Honda valve stem seals – OEM vs Supertech comparison, 5.5 mm and 6.6 mm sizes, manufacturer differences and durability
Valve stem seals are one of the key components that often decide whether a Honda engine runs clean and predictably or starts burning oil and producing blue smoke under certain conditions. This is particularly true for older D, B and H series engines, but the problem is also common in newer units with higher mileage.
In everyday workshop practice, worn valve stem seals are one of the most common causes of oil consumption, even when the engine is mechanically sound, has good compression and shows no typical symptoms of worn piston rings.
In this article we explain:
- what role valve stem seals play in Honda engines,
- which symptoms indicate worn seals,
- how the genuine OEM versions (NOK / ARS) differ and how OEM compares to Supertech in real use,
- which valve stem seal sizes Honda uses (5.5 mm and 6.6 mm) and in which engines you will find them,
- how to choose the correct set for your engine and what to watch out for during replacement.
What are valve stem seals and what do they do?
Valve stem seals are installed on the valve guides in the cylinder head. Their tasks are:
- to control the amount of oil that lubricates the valve stem,
- to prevent excessive oil from entering the combustion chamber.
Every engine has separate seals for intake and exhaust valves. Exhaust valve seals operate in much harsher temperature conditions, so their resistance to heat and material ageing is crucial for the overall durability of the set.
In Honda engines – especially high-revving D/B/H/K series – valve stem seals have a tough life: high rpm, frequent load changes, and often extended operation in high-VTEC ranges. Over time, the seal material hardens, loses elasticity and stops sealing properly against the valve stem. Importantly:
- seal wear usually does not cause any drop in compression,
- the problem is therefore often ignored for a long time or wrongly attributed to other engine components (piston rings, turbocharger, “worn-out engine”).
Valve stem seal sizes in Honda engines: 5.5 mm and 6.6 mm
Honda engines use two main valve stem diameters (and therefore two main seal sizes):
- 5.5 mm – the most popular size in many newer (and some older) engines,
- 6.6 mm – less common, typically found in selected D/B/H/B20/H23 engines.
It is the valve stem diameter, not the outer diameter of the guide, that determines which seal you need. A seal is matched:
- on the inside – to the valve stem diameter (5.5 or 6.6 mm),
- on the outside – to the valve guide in a specific engine head.
Therefore:
- you must not mix 5.5 mm and 6.6 mm seals “by eye”,
- a 6.6 mm seal will not correctly seal a 5.5 mm valve (it will be too loose → oil will enter the cylinder),
- a 5.5 mm seal will not properly fit a 6.6 mm stem, and attempts to install it usually end with damage to the seal or the valve.
In practice, seal size is always chosen based on:
- the engine code (D16Z5, B16A1, H22A, etc.),
- the OEM valve stem seal part number (Honda),
- and, if necessary, a direct measurement of the valve stem with a micrometer (for deep head rebuilds or mixed-spec heads).
Applications of 5.5 mm valve stem seals – list of Honda engines
Below is a list of selected Honda engines that use 5.5 mm valve stem seals:
1.0 – ECA1, P10A2
1.2 – L12A1, L12A2, L12A3, L12A4, L12B1, L12B2, L12B4
1.3 – L13A1, L13A3, L13A5, L13A6, L13A7, L13B2, L13Z1, L13Z2, L13Z4, LDA1, LDA2, D13B1, D13B2, D13B6, D13B7, D13B8
1.4 – D14A1, D14A2, D14A3, D14A4, D14Z1, D14Z2, D14Z5, D14Z6
1.5 – D15B1, D15B2, D15B6, D15B7, D15B8, D15Z1, D15Z3, D15Z6, D15Z8, D15Y3, L15A1, L15A6, L15BA, L15BB, L15B7, L15BY, LEA1, L15C2, L15BE, L15BG, L15BJ
1.6 – D16A6, D16A7, D16Z1, D16Z2, D16Z6, D16Z7, D16Z9, D16Y2, D16Y3, D16Y5, D16Y6, D16Y7, D16Y8, D16B2, D16W1, D16W2, D16W3, D16W4, D16W5, D16W7, D16B6, D16B7, D16V1, B16A1, B16A2, B16A3
1.7 – D17A2, D17A5, D17A8, D17A9, D17Z2, D17Z3
1.8 – B18C1, B18C4, B18C6, R18A1, R18A2, F18A2, F18A3, F18B2, F18B3, R18Z1
