04/03/2002
The MPJG Engine: Understanding its Design and Performance
The MPJG engine, a powerplant found in the classic MG TA, carries a lineage that stretches back to the utilitarian Morris 10/4 Series 2. While it boasts an overhead valve conversion, its fundamental design, rooted in an older side-valve architecture, dictates its performance characteristics. This engine was not engineered for high-revving agility but rather for robust pulling power and substantial torque, making it a dependable, albeit not overtly sporty, unit for its era.
A Heritage of Morris and Wolseley
The MPJG engine's journey began with its integration into the 1935 Morris 10/4 Series 3 (MPJM) and the Wolseley 10/40 (MPJW) before finding its home in the MG TA. This engine displacement of 1292cc was achieved with a bore of 63.5mm and a notably long stroke of 102mm. This long stroke measurement can be traced back to the very early Morris Bullnose engines, highlighting a continuous evolution of a core engine design.
Why Not a High-Revving Engine?
Several key design elements preclude the MPJG from being a high-revving engine. The long stroke, while contributing to torque, inherently limits the engine's ability to safely and efficiently reach high rotational speeds. Coupled with an un-counterbalanced crankshaft, which can lead to vibrations at higher RPMs, and a heavy flywheel designed to smooth out power delivery, the engine's rev ceiling is naturally constrained. Furthermore, the original cylinder head featured siamesed inlet and exhaust ports. This design, where ports share a common passage, can restrict the efficient flow of gases in and out of the cylinders, particularly at higher engine speeds. Finally, the presence of a wet clutch, while offering smooth engagement, also adds to the rotational mass that the engine must overcome, further contributing to its lower revving nature.
Despite these limitations, the MPJG engine was praised for its good pulling power and ample torque, making it well-suited for cruising and everyday driving in the TA.
The Quest for Crankshafts
As these engines approach their venerable age of 86 years, the availability of good original crankshafts has become a significant challenge for restorers and enthusiasts. Requests for these critical components are frequent, but supply is scarce. Many crankshafts that do surface are often found in poor condition, suffering from cracks or having been ground down to their maximum tolerances. This makes the careful selection of a replacement crankshaft all the more crucial.
This scarcity led to an initiative to produce a small batch of new, counter-balanced crankshafts for the TA. This project, initiated by Mike Williams, involved collaboration with Gosnays, a respected engineering firm. The process began with the examination of existing crankshafts, including a standard MPJG unit and a rare Laystall counter-balanced crank that had been used in TA Trials cars. The latter, though ground to –60 thou and showing a crack, served as a valuable pattern.
The result of this collaboration was a batch of five superb new counter-balanced TA cranks. While not inexpensive, costing £1850 plus VAT each, their quality was undeniable. These new cranks were distributed among enthusiasts, including Mike Williams, Roger Muir, and the author. The availability of such high-quality replacements offers a vital solution for preserving these classic cars.
Comparing Crankshafts
To illustrate the differences, a comparison of various crankshafts provides valuable insight:
| Crankshaft Type | Origin/Application | Key Features |
|---|---|---|
| Morris 10/4 Series 2 Crank | Original Morris 10/4 Series 2 | Precursor to the MPJG, typically un-counterbalanced |
| Standard MPJG Crank | Standard MG TA | Long stroke, un-counterbalanced, heavy flywheel |
| Laystall Crank (TA Trials) | Special application for TA Trials cars | Counter-balanced, potentially lighter than standard |
| New Gosnay Crank | Modern reproduction | Counter-balanced, high quality engineering |
Alternative Sourcing: The Morris 10 Crank
An interesting avenue for sourcing crankshafts involves the older Morris 10 crank. While visually similar, a key difference lies in the crankshaft nose. Adapting a Morris 10 crank to a TA engine would necessitate the fabrication of a new crank pulley. This pulley would need to be offset by 42mm to ensure proper alignment with the TA's water pump and dynamo pulleys. The advantage of pursuing this route is the greater availability of second-hand Morris 10 cranks, which may have led less demanding lives than their dedicated TA counterparts.
