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O-ring Gap

793 Views 7 Replies 5 Participants Last post by  andylarry
Hello Guys,

So I bought my 67 Giulia Super 1600 with an engine that hasn't run for god knows how many years. The engine wasn't seized or anything, and I was able to fire the engine right away. Then I did a compression test and it showed very low and inconsistent results (90, 90, 75, 120). Then I performed a leak down test and all four cylinders had a leak coming from the oil filler cap, dipstick, etc... So I suspected that I have an O-ring issue so I took the engine out and disassembled it to inspect the problem. I found a radiator mixed with oil between the liners, also the oil on the oil pan had greenish fluid with it which is obviously coolant (hopefully a head gasket problem).

I took the pistons out to measure the o-ring fitted in. The specs for all rings should be between .0118 - .0177. I did the measurements using a feeler gauge, and it was way out of specs.
Here are the results (I only did the top two rings)
Cylinder 1: Top ring: .018
Second ring: .25

Cylinder 2: Top ring: .020
Second ring: .022

Cylinder 3: Top ring: .016
Second ring: .026

Cylinder 4: Top ring: .020
Second ring: .021

I couldn't do the piston-to-wall clearance because I didn't have the appropriate micrometer. Now, I'm not sure what should I do to resolve the issue. Can I just get a new set of piston rings and that would solve the issue? or do I need new liners since the rings did scrape them? Are there any more measurements I need to do to be certain of what I need to change?

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I am sure someone will have more to say but the numbers you show look like ring end gap with the ring in the cylinder at some distance from the top, IIRC 10mm from the top a 0.020" end gap is in spec.
But they could have been overheated and lost their tension.
Check the head for flatness and cylinders should be a couple of thousandths above the block.
Fresh rings and bearings if the cylinders are not scored or have a massive ridge might be all needed.
PS don't break the seal at the bottom of the cylinder to block.
I would remove the liners and hone them with a flex hone (and a scraper hone first if you can feel a step near the top of the liner). Thoroughly clean the liners after honing. Buy a new set of Hastings rings - measure yours for thickness and depth and call the factory. They will sell you the right ones. Gap them according to your engine specs. Replace the very thin O rings that seal the liners to the block. Lube the liners and rings with WD40. Use a good quality head gasket in the rebuild.
Others will no doubt add more details and special tips.
Ok, here are some pictures of the 4 pistons, I don't have the appropriate equipment to do the measurements. So please excuse my ignorance and help me inspect the pistons visually. I'm not sure if the inconsistent wear is an indication of an issue or not. But is it obvious from the pictures that I might need new pistons and liners?

Automotive piston Auto part Piston ring Automotive engine part
Mason jar Auto part Metal Tableware Piston ring
Automotive piston Mason jar Piston ring Auto part Automotive engine part
Auto part Automotive engine part Cylinder Metal
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Get at least a feeler gauge.
Get at least a feeler gauge.
I was going to do it but I'm not sure if it will get me reliable results or not. I was also concerned about the wear on the pistons if it can indicate anything.
Pretty typical wear, though the angular wear on #2 is unusual. You'll always find minor scraping/galling on the thrust side of the piston. Yes, rings have both a gap to measure, and vertical clearance in the groove. To reuse pistons you want to make sure that gap isn't out of spec. Otherwise new rings, which have more friction, will pound heck out of the ring lands at a higher rate and start to pump more oil up, not less.
In general the cylinders wear more than the pistons. Pistons are not round but are oval. Cylinders are round.
Ring gaps, do what the manufacturer recommends. A slightly large gap is better than a slightly small one; if the engine gets very hot and the rings expand enough to close the gap, broken ring results.
The existing rings I'd guess are Borgo; one-piece oil ring. Modern three-piece oil rings are better.
You can purchase long feeler gauges online for less than $20 to measure the piston to liner clearance. Clean everything with hot soapy water, then lube with thin oil or WD40 for protection until reassembly.
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