Vintage Triumph Engine Parts: 500, 650, 750 Twins & Triples

Shop engine parts for classic Meriden Triumph motorcycles: pre-unit and unit 500 and 650 twins, oil-in-frame T120 and T140 750s, and T150/T160 Trident triples. The range includes:

• Hepolite, Hastings and Grant pistons and rings
• G&S and Kibblewhite valves, guides and springs
• camshafts, cam bushes and tappets
• crank bearings and big-end shells
• cylinder barrels and heads
• Aerco 650-to-750 big-bore kits
• gasket sets and year-specific engine bolt kits

Triumph engines changed a great deal between 1937 and 1983. Before you order, confirm your engine number, model, year, capacity and era (pre-unit, unit or oil-in-frame), and measure what’s worn. The guide below explains the history and the key things to watch for.

A Short History of the Triumph Engine

Era	Years	Key engines	What changed
The Speed Twin arrives	1937–1939	5T Speed Twin 500, T100 Tiger	Edward Turner’s 498 cc 360° parallel twin was lighter than many contemporary singles, with more power and torque. It set the template for British twins for decades (Wikipedia: Speed Twin; Edward Turner).
Pre-unit 650s	1949–1962	6T Thunderbird, T110, TR6, T120 Bonneville	The 650 Thunderbird (71 × 82 mm, 649 cc) was launched in September 1949 for the US market. The Bonneville followed in 1959 (Wikipedia: Thunderbird; Wikipedia: T120). The engine and gearbox are separate units, with magneto ignition and dynamo or alternator charging.
Unit construction	Late 1950s (350/500 C-range); 1963 (650 B-range)	3TA, 5TA, T90, T100, 6T, TR6, T120	Engine and gearbox share one casing. The 650s gained a 9-stud head and barrel in 1963 (JRC Engineering; webBikeWorld).
Triples	1968–1975	T150 Trident, X75 Hurricane, T160, BSA A75	Triumph’s 750 cc OHV triple. The T160 added electric start and forward-inclined cylinders (Wikipedia: Trident/Rocket 3).
Oil-in-frame (OIF)	1971 on	T120, TR6, T100	A shared BSA/Triumph frame carries the engine oil, and rocker boxes are located by dowels (Wikipedia: T120; BMC Motorcycles).
750 twins	1973–1983	T140V, TR7, T140E, T140ES, TSX, TSS	Early T140Vs were 724 cc, then 744 cc with a 76 mm bore, a 10-stud head and a 5-speed gearbox. The E (emissions) model arrived in 1978, and the ES with electric start in 1980 (Wikipedia: T140).
The Meriden Co-operative	1975–1983	T140 range	Workers restarted Bonneville production in March 1975, and the co-operative was liquidated in August 1983 (Motorcycle Classics; Run Moto Run).

For model-by-model detail, see the Ian Chadwick Triumph timeline and TMB Books’ Bonneville model list.

What Makes Triumph Engines So Good

• Light, narrow and torquey. The parallel twin made more power than a single without the bulk of a four. That’s why other British makers copied it (Run Moto Run).
• Simple to work on. It’s air-cooled with two valves per cylinder, two gear-driven camshafts, and pushrods you can adjust with basic tools.
• Very tunable. Twin-carb heads, performance cams, high-compression pistons and 650-to-750 big-bore kits have been used since the Bonneville’s salt-flats era.
• Excellent parts support. Many parts carry over between years and models. For example, T140 tappet blocks fit any 650 from 1969 on (JRC Engineering), and the original-specification suppliers are still in business.
• A huge knowledge base. Factory manuals, owners’ clubs and decades of forum experience mean almost every problem has a known fix.

What’s a Pain with Triumph Engines

Oil leaks, especially at the top end

Triumph twins use external pushrod tubes. Meriden revised the tappet blocks, tubes and seals many times, but never fully eliminated leaks (our top-end sealing article; JRC Engineering). On 1970 and earlier engines, head bolt tension is applied through the rocker boxes, so squashed rocker box gaskets lose clamp and leak (BMC Motorcycles).

The sludge trap

The crankshaft has a sludge trap that acts as a centrifugal oil filter. It can only be cleaned with the crankcases split. Cleaning it is mandatory on any bottom-end rebuild, because packed sludge starves the big ends (Classic British Spares; BMC Motorcycles). We stock the 350/500 sludge trap tube.

Wet sumping and the plunger oil pump

Grit under the pump’s check balls, or a worn scavenge plunger, lets oil drain into the crankcase or stops it returning to the tank (JRC Engineering). Late T140s received a revised four-valve pump to address this (webBikeWorld).

Main bearings

Unit 650s up to mid-1972 generally use a ball bearing on the timing side and a roller on the drive side. Five-speed models moved to a metric timing-side bearing, and some builders report cage failures with the standard 8-ball type (BMC Motorcycles). Fit the correct bearing for your cases, such as the NSK CN main bearing listed for 1966–72 650s and 1973–76 750s.

Vibration

A 360° twin vibrates, and the stiffer unit-construction engine passed more of it to the rider (Hagerty). Check fasteners, the head steady and engine mounts after a rebuild.

Mixed threads and constant change

Triumph changed parts almost every year. Pre-1969 engines use mostly CEI threads, and later engines use UNF/UNC. Early T140s still had four 3/8″ CEI head bolts until mid first year (BMC Motorcycles). See our Triumph hardware guide.

Early T140 quality

The first 750s had well-documented quality problems (Hagerty), and head-gasket sealing on 10-stud heads needs care.

Key Things for New Triumph Mechanics to Watch For

1. Identify the engine before buying anything. Read the engine number, then use a Triumph parts book and workshop manual for that year. Engines are often swapped between frames.
2. Know your era. Pre-unit, unit and OIF parts often look alike but don’t interchange. For example, an 8-stud pre-unit barrel and a 9-stud unit barrel have different stud spacing, so a 9-stud head won’t bolt to an 8-stud cylinder (JRC Engineering).
3. Match the bore:
   • 69 mm for 500s
   • 71 mm for 650s
   • 76 mm for 750s (early T140Vs were 724 cc)
   • Order pistons in the bore’s current size (standard or oversize) after measuring.
4. Set pushrod tube crush. The head should sit about .030″–.040″ off the gasket before torquing. Adjust with seal thicknesses or head gasket thickness. Too much crush warps the head, and too little leaks (our article). Thicker copper gaskets, such as the .080″ T140 head gasket, help after head skimming.
5. Remember 750 pushrod tubes are shorter than 650 tubes (JRC Engineering).
6. Always clean the sludge trap whenever the crank is out.
7. Check the cams and followers together. Fit new or reground followers with new cams, and use nitrided cams where available. Check the cam bushes for wear: 1950–69 or 1970–88.
8. Use original-specification fasteners. Use the correct-thread engine bolt kit and rod bolts for your year, and never reuse rod bolts.
9. Retorque and readjust. Retorque the head and reset tappet clearances after the first heat cycles and short run-in, as the manual specifies.
10. Fix the oil system first. Clean the oil tank and frame (OIF frames trap debris after an engine failure), replace the filters, check the pump, and confirm oil returns to the tank on first start. An oil pressure gauge kit makes this easier.

Shop Triumph Engine Parts by Type

Pistons and rings

500 (69 mm):

• T100 Hepolite piston set 1967–74
• T100 Hepolite set 1958–66
• 500 pistons with Grant rings 1967–74
• 500 Hepolite rings

650 (71 mm):

• 650 Hepolite piston set 1959–72
• T120/TR6 pistons with Grant rings
• Pre-unit 7:1 piston set
• 650 Hepolite rings
• 650 AE/Goetze rings

750 (76 mm):

• 750 Hepolite set 1973–78
• 750 low-compression Hepolite set 1979–83
• TR7/T140 pistons with Grant rings
• 750 Hepolite rings
• T140 Hastings rings

Big bore and triples:

• Aerco 650-to-750 big-bore kit
• Aerco 76 mm replacement pistons
• T150/T160 Hepolite triple rings
• Ring installation tool

Valves, guides and springs

• 650/750 G&S valves with Kibblewhite bronze guides, complete set 1964–78
• 650/750 G&S inlet valve 1966–83 and exhaust valve 1966–83
• Kibblewhite Black Diamond inlet and exhaust valves
• 500 T100 G&S inlet 1967–74 and exhaust 1967–74
• T150/A75 G&S inlet and exhaust valves
• Kibblewhite manganese-bronze guides with seals
• T140 premium exhaust guides 1979–82
• Kibblewhite valve spring sets: 650 and 750

