Thumper or not ?

[Garf]

I always presumed that 'Thumper' referred to any large capacity single cylinder motorcycle. Indeed, the motorcycling press and forums such as the 'Thumperclub' have served to reinforce that view over the years.

However, there have been a few posts by Bill J on this forum which have caused me to question this viewpoint since he has said that our engines are not Thumpers.

To anybody who has read Bill's posts it is clear that he is a knowledgeable guy and engineer so his words carry some weight.

Anyway, open to the floor. I am curious, what constitutes a Thumper engine and why shouldnt our engines be classed as such ??

Cheers
Garf

[DAVID THOMPSON]

i refer to any single as a thumper
some do not think of the mz bikes as thumpers
because of the very short stroke of the piston the high rev's
and both my saxon tour and rt125 have balance shafts
and they sure do not thump like my old 441 bsa

i guess the bsa was a thumper it shook so bad i sold it

its the only bike i ever sold on that was running it had tooo many issues
like if no oil leaks... it was out of oil and electrical system by JOE L the prince of darkness.....and warm beer

[kman.45]

Any single = thumper.
Not sure what any level of vibration should have to do with it. KTM LC4s were not balanced and vibrated like hell. The new 690 motor doesn't. Does that mean it's not a thumper anymore? Guess you'll have to convince about a million ADVrider forum members that "Thumpers" forum should not include anything counterbalanced. Wonder what ThumperTalk forums would say.

[Bill Jurgenson]

just for the books:
a thumper is a long stroke, big displacement single with a heavy flywheel and usually relatively high torque. It has nothing to do with having a counterbalancer or not and nothing per se to do with vibrations. Real thumpers don't vibrate all that much due to the heavy flywheel. Because of the heavy flywheel and high torque output at low rpm, they can pull away with only slightly more than idle and are pretty flexible. Not exhilarating.

None of the modern singles qualify on on any of these characteristics.
Not one. In particular not the KTM which not only did not have a balancer (which it didn't need as a motorcross racing engine), but also virtually no flywheel and no oil pump and a short stroke.
A typical thumper should be able to idle at 500-600rpm, 800 at the very highest. None of the modern singles will even come close to that. Nothing under 1000 or more like 12-1300.

Thumpers obviously do not rev very high. 6000 being near the upper limit unless serious tuning is involved, e.g. a BSA B34 (Gold star) in club racing trim or similar Norton Inter. Or a Guzzi Condor or Dondolino. Or a Standard with Motosacoche beveldrive single. Or a Panther...

The later AJS A7/Matchless G50s are not thumpers anymore; short stroke, low mass, relatively high rpm engines. The last of the Norton Manx as well, the so-called short-stroke Manx, which also had modern coil valve springs instead of the traditional hairpin springs to cope with the much higher rpm.

Other good examples of thumpers are the Guzzi Falcone flat singles in the road versions, complete with exterior flywheel as big as a manhole cover.

The India Enfield is the sole thumper in production today. But that one is doomed as well and a new modern engine is in development.

In the narrow confines of the MZ list, the use of the term is very misleading and potentially dangerous as well as far too many damaged engines testify. I mean too many xt/xtz engines in general not particularly those present here.

-----

That fact that the majority is wont to use the term incorrectly does not make incorrect usage correct. Nor doies it make a modern low mass high rpm single a thumper.
Most of those using the term incorrectly do not know what a thumper is to start with.

[keithcross]

While I understand Bills definition of a big thumper, many manufacturers refer to any motorcycle with a large single cylinder engine as a `thumper'. The follwoing link leads to a page advertising oils for motor cross bikes
http://www.belray.com/consumer/products ... =motocross
This in tern advertises `Thuimper' oil and leads to a page containing the following text
The following is taken from the Bel Ray motor cycle oil web page
Bel-Ray Thumper 4-Stroke Racing Motor Oil is specifically engineered to meet the demands of single cylinder, multi-valve 4-stroke racing engines. The high temperatures and severe loads of racing require the exceptional film strength, shear- and temperature stability of Bel-Ray Thumper 4-Stroke Racing Motor Oil.
Even a modern motocross engine is reffered to as a `thumper engine'.
I think this one may be down to personal interpretation.

