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This page is dedicated to:

HPN Motorradtechnik GmbH

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HPN ( Halbfeld - Pepperl - Neher ) : Alfred Halbfeld and Klaus Pepperl are two Bavarian experts who worked on the official BMW Paris-Dakar bikes during the eighties. Their main business is preparing a special 1043cc engine and highly modified GS models upgraded suspension (Marzocchi or White-Power fork, and White-Power rear shock) and many other improvements for extreme use.

"It's with out doubt the smoothest Boxer I have ever ridden... I always have a smile on my face when I get off it" explain Peter Young, the lucky owner of the HPN #5 (pics of this bike and other on "Possi's pages").

Three different rear suspensions are available:

Monolever Monolever: extended by 10cm and reinforced.
Twinshock Twinshock, two arms with +10cm, as on the official Paris-Dakar GS
Paralever Paralever, with their own design swingarm. Also they fit existing type 259 (BMW R1100 and R1150) Paralever swingarms to type 247E models.

The transformations are "à la carte" (fork, tank, auxilliary tanks, mono/double seat, cockpit...) but 6 specific models are available:

Basic: without rear suspension modification
HPN Basic HPN Basis, just a high-performing bike with standard ride height.
Rear suspension with longer arm(s) (+ 10 cm.)
HPN Baja HPN Baja, a lightweight Monolever enduro
HPN Adventure HPN Adventure, a Monolever rally bike
HPN Paris-Dakar HPN Paris-Dakar, an endurance tourer with with twinshock rear suspension
The Sport family with Paralever rear suspension
HPN Sport HPN Sport, a very light enduro using a type 259 swingarm
HPN Rallysport HPN Rallyesport, THE rallye-raid bike using HPN Paralever.

A version with a modern dress: the HPN/KRONSEDER
The actual and wonderful official rally BMW boxer: the GS-RR
More info about these bikes on the "Rallye OPTIC 2000 Tunisie" racer GS page

Some good HPN links:

HPN Motorradtechnik
Hofmarkstrasse 1
84375 Seibersdorf (it's around 100 km East of Munich) - Germany
phone: *-49-8571/5300, Fax: *-49-8571/1081
E-mail: info@hpn.de
URL: The HPN official web pages

Company Overview

The name "HPN" is the abbreviation of the initial letters of the company's founders, Alfred Halbfeld, Klaus Pepperl and Michael Neher, who brought the company into operation in 1979. The company became known for the further development of a road-racing tubular chassis made for BMW-boxers, which company founder Alfred Halbfeld already raced together with Peter Zettelmeyer. The work on the frame was also the basis for Peter Zettelmeyers thesis (diploma). The tubular chassis was sold in a limited series by Krauser, manufacturer of motorcycle-accessories, under the name MKM1000.

The break-through on the rally circuit first occurred in 1981, as Hubert Auriol won the Paris-Dakar Rally on a BMW, specially developed by HPN to BMW's specifications. Besides winning the Paris-Dakar Rally, other similar races were won during the 80's. Among the riders were well known names like Gaston Rahier, Eddy Hau and Richard Schalber.

The BMW-factory is still HPN's main client, assigning development work for both production, and competition motorcycles to the 5-man operation located close to the Austrian border. For example: the first prototypes of the frame for the K-model and Paralever-swingarm were built by HPN. BMW's decision to outsource such jobs, confirms the know-how of today's managing directors, dipl. Ing. K. Pepperl and A. Halbfeld.

A second line of business, is the production and selling of accessories for BMW motorcycles, both to customers and retailers. Here, benefits of the fact that, contrary to Japanese manufacturers, BMW-motorcycles are built to a "baukast" (backward compatibility) system are quite evident. For example, an oil cooler-thermostat developed by HPN, can be fitted to any BMW motorcycle manufactured during the last two decades, as engines and frames of the different series varies only slightly. These facts do not apply to the Japanese competition motorcycles.

Third and last line of business, is the refinement of BMW-motorcycles, in particular the older R 80 G/S-models and the newer R 80 GS or R 100 GS's ("Reise-enduros") for private customers. These are individually modified depending on customer's wishes, either towards competition or "reiseenduro extreme". Earlier HPN rally motorcycles are used as models. The modifications depend fully on customer's request, ranging from above mentioned accessories, to a complete modification of the motorcycle, where, e.g., engine capacity is increased to 1043 cc, dual ignition is fitted, reinforcements are welded to the frame, rear swing arm is lengthened by 100 mm's, etc... The cost for a modification ranges from 25000. to 40000. DM, depending on the customer's wishes. The overall impression of the operation is one of an attitude of professionalism and absolute accuracy by which they perform their work, not to be compared to some dubious "do-it-yourself" tuners. The basis for this professionalism lies in the enthusiasm of the company's two managing directors. Quality is given absolute priority--profit comes second. Work is not performed "as exactly as necessary", but primarily "as exact as possible." The sense in this philosophy can be argued. Fact is, however, customers benefit from this and coworkers enjoy their work, no time-pressures develop and good workmanship is first and foremost.