Future Crankshaft Production
The author has identified a local engineering firm with a specialization in crafting longer-throw cranks for Sunbeam Lotus engines. Given their expertise with high-revving performance engines, the prospect of them producing TA crankshafts is highly encouraging. Plans are underway to solicit a quote for another small batch of counter-balanced TA cranks, similar to the successful Gosnay units. Interested parties are encouraged to contact the author for updates.
The cost of refurbishing an old crank, with one owner being quoted £1365 plus VAT for metal spraying and grinding, puts the price of a new, precision-engineered crank into a more favourable perspective.
Spare Parts and Services for MG TA
For owners of MG T-type and pre-war models, a comprehensive spares service is available, offering a vast array of new and secondhand parts. This service, established in 1968, covers all aspects of the vehicle, from engines and chassis to bodywork and electrical components. They also provide invaluable technical advice and assistance, drawing on over 54 years of experience with MMM and T-type MGs.
The extensive stock includes:
- Engine components (crankshafts, camshafts, cylinder blocks)
- Chassis and suspension parts
- Bodywork and trim
- Electrical components (dynamos, starter motors, wiring harnesses, instruments)
- Wheels and tyres
- Brake and steering system parts
- Carburettors and fuel systems
- Gaskets and engine rebuild kits
Prices for some key components include:
- Rebuilt J & P gearboxes: £2250
- Rebuilt MG 'M' / Morris Minor gearboxes: £1950
- Rebuilt steering boxes (all models): £550 - £1150 (exchange or outright)
- Water pumps (PA/PB/NA/NB/L/K): £535
- Carburettors (various types): from £475pr to £950pr (restored)
- Complete TA carburettor sets (restored): £880pr
- Re-ground TA crankshafts: £350ea
In addition to parts, a range of specialist services are offered, including the full rebuild of steering boxes, gearboxes, differentials, and electrical boxes. These services provide peace of mind with firm quotations, delivery dates, and quality workmanship.
Attending Shows and Events
The supplier also attends major classic car shows, providing opportunities for owners to meet the team, view parts, and discuss their requirements. These include the MG Spares Day at Stoneleigh, Pre-War Prescott, and the Beaulieu International Autojumble.
For those seeking specific or rare parts, the advice is simple: just ask. With over 1000 parts in stock, the likelihood of finding what you need is high.
Conclusion
The MPJG engine, while not built for high-revving performance, remains a characterful and capable unit for the MG TA. Its design prioritised torque and usability. The challenges in sourcing original crankshafts are being addressed through modern reproduction efforts, ensuring the continued preservation of these beloved classic cars. The availability of a wide range of spare parts and expert services further supports the ongoing restoration and enjoyment of the MG TA and its contemporaries.
Frequently Asked Questions
Q1: Is the MPJG engine a high-revving engine?
A: No, the MPJG engine is not designed for high revving. Its long stroke, un-counterbalanced crankshaft, heavy flywheel, and siamesed ports limit its high-RPM capability. It is better suited for torque and pulling power.
Q2: Where can I find spare crankshafts for an MG TA?
A: Original crankshafts are rare. New, counter-balanced crankshafts are available from specialist suppliers, though they are a significant investment. Second-hand Morris 10 cranks can sometimes be adapted.
Q3: What are the main characteristics of the MPJG engine?
A: The MPJG engine is characterized by its 1292cc displacement, long stroke (102mm), and emphasis on torque and pulling power rather than high revs.
Q4: Are spare parts readily available for the MG TA?
A: Specialist suppliers offer a wide range of new and secondhand parts for the MG TA and other pre-war and T-type models, though some components like crankshafts are particularly scarce.
If you want to read more articles similar to MPJG Engine: A Look at its Characteristics, you can visit the Engines category.