yellow1150GS

2000 S2000 with 119k miles. Got a cylinder 1, random misfire that was coming and going until just recently. I have installed new plugs, injectors and done a very careful valve adjustment. Finally did a compression test and found that front to back I got 140, 230, 215, 235. Purchased a borescope from Amazon (it is a Teslong two way articulating probe with a 5" LCD screen and the picture quality is amazing) and inspected all the cylinders. Everything looks great except some pitting on one intake valve seat. Valve also looks like it has been a littlehot The rest of the seats and valves still have a mirror finish.
Neat thing about the borescope is with the 1/4 diameter probe (which has an adjustable end that will move up to 180 degrees) you can actually get in and examine the valve retainers which are all crack free. We were even able to go into the intake runners and inspect all the valve guides. What I did notice was a serious amount of black deposits in the intake runners until about 2" from he valve guides. Pistons are clean under the intake valves with a lot of carbon in the middle of the piston.
What I have done is use non-ethanol gasoline since we purchased the car with 92k miles and used Redline fuel cleaner twice. Misfire cleared up with the treated fuel but returned almost immediately with the next tank. Looks like I will be pulling the head to have a valve and seat repaired and the others freshened up. Also going to put Ap-2 retainers and keepers.
Question is who does the best head work on these cars and where are they located. I am in East Tennessee. As for the mechanical side, I have a grandson who is an ASE master technician that can't wait to get his hands on the car.

yellow1150GS

After talking with InlinePro, we are going to do two more tests to make sure that the valve is the suspect. He suggested a wet compression test and doing a cylinder leak down test. When I questioned him about the carbon build-up on the pistons, he advised me not to clean them as some debris could get lodged in the piston rings and scratch the cylinder bores. Seems the fiber infused cylinders are very prone to scratching and since I do not have an oil consumption issue it would be better not to chance it by messing with the tops of the pistons. They also prefer to rebuild your cylinder head since there is a VIN number involved. Turnaround will be about two weeks. We should know Tuesday which direction we need to go. While the head is gone I intend on thoroughly cleaning everything in the intake as I could see a serious amount of deposits downstream from the injectors. I will post the progress as we go on from here.

yellow1150GS

Rechecked all valve clearances and found all within specifications.Wet compression didn't change numbers much. Leakdown was another story. You could hear air coming out of the exhaust and the gauges lost pressure quickly. Pulled both manifolds and found front exhaust valve heavily carboned up and you could see discoloration in the valve stem. Also stain marks on the valve stems coming down from the seal areas. I am thinking the amount of time this car sat didn't help matters, and with the amounts of deposits everywhere I don't believe that quality fuel was used. Head is coming off tonight and we will get a better look at everything.

windhund116

Good luck! Hopefully, not too $$$ to fix.

Jub

I did a stage 0 InlinePro head rebuild last year @ 112k miles due to burnt exhaust valves. I'm at 119k now and have done some autocross and track days. It gained me back all my compression from leaking down 80% on cylinder #4. Car has sat on my 8400 RPM rev limiter (AP2) some and has been fine.

yellow1150GS

Head left for InlinePro today. Found two exhaust valves were a ghastly white, one in cylinder 1 and one in cylinder 4. When I bought the car it had 92k miles on it and seemed to run extremely well, but I did notice what felt like a slight misfire occasionally at idle when it got closer to 100k miles. When I did the valve adjustment at 100k miles, both of the offending valves were extremely tight. .007" on cylinder 1 and .008 on cylinder 4. I didn't realize that just a few thousands would cause that much grief later. Oh well.

yellow1150GS

Heard from InlinePro today. Head will be ready to ship back to me early next week. In the meantime I have procured everything I will need to complete assembly when the head arrives. I haven't done much as this is Christmas Prime with Amazon and I have been working 11 hours a day since the week before Thanksgiving. Everything will arrive at the best time since after Christmas everything will be somewhat back to normal.

yellow1150GS

Well at 7:30 last night the head arrived via UPS. It was extremely well packaged and when I unpacked it I was very pleased with the final product. After exchanging e-mails with John he explained what the root cause of my compression problems were, mainly seriously worn exhaust valve guides. The front exhaust valve in cylinder 1 and the rear exhaust valve in cylinder four wobbled so badly that they would not properly seal causing the misfire and compression loss. They replaced the exhaust valve guides with new longer ones to give the valves more support, did a competition valve job, replaced seals and installed AP2 valve retainers and keepers. Head was vapor blasted and trued up. Looks brand new. Now to begin the reassembly and get Giz'mo back on the road.

umair

What was the leakage at when you did the leak down test? I am glad you are getting it sorted out

yellow1150GS

We bought a leak down tester at Harbor Freight and when we hooked it up the leakage was so bad that the gauge just rapidly went to zero. You could hear the air coming out the exhaust pipe at the back of the car.