black nitrided valves

[sonicnofadz]

I'm in the middle of rebuilding my head on my 91 GST. The valves are pretty disgusting so I've decided to go with some nice aftermarket valves, but I was wondering if anyone has ever tried the nitride coated valves? Supposedly it decreases valve-stem to valve guide friction. I am actually considering using this type of valve, but I have some concerns. Does the coating wear off? If it does can it damage engine internals (bearings, pistons etc)? Does it actually affect performance (i.e. rev time)? Would I be better off with swirl polished stainless valves? If anyone has any experience on this topic, some input would be GREATLY appreciated. Oh and by the way I am also putting in brand new bronze valve guides (not sure how well this will go with the nitride coating, perhaps a lower frictional coefficient).

 

[Defiant]

DSMs are easy on valves and guides, because there's so little sideplay on the stems from the lifter scheme. Sounds like wasted money, but see what your machinist recommends.

 

[sonicnofadz]

Yeah I'll have to ask him. I can't seem to find any real proof that these are beneficial. I will probably end up just going with a nice set of stainless steel valves (swirl polished).

 

[Groomz]

On an OHV engine, the valves might be getting pushed against the guides more than a 4G63s, and I think that the nitride coating is more for those type of engines anyway. It definitely doesn't hurt anything, so I would go for it if I had the extra cash. I would recommend ceramic coatings on the piston top and sides, and maybe even a low friction coating on the bearings.



www.swaintech.com

 

[NDgsx]

Nitriding is not a coating, it's a surface hardening treatment. It does not wear off. 6 bolt crank journals are nitrided, that's why it says clearly in the service manual to not turn them for undersized bearings.
On a racing engine many people prefer to run smaller seating surfaces on the valve seats to reduce airflow restricion at low lift. With higher rate valve springs a standard stainless valve can be "pounded out" over time. Nitriding increases valve seal life in this case.

 

[Kingdom]

Originally posted by NDgsx
Nitriding is not a coating, it's a surface hardening treatment. It does not wear off. 6 bolt crank journals are nitrided, that's why it says clearly in the service manual to not turn them for undersized bearings.
On a racing engine many people prefer to run smaller seating surfaces on the valve seats to reduce airflow restricion at low lift. With higher rate valve springs a standard stainless valve can be "pounded out" over time. Nitriding increases valve seal life in this case.

Then what does the service manual recommend when you spin a rod bearing real bad?? or main bearing? a new crank?

 

[silverbulletAWD]

Originally posted by Kingdom
Then what does the service manual recommend when you spin a rod bearing real bad?? or main bearing? a new crank?

Yup, or just get the ground crank re-nitrided.

Back to the valves. I wonder how nitriding affects heat dispation from the combustion chamber? I imagine it would hinder it. Being that the hard coating would probably make it harder for any heat to soak into the valve stem to be taken away. Although stainless doesn't disipate heat very well in the first place.