Bronze valve guides

[Unlpower]

I want your input on valve guides and seats. I want to know in your experince how is the life of bronze guides. I know people who just use the factory type because they say bronze doesn't last long enough. I would think in a performance motor that bronze would be an ideal choice and I've noticed that you seem to use them all the time. Last thing on the guides, at what point should you cut them?. Lastly, on valves and seats on a full out race motor or any motor really is it worth using titanium? Money vs. Gains Thanks

[Guy Croft]

Hi Doug

There are many types of bronzes. Years ago I signed up for Columbia Metals 'Colsibro', a high strength copper alloy. Quite new then. And over the last four years I've been using their latest 'Trojan' super high strength (800mPa UTS) silicon nickel copper alloy. This alloy is really something. Guides from these materials esp Trojan will last for 10 years easily in a 'fast-road' motor and several seasons in a race engine. These alloys have almost half the friction (even dry) compared with OE cast iron ones, twice the thermal conductivity and thermal diffusivity. The latter mean that they warm up quicker and disperse heat way faster, good for valve head, stem, seat and guide too. You must never run plain stainless stem valves in cast iron guides, they pick up.
Moreover bronzes are ductile, cast iron are brittle, aggressive cams (and heavy handed technicians) can easily fracture the weak section of the guide where the seal sits.

The longevity is often questioned. It depends on the quality of the lubrication regime. Fuelling quality too - gasoline in the oil due to over-fuelling degrades them quickly. They are not as hard as cast iron, but that said cast iron ones wear pretty quick in that situation. As do rings, bores, bearings and everything else in the oil stream.

Because they are so long lasting, something I discovered 4 years ago when doing rebuilds of engines I built in the early 90's, I decided not to continue the practice of shaving guides except at full race level. I was surprised to see the guides on these well-maintained engines were almost untouched by wear. But I had to junk them because I'd shaved them., because you cannot pick up a seat grind easily on a shaved guide.
How much intrusion do they make? Well, aerodynamically shaped the 14mm TC ones - they're not bad, but the 15mm TC types are very intrusive whatever (save for shaving) you do to them.

For your interest we used Hidural 15 guides and Hidurax or heat-treated beryllium copper seats in F1 with Hartpower and the guides easily lasted all season at 700bhp plus. The seats needed recutting after every race but only a few microns. The copper alloy seats give a fantastic seal, and being quite soft survive carbon impact damage without knocking the valve to pieces in the way super high nickel chrome seats do. Plus of course the heat transfer is better than anything on the planet (esp Cu Be).

It's worth mentioning that apart from fuelling and oil, cam bucket slop, cam ramp, valve unsupported length and seat/valve grind quality (concentricity) play a HUGE part in how long the seats and guides last. Engine temperature and back pressure etc..
These things never get the blame for guide wear. Me I don't give any credence at all to the notion that bronze type guides don't last and I figure you don't either maybe (?). Sure OE guides are OK for what they are, but they're not that good..


GC