's viscocity(thin). Also after covering so many kms, if the engine oil had been low for that period & running at a good speed you might require a change of piston rings( 1 oversize) and then filed to fit without jamming the piston.........sodeep

If you changed rings and valve gaides before you fitted new rings have you check cylinder block?it mybe cylider worn out so it was to rebore engine block and put new piston with new rings.
the ather thing it hapen sometimes when you fitting piston rings, check how piston rings is it should be all piston rings defrent direction inside the piston groves.
Use original parts.

You should be able to ask the Subaru Dealership politely if this calculation exceeds the recommended interval by Subaru.

If it does exceed their recommendation. Your engine's piston rings are probably worn out, or possibly a blown head-gasket to an oil passage.