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

A leakdown test should tell you for sure, but I suspect head gasket.

I have this one.

Would a HGF account for condition of spark 2?

https://cimg4.ibsrv.net/gimg/www.mia...113ae6ee75.jpg

It depends where the HG failed. It could also be a ring issue.

All we know for sure is that cylinder two is angry. Leak down time.

Sure, I'll get a leak down tester.

I hope it's not the damn rings.

did you hold the throttle open when you did the test? Those numbers are VERY low across the board. You should be seeing 180 per cylinder, 130 is super low. I think that engine needs a rebuild personally.

Yes, held throttle down. The numbers are really low. Engine has 100k miles, not sure about its track history but previous owner kept lots of history and he seemed to take good care of it. Still makes me think, pistons, cylinder walls, valves etc.

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.

I have one tester that reads a full 30 psi lower than another one. The actually value means little. What is important is that the readings for all cylinders are at least similar. In this care they are not.

Leak down information is far more telling.

Then you should replace your broken compression tester, numbers do infact matter....but yes a large variance is obviously the biggest issue here.

Not the point. We don't know the accuracy of OP's tester, and making assumptions about the total health of OP's engine based solely on compression numbers that can very wildly between testers isn't going to do him any good.

The values matter only when we can be certain they are accurate.

the actual numbers only matter if you know FOR A FACT that your particular tester is 100% flawlessly calibrated to read correctly and accurately. Which, 99% of them aren't.

Im surprised noone said anything about his wet - dry numbers the wet numbers indicate worn rings and probably a bad valve or head gasket issue on the lowest cylinder. Seeing as how the wey/dry numbers are way past 10% increase. Neg cat me all you all want, lol.

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.

​​​​​​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.

I never said that. It did an excellent job of confirming he has a problem. It won't reliably point him to what the actual problem is.

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.

So, plan is to make a leak down test kit, test for inevitable engine failure be it HG, valve or piston rings. Once I have more info, probably lift head confirm test findings and most likely rebuild rather than replace (personal preference).