Motor revision with the help of a checklist

The construction of an engine for the Puch 500 or Haflinger can only be described to a limited extent in a contribution, a joint overhaul with an experienced screwdriver is preferable to all theory. Consider that the parts are expensive and rare, the probability of error can usually be reduced by experience. Many thanks to the experienced screwdrivers, especially Erwin and Heinz for their always open ear and their esteemed answers. And to the classic car practice with a comprehensive contribution about the small boxer engine.

Time: 20 – 40 hours

Cost: 200 – 3,000 euros

Tool: standard, spare parts catalog, torque wrench 10-400 Nm, fine measuring tools, piston ring clamping belt, div. Holding and assembly aids

Step 1: The standard engine

In the first step, we deal with the overhaul of a standard engine. 

It depends on the individual case whether only a new sealing is carried out or extensive wear has to be eliminated. A Puch engine from the series usually stops at 40-50,000 km, then a first major revision is pending. Decreasing compression with increasing oil consumption or oil combustion due to no longer round and bulbous cylinders is the first source of wear. This can be measured by a 4-gas analysis or even better by a pressure loss test. The acceptable value for the pressure loss is 10 to 15 percent, for engines with high mileage up to 20 percent are possible. The deviation of the two cylinders should not be higher than 25 percent.

A possibly small revision at this stage would already be the renewal by suitable piston rings. In the further course, the oil coal settles on the valve plates (Blue), the cooling of the valves decreases, the valve plates begin to tear (Red). The compression decreases further and due to the worse combustion conditions the candles begin to swell.

It is interesting how long a Puch engine still runs or is driven with this damage picture. With the required decomposition of the cylinder heads, the wear of the valve guides due to the slanted valves can be quickly detected.

Unfortunately, with the revision of the cylinder heads, pistons & cylinders it is not yet done. Putting a good head on an old block is not a good solution. How long will the used cone camps last? The main bearings are rather robust, but the axial play of the crankshaft due to advanced wear of a main bearing may no longer be adjustable in the tolerance range. Turning the flywheel is only one variant at the point.

In summary, such a revision is the evaluation and implementation of measurement results. 

Screws

Where does which screw come in? From the left or from the right? We find all this in great detail in the spare parts catalogue. In the corresponding designation, the dimension of the screw is also recorded.

There we also find 2 passport screws No.5. These are completely removed to separate the motor housing halves. The mother is often overlooked at picture position 14.

The checklist

With a lot of experience on the subject of revision, an engine data sheet with a checklist has been created. This makes it possible to build up a fuselage motor in about 8-10 hours. Before that, there are usually 3-4 days for cleaning, cleaning, measuring, measuring, sorting out, reworking, painting, components such as pistons, cylinders, heads… to overtake (leave)

—> The checklist is available for download here from mid-September

Step by step in the picture

Please do not do

Blasting work on motor parts for optical treatment

Blasting material and oil cycle behave like fire and water. Unfortunately, there is already expensive experience and many parts are no longer produced. Not every jet operation works with the necessary care (but there are some).

Separation tests of motor parts by means of screwdrivers, meissels

Cooling fins tend to give way and break, engine housings need no force after removing ALL screws, piping screws and nuts for separation, at best a beech wood in 2-3 possible places.

Step 2: Motor tuning

The next step is to follow terms such as ausliters, compression, control times, displacement expansion, camshaft variants.
.. Then we also leave the budget. As an unconfirmed formula of thumb, we expect 1,000 euros per 10 hp.

As of: August 2019