Compression test readings - cylinder two low
#1
Compression test readings - cylinder two low
A little background on the car. When I purchased my mk1 1.8 Eunos recently I knew it ran a bit rough but was hoping it was sparks, HT leads, coil pack etc. When I went to change the spark plugs I noticed cylinder two was very dark and a little oily. I changed the leads and sparks with little improvement. There was also quite a bit of blue smoke on start up, this usually disappeared once warm, I suspected the valve seals and thought I'd try some forte seal conditioner, this worked well and it no longer smokes.
So all this led me to doing a compression test (I should have done this sooner), after the wet test I started the engine to check coolant for bubbles and there was tinny tiny bubbles appearing from the edges. I now suspect valve problems in cylinder two or maybe a failed gasket between 1 and 2. Any help appreciated.
Cylinder 1 - Dry 135 / Wet 150
Cylinder 2 - Dry 80 / Wet 90
Cylinder 3 - Dry 130 / Wet 165
Cylinder 4 - Dry 130 / Wet 160
So all this led me to doing a compression test (I should have done this sooner), after the wet test I started the engine to check coolant for bubbles and there was tinny tiny bubbles appearing from the edges. I now suspect valve problems in cylinder two or maybe a failed gasket between 1 and 2. Any help appreciated.
Cylinder 1 - Dry 135 / Wet 150
Cylinder 2 - Dry 80 / Wet 90
Cylinder 3 - Dry 130 / Wet 165
Cylinder 4 - Dry 130 / Wet 160
#3
A leakdown test should tell you for sure, but I suspect head gasket.
I have this one. https://www.amazon.com/OTC-5609-Cyli.../dp/B0030EVL60
I have this one. https://www.amazon.com/OTC-5609-Cyli.../dp/B0030EVL60
#7
I've never done a full rebuild although an mx5 seems to be a good engine to learn on. My goal with this engine was to turbo in the new year and get about 200whp but if I rebuild I may as well upgrade to forged Rods, upgrade clutch and aim for 300whp.
Last edited by Stee1e; 04-14-2018 at 06:23 PM.
#13
Wet/dry is also prone to bad data. The oil you add for a wet test is an in-compressible fluid. It's increasing the compression as long as it's in the combustion chamber. I wasn't holding the OP's hand while he did the test so I don't know how much oil he put in each cylinder. More oil=more difference between wet and dry. That's why a wet-dry difference over 10% still means diddly.
#14
Wet/dry is also prone to bad data. The oil you add for a wet test is an in-compressible fluid. It's increasing the compression as long as it's in the combustion chamber. I wasn't holding the OP's hand while he did the test so I don't know how much oil he put in each cylinder. More oil=more difference between wet and dry. That's why a wet-dry difference over 10% still means diddly.
#15
Well gee golly willikers aren't you a fountain of knowledge. I guess there was zero point to the op doing his tests then? I know I've done these tests on my engines and it's always given me a nice glimpse into how well the cylinders are wearing. In the op's case I think he should pull the head and inspect the gasket and check the head make sure the valves are sealing on the low cylinder. Check the cylinder walls for wear. Could just be a valve that's not seating causing the low compression numbers.
All three possibilities for low compression that you listed can be identified by simply doing a leak down test. What if a leak down test shows the rings are toast and the OP would prefer to swap in a used engine than rebuild the one he has? Then he just spent the time pulling a head instead of pulling the engine.
Thread
Thread Starter
Forum
Replies
Last Post
rharris19
General Miata Chat
24
11-18-2009 12:30 AM
miatamania
MEGAsquirt
7
11-09-2008 01:06 PM
blue89turbo
General Miata Chat
0
07-10-2007 08:44 PM