Charlie944

Zero10: The head has a 951 part # and the exhaust valves are the Sodium filled type. My guess is a crack developed, a hotspot(s) was then created, and then under pressure and load on that last pull the hole formed. I would be happy to have Chris's take on this as well. I was thinking of sending the head out to EBS for their Race1 head work, and have the chambers and valve faces Thermal Barrier Coated as well. Would there be a downfall to not having the piston tops coated and the head coated? I wonder if this would reflect more heat to the pistons then and be detrimental. I will move the EGT sensor over to #4 and I might upgrade to Lindsey's Fuel Rail to ensure even fuel distribution for the 75# injectors...even though they are flowmatched.

Charlie944

I know per the Datalog that I was infact running lean, but all of this occured after I richened it up and went out for a test run. Maybe there was always something wrong with the that cylinder seeings how the spark plug would always be carboned up due to oil burning, and the other 3 cyls looked better.

Chris White

Good time to pick up a turbo head. The callaway cars had the NA heads without the sodium filled exhaust valve and the ceramic lined exhaust ports.

A burnt valve is caused by a combination of high EGTs (we all have that problem!!) and some thing that gives it a starting point. A small carbon particle lodged between the valve face and seat will prevent the valve from completely sealing and then you have extremely hot gases leaking through at very high speeds and pressures….very much like an acetylene cutting torch. The back side of the valve will look like it was cut with a torch.

Not too much you can do to prevent it other than not running too rich – this will prevent carbon build up to some degree.

Chris White

Charlie944

The car does have a 1986 951 block, pistons, crank, rods and head. The turbocharger system is still the Callaway setup however. I have noticed a small chip on the #2 cyl deck surface, and I wonder if this would prove promblematic to me if I chose to run a MLS Cometic headgasket. Also here is a pic of the IHI RHB6 turbine, it has a piece missing from it, and would this warrant me having to get it rebuilt? I would hate to have it out of balance while turning a max of 140,000rpm. I do have an exploded parts diagram (thanks to fellow rennlister John Kuhn) and it is a part of the turbine not an end cap or nut, so the turbine shaft would have to be replaced if it is a problem.

Chris White

The ‘Chip’ missing on the block should not be a problem and the missing metal on the turbo is where they grind of material to balance the assembly.

There you go, I just saved you a bucket of money!

Chris White

Peckster

I doubt running rich ever caused a burnt valve, and I also doubt a particle of carbon would last long on the seat.

Burnt valves are usually caused by too high temps in the cylinder (usually lean mixture or timing advanced too far) or a valve that isn't seating well. That can be caused by a bent valve, bad guide or worn seats. If the valve isn't making good contact with the seat or gasses are escaping, that will overheat the valve.

Chris White

Running rich doesn’t burn the valve directly – but the build up of carbon on a valve creates the seed for a hot spot. The other possibility is a loose piece of carbon gets trapped between the valve and seat – this will only take one or two cycles to create the heat and velocity needed to melt the valve.
Carbon deposits can get quite hot and will contribute to a good starting point for the cutting action or, equally as bad, contribute to preignition.

It looks to me like you are sort of agreeing with my point (!) that the valve not seating will melt a valve quickly (I have done that myself).

Chris White

Charlie944

Excellent, I was not looking forward to rebuilding the turbo too! I can definitely see how a stubborn piece of carbon could start the reaction for a burnt valve. Based on how that spark plug often looked tells me there was a high possibility of that happening.

hosrom_951

Chris/Charlie: Would any of the fuel cleaner/combustion cleaning products aid in removing the carbon deposits? Is there a way (without the removal of the cylinder head and running rich) to "clean out" carbon deposits?

Ian Carr

The chip in the block should not be a problem.

OT: sort of.. I LOVE THAT HEADER AND TURBO COMBINATION!! Im jealous.

Charlie944

Hos, ironically enough I ran a 20fl.oz bottle of Techron Fuel System Cleaner by Chevron in the car while going up to Road America for the day, knowing it would be a good highway run. I have also run Redline's Sl-1 FI cleaner as well. To be honest I was expecting the pistons and valves to alot more carboned up than they were! I am hoping the chip will not be a problem child. Tom M'Guinn and I have been conversing seeings how we are in the same boat with this chip. Based on his coversation with Scott Gnomes I will stay away from the Cometic for the "hopefulyy it will seal" rep the MLS is getting. I will go with a WFHG instead. Thats what was on the car prior and I had no problems. Does anyone think that the chip will spawn new problems such as stress cracks?

TurboX, thanks man! The spool up is great and the IHI uses a low inertia wheel on top of it! It spools up pretty good for having a 20cm^2 Turbine housing on it. IIRC the K26/6's has a 6 or 8cm^2 orficice housing. Every great once in a while you will run across a Callaway turbo conversion kit on ebay. After Reeves did his initial run of about 15 cars in 1983 at his shop in Old Lyme, CT he produced some 'kits' to sell outright, or have fitted at his shop after the 83' run. My car was one of the fifteen to get converted as a newborn persay in 83'.

Charlie944

Well I dropped the head off to a guy that was reccomended to me by a couple of friends who have had some Chevrolet V8 and Supra Turbo stuff done by him with great results. He is fairly close, pretty reasonable, and does beautiful work. He specializes mainly in NASCAR and Truck/Tractor pull applications (cause were in corn country out here yall!) To get a 5-angle valve job using cutters not stone grinding (not even an option) will be $130, and he is going to O-ring the head for $100. I will supply the valve (hopefully not more than one), springs if necessary, and valve stem seals. Surfacing the head would be $35 if it needs it. He was showing me some niiiice looking 18deg Chevy heads and the valve job he did on them. I was impressed, next to those head was a set of HEMI heads set up for a Supercharger which will be putting out 1600hp! Not sure of the displacement though. Anyhow, I will keep you all updated on what occurs, and I will supply pics when I get the head back.

Chris Prack

There is another possibility that has not been mentioned. Excessive valve guide clearance could also result in a burnt valve. The valves transfer heat to the guides and too much clearance could have burned the valve. I had this happen on my car three years ago or so. I ended up replacing all the guides, valves, springs, retainers, etc. while having the seats cut. It's not uncommon for the valve stems to be at or below spec. close to 100k worth of sevice.

Charlie944

You bring up a great point Chris, thank you for the insight! I will bring that up to the man who is doing up my head.

Charlie944

I have received my head back from the machine shop (Pfieffer's Racing Engines in Freeport, IL) and Steve Pfieffer did a great job! Pretty ecenomical too, for a 5-angle valve job, boiling, magnaflux, welding up some electrolysis pitting on the surface, resurfacing, and O-ringing the bill came to a hair under $380.00. While the head was being redone, I sent my exhaust manifold out to SWAIN Tech to get White Lightening coated. $162.00 for everything there incl S&H. I will start putting everything back together here shortly, but first I want to move my EGT sensor over to #4 cyl exhaust runner. Here are some pics: