Compression Test Questions - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Engine Performance This section is for discussion on all engine building related questions.
Sponsored by:
Sponsored by:

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 11-20-2013, 01:04 AM   #1
Newb
Thread Starter
 
Join Date: Nov 2013
Location: TX
Posts: 5
Total Cats: 0
Default Compression Test Questions

Hi guy's new user here.
I have an oil leak in my car which was slow enough that I could put a quart of oil every 2 or 3 weeks and be fine with it. Today the leak got worse as I was driving to school and when I got off the highway I heard the engine knocking. I parked at school and had a friend drive me to walmart to get some oil. I ended up replacing 2.5 quarts of oil.

I did a compression test to check if there was damage to the cylinders and got
Dry: 1 - 150 psi, 2 - 149 psi, 3 - 150 psi, 4 150 - psi.
Wet: 1 - 178 psi, 2 - 175 psi, 3 - 178 psi, 4 - 160 psi.

However I forgot to press down the throttle while cranking the engine , any idea if this would cause a significant error in the readings? I could go and rent the gauge again but I'd rather not.

Thanks in advance
seuss1337 is offline   Reply With Quote
Old 11-20-2013, 01:49 AM   #2
Senior Member
 
Join Date: Aug 2010
Location: Arl. Texas
Posts: 937
Total Cats: 23
Default

For your test purposes you should be fine. The numbers look normal and the test was done without the throttle open across the board.

Can you tell the if the noise was from the top of the motor (HLAs) or lower like a bearing?
Miater is offline   Reply With Quote
Old 11-20-2013, 01:52 AM   #3
Newb
Thread Starter
 
Join Date: Nov 2013
Location: TX
Posts: 5
Total Cats: 0
Default

No I couldn't, I'm hard of hearing.
seuss1337 is offline   Reply With Quote
Old 11-20-2013, 08:23 AM   #4
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,872
Total Cats: 1,790
Default

the wet test suggests your rings are failing.
Braineack is offline   Reply With Quote
Old 11-20-2013, 08:30 AM   #5
Moderator
iTrader: (11)
 
sixshooter's Avatar
 
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 15,669
Total Cats: 1,561
Default

The 2.5 quarts of oil suggest your bearings are failing.

Oil leaks can bite you in the *** if you don't keep after them religiously. It's too late now, but it sounds like you should have pulled the dipstick every morning as a preflight check.
sixshooter is offline   Reply With Quote
Old 11-20-2013, 07:31 PM   #6
Newb
Thread Starter
 
Join Date: Nov 2013
Location: TX
Posts: 5
Total Cats: 0
Default

Car was fine when I started it and wasn't knocking, school is ~60 miles away so the leak could've worsen on the way there, I try to keep on top of maintenance on this car.

Woke up today to find a big puddle of oil in the driveway, so the bearings should be fine as it's a leak.

How big of an issue issue do you guys feel I have on the rings? Is it something I could run with for a few months/years? I track the car so a rebuild/swap is planned to hold fi in the near future.
seuss1337 is offline   Reply With Quote
Old 11-21-2013, 09:33 AM   #7
Elite Member
iTrader: (1)
 
Leafy's Avatar
 
Join Date: Jun 2012
Location: NH
Posts: 9,093
Total Cats: 90
Default

Quote:
Originally Posted by sixshooter View Post
The 2.5 quarts of oil suggest your bearings are failing.

Oil leaks can bite you in the *** if you don't keep after them religiously. It's too late now, but it sounds like you should have pulled the dipstick every morning as a preflight check.
Its not that bad, thats only ~1.5 quarts in the car. Some spec miatas race with only 2 quarts in the thing. But the knocking sound suggests that 1.5 quarts was not enough. Its still totally possible that the soft bearings did their job and the short time you ran low on oil only took a bunch of life out of the engine rather than killing it completely.
Leafy is offline   Reply With Quote
Old 11-21-2013, 09:40 AM   #8
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,872
Total Cats: 1,790
Default

