Draper Cylinder Leakage Kit (7 Piece)

Know Not Just That There's a Problem — But Exactly What It Is

A compression test is a valuable first step in engine diagnosis, but it has a fundamental limitation: it tells you that compression is low in a cylinder, not what is causing it. Is it worn piston rings? A leaking valve? A blown head gasket? A cracked cylinder head? Each fault requires a different repair — and misdiagnosing the cause can mean unnecessary strip-downs, wasted parts and avoidable labour costs.

The Draper Cylinder Leakage Kit takes engine diagnosis to the next level. By introducing regulated compressed air into a cylinder at top dead centre and measuring precisely how much escapes — and where — it gives you the diagnostic information needed to identify the specific fault with confidence, before a single component is removed.

How Cylinder Leakage Testing Works

With the piston at top dead centre on the compression stroke and both valves closed, compressed air is introduced into the cylinder through the spark plug bore. A healthy cylinder will retain the vast majority of that air. A cylinder with internal wear or damage will allow air to escape — and the path that escaping air takes tells you exactly where the fault lies:

• Air escaping from the oil filler cap — Worn or damaged piston rings
• Air escaping from a neighbouring cylinder's dipstick or oil filler — Blown head gasket between cylinders
• Air bubbling in the coolant expansion tank — Cracked cylinder head or blown head gasket into the cooling system
• Air escaping from the inlet manifold — Worn or leaking inlet valve
• Air escaping from the exhaust — Worn or leaking exhaust valve

This diagnostic precision makes cylinder leakage testing an indispensable technique for any workshop carrying out serious engine diagnostics, and the Draper CTECL makes it accessible in a compact, well-priced 7-piece kit.

Twin Gauges for Complete Diagnostic Data

The kit features two 63mm diameter gauges working in tandem to give you the full diagnostic picture in a single test. The first gauge displays supply pressure from 0–100psi/0–7bar, confirming that the regulated air input is at the correct test pressure. The second gauge displays the percentage of cylinder leakage — a direct, easy-to-interpret figure that tells you immediately how much air the cylinder is losing relative to the supply.

Industry-standard thresholds give these leakage percentages clear diagnostic meaning: a cylinder retaining over 90% of supply pressure (less than 10% leakage) is generally considered healthy. Leakage between 10–20% indicates wear beginning to develop. Anything above 20% points to significant wear or damage requiring investigation, and figures above 30% typically indicate a major fault demanding immediate attention.

Both gauges are individually fitted with heavy duty rubber protectors, shielding the precision instruments from the workshop knocks and drops that precision gauges inevitably encounter in daily use.

Broad Spark Plug Thread Compatibility

The CTECL covers direct and indirect petrol engines using 10mm, 12mm, 14mm and 18mm spark plug threads — the four sizes that between them account for the vast majority of petrol engines encountered in a general workshop, from small motorcycle and compact car engines through to larger capacity performance and classic car units. Three adaptors are included to achieve this coverage, each threaded precisely to seal effectively in the spark plug bore during testing.

Air Supply Connection

The kit connects to a standard workshop compressed air supply via the included ¼" BSP air coupler — compatible with most workshop compressor and airline fittings. A regulated supply is required for accurate, consistent results; a pressure regulator between the compressor and the test kit is recommended if not already incorporated into your air supply system.

7-Piece Kit Contents

• 2 x 63mm diameter gauges (pressure and leakage percentage)
• 1 x 600mm flexible hose
• 1 x ¼" BSP air coupler
• 3 x Spark plug thread adaptors (covering 10, 12, 14 and 18mm)

All components are supplied in a fitted plastic storage case, keeping every adaptor and fitting organised and protected between uses.

