Knocking Caused by Piston Experiences

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xirdneh
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My tercel:: 87 tercel 4x4 wagon w/reringed engine, 83 tercel 4x4 wagon w/salvaged engine and 4.1 Diff's
Location: seabeck, washington, USA

Knocking Caused by Piston Experiences

Post by xirdneh » Fri May 19, 2017 2:44 pm

I have had several Tercels that had a knock caused by a cracked or broken piston. All had over
200,000 miles on them.
Symptoms: cold engine knock that quiets or goes away when engine warms up. The knock is a mid tone pitch (not high not low).

In my experience it has always been #3 cylinder.
The piston will have a crack or pieces of the skirt will have fallen off. The one I am driving now only had wear patterns on the piston skirt that were not normal as compared to other three pistons. I installed a new piston and it still knocks but its mild and knock goes away quickly after engine warms up a bit. It’s been that way for two and a half years and it is not getting any worse.
Years ago I had another knocking Tercel that had a cracked piston. I drove it for six years before taking engine apart to find out what was going on. It never got any worse over that 6 year period.

Cylinder: On engines I have dissected, some cylinder walls were cracked or had obvious severe wear groove caused by broken piston while others showed little to no wear. I tossed the cracked and grooved blocks.

Recently a friend took his engine apart. It had been knocking when cold for years but eventually knocked all the time. His entire piston skirt had fallen off. He took the block to an auto machine shop to have the cylinders checked. They all checked out OK so he will be installing a new piston in #3 and new rings for the others. They charged $24.00 to check it.

Honing the cylinder glaze off: This has to be done or new piston rings will not seat and blue smoke will be billowing out your exhaust in a hundred miles or so. It also has to be done right or you will get the same result. The first engine I re-ringed failed cause I did it wrong
The scratch marks made by honing have to be at a 45 degree angle or more. It’s extremely important. The only way to get this pattern is by moving the hone up and down quickly while it is spinning in the cylinder. All the way down and all the way up the cylinder. I use three stone type honers and knife honing oil. I tried the ball type once and rings did not seat.
My friend recently did one but he did not go up and down at all and he was blowing blue smoke after 150 miles.

Replacing the piston: I recommend having a shop press the wrist pin in unless you have proper equipment. It’s easy to crack or ruin the piston.
Love those Tercell 4x4 wagons but they sure suffer from road noise.

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splatterdog
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Re: Knocking Caused by Piston Experiences

Post by splatterdog » Fri May 19, 2017 4:10 pm

Yep, I've noticed that almost always #3 is the troublemaker. Someday I will look inside T4 #1's engine. It made it over 400k, tired but still ran when "put out to pasture". And it fully defied Petros as it had over heated numerous times and survived, including an entire summer hot period due to rotted rad fins after I gave it away.

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Petros
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My tercel:: '84 Tercel4wd w/extensive mods
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Re: Knocking Caused by Piston Experiences

Post by Petros » Fri May 19, 2017 9:49 pm

I have seen this several times before, it is too much clearance in the bore. I learned this the hard way, the cause is piston slap. too much clearance in the bores allows the pistons to slap against the cylinder walls, eventually it fatigues the cast aluminum piston skirt and it break off. I was surprised when I lost almost half the skirt on the #3 piston and it was still running (though it smoked like crazy, allows the piston to rock back and fourth about 20 degrees in the bore).

The first 3ac I rebuilt had the annoying piston clap, I rebuilt it and also measured the bores, they were worn but within spec. so I thought if I just get new standard size pistons it will solve the problem, reducing the clearance slightly. No such luck, it had the annoying piston slap on star up. I was also disappointed that I did not get a little more power, the new rings sealed as good as the old ones, perhaps because the cylinders were slightly oval.

the new pistons failed because the skirt very quickly became fatigued. So I took the engine apart again, bought oversized pistons and had the block bored to match. the machine shop owner was very knowledgeable about such things, he said if there is any wear on the bore it should be over-bored. No point in doing a rebuild unless you replace the pistons, rings and over bore the cylinders. There is not that much tolerance to the piston clearance, he made sure all of them were right at the low end of the range, as I recall it is .002-.003' clearance between bore and piston skirt. That is all, no more no less. he also numbered each piston and honed each bore to exactly match the dia of each one of the pistons. that did the trick, and made it last several hundred thousand more miles with no slap.

now if I hear a car with that piston slap I put STP or some similar heavy additive in the motor oil, and expect to have to replace or rebuild, with new oversized pistons and rings. No other way to fix it, even if the bore is within spec.

The #3 wears the fastest I suspect because the way the oil flows through the galleys it reaches the #3 last, so it runs dry the longest on start up. That is always why the #3 connecting rod bearing is also the first one to go bad.

The best way to avoid this is to always run clean motor oil, frequent oil changes, and use the low fiction additives in the motor oil. Once you have piston slap, there is no fixing it without an major overhaul. It may last a while this way, but it can also fail in rather short order too.

There is a careful trick BTW to measuring the bore dia, it has to be measured at all depths and in all directions. the nature of the piston movement I suspect makes it wear in one spot faster, so measuring the top and bottom of the bore will not reveal the actual worn spot part way down.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

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