Valve Guides for Performance Engines
1 - Intro
If you are here, it is probably because you are searching for higher performance from your engine… in this quest there are common modifications like more aggressive camshafts, bigger valves, head porting, exhaust system or racing carburetors and ignition.
The truth is valve guides are often forgotten when building a high performance engine… but they are very important!
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2 - Valve Guide Function
The main function of the valve guide is to support the valve during its motion, thus guaranteeing concentricity between the valve and the valve seat – a requirement for good combustion seal and engine performance.
Secondly, valve guides must also remove heat from the valve stem, mainly from the exhaust valve.
On top of this, the guide usually receives the valve stem seal, preventing oil from entering the combustion chamber.
Our friend – The Valve Guide
3 - Valve Guide Malfunction
As the valve guide naturally wears out, excessive clearance or ‘play’ between the valve stem and valve guide is the result. The consequences of this are:
• Irregular valve motion or wobbling – because the guide can no longer locate the valve and maintain concentricity with the seat the combustion chamber will not seal adequately, resulting in reduced performance
• Accelerated valve wear – as the guide wears, its ability to remove heat from the valves is compromised, reducing valve longevity – particularly in the case of exhaust valves
• Higher oil consumption – with the increased space between the valve and the guide, higher oil consumption is natural resulting in blue smoke out of the exhaust), burnt oil deposits on the spark plug, valves and ports and overall loss of performance.
Worn out guides will result in a slight oil residue
4 - Valve Guide History
The original valve guides were usually made of Cast Iron and this is still a reasonably good valve guide material that is used on most modern street engines.
On some cases (mostly auto engines), as the heads were made of cast iron, there wasn’t a separate guide, the guide was integral with the head - basically hole was drilled directly into the head for the valve to slide in.
On the other hand, motorcycle engines are mostly made out of aluminum which is a terrible valve guide material, so a separate guide is required for these cylinder heads. Original aluminium cylinder heads generally have cast iron guides that are pressed into the aluminium head with an interference fit.
Cast Iron Valve Guides are the manufacturers choice for obvious reasons... ($$$$)
Bronze Alloy Valve guides have been a performance modification for a long long time but the manufaturers (Honda, Yamaha, Suzuki, Kawasaki,…) only recently started using them on their highest performance motorcycles that come with Titanium Valves from the factory – Yamaha R1, GSXR 1000, ZX10R, CBR1000RR…
Needless to say that the vast majority of purpose built racing engines (cars, bikes, boats, etc) also use bronze alloy guides.
5 - Why Should I Care?
Valve guides are a wear item so the older the engine the more likely it is that the guides will be out of spec.
So, even if we are only reconditioning a cylinder head to original conditions without further modifications, valve guides can be out of spec and need replacing.
If we are preparing a head for higher performance or racing and we want to port the cylinder head, the first step before any porting can begin is removing the old valve guides because otherwise porting will be compromised by lack of access to critical areas of the port, resulting in a less than adequate job.
Grinding the guide away while porting is not the solution as the resulting increase in port flow will be negligible and the actual result will be a substantial loss of support to the valve stem, resulting in accelerated wear of both the guide and the valve with the known consequences – loss of sealing, oil consumption, valve damage and overall loss of performance.
After removing the original guides and porting the cylinder head, you must now reinstall the new guides before the final valve job – a 3 angle performance valve job or equivalent is in order.
Used valve guides should not be reused
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6 - High Performance Valve Guides - Bronze Alloy
The original valves guides on most auto and motorcycle engines are made of Cast Iron. This is an adequate material and works perfectly well but there it was also chosen because of cost constrains as there are better materials available.
F1 Bronze Alloy Valve Guide with pneumatic actuator (replaces valve spring)
Bronze Alloy (with other metals mixed in in various proportions) is the best material available for valve guides and here are the main advantages:
1. Reduced Valve Wear - Bronze Alloy is very kind to all types of valves - Steel, Stainless Steel (like ABUSO) and even Titanium - preventing scuffing and galling of the valve stem
2. Heat Transfer – Bronze Alloy is has much better heat conductivity than cast iron, excelling at removing heat from the valve – one key function of the valve guide
3. Reduced Valve to Guide Clearance – As the Bronze Guide is able to remove more heat from the valve and has better lubricity, the clearance between the guide and the valve can be reduced and because a tighter guide better locates the valve head the results are improvements in combustion seal as well as valve and seat longevity
4. Flow Increase – All guides protrude into the intake and exhaust port and represent an impediment to flow. Aftermarket Bronze Guides are designed with optimized profile to reduce this issue and increase flow by a small margin
5. Price – Incredibly, despite the substantially lower production costs of the original Cast Iron guides, motorcycle manufacturers (looking at you Suzuki, Yamaha, Kawasaki, Honda, etc…) charge BIG MONEY for replacement guides for no apparent reason (around 40€ each is not uncommon). Multiply by 16 and cry all night…
6. Availability – If outrageous prices were not bad enough, some guides for older models are no longer available from the Manufacturers – the Yamaha FZR 1000 comes to mind
7. Retainer to Valve Seal Clearance – on most modern motorcycle cylinder heads, the valve seal is mounted on top of the guide. When installing performance camshafts that have higher valve lift than stock, the distance between the bottom of the valve spring retainer and the top of valve seal decreases – This is a problem because If contact occurs, the valve seal will be damaged and oil will enter the combustion chamber among other potential problems.
Bronze guides can alleviate this situation, locating the seal further down, ensuring at least 1mm of clearance between the bottom of the retainer to the top of the seal at the maximum valve lift point.
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Conclusion
Valve guides may not be the sexiest part of an engine but they are vital for a well running engine.
Older engines such as the Honda CB, Suzuki GSX, GSXR and many others will have more wear and so the valve guides will often need to be replaced when refreshing the head or making performance modifications.
Aftermarket Bronze Alloy Guides are the best alternative for your performance cylinder head because they have many advantages and are usually cheaper than those available at the dealer, if they are still available.
Honda CB750 SOHC refreshed with Bronze Alloy Guides