Side flaps. Endearingly dated

Side flaps are more than dated. And in the motorcycle world it's about power, power and more power. That is a rather pointless process with all those roadside checkouts and the current traffic supply. Indeed, often less is more. And you can simply teach a monkey to drive fast. Less power, more organized fun and a minimum of almost death experiences. And that is why side flaps - no pee flaps, because that's bland - are so much fun.

Side flaps are sweet

Even the most limited-minded green fundamentalists are endeared by the sonorous hum of side valves. The lack of compression and the 'tame' cam timing makes the 'flat heads' very civilized - or at least not threatening - sounding machines. But there is always something to be considered. Just after HM 117, I was scolded by a natural, pale-looking blonde because my 75-year-old Russian side-valve had a faded hammer and sickle on the side of the sidecar. She saw it. But she had no eye for technology.

Basic technology

Side flaps are technically simple and not very effective. With a minimum of technology, they mainly convert fuel into heat. The concept is structurally handicapped. The low compressed blocks (think of 1 on 5, 1 on 6) run on just about everything as long as it doesn't come from a ditch. By the way, try to play with the ignition timing. The excise juice that nowadays has to pass for gasoline has a very different ignition character than that of old-fashioned gasoline.

Of course, the look of a side valve is much more nostalgic than an OHV. The power delivered is quite different compared to an OHV. Think of a 750 cc SV, whether it is a Harley-Davidson WL model or a Russian IMZ M72 or KMZ K750 with a horsepower or 23. That power means nothing twice, because such a side-valve has to rely on its torque. And that torque is delivered at 'almost no revs'.

It's just fun driving

With the right approach, such a satisfied humming side-valve is a very pleasant and reliable travel companion for people who find a kilometer or eighty per hour a pleasant driving speed. Please note that the lubrication system does not like long-term 'high' speeds on those types of old workhorses. In their time there were no asphalt roads or long straight motorways. So regularly change the speed and when working on the block make sure that a fresh oil pump first comes in.

The cheapest gasoline, the cheapest oil

Lubrication technically every current oil is better than the oil from back then. As long as he is not thin. The function of oil used to be: lubricating, cooling and sealing. With side valves, cooling has never reached great heights. But the production tolerances were 'earlier' considerably wider than they are now. And many side valves already broke after they were assembled in a modern overhaul company to the state of the art of too tight tolerances for 'then'. Sometimes 'better' is simply 'too good'.

Oil use allowed

A good side-valve block may use oil - I am not worried as long as it stays below one liter per 800 km - and it is not a bad idea to change the oil around the 2000 km. Because with a block that has to do without any form of oil filtering you simply want to get rid of the dirt before it can do damage.

The Harley and BSA side valves and in the meantime the Russian side valves are well known. But before World War II there were many engine manufacturers who applied this construction. It is therefore a very dated system and because side valves are so dated and they are not macho racing machines, the prices are generally not too bad. Except for the old Harleys. On a new Harley you must seriously write off after purchase. But the prices of the side flaps continue to rise quietly, with the 1200 cc units being even more expensive than the 750 cc machines.

The girl in the photo, we don't know anything about that. The boxer in the featured image is a late KMZ 750 block that was newly specified for 23 pk. That 23 pk block will be replaced in the coming winter the 36 cc head valve block specified for 650 pk from an 1991'er Ural.