My 4BD1T has had a bad run due solely to aftermarket parts.
Aftermarket valve seals which came loose, got hammered apart and went through the oil pump.
Aftermarket rings which weren't compatible with the chrome liners (27,000km and needed a full rebuild).
Aftermarket gasket set with seals that fall apart in the presence of oil.
An air cleaner that wasn't dust tight.
Rebuild with the genuine parts and you'll have no problems.
The problems in mine started when the previous owner (my father) got it balanced and rebuilt with cast iron liners.
The engine didn't need new liners, but the local engine recondition suggested it while we had it apart for balancing.
Cue the valve seals coming apart.
Rebuild #2, courtesy of the parts maker.
This is when I got it.
I find that blowby is excessive, pull apart the aircleaner and find nothing fits properly.
Make a new aircleaner which is less restrictive, the engine can now get a cylinders full of air and produces enough blowby to lose all it's engine oil in 800km.
A fantastic example of fixing one problem and finding another.
New rings were tried (one weekend insitu rebuild). But the results weren't good enough.
3 months later rebuild #3.
Buy a piston/ring/liner set and gasket set from a well respected engine parts supplier.
Pull engine, full rebuild back to chromard liners.
Engine takes a long time to bed in, the resulting blowby pushes oil out the seals. I find the seals have gone soft, being eaten by the oil they're supposed to keep in.
Engine is pulled several times over the next year, and both crank seals are replaced with genuine items.
1 year old from rebuild #3 and the engine finally frees up, feels like it's broken back in. Blowby hasn't improved, engine smokes a little at idle.
2 years on from rebuild #3, the blowby is getting worse, the engine is starting to use oil and blows blue smoke when cold.
I made the call to rebuild it, on the last trip before rebuild it used 2L of oil in a 200km drive.
Total 27.000km from rebuild #3.
Rebuild #4.
Genuine gasket set actually costs less than the problematic aftermarket one.
I pick up an unused set of liners from a bus company, buy genuine rings but cannot buy genuine pistons seperately (only come as a matched piston/ring/liner set). Settled for aftermarket pistons.
Rebuild engine insitu, notice genuine ring set has about 1/3 of the friction of the aftermarket ones I just pulled.
Head valve guides and seals were also done (but not by me).
Start up the engine after the rebuild, within 1 minute the exhaust is clear enough to see right up. Despite the oil that was poured onto the pistons and down the bore during assembly.
Blowby is minimal, fuel economy improves by approx 20%.
Truck has done about 8,000km since rebuild #4, I've currently got the engine back out for a gearbox swap.
Often you can get away with using aftermarket parts in an engine. But for these I'd never stray from the genuine rings and gasket set.
I used aftermarket pistons solely due to getting a deal on liners and not being able to buy the genuine pistons. Aftermarkets are visually identical but I don't think I'd do it again.