OHV - this enigmatic acronym holds more power than it might seem. Knowing what OHV means and how an overhead valve engine works once gave me an unexpected opportunity to look at the world of the nineties from a very interesting perspective. How did this happen and what did I experience? You'll find out soon. First, however, it's worth explaining the acronym itself.
What is OHV?
OHV (Overhead Valve) is an internal combustion engine design in which:
- the camshaft is located in the engine block,
- the intake and exhaust valves are located in the cylinder head,
- valve actuation occurs via tappets, pushrods, and rocker arms.
In practice, this means a mechanical system in which the camshaft lobe transfers motion to:
- tappet,
- pushrod,
- rocker arm,
- valve in the cylinder head.
It is this mechanical "chain of events" that is responsible for opening and closing the valves at the appropriate time in the engine's operating cycle. The problem is that in an OHV system there are several critical points which – if poorly aligned – cause uneven engine operation, characteristic knocking, and sometimes even what mechanics describe as the engine "coughing."
A story with an OHV engine and the Fiat 126p
Seemingly obvious – yet not everyone knew about it. Or more precisely, none of the volunteer mechanics knew about it, who undertook to repair Fiat 126p, belonging to the company boss. Never mind where it was. More important is how long the repair took. It lasted so long that the boss – annoyed by the situation – promised a vacation to anyone who could get the car running. And since the repair was taking an unmercifully long time, the very next day I was on a train, heading for a 72-hour pass. Three days of freedom from the good old "Maluch."
Problem in the OHV valve train
The reason for the failure was prosaic. The cam, tappet, pushrod, and rocker arm on one of the valves were improperly installed. The pushrod did not properly support the rocker arm, causing the valve to not operate as it should.
The effect:
- uneven engine operation
- lack of power
- characteristic "coughing" of the engine unit
The repair was actually very simple. All that was needed was to remove the valve cover, see the problem, and correctly seat the pushrod. I don't know, however, how one could have overlooked the protruding stub of the pushrod, which stuck out of the cylinder head like a lone stake waiting for its beloved. Ignorance of the OHV engine's design apparently didn't help the mechanics – but it did help me in realizing my planned 72-hour trip.
OHV engine in Fiat 126p – technical specifications
From today's perspective, the technical solutions used in the Fiat 126p seem incredibly interesting. It's a design that today looks like a relic of automotive archaeology, but for years it was a symbol of mobility in Poland.
Key technical data of the Fiat 126p
Engine displacement
652 cm³
(a 594 cm³ version was also available)
Fiat 126p power
24 HP at 4500 rpm
Torque
42.5 Nm
Compression ratio
8.0 : 1
Engine type
- four-stroke
- air-cooled
- 2-cylinder
- OHV (overhead valve) system
- timing chain drive
- spark ignition with carburetor
- ignition distributor
Fiat 126p dimensions
Length: 305.4 cm
Width: 137.7 cm
Height: 133.5 cm
For comparison – the car's dimensions were similar to today's trunk in a Fiat Doblò.
Weight and payload
Curb weight:
600 kg – as much as a battery in a modern hybrid can weigh.
Payload capacity:
320 kg – which is roughly the weight of a five-person family going on vacation in the nineties.
Why are OHV engines still interesting?
Although OHV technology was developed over a hundred years ago, it can still be found in many engine designs. It is valued for its:
- simple construction
- high durability
- compact size
- high resistance to overloads
For many people, the OHV engine in the Fiat 126p is not just technology, but also a part of automotive history. And sometimes – as in my case – also a ticket to 72 hours of freedom.