Clacking On Starting *Update* Compression Test

[Devin]

I just got home from a 3,000+ mile road trip out to California in my Tercel. The last 600 miles or so, the engine would clack for the first minute or so after startup. Once it got some heat going it would go away. Even stopping for gas it would a bit but less than a cold start. I pulled each spark plug wire and none of them stop the clacking. It doesn't sound like valve train either. It's more to the left and down. Like water pump area. Definitely up front and not the fuel pump.
Maybe exhaust leak? But I've always had exhaust leaks get worse with heat.
Any thoughts?

[dlb]

sounds like piston slap. that means the rings are worn a little bit and allow lateral play of the pistons when the engine is cold. once it warms up and everything expands and tightens up a bit, the slap goes away. i think the best test for this would be to do a compression test when the engine is stone cold, and again after it has warmed up.

i know you said it doesn't sound like the valve train but you could still check the valve lash just to rule that out, too.

[Devin]

I will check the valve lash. What is the clearance for intake and exhaust?
I thought that piston slap would stop if the spark plug wire was pulled for that cylinder? I pulled each wire and none of them stopped the clacking.

[dlb]

i can't remember the valve lash clearances offhand but they're in the FSM in the tune up or maintenance section.

i don't think pulling the spark plug wire would stop piston slap since the piston would still be rattling around as it goes up and down. the issue in piston slap is too much clearance between the rings and cylinder wall, and that would be present regardless of whether or not there is spark or combustion.

[marlinh]

Piston slap is clearance between the piston and cylinder wall. Pulling the wire would change the sound in that cylinder because you don't have combustion pressures on that piston.

[dlb]

eep, my bad. sorry for the misinformation.

i was just looking this up more and it sounds like pulling the plug wire will reduce the slapping sound but not eliminate it, so when you pull the plug does the sound change at all?

[irowiki]

You might try the old ear to long screwdriver over each piston trick as you disconnect each spark plug to check if it changes at all.

[Petros]

try removing both the power steering belt and the alternator belt and run it for about 30 sec to a min max, just to listen for the noise. there will be no coolant circulating, but this is a simple test, if the problem is in the power steering pump, water pump or alternator, you will find out this way.

Also check the valve clearance at the rockers. if one came loose and it has a lot of clearance it will act this way, and pulling a spark plug will not stop the clacking. possible even a broke valve spring, but not likely. I have had an adjuster come loose and the valve clearance opened up to a 1/4" or so, sounded really bad. easy fix and no harm done.

[Devin]

Finally got some time to wrench on the Tercel. I took off the two belts like you said Petros and ran it for 30 secs or so. No change in clack.
Took off the valve cover and checked out the valve clearances, nothing out of the ordinary.
I fiddled around more removing spark plug wires and removing the number one wire definitely stops the sound. So I'm thinking piston slap, but check out these compression test numbers.
Cold: Cold with oil: Hot: Hot with oil:
1) 120 1) 135 1) 115 1) 115
2) 120 2) 130 2) 90 2) 105
3) 95 3) 110 3) 100 3) 110
4)122 4) 130 4) 105 4) 110

Weird because the sound definitely is from #1 not #3. You guys know what these compression numbers say more than I do. Any thoughts?

[dlb]

i don't know how good my advice to do cold/hot compression tests was. i misunderstood the cause of piston slap so i'm not sure how much use the cold #s actually are. sorry about that. usually, compression tests are done once the engine is warm.

that being said, those #s don't look good. new, these engines should be around 180 psi so considering how low those #s are and the likely piston slap you have, it looks like it's time for a rebuild.

did you make sure to have the battery fully charged, all the spark plugs removed, throttle wide open, and crank the engine the same # of times for each cylinder? those are all very important to accurate readings.

[Devin]

Oh snap, wide open throttle? I missed that part. Should I do it again?

[Devin]

Ok new numbers. I redid the test with the engine hot, spark plugs out, wide open throttle , cranked it 8 times each and had someone watching the gauge, so I think these are the good numbers:
115 psi across the board with no oil. 120 psi on #1 and #4 with oil. 125 psi on #2 and #3 with oil.
I guess now I'm just wondering how long I should drive this motor. Are the numbers really low for 230,000 miles?

[dlb]

yes, those are at the bottom end of the scale. you can definitely still drive it for a while but it's time to either start looking for a known good engine, or a bad one that you can rebuild at your leisure and throw in when your current one kicks the bucket.

[rer233]

Devin-

You might want to see if the crankshaft pulley bolt is tight (the 17 or 19 mm one in the center of the crankshaft.) Years ago i was given a 2wd wagon by a former GF (long story-not going into it here.) Anyway, the engine had a loud knock that sounded just like a rod knock. Also the spark timing was all over the place. Turned out the c/s bolt had worked loose and allowed the pulley to move back and forth radially with respect to the crankshaft. I wound up replacing the pulley, crank timing gear and woodruff key with "new" used parts (the keyway in the crankshaft was a little boogered-up to, but i smeared loctite on everything and put it back together.) 50k later that engine's still running strong and is currently in my work beater.


Good luck- hope this helps!

[Petros]

The compression numbers are low indicating worn rings and cylinder walls, but it will not harm it to drive it. It just means it will be down on power a bit. Use an oil additive that thickens the oil like STP and that will reduced the piston slap (if indeed that is what it is). I have also had good luck with "Restore" (best used on a long drive), make sure you shake it up good to get the stuff that settle on the bottom back in suspension before you add it. As long as you keep the slap down, it will run fine. continuing to run with noticeable slap will fatigue the piston skirt and have it fail, usually rendering the engine unusable (even if still running). So you may have some time before that happens, but it can fail at any time (I have had it happen on old tercel engines twice, and seen it on other engines). Or it might run that way for another 50k miles (espically if you keep oil thickening additives in it), you just do not know.

The engine needs to be over-bored and new over-sized pistons and rings installed, while you are at you can have the head rebuilt with new exhaust valves, recut valves seats and new valve stem seals. Or you can look for a low mile engine, if you can find one, and swap it out. You might consider finding a 4ac engine in a wrecking yard, take your time rebuilding it over the winter, and than swap it out over a weekend.

Good luck.