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| Engine rebuilt compression check, losing oil; 4000 miles lose of oil? | |
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| Tweet Topic Started: Feb 5 2013, 06:58 PM (771 Views) | |
| BrenBren | Feb 5 2013, 06:58 PM Post #1 |
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So i have been losing oil since i rebuild my 91 xfi engine(top to bottom), I now have right around 4000 miles on the engine after the rebuild. I just did a compression test (with throttle wide open and coil unplugged) i got the number 170/120/120. I know that 170 is ok but the 120's isnt good at all, but would that be my cause of losing oil? and bad mpg (35mpg)?. We just got standard rings (xfi pistons), should we have went with over sized rings to make up for the rings not being gapless? Or should i just wait another 1000 miles to make sure the engine is fully broken in? Just let me know what you guys think, i know im going to have to tare down the engine but what do i need? this is going to have to be a one day thing or should i wait for springbreak?(college student, commuter) |
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| mikeallen2112 | Feb 5 2013, 07:03 PM Post #2 |
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You replaced the rings too right? and lapped the valves? |
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| BrenBren | Feb 5 2013, 07:06 PM Post #3 |
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yea i replaced the rings, should i have kept the gapless rings? and i had a guy do my had top to bottom with new stainless steel exhaust valves and reg intake |
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| Deleted User | Feb 6 2013, 03:14 AM Post #4 |
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It sounds like a poor quality engine repair. Find another engine and get it ready to install. Your present engine will run for quite some time. You just won't be happy with it. GG |
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| BrenBren | Feb 6 2013, 10:42 AM Post #5 |
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Poor engine repair huh...find another engine and replace... or you won't be happy with it.. The question was..... As I said we could not get the rings that were GAPLESS, SHOULD we have gone OVERSIZED instead of standard to decrease the gap since there is only 1 ring? We did not check the the gap of the rings before we installed the pistons, just assumed (yeah I know) that the cylinders had not been bored and there would be no need need to worry about going up a size. Have 2 regular G10 engines in the Garage not in the mood to rebuild another one. Worse case we pull the head and rering with the original gapless rings or oversize and move on... Damn Geo Glenn kinda crappy response to a simple question.... |
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| Old Man | Feb 6 2013, 11:16 AM Post #6 |
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Not what you wanted to hear huh? GG aint here to make you feel good, just to give you correct information. You probably wont want this info either but I will try to get thru to you anyway........ You didnt say if you checked your bore for taper, roundness, and clearance during your rebuild. I am betting that you didnt. You probably need to get a set of .020 over pistons and rings and overbore. This time dont cut corners. If you have questions as them before its too late to keep yourself from screwing up. and lastly, when you ask questions expect a reply that will give you good information, not massage your ego |
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| BrenBren | Feb 6 2013, 11:40 AM Post #7 |
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Thank you Old Man, you are right we did not check the bore other than visual. The original rebuild was done because of burnt exhaust valve and ALL the EGR passages being clogged with carbon. The cylinders all appeared to be in good shape and the mileage was well above 45 closer to 52 prior to the rebulid. with all that being said we will take your advice and look into it further. Thank you for being considerate and answering my question. The issue I had with Geo Glenn response was that it wasn't an answer to the question just an opinion. Also don't need hand held, just a 20 year old trying to go to college full time, work full time and get the most that I can out of this little car while learning how to take care of things myself instead of relying on other people to do the work for me. thanks for all the input and guidance, this site has helped me rebuild two motors and 2 cars from frame up. |
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| Old Man | Feb 6 2013, 12:11 PM Post #8 |
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Sometimes, when you are tight on monies, you can get away with just a"hone & ring" job, sometimes it bites you in the butt---you been bitten People dont normally bother to look up the clearance tolerances in these engines and, because the Metro is so easy to work on and cheap parts, they dont realize that it is important to have close tolerances inside the engines. for instance the clearances in the piston area runs from .0008 to .0015. very close tolerance. also, you can have an engine worn to the point that these tolerances are way out and the factory hone marks are still visable.-------you can see how, if you just "eyeball" it and throw it back together you might get the results you have. BTW -- the tolerances above and the hone marks statement are both taken from statements from Geo Glenn------just sayin'..................... your engine will last a long time as is-it will just piss you off every time you start it up. considering this and considering that you said you have other blocks sitting on the bench I would suggest the following: take your spare monies and spare time and build one of the "spares" up---cheaply. plasti gauge the journals, hone and ring, hand lap the valves.----make it good for temporary use. little bit at a time and less that $200 and a couple months 'spare time' and it will be a good 'get by' long block.---once it is ready take a weekend and swap it out. now you have had and still have a running transportation car with only a weekend of walking--still have an 'acceptable' engine in your car, and can take your time over the next 6 months or so rebuilding your good XFI engine........the correct way------- good luck EDIT--almost forgot. with this "program", once your good XFI engine is running good and in the car, you will have a fairly good long block sitting on the bench that you could probly sell for at least half if not more than the cost of parts in getting your XFI engine in good shape. Edited by Old Man, Feb 6 2013, 12:16 PM.