Quote:
Originally Posted by seuss1337 View Post
How big of an issue issue do you guys feel I have on the rings? Is it something I could run with for a few months/years? I track the car so a rebuild/swap is planned to hold fi in the near future.
looking at the numbers again i was probably wrong about it. You're even across, and about the same increase across with oil added. fix your leak.
Braineack is offline   Reply With Quote
Old 11-21-2013, 02:14 PM   #9
Moderator
iTrader: (11)
 
sixshooter's Avatar
 
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 15,669
Total Cats: 1,561
Default

I said your bearings were bad because you had the oil low enough to cause a knock. Knock = damaged bearings
sixshooter is offline   Reply With Quote
Old 11-22-2013, 12:34 AM   #10
Newb
Thread Starter
 
Join Date: Nov 2013
Location: TX
Posts: 5
Total Cats: 0
Default

Oh ok, I tought you meant the bearings where burning up the oil.

Thanks guys I appreciate the input.
seuss1337 is offline   Reply With Quote
Old 11-22-2013, 01:12 AM   #11
Senior Member
iTrader: (3)
 
Join Date: Dec 2007
Location: Brownsburg,IN
Posts: 800
Total Cats: 58
Default

He did not mention what year the car is, but if he has hydraulic lifters and started suckin a little air with the oil pick up as the oil level was low it may be possible that the lifters started ticking before the bearring had serious damage, it does not take much air in them to make them knock.
Does the car have hydraulic lifters? If it does, did the car kept knocking after running a few minutes once you filled up the oil to the correct level? If it stoped knocking i would fix the leak, skip a few track days and put that money away on an engine pigy bank.
HHammerly is offline   Reply With Quote
Old 11-22-2013, 04:41 PM   #12
Newb
Thread Starter
 
Join Date: Nov 2013
Location: TX
Posts: 5
Total Cats: 0
Default

Car is a 97 with the original 1.8, I'm relatively new to the miata scene so I"m not to sure if the engine comes with the hydraulic lifters. The knocking went away a few seconds after running with the right amount of oil. The same knocking comes on certain mornings but goes away after a few seconds as well.
seuss1337 is offline   Reply With Quote
Old 11-22-2013, 04:42 PM   #13
Elite Member
iTrader: (1)
 
Leafy's Avatar
 
Join Date: Jun 2012
Location: NH
Posts: 9,093
Total Cats: 90
Default

Your knocking just sounds like lifter tick.
Leafy is offline   Reply With Quote
Old 11-22-2013, 05:02 PM   #14
Elite Member
iTrader: (2)
 
Join Date: Jun 2009
Location: Istanbul, Turkey
Posts: 2,050
Total Cats: 433
Default

The knock, is it a sharp metallic sound, or a deep, thud or THOCK type?

The first would typically be the lifter tick others refer to, and the latter would usually be excessively worn bearing(s) banging on the crank.

Last edited by Godless Commie; 11-22-2013 at 07:14 PM.
Godless Commie is offline   Reply With Quote
Old 11-22-2013, 07:11 PM   #15
Junior Member
iTrader: (4)
 
Join Date: Jul 2009
Location: Morrison, CO
Posts: 472
Total Cats: 46
Default

Quote:
Originally Posted by seuss1337 View Post
Car is a 97 with the original 1.8, I'm relatively new to the miata scene so I"m not to sure if the engine comes with the hydraulic lifters. The knocking went away a few seconds after running with the right amount of oil. The same knocking comes on certain mornings but goes away after a few seconds as well.
Totally normal.
vitamin j is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Project Gemini - Turbo Civic on the Cheap Full_Tilt_Boogie Build Threads 58 12-13-2017 10:04 PM
1994 Spec Miata Race Car SM/SM2/SSM For Sale Quinn Cars for sale/trade 6 10-23-2016 08:58 AM
3rd Time's a Charm...hopefully. zephyrusaurai Meet and Greet 2 09-28-2015 11:59 PM
Are my coils failing? viriiguy General Miata Chat 5 09-28-2015 08:39 PM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 02:56 AM.