Motorcycle modifications

The modifications executed by HPN are various and complex. Thus, apparently easy modifications, such as the switch to the larger 43 liter fuel tank, even requires modifications, not only to the seat, but on some models, the oil cooler must be re-located and mounted on the frame tubes below the steering head. This in turn requires changing the front fender.

Next I would like to give an overview of the modifications HPN makes to BMW motorcycles. By reading this the reader will gain a clear understanding of the expertise and work connected to the development. The overview cannot cover everything, since each motorcycle leaving the workshop is a unique example following the customer's requests. The overview begins at the front, passing along the motorcycle to end--the tail light.

1. Front end, suspension, brakes etc:

Here, almost nothing of the original equipment remains: normally an upside-down (USD) front fork manufactured by White Power (WP), with 290 mm travel becomes standard, whereas the original fork has only 220 mm travel. A USD-fork is basically the reverse arrangement of a normal fork: slider tubes and stanchions (inner tubes) are turned "up-side-down," thus the slider tubes are mounted in the triple clamps. The stanchions acts as sliders, and are now the lower part of the fork, where the brake caliper and wheel are mounted. The result of this modification is that the upper area of the fork becomes more rigid. This is an advantage, as the bending forces are concentrated in this area. Larger tube diameters and sturdier fork triple clamps provide improved strength. The longer fork also increases the wheel-base, adding to straight-line stability.

The single disk brake assembly of the GS and particularly the G/S models leaves much to be desired. There are many possibilities for improvements available, ranging from a larger single disk to a two-disk arrangement, and in all cases a multi-piston brake caliper is used. On all pre-1990 motorcycles, a full-floating disk should replace the original brake disk. The technical designer must take the width of the brake assembly, mounting points for brake calipers along with the fork used, into consideration. Additionally, a steel-braided hose is used in place of the stock rubber hose, resulting in a more accurate pressure point and a decrease in hand-force necessary. Lastly, it may be necessary to change the size of the master brake cylinder.

The quality of the wheels can be improved, by using other spokes and rims. The final touch within the front area is done by using another handlebar, short stroke throttle, modified instruments (e.g. electronic tachometer with digital display, roadbook-holder), brush-guards, modified turn signals and fender, shrouding, and a larger headlight.

2. Frame (excluding rear subframe):

Each frame is blueprinted and straightened if needed. It is sandblasted and strengthened at critical points (steering head, frame main tube, rear swingarm and suspension mounting points), by adding sheet metal. Some of the already present support plates are doubled. Additional mounting brackets for the oil cooler, tank, frame-fixed shrouding etc. are added. Depending upon version (e.g. single or dual swing-arm, modified rear subframe), the mounting struts for the rear shock absorber must be relocated. By using welding jigs, very precise work is made possible. An outside firm manufactures the reinforcement sections, according to HPN-drawings. By using laser technology, a more precise cut is made; more precise than possible to make within the HPN workshop. Welded frames are again blueprinted and straightened, positions of bearings are checked and adjusted etc. The center stand and the sidestand must be lengthened to adapt to the increased ground clearance. Following the customer's request, the frame is finally either painted or powder-coated, by an outside firm, for better protection and durability.

Since the G/S and GS models have steel frames, modifications can be executed relatively easy. These modifications would be more difficult, if the frames, as is often the case with Japanese Superbikes, were made from light alloy, or if, like the new BMW boxer generation, where the engine and drive train are the basis for the motorcycle, onto which the remaining chassis items are added.

3. Tank:

The selection can be made from any of five versions:

As the HPN motorcycles are normally built for extreme use, usually one of two extremes from the range of tanks is selected: 19 liters tank for handy sport use, or the 43 liters tank for long races or remote journeys. With frames converted by HPN, the mounting brackets for the tanks are designed such, that either tank can be installed. The 43-liter HPN tank can be installed on any standard G/S or GS, using a special mounting kit. Modifications to seat and oil cooler may also be necessary. Polyethylene-tanks are, contrary to the nylon tanks, cannot be painted, rather they are dyed red, white or black. The range of approx. 600 km's, can be increased by adding two auxiliary tanks: one behind the seat and the other located behind the gearbox, under the seat. All tanks are made by the Italian company Acerbis.

