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Burning oil, low compression in #3 & hesitaion
Topic Started: Nov 18 2009, 03:52 PM (3,679 Views)
jmac
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I purchased my 92 LSi 1.0 last year knowing it burned oil (~quart per 700 mi.) and that it had somewhat low compression in #3 and a plugged EGR port. After purchase, I thoroughly cleaned the EGR port and valve and gave it a tune-up. I recently started to experiencing intermittent hesitation during acceleration. It will run great for weeks but, suddenly start hesitating--next day it may run just fine again.

The hesitation may or may not be related but, I'm pretty sure the head needs some attention.

Current miles: 117K

Compression (from 1 to 3)
dry: 202 199 125
wet: 215 225 137

On #3, the plug came out wet with oil and with substantial build-up around the electrode. I can also see that the #3 piston is wet with oil.

Seems like I may have a bad valve seal and possibly a bad valve.

I'm planning to yank the head and put in new seals and SS exhaust valves--following the JM head rebuild guide.

Is there anything from above that should lead me to consider a ring or piston problem?

I'd prefer to just leave the lower-end alone unless I see a problem after the head comes off.
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Dallas


well youll have to pull the head off and make the call then. could just be a burned up valve
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Johnny Mullet
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After the head is off, pour kerosene into the cylinders and check for leakdown.
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Coche Blanco
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Why do I have 190PSI or more compression, and have blowby?
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Johnny Mullet
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You can have good compression rings and bad oil rings.
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jmac
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I finally started my rebuild project. After pulling the head and inspecting the valves, I was surprised to find no apparent valve damage. The exhaust valve on the right (cyl. 3) is discoloured, "wet", and has added deposits as compared to the other exhaust valves (pic below). While the valve stem seal from the #3 exhaust valve did not look different from the others, I'm still thinking oil is leaking through that seal.

Question 1: Could carbon build-up on the exhaust valve cause a seating problem that results in the 125 psi compression it saw earlier?

I also performed a kerosene leak test on the cylinders (pic below). Here are the results as a measure loss in fluid level after 20 minutes.

Cylinder 1: 1/8" loss
Cylinder 2: negligible loss
Cylinder 3: 3/16" loss

Question 2: Do the results of my kerosene test indicate the need for new rings?


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Edited by jmac, Jan 22 2010, 08:41 AM.
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Johnny Mullet
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Replace the exhaust valves with Stainless Steel from 3Tech Performance. Do not re-use those exhaust valves. Link in my sig :thumb

There should technically be no leakdown after 20 minutes, so I would consider dropping the pan and removing/inspecting the pistons, hone, and re-ring them. You might as well since you are already there.
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jmac
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I do have the 3Tech SS valves.

I started pricing rings last night. Standard size rings when just honing, right--not oversized?
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Johnny Mullet
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Yes, standard size. Honing does not change the bore size.
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jmac
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Pistons are out and soaking. I should have new rings later today and reassembling by this evening. Based on visusal inspection, the connecting rod bearings look fine. Is there a measurement/tolerance stated in the shop manual (I don't have) that I can measure the bearing for adherence to?

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Edited by jmac, Jan 22 2010, 08:39 AM.
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Coche Blanco
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Johnny Mullet
Dec 28 2009, 12:37 PM
Yes, standard size. Honing does not change the bore size.
Correct me if i'm wrong, but don't you "bore" and engine .037 over and hone the remaining .003?
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Rooy


Yes, when a machine shop bores a cylinder oversize, the final sizing is done on a honing machine. Not a hand DIY hone.

When honing during a re-ring, all you want to do is remove the glaze and put a cross-hatch into it, not remove any material.
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Coche Blanco
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Rooy
Dec 29 2009, 03:35 PM
Yes, when a machine shop bores a cylinder oversize, the final sizing is done on a honing machine. Not a hand DIY hone.

When honing during a re-ring, all you want to do is remove the glaze and put a cross-hatch into it, not remove any material.
k, gotcha.
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Dugger
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When I look at your 3rd picture of the piston/rings I notice that #1 ring and the oil rings/spacer(#3 ring) don't look right, assuming you didn;t adjust/move them. According to my Metro manual the oil ring rail end gaps are suppsed to be at 90 degrees to the #1 ring end gap one clockwise and 1 90 degees counter clock wise. The picture shows your oil ring rail end gaps barely 45 degrees from each other and not the proper 180 degrees.

Another thing I notice is that conn rod end bearing looks in real good condtion.Is it possible this car had a rebuild already?

When I did my G10 motor my conn rod end bearings showed a lot more wear.The clyinders looked good with no signs of scoring and the end gaps were all in the proper location. I did JM's ghetto leakdown test on the head & block. I did find #3 was leaking a lot more than the others. The head seemed ok but I went ahead and relapped the valves and cleaned the head up myself.I did not hone the cylinders. I just installed new rings with new conn rod bearings. That was about 2 months ago and so far so good. The compression after about 1K mi has risen to 180 in all 3.The oil consuption is neglegible. This was my 1st time re/re a head myself with new valve stem seals. The hardest part is removing the damn keepers without losing them.

Take your time , keep track of all the parts and make sure everything is clean.

GL :cheers keep us up to date
Edited by Dugger, Dec 30 2009, 12:08 AM.
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jmac
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I did not intentionally rotate the rings in that picture but, they could have moved inadvertently. To my knowledge, this engine has not been rebuilt. I purchased the vehicle from the original owner with ~102K (single odometer turnover per previous owner) miles. I'll follow your 90 degree manual page guidance upon new ring install.

I received my new rings last night. They are Beck Arnely 013-8170, standard size rings. Visually, the new ring profile looked narrower than the rings I removed. So, I decided to take a few measurements comparing the top compression ring from the #2 piston:

Old top ring
O.D. = 3.013"
Width = 0.111"
Thickness = 0.0455"

New top ring
O.D. = 3.023"
Width = 0.102"
Thickness = 0.0455"

I'm surprised to find that the new ring is so much narrower. Maybe replacement rings are designed to accommodate carbon build-up in the grove of an old piston? Old ring is really an oversized ring?
Edited by jmac, Jan 22 2010, 08:35 AM.
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