Low compression

Tiny
NATEROHMAN
  • MEMBER
  • 2002 TOYOTA COROLLA
  • 1.8L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 110,000 MILES
I replaced the piston rings and installed new ones correctly. Upon reassembly I checked to make sure timing was aligned. I am getting spark fuel but no compression over 100 psi. When cylinder head was off it seemed like it had or would have rather very strong compression because while cranking over motor with a ratchet all cylinders would suck my hand down hard when I covered the cylinder with my hand. I have actually checked everything five times; now the first two times revealed leaky valves so I lapped them in and that took care of that problem. Now all I hear is mostly blow by going down not being held by rings and I clocked the rings like they do with race car engines. Marks all line up everything is right except compression. When I said the first two times revealed leaky valves it was with two separate cylinder heads I couldn't get the valves to seat properly on the first head. So I bought a head from the wrecking yard out of a 2006 Corolla and those valves seated better than I thought they would after a thorough lapping job.
Tuesday, June 2nd, 2020 AT 6:17 AM

5 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good morning,

Do you mean you did not stagger the compression ring end gaps when you installed the rings? If you did, that is incorrect. They need to be staggered.

Did you air up each cylinder and look for air leaks? Common spots are the intake manifold, exhaust system, oil fill cap, and radiator.

I would start there.

How did you align the marks for timing?

Roy
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Tuesday, June 2nd, 2020 AT 9:04 AM
Tiny
NATEROHMAN
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  • 6 POSTS
Well by staggered I would say that as they do in race cars I staggered the rings at 12 o'clock for the top and 6 o'clock for the second and the same for the two oil rings that are above and below the oilier; and as for the timing I set the crank with key up on the mark with yellow colored link on its mark on crankshaft gear on the right side looking at engine and the two marks on cam gears level with cylinder head and two yellow marks roughly 11 and 1 o'clock with exactly 8 links separating them as far as I could tell it was spot on. I'm not sure if I had to but I even unlocked the intake cam gear and re set it as if it was a fresh install and that did or did not have any effect at all not sure because engine will not start the only spec I could not check at the time was the bore measurement but all other specs were within service limits. So I kinda just figured it was going to be good and this is the first time I haven't been able to get something running since like I was a kid. I'm thoroughly baffled oh and I was paying attention to hear for compression leaks as I cranked the motor over by hand because of my earlier episode with leaky valves but I did not hear a leak in intake or exhaust side however I did not air up the cylinders as you described.
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Tuesday, June 2nd, 2020 AT 4:10 PM
Tiny
ASEMASTER6371
  • MECHANIC
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Okay, did you air test the cylinders and check for leaks?

Roy
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Tuesday, June 2nd, 2020 AT 4:14 PM
Tiny
NATEROHMAN
  • MEMBER
  • 6 POSTS
So I just went ahead and disassembled so that I could check the bore which coincidentally is the one thing I didn't check and the problem slapped me right in the face. It's way out of spec for service the book says 3.1102 to 3.1107 and my measurement at the top was 79.9mm which is equivalent to 3.1456 inches. So it only gets worse down in the middle of the bore where the actual measurement is supposed to be taken. And from here on out I will just save myself a lot of work and time by checking everything right the first time, but I think I needed to just unload it for a sec to get clear again. So thanks for being there I guess. Take care.
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Wednesday, June 3rd, 2020 AT 12:24 AM
Tiny
ASEMASTER6371
  • MECHANIC
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You are welcome.

Always glad to help.

If you would have done the air test as I suggested, you would have found excessive air leaking into the crankcase indicating piston or cylinder damage.

Roy
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Wednesday, June 3rd, 2020 AT 3:59 AM

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