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Compression #'s
Topic Started: Apr 7 2011, 07:40 PM (1,560 Views)
Metroid
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Metroid
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So I went and rented a compression testor from Auto Zone. Read up on how to do it and watched several youtube video after the first time I didnt open the throttle. Anyway, after getting bad fuel economy my numbers are 90 90 90 dry and 150 150 150 wet on my three banger. It runs great just getting bad fuel econony (25 in town, 30 highway roughly). Apparently the head gasket was changed not long before I bought it. Could it be timing? Perhaps burnt valves? Unlikely the valves would go on ALL cylinders? Also, when doing the test, I looked into the cylinder with a flash light and saw carbon deposits on the top of the piston. Is that normal? Experts, your words of wisdom are appreciated!
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GeoStalker
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"Chicks dig me and guys think I'm cool."

It's possible the head gasket was a used junkyard gasket, and didn't use new valves. It's weird however that all valves are reading identically. Normally when a head is rebuilt with fresh stainless steel exhaust valves, the compression is 150 in all cylinders, but builds over time.
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dayle1960
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Fastest Hampster EVER

90 is dead. 150 wet is weak. Carbon build up on piston heads is normal.

Result= 3 burned exhaust valves. You need a head job. Sorry.

The good news is that when your head is healed the car will give you 45+ mpg.

Now try this before you become too bummed out. Warm the engine up, pull the coil wire, put the compression tool in a cylinder, step on the gas, keep you foot on the gas, and let it try to crank for four seconds. Then read your compression tool. You might get some different readings on the dry test. JMTCW

Good luck
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Metroid
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Metroid
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Eek, I suppose thats not good. I guess its better then a cracked block/cylinder head. Luckily my family has used to same mechanic for 40 years and he is a decent guy. Any idea on what a new head job will run?
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dayle1960
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Fastest Hampster EVER

I get my parts from Partsdinosaur.com The parts I need usually come to about $150. I do the labor. So it costs me about $200 to rebuild the head. And If I'm in a good mood, I can do the head pulling, rebuilding, and install in a long day.

If you have a few basic tools and a few free days it is a very fun project to do yourself. That is how I learned.

If I had to guess what a shop would charge, I would say $800-$1600. That's a wild guess, but I would err on the higher side of those numbers.
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bansheetaz


im thinking the rings are all carboned up. burnt valves dont change compression values from dry to wet.
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dayle1960
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Fastest Hampster EVER

The numbers change somewhat between wet and dry. 10-20. But you are correct that a reading that different between wet and dry could be caused by something else than valves going south.
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allmountain40
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That big of change from dry to wet is rings, not valves. Oil will not seal a burnt valve and bump compression numbers up, but will seal up rings to give better compression. If it has a new head gasket, it could have possibly had valves lapped. If they did, that would stress the old rings. I'm thinking do rings and head. :thumb
Edited by allmountain40, Apr 7 2011, 08:35 PM.
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Coche Blanco
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3 burned valves? uh.... i'm thinking more like just a worn engine.
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snowfish
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Basic GearHead

90metro
Apr 7 2011, 07:44 PM
Normally when a head is rebuilt with fresh stainless steel exhaust valves, the compression is 150 in all cylinders, but builds over time.
Interesting! :hmm I didn't know that. :dunno I never checked my new build. (3Tech, stainless, cam, etc) Just started it, ran great, tweak here and there, and drove. :drivin I thought I was imagining things, that it feels stronger now, after a little over 1000 miles. :nfs I may have to check compression just for grins.
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Metroid
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So many differing views! I appreciate the help guys. Think I am just gonna have to bite the bullet and take her in. If my quote is too much I'll have to make it my own project :drivin
Edited by Metroid, Apr 7 2011, 10:50 PM.
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Deleted User
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I counted 3 rings and 1 valves. Rings wins.

Try the Marvel Mystery Oil treatment. 8 ounces of Marvel Mystery oil in the crankcase oil, run it until it turns black, change and repeat. If it doesn't turn black, change your oil anyway about 500-800 miles later. The MMO will knock loose a :shit load of carbon from the rings.
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Metroid
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Metroid
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Well, you guys shall find out soon enough what the issue is. I will be sure to report back. I have learned a ton about motors just researching this little 3 banger. Good engine to learn on. :rocker
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Woodie
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joncic
Apr 7 2011, 07:40 PM
my numbers are 90 90 90 dry and 150 150 150 wet on my three banger. It runs great just getting bad fuel econony (25 in town, 30 highway roughly). Apparently the head gasket was changed

I looked into the cylinder with a flash light and saw carbon deposits on the top of the piston. Is that normal? Experts, your words of wisdom are appreciated!
No need for a vote, these are classic symptoms of worn rings. I'll bet the PO had a head job done without doing anything to the bottom end. You need the cylinders honed and new rings installed. Since that's going to require new head bolts and gasket, I'd get the valves lapped to ensure everything is fresh. New valves with old rings usually leads to burned valves again quickly.
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bansheetaz


ive been rebuilding these engines in my spare time and doing it yourself youll end up with a little over 500 bucks into a completely rebuilt 3 cylinder. that includes boring if needed and grinding or polishing the crank with new bearings.cylinder heads can be found online as well as full gasket sets. pistons and rings online also.

easiest motor to work on. you could rebuild one broken down on the side of the highway.

maybe not but its still really easy.
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