2.0 – F20A2, F20A3, F20A4, F20A5, F20A8, F20Z1, F20Z2, F20B3, F20B5, F20B6, F20C1, F20C2, F20B7, K20A2, K20A1, K20A, K20A4, K20A5, K20A9, K20A6, K20Z3, K20Z4, K20C1, LFC1, LFC2, LFC3, LFB1
2.2 – F22A1, F22A2, F22A4, F22B1, F22B4, F22B5, F22B8, H22A1, H22A2, H22A4, H22A5, H22A6, H22A7, N22A1, N22A2
2.3 – F23A3, F23A4, F23A7, F23A8, F23Z5
2.4 – K23A3
2.5 – G25A1, G25A4
3.0 – C30A1, C30A3, C30A4, J30A1, J30A4, J30A5
3.2 – C32A2
3.5 – J35A, J35A4, J35A5, J35A6, J35A9, J35Z2, C35A1, C35A2, C35A3, C35A4, C35A5
In practice this means that most popular petrol Honda engines (Civic, Accord, CR-V, Jazz, FR-V, Prelude, Integra, plus some N22 diesels) run on 5.5 mm valve stems and use matching 5.5 mm seals – both OEM and Supertech.
6.6 mm valve stem seals – applications and OEM numbers
A smaller but very important group are engines with 6.6 mm valve stems. You will find them for example in:
- D16Z5, D16A8, D16A9,
- H23A2,
- B20B2, B20B3, B20B9, B20Z1, B20Z3.
For these engines Honda provides separate OEM references – one set for intake valves and another for exhaust valves.
Intake seals (6.6 mm):
- 12210-PM7-003
- 12210-PM7-004
- 12210-PT2-003
- 12210-PT2-004
Exhaust seals (6.6 mm):
- 12211-PH7-003
- 12211-PH7-004
- 12211-PT2-003
- 12211-PT2-004
These are OEM reference numbers – when choosing an aftermarket alternative (e.g. Supertech), we use them as a starting point rather than a strict requirement to buy the genuine Honda part. Good catalogues and an experienced seller can select the correct 6.6 mm aftermarket set based on these references.
For 6.6 mm engines it is important to:
- never mix 5.5 and 6.6 mm seals during a rebuild (even if “they seem to fit”),
- not rely solely on the production year – the precise engine code and OEM part number from the documentation are what matters,
- if in doubt – measure the valve stem with a micrometer or check markings / documentation for the head.
Symptoms of worn valve stem seals in Honda engines
The typical symptoms are essentially the same for both 5.5 mm and 6.6 mm seals:
- blue smoke from the exhaust at start-up, especially after a longer standstill,
- smoke after prolonged engine braking (e.g. long downhill and then throttle applied again),
- increased oil consumption with no visible external leaks,
- oily or heavily contaminated spark plugs,
- burnt oil smell in the exhaust gases,
- at the same time usually no clear loss of power or compression.
A characteristic feature is that the smoke often appears briefly and disappears after a few minutes of driving, which distinguishes this problem from worn piston rings. In 6.6 mm engines (e.g. D16Z5, B20B, H23A2) these symptoms are very common at mileages above roughly 250–300,000 km, especially if the engine has been driven hard.
Valve stem seals vs piston rings – basic diagnostics
Distinguishing between these two faults is essential in diagnostics:
Worn valve stem seals:
- smoke after a standstill, at cold start, after engine braking,
- compression usually within spec,
- often acceptable performance,
- oil enters the combustion chamber mainly from the top (via the valves).
Worn piston rings / cylinders:
- smoke under load and on acceleration,
- high and constant oil consumption,
- often reduced compression,
- oil enters mainly past the pistons and rings.
In many cases basic diagnostics (visual inspection, compression test, leak-down test) are enough to narrow down the problem without disassembling the engine. For D/B/H engines with 6.6 mm valves, a full set of new seals is often the most reasonable first step in terms of cost.
Genuine Honda valve stem seals – differences between OEM versions
Contrary to popular belief, genuine Honda valve stem seals do not always come from a single manufacturer. Over the years Honda has used several approved OEM suppliers, and the differences between individual versions relate mainly to:
- the manufacturer,
- country of origin,
- packaging method,
- minor details such as shape or rubber colour.
