eclou

Feb 2009 took the 951 to the track and experienced significant boost creep ~17# to >20# in 20F temps. Long story short I detonated and burned out the #3 exhaust valve with no other evident damage. Just to be safe I had the 4 injectors flowed and balanced, then put in a new exhaust valve. Car ran great thru another half dozen track outings until Oct when the same sputtering occuring during a track event.

Opened it up and I find #3 again:




looks like a fresh kiss on the piston too. Granted all 4 of my pistons have had a kiss before I owned it probably due to a belt rupture, but I am thinking this valve hung in the guides or the springs are bad. Gonna send it back to Lindsey (head was their stage 1 Oringed head job from 2006).

xtaC

Did you get the seat for the valve cut at the same time?

Mike Lindsey

Looks like you need some better springs. Must be running to much boost or to many revs or
both.

eclou

I lapped it in with a drill and rubber tubing with some compound - did not recut it.


It is on its way to you Mike via Fed Ex from Houston. Should see it Friday. I cut my boost down to 16ish # on a K27/6. Was running about 50/50 104/93 octane fuel too. Bummed.

jmj951

Nobody has commented on the carbon buildup. WTF? That's absolutely terrible. Do all of your valves have that much carbon caked on? All of that carbon buildup is a serious problem because it gets hot enough to contribute to detonation. Not sure if that alone can weaken the valve enough to break it apart. Per the other post, I'm also curious about the valve seats.

Regarding the valve strike - yes, if you look at the edge of the valve where it meets the piston in that position, you can also see fresh evidence of the strike.

Chris White

Yep, burning a bunch of oil in there.
If a small piece of carbon comes loose and gets trapped between the valve and seat it will burn a valve in milliseconds out on the track.

eclou

oil fouling and making go lean? I just cleaned the head last year and added the Seiko Michi catch can. Funny thing the can is dry and my intake pipes are pretty clean. The top elbow on the Seiko Michi goes to the J pipe correct?

odurandina

"if he wouldn't over-rev the son of a bitch we'd win some races." -- Harry Hogg

best line ever.

TonyG

I'd be looking at the ignition timing.


TonyG

eclou

Guru chips

SamGrant951

I have mine with the top elbow going to the AOS. Side elbow to j-pipe.

eclou

Jeez if that is what may have caused the oil fouling I would be pretty pissed

JohnKoaWood

Nope, the top of the SM can is the inlet (to crank case), the bottom is the outlet (to j pipe..)...



You are not the first person to hook it up backwards...

Here is mine, note the hose routing, top to AOS, bottom to J pipe..

95ONE

yeah,, but this isn't the cause for #3 to do this 2xs.

jmj951

Okay, then I have another possibility to throw out:

We know that the head was already machined back in 2006, before the first burnt valve. I think that a little too much material was taken off the head to be able to use a stock spec gasket. The smaller clearances due to the machined head made the engine more prone to a valve-piston strike at high revs, and this is what led to the burnt valve - in conjunction with excess carbon deposits. Thinking about the mechanics of it, if the outer edge of the valve (approximately at the position of 1pm-1:30pm on a clock relative to the picture) was bent even slightly by the impact(s) with the piston, then other edges of the valve would not have been able to make complete contact with the valve seat. This would have allowed some of the burnt carbon particles to wedge in there without being forced in or out, even if only for microseconds, thereby burning up the valve at the edge.

One thing we need to know - when the first valve burnt up, was there any evidence of a strike on that valve or on the piston at that time?

Solution: Thicker head gasket (and reconnecting the catch-can in the right places). And I'm sure Mike is also right about using stronger valve springs for high-revving engines, so just to be safe you should probably do those as well (though I've never heard that the stock springs don't hold up to occasional DE use - I've always heard how robust the internals are - now it's got me thinking...).