Keith

[Bill Jurgenson]

advertising agencies are notorious...
Here according to Belray's (advrtiseer's) definition is a thumper:

http://www.zabernet.de/bill/mp3%20sounds/1960%2520MV%2520Morini.mp3

Provini's 1963 Morini with which he missed becoming world champion by two points - against the 4-cylinder Hondas and the Yamaha TZs. With an air-cooled, 2-valve!, DOHC single!

http://www.motomoriniclub.nl/provini.html

Pretty sure most any one will agree that that does not sound like a thumper. But a glorious and really mean sound! Never to be heard again since the original, made mostly of magnesium and elektron, can no longer be run at all. I have not heard or seen the replica shown on the page above, but it looks pretty convincing.

Here is another would-be thumper; the fantastic Ducati Supermono, as most will know a flat single with 580cc, actually the bottom cylinder of an 888:

http://www.zabernet.de/bill/mp3%20sounds/supermono.mp3

Imagine: when that bike was first announced 1992, three versions were projected: the racer of which eventually 67! were built, a road-going replica, and a naked street version! All three were at the Milano show.
I immediately ordered the naked version. But this was at a time of tremendous upheaval with Ducati just slithering by bankruptcy, changing hands a couple of times and of general confusion. The street versions were canned.

The term comes - who would have thought of that? - from the noun thump:
"a heavy dull blow with a person's fist or a blunt implement : I felt a thump on my back. • a loud deadened sound : his wife put down her iron with a thump."
just what a thumper does just off idle, i..e being used under the thumper-typical conditions.

http://jfwalker.home.mindspring.com/AJS.htm

read down the page to the descriptions near the bottom:
"The engine has mild cams, very low compression (6.35:1) and a long stroke (69x93). The engine idles so slow, you wonder how it can keep running, but the heavy flywheel takes care of that. The exhaust has a pleasant chufa chufa sound."

But even then not all were thumpers; here about the famous and fantastic BSA DBD34:
"Hot cams and high compression... it helps to be over 200lbs, wear a heavy boot, and you have to know the starting drill! The engine is not happy lugging, but when the engine gets on cam, the sound is wonderful. Although street legal, this is not a bike to be ridden in traffic..."

what more can I say?

[keithcross]

Bill

As the term `thumper' is a nickname for a big single there is real defintion, only opinions. Yours is one, other people have others.
As for the Goldstar, this bike was based on the B33, with a softly tuned low revving engine, surely a `thumper' under your defition. As such surely the Goldstar must also a thumper.
Also as far as the Goldstar goes, not all of them were road race bikes with high compression pistons, high profile cams and high first gears (the famous RRT2 close ratio gearbox), this type was known as the Goldstar Clubman. They also came in trails and Scrambles (motorcross for those not familier with this term) trim.
Personally I still think the term thumper refers to any big single. Hoever we all have our opinions.
I do however take your point about not labouring the MZ/Yamaha engine. I do tend to ride at the lower end of the rev range, particularly when going off road. The engine actually produces plently of power at these low revs. This type of riding may have been the cause of the big end failure my first engine suffered from. I am unsure of the longevity of the engine if it was riden hard all of the time, but this may prove to be difficult to achieve on the road, with all of the speed limits.

Keith

[MSW]

First of all, Garf, great topic. I've been wondering this for a long time.

Coincidentally, a couple of weeks ago, I read this in an article about BMW's new "X-motos" in American Motorcyclist (the AMA magazine):

"That’s exactly the idea behind BMW’s newest line of motorcycles, the G Series. Using the same 652cc liquid-cooled thumper engine, five-speed transmission and steel tube frame...."

By Bill's definition, BMW's new bikes are anything BUT thumpers. However, I also have to say that I always thought it just referred to a big single, and have seen it used in that context literally thousands of times over the years.

I guess the term has evolved. Kind of like "surfing."

Edited to say, BTW, that even the AMA uses the term very casually:

http://www.ama-cycle.org/roadride/Glossary.asp

[Bill Jurgenson]

Of course the B33 and B34 in civil form or trials form were thumpers.
I wrote:
"BSA B34 (Gold star) in club racing trim or similar Norton Inter"
THe casual treatment you and others refer to is, like the odious word biker, a product of the the recent past (<20 years), i.e. usage formed by advertising and those who didn't or don't know what the word means to begin with. It is not my opinion, it is the usage of the word when it was coined in Britain for what was a big single then to describe what a big single of this kind does.
Like I said, incorrect usage by many does not make it correct.

I am unsure of the longevity of the engine if it was ridden hard all of the time, but this may prove to be difficult to achieve on the road, with all of the speed limits.