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| snowfish | Feb 6 2013, 12:16 PM Post #9 |
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Basic GearHead
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In an attempt to address your original question........ .........I don't see how a tighter ring gap would produce better results. The gapless XFi rings are a special design. It's a compression ring, and compression/scraper ring, build into one. The 3 ring system is like this…………… ![]() http://courses.washington.edu/engr100/Section_Wei/engine/UofWindsorManual/Piston%20and%20Piston%20Rings.htm Using the top ring only would introduce oil into the combustion chamber. No scraping qualities. Using only the middle ring would produce lower compression. It needs the upper ring so it doesn't get the full "blast". That's why the 3 ring sets are labeled 1, 2, 3, or top, middle, and oil. I pondered this same situation on my present build. I decided to go with standard 3 ring pistons. I highly doubt that the 2 ring system produces significant mpg gains. Plus the gapless, are unavailable, unless I wanted to search for some matching snowmobile rings. Largest gains come from the XFi cam and 3.79 transmission. I'm not one to re-use rings. However, in this case, a re-hone and re-install the gapless rings, should produce better results than what you have now. Maybe. That would buy you 6 monthes, to a year, to get one of your spare blocks "snug as a bug in a rug". We're family here, not Politian's. You won't always get the answer that you want to here. Sometimes tough love, but we're all pulling for you! (OldMan, you type fast for a....well....Old Man! )Edited by snowfish, Feb 6 2013, 12:17 PM.
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| 91xfi1.0 | Feb 6 2013, 12:17 PM Post #10 |
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I have a quick question... did you hone the cylinder when you re-ringed it? Doing that helps the rings seal to the cylinder. Also, sounds like you used the xfi piston with the wrong type of rings? I am not an expert by any means, but I wonder if a honing, and normal piston and rings would solve your problem? |
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| Old Man | Feb 6 2013, 12:21 PM Post #11 |
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I am guessing that he has taper and out of round bores. If that is the case, no matter what he does, the rings will never seat. |
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| Deleted User | Feb 6 2013, 01:12 PM Post #12 |
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Yes. Go oversize. Cast aluminum is worth 28 cents per pound. Or, use the pistons as paperweights. Old Man and snowfish have taken the time to expand on the technical aspects of engine overhaul and design. There's nothing wrong with slapping an engine together without measuring anything, and using the cheapest parts available. I've been there and done that. I've done worse. Much worse. The engine ran. Not for long. Oil farted, used oil, leaked, and burned valves. I never complained about it or asked questions. Objectively, I had an operational vehicle. Point A to B. I have 13 different vendors for parts and machine shop service for my overhauled engines. I check every part. I measure everything that comes back from the machine shop. I found one new piston pin that was 10 grams lighter than the others. It did not get used. I check ring gaps and bearing clearances. When I assemble an engine for someone, I expect that it will last a long time with proper maintenance. The people who take the time to post on this forum, including myself, are here to help. I will continue to advocate the use of a Factory Service Manual. They are available on Ebay. Your present engine will most likely run for quite a while. When you find the time, motivation, and resources to overhaul one of your spare engines, do it right. $1,000 for parts and machine shop labor should be adequate. GG |
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.........
The gapless XFi rings are a special design. It's a compression ring, and compression/scraper ring, build into one.

not Politian's.
You won't always get the answer that you want to here. Sometimes tough love,
but we're all pulling for you! 
2:28 PM Jul 11