I apologize for posting another thread about a engine having low compression but I would like personal feedback from all the great people on this forum. I did do some searching, and read a couple posts of low engine compression but never got a very clear answer. I decided to compression test my 2005 s2k with 83k miles on it. The numbers are pretty consistent:

Cyl 1: 170
Cyl 2: 173
Cyl 3: 180
Cyl 4: 175

I did this test on a warm engine with fuel fuse out and WOT. The car drives perfect, engages vtec fine, nothing seems to be wrong but the numbers are pretty off from the 240 that it should be.
Now I know a leakdown test should be done but before I can perform one I would just like to see what the possibilities are.
On a side note, my car sometimes makes this very quick gear-grinding sound when I start it up cold in the mornings. Don't know if this has ANY relations with me having low compression but I thought I'd throw it out there haha. Ideas?

Would anyone know as to why the numbers are this low? The spark plugs seem to be in good shape, don't know when the last time they were changed out as I haven't switched them out since I bought the car when it had 70k miles. Now, my car did experience two mechanical overrevs since I've owned it. My friend did it the first time, I did it the second time. I was told by Billman that AP2's can handle one mechanical overrev, and my car has been running great since those anyways. I have thought about the valves but it would mean pretty much all the valves are bad, which would be horrible. Maybe a head gasket? I don't know when the last time a valve adjustment has been done either, so I do want to look into doing that as well. I know consistency is key, but I'm still concerned about the low numbers. Any info you guys can share is fantastic. Thanks!

 

if the car drives fine and you have no issues then I wouldn't worry about it. those numbers are okay, coz the key for compression test is looking for consistent numbers, not higher numbers and your numbers look fine.

 

Although the numbers are consistent, the values listed seem pretty low in contrast to those with similar, if not higher, mileage. Try and do another compression test after driving at operating temperature.

 

With the year and mileage of your car I would hope that everything is okay in the engine compartment. The numbers of your compression test are a bit low, however, they do not show a large difference between each cylinder. I would start off by purchasing or renting another compression tester and redoing the test under the same circumstances. Even a brand new car would probably not bring in a compression of 240psi. My car, MY01 with 95,000 miles, brought in 210,210,210,215 with a brand new compression tester. When I let the dealership do my compression test they said the numbers were 205 175 180 175. After they told me that the engine needed to be replaced, I took the car to a transmission shop to do another compression test. They said the engine read, 190, 190, 190, 190. This shows how different compression testers and users could result in various numbers.

The car making a very quick gear-grinding noise on a cold start is your starter sticking. It causes no harm to the engine and does not affect the compression test. My s2000 does the same thing.

In my manual Honda recommends a valve adjustment at 100k (I believe), so now would be a good time to adjust your valves. If you drive your car hard, which it sounds like, you should do a valve adjustment in shorter intervals.

To be honest, those numbers would certainly bother me and persuade me to do another test.

 

Thanks for the information. What scares me is that I actually did perform two tests using different compression testers. Pretty much got the same numbers on both. And I am pretty sure I did all steps correctly. Parameters were correct. I had the engine fully warmed up, fuel fuse out, WOT every time. The car, to me, seems to run great so I have no idea why the compression is so low. The second time I tested, it was with a 100% brand new tester as well. I definitely will look into having the valves adjusted, and retest afterwards to see if it has any improvements. I might also take the valve cover off and just inspect it just to see if there's suspicious. Other than that, I have no idea whatsoever as to what can be causing the low number. I'm not too happy with this since I am considering boosting the car in a few months time haha.

 

The noise at engine start especially during cold days is 100% your starter sticking. This is a common problem with honda starters. It's my understanding that this can cause damage to the flywheel.

 

Thanks for that! Glad it isn't anything near a big issue. I'm still daunted by the low compression though...

 

Get a leak down test performed. That will give you a lot more information than a compression test. I dont know how to perform one though. I found this on s2ki, don't know how reliable the numbers are but it may help.

"0' = 1.0
1000' = .9711
2000' = .9428
3000' = .9151
4000' = .8881
5000' = .8617
6000' = .8359
7000' = .8106
8000' = .7860

So it seems that an S2000 that generated compression values of 250 PSI near sea level would probably do about 215 PSI at 5000'. What altitude is the dealership where the car was tested?"

 

I would perform a valve job if you haven't done one recently. Then recheck the compression. If it's still low, squirt a very SMALL amount of oil into each cyclinder before rechecking the compression yet again. This is called a wet compression test (the oil helps seal the piston rings). If the values increase quite a bit, then your low compression is due to piston rings. If the numbers don't increase, or increase a very small amount, your issue is likely with valves.

 

That sounds like a good start, thank you. Ill probably do the wet test first, then a valve adjustment. I really hope its nothing too serious. Hypothetically saying it was the rings, would you or anyone know how much it would approximately cost to repair if it really is the rings? That would suck, because then all 4 pistons would have bad rings. If something is wrong with the valves, do you know what could possibly be wrong with them?



Any other information is greatly appreciated! Thanks