Camshafts, tappets and valve train

• T140/TR7 nitrided cam set
• 650 half-race cam set
• 650 nitrided inlet cam
• Exhaust cam follower
• Hepolite tappet blocks: inlet 1969–79 and exhaust 1969–79
• Allen-head tappet adjusters
• Rocker arm thrust washer kit
• Rocker spindle
• Rocker oil feed pipes: T140 and T100
• Pushrod tube seal kit 1969–79
• Trident pushrods: T150 and T160

Crankshaft, bearings and rods

• NSK CN main bearing
• Big-end shells: 650/750 Hepolite, 650/750 to 1982 and 350/500
• Triples: main bearing shells and conrod shells
• Hepolite H-beam 4340 conrods
• Forged rod nut and bolt set
• Small-end bushes
• Flywheel bolt
• Sludge trap tube (350/500)

Barrels, heads and rocker boxes

• Barrels: pre-unit 8-hole 1950–62, 9-stud 1963–72 and T140 10-hole 1973–80
• Heads (special order): TR6 9-stud head 1963–72 and TR7 10-stud head 1973–82
• 650 rocker box pair 1963–70
• Copper rocker box base gasket
• T140 head socket nut and bridge plate set
• T140 head steady

Gasket sets and seals

• Unit 650 top-end decoke set
• Pre-unit 650 top-end set
• Unit 500 top-end set
• T140 top-end set
• T120/TR6 4-speed oil seal kit
• Triples: T150 complete gasket set, T160 complete gasket set and oil seal kit
• More: Triumph gaskets

Engine bolt kits and studs

• Complete engine bolt set 1971–82
• T120 engine case bolt set 1963–66
• Unit 650 head bolt kit 1963–70
• T100 head bolt set 1961–74
• 750 base stud set
• T140 base nut kit
• More: Triumph hardware

Installation and Usage Tips

• Build clean. Wash the cases, clean all oilways and the sludge trap, and flush the oil tank or OIF frame.
• Measure, don’t guess. Check the bore, piston-to-bore clearance, ring end gap, big-end clearance with Plastigauge, valve stem-to-guide clearance, and crank end float.
• Fit valve guides with the head hot. Then re-cut the seats concentric with the new guides.
• Head gaskets. Use a new copper gasket for your engine. Anneal it if the instructions say so. Torque in the manual’s sequence, and retorque when it says to.
• Pushrod tubes. Set crush to about .030″–.040″ before final torque. Use Viton seals on 1969-and-later engines (JRC Engineering).
• Rocker boxes. On 1970 and earlier engines, use copper or wire-reinforced rocker box gaskets on flat faces, and check the head bolt torque again after heat cycles (BMC Motorcycles).
• Cams and followers. Lubricate them generously on assembly, and follow a proper run-in.
• Valve timing. Align the timing marks on the crank, intermediate and cam gears as the manual shows.
• First start. Prime the oil system, check that oil returns to the tank within a minute or so, and watch the oil pressure.
• Run-in. Vary the revs, avoid lugging, change the oil early, and recheck the head torque, tappets and fasteners.
• Tools. You’ll need Whitworth/BSF and AF spanners, a torque wrench, and Triumph-specific pullers. Browse Triumph service tools and engine tools.

Related Triumph Categories

Vintage Triumph parts · Triumph gaskets · Triumph hardware · Triumph oil & air · Triumph carburetor · Triumph clutch & primary · Triumph transmission · Triumph electrical · Triumph exhaust · Triumph frame · Triumph manuals · Triumph parts books · Triumph service tools · BSA engine · Norton engine

Brands: Hepolite · Hastings · Grant · G&S Valves · Kibblewhite · Aerco · LF Harris

Further Reading (external)

• Triumph Speed Twin – Wikipedia
• Triumph Bonneville T120 – Wikipedia
• Triumph Bonneville T140 – Wikipedia
• BSA Rocket 3 / Triumph Trident – Wikipedia
• Ian Chadwick – Triumph timeline
• JRC Engineering – Triumph tappet blocks and pushrod tubes by year
• JRC Engineering – wet sumping fix
• Classic British Spares – sludge trap information
• BMC Motorcycles – owning a T140
• BMC Motorcycles – twin and triple crankshaft issues
• Hermit.cc – unit 650 overhaul manual

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Vintage Triumph Engine FAQs