All variants described below are genuine Honda OEM parts, compliant with factory specifications and intended for the same applications.
Honda OEM – NOK (Made in USA)
Reference numbers (example PZ1 series, 5.5 mm):
- 12210-PZ1-004 – intake
- 12211-PZ1-004 – exhaust
Manufacturer: NOK
Country of origin: USA
In this version, seals are supplied in bulk packaging, usually 10 pieces of one type in a bag or box. In practice, a set for one engine is taken from the manufacturer’s bulk pack. Technically this is full-value Honda OEM; the differences compared to other versions are logistical, not functional.
Honda OEM – NOK (Made in Japan)
Reference numbers:
- 12210-PZ1-004 – intake
- 12211-PZ1-004 – exhaust
Manufacturer: NOK
Country of origin: Japan
Here, each seal is packed individually in its own small bag. Technically it is the same OEM specification, but the packaging is clearer and more convenient for the customer and the workshop (easier to count a complete set, lower risk of mix-up).
Honda OEM – ARS (Arai Rubber Seal, Made in Japan)
Reference numbers:
- 12210-PZ1-003 – intake
- 12211-PZ1-003 – exhaust
Manufacturer: ARS – Arai Rubber Seal
Country of origin: Japan
This is an older Honda OEM reference, still present in the genuine parts network. Functionally it fully meets Honda’s factory requirements.
For engines with 6.6 mm valves you also have the references mentioned earlier:
- intake: 12210-PM7-003 / -004, 12210-PT2-003 / -004,
- exhaust: 12211-PH7-003 / -004, 12211-PT2-003 / -004.
Here too there are different suppliers and series, but as long as you have the correct OEM part number and buy through an official channel, you can treat them as equivalent.
What do all OEM versions have in common?
- they are genuine Honda parts,
- they meet the same factory specification,
- they are intended for the same engines (for a given reference),
- differences relate mainly to manufacturer, country of origin and packaging, not function.
You can buy set of genuine valve steam seals HERE
OEM vs Supertech – practical comparison
On the aftermarket, Supertech valve stem seals are very popular. They are used both in stock engines and in performance builds (turbo, supercharged, high VTEC, high rpm).
In practice:
- Supertech offers very good durability relative to price, uses modern materials (e.g. Viton), and is often designed for higher temperatures and more aggressive fuels/oils,
- complete sets are available for both 5.5 mm and 6.6 mm valves, covering the popular D/B/H/K/F/R engines,
- for serious modifications (Supertech valve springs, stiffer retainers, higher rpm) a matching set of Supertech seals is a natural choice.
You ca buy 5,5 mm version HERE. If you are looking for bigger 6,6 mm, check THIS.
Honda OEM in turn is:
- the choice for those who prefer factory specification,
- a very safe option for stock engines,
- often used in “OEM-style” rebuilds and in cars where documentation and originality are important.
In real-world use both options work well, provided that:
- they are correctly specified (5.5 / 6.6 mm, correct engine code),
- they are installed properly (no damage to sealing lips, correct seating depth and alignment).
How to select the correct valve stem seals for a Honda engine
Step by step:
- Check the engine code – on the block, in the registration papers or via VIN (e.g. D16Z5, B16A2, H22A7, B20B3, etc.).
- Verify valve stem diameter – in a reliable catalogue (for most engines it is known whether they are 5.5 or 6.6 mm) or by direct measurement during a rebuild.
- Find the OEM part number – in the Honda EPC / parts catalogue / head documentation (e.g. 12210-PM7-003).
- Choose the correct set:
- Honda OEM – by OEM reference number,
- Supertech – by application list / cross-reference to OEM numbers.
- Distinguish between intake and exhaust seals – do not mix them; they often differ in shape and material.
For 6.6 mm engines (D16Z5, D16A8, D16A9, H23A2, B20B/B20Z) it is particularly important to avoid accidentally fitting a 5.5 mm set just because it is more readily available. That is a quick way to end up pulling the head again.
Valve stem seal replacement – what to keep in mind
Valve stem seals can be replaced in two ways:
- with the cylinder head removed (full rebuild, easier inspection of guides, valves, springs),
- in many Honda engines – with the head still on the block, using the correct tools (valve retention by compressed air or a rope fed into the cylinder).
