BUYING SECOND-HAND?

HERE S WAZZA’S TIPS ON WHAT TO LOOK OUT FOR

What to check

If it has spark plugs in it, take them out and see they are all the same colour and not coated in oil. Shine a torch into the exhaust ports (if there is a manifold or a set of extractors fitted, don’t be shy, and ask to remove them). Turn the engine over by hand in a clockwise direction (looking from the front), using either the flywheel or a 19mm socket on the main front nut (32mm if it’s a 20B) until you can see the bottom of the rotor housing. This is the area of the housing that commonly wears on the edges. A good engine will have none of the chrome surface missing or chipped, but a continuous surface across the entire face.

Also check what you can see of the side plates, watching out for any visible signs of corrosion/rust. Check this in all the exhaust ports and also turn the engine to check that all the apex seals are intact. Give them a push with your finger to be sure they have good spring tension. Take note of any signs of water or oil leaks. It is common to find motors that have been overheated have shrunken housing causing internal water leaks, evident with water sitting in the bottom of the housing. Lastly, be sure the engine has a rear counterweight or flywheel, as this is important for ensuring that the engine has a balanced rotating assembly.

Hard-to-

source parts

It’s now getting very hard to find good-condition parts for 12A engines, as some major components, such as rotor housings, are no longer available new from Mazda. This is something you should factor in when deciding to purchase a new engine. If later down the track you need to replace a housing, finding one in good nick will be hard, and the cost for these parts will only go up. This is also the case for 20B centre plates and crankshafts; these are common weak points, and finding replacements is a nightmare. You can repair cracked centre plates, but it is expensive to get the job done correctly. There are now aftermarket replacements, although these are not cheap.

Corrosion

Corrosion is the number-one killer of rotary engines (right up there with backyard builds and tuning), so whether you’re looking to buy a running vehicle, an engine or just components, evidence of coolant additive is a must. This is obvious thanks to the green colouring of the coolant. If the engine is stripped, pay special attention to the water-seal grooves in the side plates, making sure they are complete and intact with no corrosion. This is a common problem area in FD RX-7 engines, and if the grooves are not in good condition, there’s a chance of an internal water-leak problem (similar to a blown head gasket in a piston engine).

Housings

Check for obvious damage on the surface where the apex seals run. This chromium surface needs to be smooth and fully intact with no chipping or wear, as that can cause lost compression and in some cases pre-ignition. Look around the spark ports for heat cracks in the surface of the chrome. Check the sides where the water seals contact for damage and corrosion. If you have a micrometer, measure the width of the housing at the chrome edge. It should be no less than 79.95mm the entire way around for 13B and 20B. Housings that have been overheated often shrink around the spark plugs, and this will cause an internal water leak.

Plates

The side plates along with the housings are very comparable to the bore on a piston engine, so all those surfaces need to be free of scratches, damage, and corrosion/wear.

Any surface wear on the face where the rotors run needs to be measured with a flat bar or ruler and a feeler gauge to ensure that it doesn’t exceed 0.10mm. These plates can be repaired if machined by some specialized equipment, but will also require re-nitride hardening, as the machining removes the factory hardening process. In many instances it works out cheaper to buy new plates.

Check that any porting that has been performed hasn’t been overdone. So often we see bridgeports that have been done incorrectly and too large, to the point where the water seal in the side plate is not captive and can get sucked into the port, resulting in an internal water leak (there’s no fix for this, so be aware!).

Rotors

Check the rotors for damage and corrosion. If they are coated in black carbon, this is OK; it usually means they will clean up well. Check there are no seals rusted or heat damaged into their grooves, and that the apex-seal slots aren’t flared open at the tips or ends. The bearing surface should be smooth and scratch-free. If there is a bearing still in place, it must have no copper showing through, otherwise it will need replacing with a specialized pressing tool procedure

Eccentric shaft:

The eccentric shaft needs to be completely free of corrosion; even the slightest surface rust on any of the bearing journals renders it unusable.

Bearings

The bearing surfaces in both the rotors and the stationary gears should be smooth and scratchfree. Any sign of copper showing means these are no longer of any use, and they will require replacing using specialized procedures mentioned earlier.

Stationary gears

Stationary gears are actually very hardy and last a long time; however, be sure to check the gear teeth for excessive wear and ‘burring’

(marking).