When I was prepping my 1HZ for a lap of Australia — including some of the most remote and longest tracks in the country — I decided to go overboard on preventative maintenance. My thinking was simple: spend the time and money now so I wouldn’t be stranded in the middle of nowhere later.
One thing I was unsure about was Big End Bearings (BEB).
If you search online (and on IH8MUD), you’ll find tons of info about BEBs on the 1HD series engines, with many owners replacing them as a known wear item. But for the 1HZ — especially naturally aspirated, unmodified ones — the data is far less available. From my ignorant understanding, the 1HD and 1HZ share a lot of the same bottom-end design, so I assumed the wear patterns might be similar.
My situation:
Problem:
There wasn’t much first-hand info on BEB wear in high-kilometre 1HZ engines — just scattered anecdotes and workshop hearsay.
What I found:
When I pulled mine apart, the bearings looked almost new. There was a bit of visual wear on the top cap, but honestly, it looked more like what you’d expect after break-in — probably within the first 10,000km of the engine’s life. There was no copper showing, no scoring on the crank journals, and no signs of impending failure.
I plastigauged a few of the journals and found the OEM bearings to be sitting at 0.050mm of clearance, which is in spec.
I also plastigauged some of the new ACL bearings (Duraglide 780), and also came up with 0.050mm of clearance - which is in spec according to Toyota but not according to ACL (see data at end of post).
I ended up throwing in the ACL bearings because I had them, and I like the idea of "new". Part of me wishes I'd put the OEM Toyota bearings back in. I dunno.
After installing the ACL bearings I've noticed zero difference in oil pressures, according to the gauge on the dash (sits @ 2/3 mark when driving, 1/3 mark when idling.)
Takeaways for anyone else wondering:
Various Data:
If you're going to buy ACL bearings - don't get the "X-STD".The "X-STD" is not "standard" as you might imagine, but instead it is identical to the ".025" increased oil clearance bearing. Why have 2 different part numbers for the exact same product, I'll never know.
Hopefully this helps anyone else hunting for real-world info. I’ll attach clear photos of my 500,000km bearings below so you can see for yourself.
One thing I was unsure about was Big End Bearings (BEB).
If you search online (and on IH8MUD), you’ll find tons of info about BEBs on the 1HD series engines, with many owners replacing them as a known wear item. But for the 1HZ — especially naturally aspirated, unmodified ones — the data is far less available. From my ignorant understanding, the 1HD and 1HZ share a lot of the same bottom-end design, so I assumed the wear patterns might be similar.
My situation:
- Engine: 1HZ
- Configuration: Naturally aspirated (non-turbo), never modified
- Odometer: Over 500,000km
- Maintenance style: Oil & filter changes done every 5,000km with quality fluids - but I bought the car @400,000km with no idea of history.
- Usage: Mostly touring, no towing
Problem:
There wasn’t much first-hand info on BEB wear in high-kilometre 1HZ engines — just scattered anecdotes and workshop hearsay.
What I found:
When I pulled mine apart, the bearings looked almost new. There was a bit of visual wear on the top cap, but honestly, it looked more like what you’d expect after break-in — probably within the first 10,000km of the engine’s life. There was no copper showing, no scoring on the crank journals, and no signs of impending failure.
I plastigauged a few of the journals and found the OEM bearings to be sitting at 0.050mm of clearance, which is in spec.
I also plastigauged some of the new ACL bearings (Duraglide 780), and also came up with 0.050mm of clearance - which is in spec according to Toyota but not according to ACL (see data at end of post).
I ended up throwing in the ACL bearings because I had them, and I like the idea of "new". Part of me wishes I'd put the OEM Toyota bearings back in. I dunno.
After installing the ACL bearings I've noticed zero difference in oil pressures, according to the gauge on the dash (sits @ 2/3 mark when driving, 1/3 mark when idling.)
Takeaways for anyone else wondering:
- 1HZ BEBs are seriously tough if the engine has been looked after.
- Service history trumps kilometres — mine were fine after 500,000km of good care.
- Replacement is still cheap insurance, especially before long remote trips.
- There’s no clear evidence of widespread BEB failures in stock, well-maintained 1HZs like there is with the 1HD series.
Various Data:
If you're going to buy ACL bearings - don't get the "X-STD".The "X-STD" is not "standard" as you might imagine, but instead it is identical to the ".025" increased oil clearance bearing. Why have 2 different part numbers for the exact same product, I'll never know.
Recommended Oil Clearances
Toyota Factory Spec:- Clearance: 0.036-0.054mm
- Absolute service limit: 0.100mm
- ACL Formula: 0.020–0.025mm per 25mm of journal diameter + 0.013mm
- 1HZ conrod journal = 59mm diameter
- This gives: 0.060–0.072mm ACL recommended oil clearance
Hopefully this helps anyone else hunting for real-world info. I’ll attach clear photos of my 500,000km bearings below so you can see for yourself.
