Differences between Wet Clutch and Dry Clutch Power Units for VAs

by Jim Andrews

This article has been compiled to assist VA owners to identify the differences between the Wet and Dry clutch engines and also to identify the non-exchangeable component parts.

Part 1 of the article is a simple guide to the external changes enabling a non-technical individual to identify the different power units. Part 2 lists and identifies all the individual component changes.

The change to a Dry Clutch power unit during the production run of the VA model was a very significant event necessitating many component changes. Many VA owners have had problems having purchased second hand VA spares only to find they did not fit as they were for the other type of power unit. Significant other changes to the Dry Clutch power unit also occurred at engine TPBG 1891 and at TPBG 2237 (See Part 2 Component identification).

I would like to acknowledge Walter Prechsl, whose initial document was the incentive for me to compile this article.

PART 1

Factory Notification

The MG Factory issued a confidential Technical Information notification on 7^th March 1938 advising of the change from a wet clutch power unit to a dry clutch unit for the VA models.

The wording of the notification was:

Power Unit Identification

There are a number of visual changes that enable a non-technical individual to easily identify which power unit is fitted to a VA, or to identify a complete power unit if is for sale. NOTE: The actual engine number may differ to the one on the cars guarantee plate.

The visual indications are:

1. Engine Number (right hand side of block behind exhaust down pipe) Dry Clutch units are Number TPBG 1510 or higher.
   NOTE: If a replacement engine has been fitted the TPBG number may have been replaced with a Morris Motors Replacement Engines plate.
2. Oil Filter position on block. The Wet Clutch oil filter has two pipe connections, the Dry Clutch oil filter has only one connection and connects directly into the internal oilway in the block.
   

   Picture b – Wet clutch & Dry clutch

3. Dry clutch engines have a timing inspection cover in the top of the clutch bell housing.
   

   Picture c – Timing inspection cover

4. The Crankshaft on the Dry Clutch engines are fitted with an oil return scroll whilst the Wet Clutch engines have no scroll.
   

   Picture d – Wet clutch & Dry clutch

5. Dry clutch engines have an oil leakage tell-tail hole with a loose split pin at the bottom of the clutch bell hosing.
   

   Picture e – Hole in clutch bell hosing

6. The clutch operating leavers are a different shape. The Wet Clutch has a curved lever, the Dry Clutch has a straight lever.
   

   Picture f – Wet clutch & Dry clutch

7. The gearbox input shaft have a different number of splines. The Wet Clutch has 6 splines, the Dry Clutch has 10 Splines, and has a different shaft design.
   

   Picture g – Wet clutch & Dry clutch

Part 2

Individual Component Identification

All the items listed below have been identified as either for a Wet Clutch power unit (ceased at TPBG 1509) or Dry Clutch power unit (commenced TPBG 1510) and are not interchangeable. Part Numbers are taken from the Revised 1946 Factory Service Parts List.

Starter Motor

The starter motors are not interchangeable as they have different mounting flanges. The Wet Clutch starter motor has a three bolt fixing with the bolts equally spaced at 120 degrees. The Dry Clutch starter motor is also a three bolt fixing with two of the bolts diametrically opposite each other and the third bolt at 90 degrees to the other two.

Additional changes to power unit

The document covers the major changes on the change to a dry clutch at engine number TPBG 1510, further changes to the power unit occurred at:

• TPBG 1254 Engine front steady rubber (replaces tie straps).
• TPBG 1770 Bolt for oil filter banjo and washers.
• TPBG 1790 Sump changed. (Illustration No.1)
• TPBG 1891 Counterbalanced crankshaft installed.
• TPBG 1891 Oil suction pipe changed.
• TPBG 1891 Gearbox mainshaft.
• TPBG 1891 Gearbox front spigot bearing.
• TPBG 1891 Gearbox sliding hub with synchronizing cones.
• TPBG 1891 Gearbox spring for mainshaft striking dog.
• TPBG 1891 Gearbox mainshaft 3^rd speed gear, rollers, and locking plate.
• TPBG 2100 Oil feed pipe to cylinder head.
• TPBG 2237 Gearbox striking dog (top and third).
• TPBG 2237 Gearbox mainshaft 1^st speed gear.
• TPBG 2237 Gearbox ball for mainshaft.
• TPBG 2237 Gearbox selector fork (1^st and 2^nd).
• TPBG 2237 Gearbox selector shaft (3^rd and top).
• TPBG 2237 Gearbox selector shaft (reverse).
• TPBG 2286 Piston Change.
• TPBG 2292 Piston Change.
• TPBG 2250 Support bracket for rocker shaft.
• TPBG 2511 Oil feed pipe to cylinder head.
• TPBG 2751 Top cap valve springs.
• TPBG 2731 Push rod change.
• TPBG 2822 Connecting rod change.

It can be seen from the list above the significant other changes to the power unit also occurred at engine TPBG 1891 and at TPBG 2237.

Figure 1 – Sump Dry Clutch Engine (From TPBG 1790)

NOTE: The counterbalanced crankshaft cannot be fitted to the early dry clutch power units (TPBG 1510 to TPBG 1890) without changing the sump (up to TPBG 1790) and changing the oil suction pipe as they foul the crankshaft and stop it rotating. The clutch housing also has to be machined out by approximately 1mm as the flange on the crankshaft is slightly larger.

Figure 2 – Engine Components – Wet Clutch

Figure 3 – Gearbox Wet Clutch Engine

Figure 4 -Wet Clutch

Figure 5 – Dry Clutch