We recently had our 1992 3.0 EFI Toyota truck engine rebuilt - we live in a third-world country and bent a piston rod when the engine flooded (literally) crossing a river. Before the event the engine ran clean and burnt no oil. We replaced the piston rod with a used one - had the heads serviced and put new piston rings in. We have flushed the engine to remove any sludge and the PCV valve works…the compression is 160 +/- in all cylinders. We burn a quart per 120 miles - all of the spark plugs look the same so I don’t think it is one cylinder - black-dirty.
Any ideas? The rings were installed by the local mechanic but I don’t think he used a micrometer or prepped the cylinders at all…HELP!
One mistake that’s made when installing new piston rings is failing to clock the ring gaps. Clocking the ring gaps means to position each ring on the piston such where the gap of one ring doesn’t line up with the gap of another ring. If this isn’t done and the oil control ring gaps are aligned with the compression ring gaps this allows oil to easily pass past the compression rings and the engine burns a lot of oil.
“I don’t think he used a micrometer or prepped the cylinders at all”
I wholeheartedly agree with Tester, but this statement bothers me too. If cylinders aren’t properly honed prior to ring replacement, they stand a good chance of burning oil. They simply won’t “break in” properly. Honing creates a cross-hatch pattern of controlled “scratches” that allow the cylinder walls to retain a film of oil for the rings to slide down and also creates the opportunity for the walls to wear to match the passing rings. Honing is critical to proper break in.
Compression rings are designed to press against the walls when top loaded. Oil rings are more properlly called “wipers”, and they wipe the surface down and allow just enough film to lube the compression rings on their way by. Without honing, this won’t happen.
Normally I’d suggest that measuring the cylinders for wear would be critical too, but since you’re in a third world country and reboring probably isn’t an option anyway, i’ll skip this thought.
Thanks to both of you! I think we will have to pull the engine apart again and re-do to the bet of our resources…“the same mountainbike” - had to give away my fluroscent pink (custom spray paint job) Specialized stel-frame Stumpjumper whe we left…some good memories. Thanks again!
I agree with the same mountainbike, but if you don’t have access to a hone, you can use a fine grit sandpaper. I have done that in an emergency and it worked. But, before you teardown the engine, try lugging it a few times. If you have a manual transmission, put it in the highest gear at about 30 mph and floor it to about 50 mph (48kph to 80kph) and repeat a few times. It makes the rings scrape the cylinder walls and will sometimes get them to break in.
If you pull the pistons, you have to use new ones, but since they are new, you might get by with just sanding the edges of them. I knew a 15 yo kid that did that to an engine and it worked, but he did hone the cylinder walls.
The 160 compression is too low, especially on an engine with new rings. Odds are if you run a wet compression test that number will jump up quite a bit. That would be a piston ring issue, or plural.
There’s a lot of reasons why the rings aren’t sealing. Lousy hone job (or no hone at all), egged or tapered cylinders, scored cylinders, poor piston ring fit, or even installing the rings upside down on the pistons. (Yes, many piston rings are a one way fit and if one is not aware of any subtle hint as to why they are proprietary it would be very easy to install them incorrectly.)
A number of years back, a friend who was a heavy diesel mechanic, often stated how he would “fix” an overhaul where the rings didn’t seat. His “fix” was to throw a handful of Bon Ami into the air intake while the engine was revved up. He said you could even hear the rings seating-in. After an oil change, all was good to go.
I certainly wouldn’t recommend this approach, but has anyone heard of doing this?
The BonAmi fix was used by Chevrolet dealers in the 50s to improve compression and reduce oil consumption but this Toyota sounds like it needs close inspection. And I am curious as to how the piston and rod were damaged. Did the damage occur when the starter was used to attempt to start the engine or was there an attempt to push or tow the vehicle to start it?
Yeah the guys make good points as usual. I think I am a bit worried about your sort of Cavalier attitude to “Rebuilding” the engine.
Its fine to use a Used Con Rod…but there are so many things that you need to have correct when doing a rebuild like this. Did you number the pistons upon teardown…Did they go back into their HOME locations? Did you CLOCK THE NEW RINGS? on every piston? Did you reuse the original piston from the bent Con Rod? Did you MAKE SURE to install the rings with TOP SIDE TOP? Rings are actually tapered…if you install them upside down they will actually PUMP oil up above the top of the pistons…and then burn the oil. You also need to rough up the cylinder walls to allow NEW rings to bed in. You would have had much better luck using the old rings…but I understand why you installed new. They just have to be done correctly…this is where I think you went astray. I highly doubt this can be corrected now until the engine is torn down again and ALL of these points given attention
Thanks for all of the insights we will have to tear the engine down to rework the pistons and rings…Was hoping for a “simple” solution (although I expected that was a dream). Everything sounds so easy and simple - but when you live in a place were oxcarts are common and most people have dirt floors, no electricity or water - the simple thing like finding a new/used part is a challenge.
But I wouldn’t change a thing! Thanks again to everyone!