4. Engine:

The capacity of the two valve boxer-engines used in the G/S and GS models is either 800 cc (50 HP) or 1000 cc (60 HP). In addition to these versions, HPN offers a conversion to 1043 cc.

The performance of the engines can be increased in several ways. The intended use of the motorcycle must be taken into consideration when deciding which modifications to perform. The engine can permanently produce approximately 70 HP without loosing reliability. From many years of experience it has been realized that increasing the engine's output is only of interest in sporting events because the durability of the engine comes second to performance.

The most substantial points, in which the engine can be modified:

As a result of converting to 1043 cc, done by using shorter cylinders and lower/ lighter pistons, the engine runs noticeably smoother. This modification also results in a decrease of the overall width of the engine by 26 mm (and as a consequence, pushrods, pushrod tubes, exhaust system etc must be modified). Additionally, it's recommended that with the higher engine performance, the transmission should also be modified by installing a taller fifth gear, and a stronger clutch developed by HPN should be installed to take the extra power.

5. Seat and rear subframe:

The rear subframe is attached to the mainframe via four bolts, and acts simultaneously as rear support for the seat, luggage carrier, support for luggage racks (panniers) and rear fender, and partially as mounting points for the exhaust system. Particularly, when carrying a passenger and luggage under high stress, the original rear subframe has proven to be rather weak. To improve strength and stability struts and braces are welded to the subframe. Additionally, a complete subframe made of high-quality steel can be fitted. Depending upon the customer's request, the standard seat is shortened and padded differently. The possibilities are varied, and an outside company does seat-upholstering work.

6. Rear swingarm:

The one-piece swingarm is still state-of-the-art at HPN. This solution has the disadvantage of "shaft-effect" or "elevator-effect", well known to old BMW motorcycles, i.e., while accelerating the rear suspension stiffens and the machine lifts itself, when decelerating the rear suspension is compressed giving the opposite effect. For this reason BMW now uses the Paralever rear suspension, which prevents these side effects. The skill full rider can use the "shaft-effect" to their advantage by blipping the throttle, thus temporarily increasing ground-clearance of the bike while passing over large objects.

HPN treats this in another fashion: an extended version of the old, one-piece G/S - swingarm is used. The old swingarm is cut in two pieces, lengthened by adding a 100-mm long tube, and re-welded. The drive shaft must of course be lengthened in the same manner. The result is a longer wheelbase, resulting in clearly better straight line stability in conjunction with longer suspension travel. The benefits of these modifications become quite evident in tough off-road conditions. If so desired the standard monolever swingarm can be converted into a double for a substantial increase in stability. An advantage of the HPN-swingarm, actually an outdated construction, is its high-durability when compared to the modern Paralever. White Power delivers state-of-the-art suspension components the high quality.

7. The future:

The next project to benefit from HPN-knowledge is the Paralever-swingarm. At present, the rear swingarm of the new BMW-generation (1100 cc four-valve boxer featuring the Telelever front fork) is modified and adapted to the frame of the older boxer models. This modified swingarm is stronger compared to the original Paralever-swingarm, and is controlled by a single, centrally mounted shock absorber.

As the production of air-cooled boxer models eventually comes to an end, HPN will most certainly develop and improve the newer oil-cooled models. However, this is more difficult as the crankcase/gearbox also serves as a stressed member of the chassis. The concept of the new boxer is more complicated and sophisticated than previous models: simple modifications are made impossible by using different and new materials (forged steering head, use of aluminum alloys, plastic materials); the engine uses SOHC four-valve cylinder heads and Motronic fuel injection; Telelever front fork, where the A-formed suspension link makes longer suspension travel distances impossible due to interference with cylinders and/or crankcase.

As the old versions of BMW works rally-motorcycles, developed by HPN, become non-competitive, one can only hope that, upon BMW's orders, HPN is given the task to develop and build new, competitive rally-motorcycles based of the new boxer-models.

Source is the first "official" HPN presentation web page made by Markus Kraus.
Last modifications to original text done by Markus Kraus 971026.
Translated into English by Joe Kletch, using a PC-based translator 980301 (Joe had a few good laughs after the translation).
Corrected rather freely by Matz Rosenquist 980305 (while trying to keep the laugh off his face).
Spelling and grammer checked by Joe 980322.

Updated November 2009