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low compression readings on 4-cylinder by fierosound
Started on: 09-03-2006 10:47 AM
Replies: 4
Last post by: fierosound on 09-04-2006 11:07 PM
fierosound
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Report this Post09-03-2006 10:47 AM Click Here to See the Profile for fierosoundClick Here to visit fierosound's HomePageClick Here to Email fierosoundSend a Private Message to fierosoundDirect Link to This Post

We're working on a Fiero 4-cylinder engine that hasn't been run in some time. We did a compression check and the readings are somewhat disappointing.

We had all the plugs out when we cranked the engine to circulate the new oil and pump up the lifters. The first tests gave us 90-92 lbs per cylinder (cold)
We then shot some oil into the cylinders, cranked the engine to distribute the oil and repeated the compression test. We got 125-130lbs per cylinder (cold).
It's good that the readings are even, but this is supposedly has a 12.8 CR. We haven't removed the oil pan or head yet.

By comparison, my 3.4 V6 will give a reading of 185 lbs per cylinder when cold. It has a 9.2 - 9.5 compression ratio.

Opinions? Is this potentially a boat anchor?


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[This message has been edited by fierosound (edited 09-03-2006).]

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Jax184
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Report this Post09-03-2006 03:18 PM Click Here to See the Profile for Jax184Click Here to visit Jax184's HomePageSend a Private Message to Jax184Direct Link to This Post

You'll probably be burning a lot of oil, but it should still run.
Ahh the joys of a rebuild...

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AP2k
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Report this Post09-03-2006 05:16 PM Click Here to See the Profile for AP2kClick Here to Email AP2kSend a Private Message to AP2kDirect Link to This Post

 
quote
12.8 CR


HOLY SHNIKEYS!!!

Errm, unless your working on a stupidly high performance Duke, the compression ratio is only supposed to be 9.0:1. Still, your numbers are low. How many miles does the engine have?

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theogre
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Report this Post09-03-2006 08:23 PM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreDirect Link to This Post

The fact the compression came up that much with some lube means the rings could have problems. If that is the case, you need a rebuild on the short block.

Being that the engine wasn't run in some time... You should have lubed the rings before any cranking. Too late now. Hopefully you didn't hurt it any.

All you can do now is give it fresh oil and coolant and see how it runs.

Expect that the water pump will probably die soon if it isn't bad now. Parked water pumps tend to build corrosion next to the seal that often ruins the thing in short order once they are running. The problem is caused by the fact that the "Antifreeze" will settle into the bottom of the cooling system over time, leaving the high parts to rot.

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fierosound
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Report this Post09-04-2006 11:07 PM Click Here to See the Profile for fierosoundClick Here to visit fierosound's HomePageClick Here to Email fierosoundSend a Private Message to fierosoundDirect Link to This Post

 
quote
Originally posted by theogre:

The fact the compression came up that much with some lube means the rings could have problems. If that is the case, you need a rebuild on the short block.

Being that the engine wasn't run in some time... You should have lubed the rings before any cranking. Too late now. Hopefully you didn't hurt it any.

All you can do now is give it fresh oil and coolant and see how it runs.

Expect that the water pump will probably die soon if it isn't bad now. Parked water pumps tend to build corrosion next to the seal that often ruins the thing in short order once they are running. The problem is caused by the fact that the "Antifreeze" will settle into the bottom of the cooling system over time, leaving the high parts to rot.



Now that's wonderful news! NOT!!! The engine is out now, but I haven't gotten the pan or head off yet.
I was expecting I may have to to freshen it up, not rebuild the damn thing.

[This message has been edited by fierosound (edited 09-04-2006).]

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