Key Features & Benefits

• Twin 63mm gauges — Simultaneous cylinder pressure (0–100psi/7bar) and leakage percentage readings
• Percentage leakage display — Direct, interpretable figure pinpointing the severity of cylinder loss
• Fault-specific diagnosis — Identifies worn piston rings, valves, cracked heads and blown gaskets by leakage location
• 10, 12, 14 and 18mm spark plug thread coverage — Broad petrol engine compatibility across motorcycles, cars and light commercial vehicles
• Direct and indirect petrol engine compatible — Covers both principal petrol engine configurations
• 600mm flexible hose — Generous length for comfortable gauge positioning during testing
• ¼" BSP air coupler — Compatible with standard workshop compressed air supplies
• Heavy duty rubber gauge protectors — Workshop-durable precision instruments
• 7 pieces in a plastic storage case — Organised, protected and ready for use
• Complements compression testing — The logical next step when compression testing reveals a problem

Who Is It For?

The Draper CTECL is an essential tool for independent garages, engine specialists and experienced DIY mechanics who carry out engine diagnosis beyond basic compression testing. It's particularly valuable for anyone who wants to avoid unnecessary engine strip-downs by confirming the exact nature of a fault before committing to repair work — saving significant time and labour costs in the process.

Used alongside the Draper petrol compression test kits, it completes a professional engine diagnostic workflow: compression testing to identify which cylinders are affected, leakage testing to determine precisely why.

Technical Specifications

• 7-piece cylinder leakage test kit for direct and indirect petrol engines
• Accurately identifies worn piston rings, worn valves, cracked cylinder heads and blown head gaskets
• Twin 63mm gauges display cylinder pressure (0–100psi/7bar) and leakage percentage simultaneously
• Pinpoints fault location by identifying where compressed air is escaping from the engine
• Covers 10mm, 12mm, 14mm and 18mm spark plug thread sizes
• 600mm flexible hose with ¼" BSP air coupler for standard workshop compressor connections
• Both gauges fitted with heavy duty rubber protectors
• All 7 pieces supplied in a fitted plastic storage case
• Product Code: CTECL | Brand: Draper

Q: What is the difference between a compression test and a cylinder leakage test? A compression test measures the maximum pressure a cylinder can generate during cranking, indicating whether compression is within acceptable limits. A cylinder leakage test introduces compressed air into a static cylinder at top dead centre and measures how much escapes — and crucially, where it escapes from. This tells you not just that a cylinder has low compression, but specifically whether the cause is worn piston rings, leaking valves, a blown head gasket or a cracked cylinder head.

Q: What does the leakage percentage reading mean? The leakage percentage indicates what proportion of the regulated supply air pressure is being lost through the cylinder. As a general guide, under 10% leakage is considered good, 10–20% indicates developing wear, 20–30% suggests significant wear or damage, and above 30% points to a major fault. These thresholds can vary between manufacturers, so always cross-reference with the vehicle's service data where available.

Q: How do I identify which specific fault is causing leakage? With compressed air introduced into the cylinder, listen and feel for where air is escaping. Air from the oil filler cap indicates worn piston rings; air from an adjacent cylinder points to a blown head gasket between cylinders; bubbling in the coolant expansion tank suggests a head gasket or cracked head leaking into the cooling system; air from the inlet manifold indicates a leaking inlet valve; and air from the exhaust indicates a leaking exhaust valve.

Q: What air supply do I need to use this kit? The kit connects to a standard workshop compressed air supply via the included ¼" BSP coupler. A regulated air supply is recommended — typically between 90–100psi — to ensure accurate and consistent leakage readings. If your compressor output is not already regulated, a separate in-line pressure regulator is advisable.

Q: Is this kit compatible with diesel engines? No. The CTECL is designed for petrol engines using 10, 12, 14 and 18mm spark plug threads. Diesel engines use glow plugs rather than spark plugs and operate at significantly higher compression ratios. For diesel compression testing, see the Draper CTED2 or Draper Expert CTED1-E diesel compression test kits.

Q: Can I use this alongside the Draper compression test kits? Yes — and this is precisely how professional engine diagnosis is most effectively carried out. Use a compression test kit first to identify which cylinders are affected and by how much. Then use the CTECL to perform a leakage test on the affected cylinders to determine the specific cause, giving you the full diagnostic picture before any repair work begins.