Balancing a single cylinder engine


Staff member
Deal, Kent UK
A3 1.4 TFSI 150 COD
How would one go about balancing a single cylinder engine? (This question came to me via email and I thought i'd see what the community thinks...)

I'm guessing we probably are looking at a simple 2 stroke engine, I'm not sure where you'd find a single cylinder engine though.
small agricultural - we have a single cylinder mower, but this is a four stroke unit. It's far from balanced. Chainsaws, commercial cutters etc are more often 2 stroke units because of their light weight and high revving nature.

It's not possible to fully balance a single cylinder engine no matter what you do with shafts and counterweights etc.
They have huge flywheels relative to their power outputs.

The also have heavily counterbalanced crank throws and very limited rev ranges.

Even a two stroke 1 cyl engine is producing usable torque for at most 180 degrees of every 360 degrees of crank rotation.

A four stroke is worse.

180 degrees maximum power stroke followed by 540 degrees of nothing before the next power stroke.

THe power stroke will always be shorter than 180 degrees because the piston is not moving at all at the top and bottom of it's stroke.

That's why 4 cylinders is generally considered the smallest number which is workable for road car applications. Even these need careful usage of counterbalancing to be acceptably smooth. Balancer shafts are a must to make a four really likeable. Four cylinder engines have high levels of second order harmonic vibration.

I wish Waynne would tell us a bit more about the application intended in this ********* *********** situation.
I think you're confusing rev range with high revving ability.

Two stroke singles do rev hard - exactly what I mentioned when discussing lightweight handheld powered agricultural tools. However, the usable rev range is narrow and all at the high end. Max power is produced at over 10,000rpm and they're doing nothing impressive below about 4000rpm.
Mate have a go on a 4 stroke moto x bike an you'll soon change your mind. I've had 2 stroke moto x too and they have power from the minute you twist the throttle.
Sorry guys, I just had an email asking for more information on balancing a single cylinder engine so I cant shed anymore light on this at the moment.
I would have thought it would be difficult as there isn't really anything to balance it against, like in a 4 cylinder it would be balanced against the opposing cylinders. (the parts there of...)
I suppose the closest balance you can get is with the crank counterweights? This is the only way I can see any form of balancing being possible.
The dynamic crankshaft balance already comes with a four stroke single cylinder engine(used in motorbikes, mowers, scooters) done with the help of counterweights & webs & further reduced by the small flywheel on the magneto side. So, there is no requirement of further dynamic balancing but a bit vibration(not torsional vibration) might be felt as this type of engine could not be power balanced as it delivers only one power stroke in 720 degrees of revolution...
A single cylinder engine, elseplace than lawn-mowers, can be found in motorcyles called “Bullet” in India, or “Le Enfield” in the UK.

These motorcycles, are pre-WW bikes, having an original displacement of 350cc., and now available in 500cc too.

In India these are the most common of bikes, till now and have been used for various puposes, from delivering milk, policing, or or even for border control by the army, as ronnie would tell you.(incidentally ronnie biswas 4m juhu in '82-84?)

In fact bikes as old as 1952 are still maintained in mint condition, and that is regarded as somewhat as a world record.(check guiness? mebbe?)

These engines do not have a fly-wheel but incorporate the magneto and the clutch assembly to compensate for that. In fact they have a completely detachable gear-box, which can be taken off one bike and put on another in 20 minutes.

Low end torque is substantial, and they, even with the lack of mid-range HP, have a sweet high end ride with speeds (when tuned) 110 mph, which is more than adequate on Indian roads.

Balancing the engine is not so much about weights etc, what my bretheren here talk about, being all into hi-tech vehicles.

Balancing the engine on a 4 stroke, single cylinder bike is all about alignment, because what are you gonna balance it against?


It is about all the angle being either 90 degrees or in a straight line.

When you are balancing a single cylinder engine, all you gotta do is make sure that the crank is absolutely true, the bearing seats are true, (because if they are not, you would have an anomalous wear of the bearings) and the final drive sending the power to the gear-box is perfectly aligned.

Then, instead of timing belts in this particular engine we have tappets, which work to open and close the valves.

So instead of cast iron rocker housings, we can install alloy housings, to reduce the noise, and instead of the regular high-tensile timing gears we can install fiber wheels.

These, along with a few other changes from the original manufacturers spares, will give you an engine which is vibration free, and the only sound you hear in idling, would be a “boob!” at every other rotation.

Incidentally these engines can idle at 350rpm comfortably.

My knowledge come from the fact that I was rebuilding carburetors of these bikes at the age of 7, when I was 1/6 the weight of the bike itself(and earning money for my labors.

I could even set the timing of these bikes with touch, in pitch dark, with just a screw-driver and a 10mm spanner, and touch.

And while we are at it, lemme tell you that the ¼” spanner would work on most parts of the bike. You have 2 of them n u r set……

So lets not all get “techhy” about it, 'coz such engines do exist. And anyone who needs more info can feel free to contact me if he/she pleases.

In fact, if anyone of the members wants to come down to India n ride one of these bikes lemme know, I have not done a tour in some while and would love to take them along ths spring.

Excuse the tone, but this is something I hold dear to me heart.

And don't get me started on 2-stroke engines, please…………. ;) ;) ;)
Last edited:
Sorry guys, I just had an email asking for more information on balancing a single cylinder engine so I cant shed anymore light on this at the moment.

Wayne what we would need to know is if the author of the mail sent you was asking about motor vehicles or other engines.

And just to state a fact, don't blame the engine, if ur end drive is non aligned, please?

Its like blaming the graphics card for a bad picture when your monitor cannot deliver a picturesque picture............;) ;)

Single cylinder engines are the most reliable in their own limited arena....
@picassoonwheels: No, actually I'm not that Ronnie you may be thinking of. Anyway, your points are well said if the owner is in need to know how put the transmission on a right axis & keep it moving. But if you go for the internal engine construction, then some certain points regarding engine balance will have to be there including the compensation for single power stroke in 720 degrees of revolution & crankshaft thrusts generated due to transverse mounting by introducing some counterweights & balance shaft. It's not only applicable for RE Bullet, but all single cylinder engines & engines with an odd number of cylinders.

Similar threads

Please watch this on my YouTube channel & Subscribe.