Concerned about fitting up-rating parts to injection engines?

A short while ago I had several conversations via e-mail with folk abroad who were a little concerned about fitting up-rating parts to their injection engines - like one of the many 'GSi' tuning kits available. A rumour had been put about that fitting this kit caused engine damage. Closer questioning culminated in the rumour saying that the high lift (1.5 ratio) rockers were causing camshaft and valve/guide damage. You know me - I can't let things like this alone until I find out the root cause. After some more digging and goading, I believe I've found the problem.

Cam damage is usually caused by something amiss in the valve train - obviously. Since the engines concerned were as they came from Rover and had done many thousands of miles without issue, it had to be something to do with these kits. The finger was pointed at the rockers because somebody got hold of the wrong end of the stick. Proven by the fact that not ALL folk using the variously available kits were having problems. In fact I came across a guy that had had a problem with the standard head and rockers - turns out he'd re-conditioned the head. So what was the common cause? Valve springs. Having checked various installations, including Mr Standard's re-built head I found the valve springs used were somewhat over the top for road use - to the order of 300lb! So for those contemplating up-rating your engines (any type, not just injection ones) with a modified head, make sure you ask questions about valve spring rates. 180lb free rate is generally enough for all road applications up to about 7,200rpm. Even most race engines don't need more than 240lb springs.

The valve guide thing was a little more difficult to sort out as there were various scenarios being discussed. Generally I think it was an issue with miss-matching components. There are several does and don'ts when it comes to valve guides and valve compatibility, so here's a quick run down on what will and won't work.

Material choices for guides are down to two distinct types - cast iron and bronze. Yes, cast iron. NOT steel as described in many adverts and by vendors. Never have been never will be. These are as fitted to the various Mini cylinder heads as standard in all applications. Cast iron is used because it is a very dissimilar metal from any used in valve manufacture - important to eliminate galling that causes seizure of the valves in the guides, is softer yet wears well. Bronze, on the other hand, is a very general description as there are a variety of 'bronzes' used by various folk. In the days of yore, the bronze base type used was 'PB1' (also known as 'Navy Bronze') - a phosphor-bronze alloy that was very orange in colour, and very soft. Used primarily in race engines, unfortunately they wore out very quickly. Silicone-brass content bronze is probably the most popular now - often with a high aluminium content, is very yellow/gold in colour - along with manganese-bronze used by many mainstream car manufacturers.

Valve materials are very varied, but essentially there are three groups. The first is the standard road spec, second up-rated standard road spec, and lastly race spec. The material types for both road spec valves are both complicated and irrelevant. All you need to know is that the early types had plain finished stems and seats, the up-rated (or modern) ones have chrome-plated stems with triple-material heads giving a super-hard seat area - both to improve longevity, particularly where unleaded fuel is used.

Race spec valves are almost universally EN214N stainless steel. Despite what folk have been lead to believe, they are not necessarily as hardwearing as the standard type valves unless treated in a certain way. This material is used because it is easy to form and machine yet resilient enough to perform reliably in the combustion chamber's extremely harsh environment. Used in their 'raw' form, they're OK when used with leaded fuel, effective lead-substitute treated fuel, or proper race fuels but wear very quickly when unleaded fuel is used. Paul Ivey's 'Specialised Valves' company have been chrome-plating the stems for many years - instigated on his Rimflo valves so folk could use them in the standard cast iron guides. A very expensive process and difficult to apply correctly without causing weakening of the valve stem - something Paul Ivey found out early on - so up-to-date designs use Tuftriding or Plasma Nitriding instead. Unleaded fuel is the bugbear as can be seen from the former text, largely because of the 'high-drying' solvents used in it.

These are extremely abrasive, cleaning away any traces of normal lubrication - such as engine oil. Material miss-match between valves and guides will cause galling leading to seizure of the valve in the guide, exaggerated by the unleaded fuel thing. So what valves do you use with which guides? Cast iron guides; use either standard road spec valves - preferably the up-rated, chrome-stemmed items - or race spec valves that have been hard chrome plated, Tuftrided or Plasma Nirided on the stems. DO NOT use raw EN214N race valves, they will seize in the guides. Bronze guides; you can use any type of valve material you like.