[rtonder]

I've been somewhat absent from the forum over the past two years as my small block chevy / 4.6 bosch engine swap idea led to finding more shop space, then more equipment, etc. Anyhow, I've now got the new shop up to speed and spent some time on the 305 conversion, which is moving along more as problem solving training than anything else. Current hurdle is the cam sensor and getting the right signal from a chevy cam gear.

The above aside, I also acquired an 03 disco which had the usual misfire codes, and I assumed that since it had a new coil pack and wires, someone gave up and traded it in. Turns out it was a burned exhaust valve, so I have the top of the engine apart and replacing the bad valve and touching up the rest. While it's apart, I was thinking of matching up the ports and smoothing out the runners. It wouldn't take much work, and I've done it on a number of small block chevys with good results. Anyone tried it? Seems like the runners have a fairly smooth cast finish, but there's flashing here and there that could go, and the upper/lower IM port match is so-so.

 

[viperover]

Disco 3 with a burnt valve, thats a new one.
Any idea what may have caused it.

 

[RRToadHall]

Disco 3 with a burnt valve, thats a new one.

The '03 Disco (not not to be confused with a Disco 3) have the same Bosch 4.6 as the P38s.

 

[rtonder]

Disco 3 with a burnt valve, thats a new one.

The '03 Disco (not not to be confused with a Disco 3) have the same Bosch 4.6 as the P38s.

And for whatever reason, uses different exhaust valves than the 02 RR. Same as a classic. I think most of the burned exhaust valve problems in the 4.6 rise from cheap gas or overheating. I was reading a disco forum where someone with bad headgaskets found a way around the combustion gas in coolant problem by drilling holes in the tstat. No more gas around the tstat coil to keep it from opening. Imagine the gas trapped inside the heads. Probably hotter than the hub of hell and the thing keeps going.

 

[Rich998a]

Are you talking about 'gas flowing' the heads? :think:

 

[rtonder]

Are you talking about 'gas flowing' the heads? :think:

Actually the poster in the other forum had a severe head gasket leak that was pressurizing his system, and noticed the new tstat would not open. He did not have the money for the head gasket repair, but found that drilling holes through the tstat baffle (essentially gutting it out) allowed it to open and the engine started running cooler. His conclusion was that the pressure from the head gasket leaking combustion gas into the coolant was forcing the tstat to stay closed, but since both sides of the tstat are exposed to the same pressure, I'm guessing that the combustion gases were collecting around the tstat coil and not transferring heat as well as the liquid, and subsequently keeping it closed. The hoses must have been like carnival balloons.

If that's the case, then I can only assume that there were also a number of other areas trapping gas which would also not transfer heat, such as the pockets in the head around the exhaust ports. If all of this seems plausible, then it suggests that a head gasket leak would contribute to the burned valves in short order.