I am not at all. It can take hard riding with no serious problems, no more than any other engine if treated correctly while riding hard. I have quite a bit of experience with this engine, not only the 4 bikes I have had or still have, but with several more engines. My racer has never had a big end or cluster failure. The only real damage was when the timing chain broke, this twice until I finally got the message. This meant new valve guides, new valves, a broken rocker arm.
It should be obvious that the racing engine gets HARD treatment with its 80hp. Revs up to 9000 and very occasionally beyond, winding out out of every corner hard.
The 1994 blue "toy," which I bought new, now has almost 90000km of hard treatment, including race track. Still has the original conrod, valves, guides, etc. AT 80tkm it got a new oversized piston. At 60tkm it got a SZR layshaft, new 2nd 3rd and 5th gears and new timing chain. But it is never overloaded at low rpm. The same can be said for my 1995 Sport, bought used and the 1997 SZR, also bought used and from which I know that it was used on the track.
The Sport got hard european expressway riding including the 200kms from Milano to Torino at 190kmh(118mph, calibrated electronic speedo) = constant 8000rpm. The SZR is also run at constant 100mph+ and more on german expressways.

xtz with over 100000km = 62+tmls are not at all rare.

For today's usage, go for a much shorter final drive ratio:
15/44
or better
16/47 which is the same and will also reduce the load and wear on the layschaft bearing.

Do NOT go to a 14t cog.

And keep the thing running between 4500 and 6500 - at least.

It is the street versions like the srx that get funky before 20tmls because people think they are thumpers and treat them like one. In the srx congregation, 20tmls is are considered a good distance without overhaul!
srx are even longer with 15/39 or even 15/37 coupled with an 18" rear wheel. No wonder they pit before they get 20tmls on them.

b

[keithcross]

Bill

I would not chanllage you on your technical knowedge of the engine fitted to our bikes.
I do however disagree that the term `thumper' is set in stone and only your version is correct.
The meaning of words in the English language do change if they are used differently for a period of time. An example of this is the word `gay'. This words meaning has changed drastically over the years. It used to make me smile when my Grandmother used to proclaim to all `I feel really gay today', and did so on many occasions before someone brought her up to date
Like it or not the term Thumper is now being used to describe any motorcycle with a large capacity 4 stroke engine by many people, in many articles and in many web sites, and that includes the engine fitted to our 660 MZ motorcycles.

Keith

[Fil]

What a bizarre thread!

Whilst I accept that someone has come up with technical definition for 'thumper', I and the vast majority of us will continue to call our bikes 'thumpers' by virtue of the fact they have large displacement single cylinder engines.

As for wrecking your engine because you are riding it like a true 'thumper' when it techincally is not...
Surely as with any other vehicle with an engine, you learn to ride/ drive it in a way that suits the characteristics of the engine. You don't ride your XTZ engined MZ in a certain way because someone suggests 'you should keep the revs between 4500 and 6500'. You may well end up riding it that way because that is what the torque and power delivery dictate is the best way to use the engine.

I'm with Keith on this one - lets spend more time riding our thumpers instead of worrying whether they are actually thumpers or not, and whether we're going to wreck the engine because we thought it was a 'thumper' when it's not.

[beamisinbtw]

Well said Fil All I know is I love my Baggy and I love terrorizin the streets on her! Thumper or not she thumps Have a great weekend all!

[Bill Jurgenson]

if you spend any where near as much time riding as I do and have done, then maybe.
And I did not come up with a technical definition, it is the historical reality of the bikes for which the termed was coined long ago and with which none of the modern singles have slightest similarity.

[Bill Jurgenson]

if you spend any where near as much time riding as I do and have done, then maybe.
And I did not come up with a technical definition, it is the historical reality of the bikes for which the termed was coined long ago and with which none of the modern singles have slightest similarity.

[OLDMTNCARVER]

After following this thread I remembered a sound that I was amazed with.
At a friends ranch I heard an engine running and quite honestly, couldn't understand how it could run at such a low rpm. It really did make a thump like sound.
The neighbor, on an old tractor and I mean old, was plowing the field.
As the tractor idled back and forth it sounded more like an old steam locomotive, no steam though.
I had a hard time understanding the engine running so extremely slow while waiting for the thing to make a horrific bang, stopping where it was at as I considered the stresses on the connecting rod, with only a super low compression to deter its demise.
I wish I had a video with sound
Bill, great pictures, great bikes!