The key points are:
- correct installation technique,
- protecting the sharp edges and grooves on the valve stem (with a sleeve/tube while sliding the seal on),
- keeping intake and exhaust seals in their correct positions,
- checking and, if necessary, adjusting valve clearances after the work,
- inspecting guide wear (excessive clearance → new seals will not help for long).
Practical tips:
- always replace all seals as a complete set, not just those that “look bad”,
- use a proper installation tool – hammering with a random tube or screwdriver usually destroys the new seal,
- after reassembly, monitor oil consumption and any smoke for the first few hundred kilometres – some oil left in the exhaust ports may burn off for a short time,
- on high-mileage engines, it is a good idea to install new spark plugs after the job – the old ones are often oil-fouled and can make it harder to assess the improvement.
Summary
Worn valve stem seals are a common, yet often underestimated cause of oil consumption in Honda engines. In many cases, replacing them (especially on engines with 6.6 mm valves) can restore correct engine behaviour without the need for an expensive bottom-end rebuild.
The key points:
- Honda uses two main valve stem seal sizes: 5.5 mm (most common) and 6.6 mm (e.g. D16Z5, D16A8, D16A9, B20B/B20Z, H23A2),
- when selecting parts, always start with the engine code and OEM part number, then look at the brand,
- both genuine Honda OEM seals and Supertech seals are proven solutions,
- correct installation and awareness of the differences (size, intake/exhaust, OEM/Supertech) matter more than the logo on the box.
Choosing the right seals and replacing them properly is often the most cost-effective way to bring a “oil-burning” Honda engine back to health.
FAQ – frequently asked questions about Honda valve stem seals (OEM and Supertech)
Can worn valve stem seals cause oil consumption without loss of power?
Yes. Worn valve stem seals allow oil to enter the combustion chamber but usually do not affect compression. The engine can still deliver full power while oil consumption and occasional blue smoke increase.
Is blue smoke on start-up always caused by valve stem seals?
Not always, but very often. Blue smoke:
- after the car has been parked,
- after long engine braking,
is a typical symptom of worn valve stem seals. If the engine smokes continuously under load and during acceleration, the cause is more likely worn piston rings or, on turbo engines, the turbocharger.
Will replacing valve stem seals solve the oil consumption problem?
In many cases yes, especially if:
- compression is good,
- there are no heavy blow-by gases,
- cylinder walls are not deeply scored,
- the head is in reasonable condition.
If the bottom end of the engine is worn out, seals alone will only partially reduce the problem or make little difference.
Can I replace valve stem seals without removing the cylinder head?
In many Honda engines it is possible using the correct tools and valve retention (compressed air or a special rope in the cylinder). This does require experience – incorrect installation can damage the new seal immediately. For a full head rebuild it still makes sense to remove the head.
Do Honda OEM and Supertech seals differ in durability?
Both options are proven. In simple terms:
- Honda OEM – fully factory correct, ideal for stock engines,
- Supertech – very good durability for the price and designed with performance engines in mind.
The key is choosing the correct set (5.5 / 6.6 mm) and installing it properly.
How do I know if my engine has 5.5 mm or 6.6 mm valves?
The simplest approach:
- check the engine code (e.g. D16Z5, B20B3, H23A2 – typically 6.6 mm),
- use an application table or a reliable parts catalogue,
- during a rebuild, measure the valve stem with a micrometer.
If you are unsure, it is better to ask a Honda specialist than guess based on model year alone.
Can I mix OEM and Supertech seals in one engine?
Theoretically yes (for example OEM intake, Supertech exhaust), but it is not a good practice. It is best to use one type of seal throughout the engine in order to:
- maintain uniform operating conditions,
- avoid differences in ageing between materials,
- avoid confusion during future diagnostics.
Do I need to adjust valve clearances after replacing the seals?
Yes – on Honda engines with adjustable valve clearances, checking and, if necessary, adjusting them after seal replacement is recommended. This ensures correct valve operation, less valvetrain noise and longer service life of the new seals.
Can worn valve stem seals damage the catalytic converter?
Yes. Long-term oil burning can lead to:
- contamination of the catalyst substrate,
- overheating of the converter,
- in extreme cases – damage or blockage of the catalyst.
That is why it is not a good idea to postpone seal replacement if the symptoms are clear – especially on 6.6 mm engines, which can burn a lot of oil once the seals are worn.