carchitect

iTrader: (1)

They are probably different manufacturers. I've seen this before on other engines. The difference is too small to make change the CR.

carchitect

iTrader: (1)

The vehicle was already running poorly so I doubt the ecu was aware of the foul gas mix. Regarding the valves, they maybe stainless but the grade is unknown. The aftermarket valves are not necessarily a better material either. The burn't intake valve is probably a result of overheating in that area. The valves are about the only things in the combustion chamber that aren't cooled directly. The piston is cooled by the oil jets and the combustion chamber and cylinder walls are cooled by the engine coolant. The valves only have the fuel and proper AFR to help maintain their livelyhood. In the event of a lean run the valves could be the first things to get torched. It has also been my experience that lean burn doesn't necessarily cause detonation. It generally creates a lot of heat that could lead to detonation but it usually causes meltdown or damage to internal components first.

nabbun

damn. I want boost =D

Gernby

iTrader: (1)

That seems really strange to me too. At least the intake valves are cooled by the intake charge instead of heated by the exhaust. Could there also be a problem with the valve lash that was preventing the valve from seating properly?

HKS350

iTrader: (4)

I wonder if this has anything to do with the TSB (knock@ start up). They replace the cam gear which would/could have an effect on valve pos.(overlap) This prolbem and the bad/lean gas mix could burn a valve at start-up. It is hard to burn a valve. Most valves I've seen have a temp range between 1800-2200 degrees F. E85 would burn cooler if enough was their. Intakes @ 1800 exhaust @ 2200. I don't know I think something else is also to blame.

carchitect

iTrader: (1)

I more than likely was from the way the flame propagated within the combustion chamber. I have seen a lot of engines have piston meltdown on the intake side too.

Valve lash wasn't a problem since the lifters compensate for it and the valve installed height was normal.

The valve could've had excessive difference in temperature and that could've chipped it too. Or the flame could've begun at the valve. During the misfires the fuel could've had issues burning and pooled at the base of the valve. The next spark interval the fuel could've ignited there and created the issues we experienced.

The engine had never previously been into so we can take out the installation/assembly issues.

Gernby

iTrader: (1)

I realize that we have hydraulic lifters, so I understand that valve lash isn't adjustable, but what if the hydraulic lifter was messed up? They use oil pressure, right? What if something was clogged by "gook"?

carchitect

iTrader: (1)

If it was clogged they would've ticked like no tomorrow from excessive valve lash. If the lifter drain was clogger you could see it after you take off the valve cover. They were all full of oil and after the repair the vehicle had about 30 miles put on it to pass all OBD readiness monitors. The fuel sample we extracted from the tank smelled like E85 and the tail pipe smelled a little sweet. We were fairly confident there was some corny-alcohol in there.

Gernby

iTrader: (1)

^^ I don't really understand totally how hydraulic lifters work, but I assumed that if they were clogged up, there would be insufficient lash (too tight, preventing valve seat contact).

carchitect

iTrader: (1)

They work on the principal of using the viscosity of the oil itself to help reduce the valvetrain slack. The spring in the plungers will take the slack away. The oil find its way under the plunger and fills in the void. When the cam lobe is about to begin lift, the orfice size and oil viscocity will prevent the lifter from collapsing.

After the cam lobe has allowed the lifter to relax, the oil inside will find its way out thru the vent port. The cycle continues continuously and new oil finds its way into the lifter. (not really new but you get the point) If the old oil stayed in there the oil will begin to gel and cause a problem.

The biggest downfall of any HLA (Hydraulic Lash Adjuster) system is the weight penalty. But this isn't much of an issue on these engines.

You're correct about the fact that too tight could prevent valve seat proper closure and burn thru. This was a problem on a few honda engines. Some times guys would get them too tight to quieten them and create a burned valve several thousand miles later. It didn't help that they wouldn't let the engine cool down before the valve adjustment. On adjustable valvetrain engines, there is a min and a max and I always try to go for the center of them. That is spec the min and max is the tolerance. Knock on wood, I have yet to have an engine burn a valve after a valve adjustment and I've done all sorts of valve adjustments. Shim over bucket, shim under bucket, adjustable rocker arm, ect. Only one I haven't messed with yet is the DUcati Desmodromic valvetrain. Apparantly there is a science to them.

Gernby

iTrader: (1)

Thanks for the explanation. I've done several dozen valve adjustments on my 8 Hondas over the years, and I kind of miss it. I always went for the extreme lowest end of spec just for that little bit of extra lift. I know it was risky, but I adjusted them very often.

lobuxracer

iTrader: (2)

I burned the exhaust valves in a Honda 750 (mine) because I wanted the tightest fit possible. I learned a loose valve is a happy valve. I also learned there is no measurable performance difference between the loose end and the tight end of the specification.

One thing about valves, they do have more than air cooling them. They transfer a lot of their built up heat through the valve seat. This is one of the reasons seat width is such a big deal. There is also a balance to be struck between too wide (not enough carbon crush on closure) and too narrow (not enough surface area to cool the valve sufficiently) along with the usual flow concerns from seat and valve face geometry. The valve guide also helps a lot with heat transfer to the head where the cooling system can move the excess heat out of the engine.

It is very unusual to burn an intake valve. IME, if there is a lean condition the exhausts will die very quickly but the intakes will be fine. If the intake is even slightly tight the combustion blows back into the intake port (this would be obvious even to a blind man) and the valve burns even more quickly than an overheating exhaust. FWIW, exhausts and intakes are not made the same in street engines - exhausts are made to handle a lot more heat.

carchitect

iTrader: (1)

You're right about the performance between the valve clearance won't make a difference. For this reason I try to always get close to spec as possible and not to the minimum tolerance. The longevity and dependability is very important.

Whenever I cut valve seats and I always have to keep the seat width and valve margin under consideration. The shape of the port and combustion chamber also make a difference in the amount of cuts you can make. The more valve angle seat cuts and the lesser your seat width so I typically won't go beyond 5 angles on 4 valve engines. There isn't much of a benefit in it compared to the loss of dependability, increased wear from the reduced seat width, or increased maintanance on the valve adjustment.

I also agree that you generally see more burnt exhaust valevs that you see intakes but they do happen. The burn in the cylinder doesn't always happen as a forest fire as we all would like for it to happen. Explosions can happen which most of us precieve of them as detonation but its known more commonly as pre-ignition. Usually heat is the prime contribution to it but doesn't have to be. Other things could factor in as in this vehicle's case the fuel was defective.

Gernby

iTrader: (1)

I disagree about the difference in performance that can occur from a few thousanths of an inch of clearance. The first time I adjusted the valves in my S2000, I accidentally set the clearance by mearsuring between the cam lobe and roller rocker. This meant that my clearances wound up being about .003" too large. There were some interesting changes to the sound of the engine at WOT, and the VTEC kick was much more pronounced. Unfortunately, when I attended an S2000 club dyno day, my low end power was significantly lower than everyone else's. After discovering my error and fixing it, my dyno's looked like everyone else's again.

My belief is that Honda specs their clearances really high to give it a 100K service interval. I find it hard to believe that the S2000 really needs the .008" for the intake valves and .009" for the exhaust. I ran .001" below minimum spec for years without problems

Lama

Thank you for the pictures. Very informative, and a very good look at how well built and hi-tech the ISX50 drivetrain package really is.