Over-revving experience: DIY Engine Inspection and Test
Original DIY write-up by chilicoke
This thread is intended to document my experience of a mechanical over-rev on my F22C (07, AP2v2) and the inspections/tests I have done to check for signs of damage as well as the condition of the engine.
The procedures I’m going through below are what I had learned with information gathered from multiple threads/sources regarding mechanical over-rev.
This section seems to be lacking a “go-to thread” on this topic so hopefully this can serve as a to do “checklist” for those who had experienced (an) over-rev. Please help me look though details and double check if my methods and findings are correct as I’m sure others might find my experience helpful.
How it happened:
Long story short, I let a friend drive my car and he miss-shifted from 3rd-to-2nd instead of 4th at approximately ~7500rpm, revs shot up and the “red-line” flashed for approximately 1-2 second before shifter was pulled out of gear. A mechanical over-rev was apparent considering the speed, revs, and the gear he (wrongly) went into.
This S2k is my first car, I have no previous experience with mechanical work on car cars besides a few simple aftermarket parts install and few DIYs. Feared of costly engine damage, I quickly phone a local s2ki friend to inspect the engine in a few days.
However, being a very hands-on type of person myself, waiting a few days not knowing the condition of my car while it sits lifelessly in the garage was just too much for me to handle. I do have decent understanding of inner workings of an engine and had previously spent quite some time reading though the stickies of this section on S2ki, I decided to have go at it myself.
After reading some very helpful posts from fellow s2kiers (especially Billman250), I’ve concluded it would be best to perform all three inspections/tests in order:
1. Pull valve cover and visually inspect condition of valve retainers/keepers.
2. Compression test on all cylinders.
3. Leak-down test on all cylinders.
Visually inspect valve retainer
Must have, it would be almost impossible to inspect retainers (especially intake side) without a mirror if you decide to leave the head in.
To someone who had never done any engine work before (me) the idea of taking off the valve cover was a bit daunting, but it was actually very simple and straight forward.
Please refer to nibble’s thread on how to remove the valve cover.
Hardest part of removing the valve cover was to finding enough space to wiggle it out, I’ve found it a lot easier to dismount this hardness clip, unbolt it’s mount, and zip tie it out of way to the nearby AC line.
Please refer to these threads on retainer inspection:
VALVE RETAINER CHECK 101, an idiots guide
Cracked valve spring retainer….., Replace with OEM or aftermarket Ti???
Use your mirror to check retainers. I’m not sure if it’s necessary to check both intake and exhaust side, but I did (about 20 times) just to be safe.
All my retainers look good, PHEW!
*these test order might not be the most convenient as from what I understand it’s safer to have valve cover on for compression test. However I felt more comfortable cranking the engine knowing that valves/retainers are in good condition. Maybe someone more knowledgeable can chime in.
Please refer to fadiss2k’s DIY Compression Testing thread for details.
Tested between 233-235psi across all cylinders (semi cool/warm engine, no addition of oil), another pass. Phew!
Leak-down test…. if you already got a compressor
So far everything has been looking good, but I still decided on doing a leak-down test. According to the individuals I’ve talked to (thanks you know who you are!) a leak down test is a much better indication of engine (valve) condition than compression test in case of mechanical over-rev, which is why I made it my last test for reassurance.
I don’t believe there’s a guide here on how to do leak-down test. Basically a leak-down test is compression test in reverse as it tests the seal of each chamber by pumping in compressed air. If a bad seal is found you can determine where the problem exists (intake or exhaust valve) by listening where air is escaping from.
Leak down test requires an air compressor so you might/might not be able to do this at home.
I’ll leave the details of leak-down test to someone more qualified to explain. If you’re in a situation and need to know right away, there’s always Google.
In additional to a compressor, leak-down test also also requires….. you’ve guessed it, a leak-down tester.
How to do it cheaply *If you have access to a tester skip down to “Leak-down test”
Testers are available through number of retailers and are quite expansive. Harbor Freight sells a much affordable model but the reviews aren’t very inspiring (10psi?!).
While I was looking around the store (Harbor Freight) after checking out the above tester in person I realized I could make a much cheaper and better tester myself using off-the-shelf compressor parts from the same store. Came home with what I needed and decided to look it up online, sure enough the same has been done before. Armed with confidence I went at it.
These are the parts you’ll need:
– Compressor air regulator with gauge.
– Quick connect fittings (it must self-sealing when disconnected)
– Spark plug air hose. (I used the same hose from compression tester earlier)
Total cost = less than $10
* you may/may not need additional fittings to hook everything up together depending on the fittings on each parts.
We’ll have to slightly modify the spark plug air hose for this to work.
At the tip (where it goes into the spark plug hole) is a check valve, this allows air to travel only in one direction. In the case of compression test it’s out of the cylinder and not the other way around so the gauge would be able to read each cylinder’s pressure without letting air back in.
For leak down test we need air to flow into the cylinder, so we’ll need to remove/unscrew the check valve. Keep it in a safe place as we’ll need to put it back in for future compression tests.
Hook everything up as follows:
Compressor > regulator > quick-release fitting > spark plug air hose
*make sure you use sealant tape to ensure good seal.
Remove your valve cover once again.
Each cylinder should be at top dead center to test for leaks following the firing order, piston 1 > 3 > 4 > 2. (similar to valve adjustment)
Taken and edited from service manual:
Turn crank with 19mm ratchet/socket and set piston 1 to TDC.
Pump up your compressor and set regulator/tester to 100psi (I used 100psi to make calculating percentage of leak easier)
First screw your spark plug air hose into cylinder #1, then connect your tester’s quick connect end onto the air hose.
Once connected the regulator gauge now reads 96psi. 4psi decrease from 100psi = 4% leak.
According to Slows2k in this thread, my cylinder 1 looks healthy and valves are sealing great.
5% or less is considered very good for a street engine. 10% is when you need to start looking where the leakage is from.
Also: “Leakdown test results…” thread.
It is also worth mentioning that compression test and leak down test should be done when engine is at normal operating temperature for most accurate results. I did warm up the engine ahead of time but because the amount of time it took to take off the valve cover (noobiness) the engine had already cool quite a bit when I started the test.
*if the crankshaft rotates when you apply air pressure that means the cylinder wasn’t exactly TDC. Just reset it and retest the cylinder.
Turn crank again till cylinder #3 is TDC.
#3 also look great! 4% leak.
Cylinder #4 TDC.
#4 is good too! ~5% leak.
Cylinder #2 TDC.
#2 is a little big higher at ~6%, still good. Perhaps this small increase of leak #4 and #2 is due to the cooling of engine temperature?
Looks like I might have dodged a bullet on this over-rev, as far as I could tell the engine is in great condition. After putting everything back together the engine fired right up and idles smoothly. Data logged the idle and a short drive with FlashPro and everything looked normal, will continue to data log for the following week and be on the look out for any abnormalities. PHEW!
This took a good 6 hours but it was a great experience, learned a lot.
Did I overlooked anything or is there anything else I should be checking?
Thanks for the long read.
S2000 Forums-> My over-revving experience & inspections/tests
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