SKS Rennkompressor, Review And Modifications.

[Blackbike]

I bought a new Rennkompressor pump and found it very well built, I liked the all steel construction and the cast iron base. Nice details are the wooden pump handle and folding feet. Its very old school and the weight is substantial, as it should be. Pumping action is nice an easy to 150 psi (tested with a closed presta valve), PSI range on my tires is from 80 PSI to 120 PSI on the bikes that I own, and the pump is perfect within my pressure range. The claimed maximum pressure for this pump is 240 PSI.

Things I did not like, first is the pressure gage.
The gage face is black and the PSI increments are every 10 PSI, so good luck trying to set your tire pressures accurately. The psi scale is gray in color and invisible when in use, the diameter of the gage is 2 inches and the protective plastic cover casts a shadow over over the gage face when the lighting isn't perfect. The gage itself has a plastic case.
Second the hose connection to the cast iron base.
The hose connection to the pump base is a straight thread connection sealed with an o-ring, good in theory but the hose connection fitting does not make contact with the base, it sits on top of the o-ring and cannot be tightened enough to keep the fitting from unscrewing from the pump base if there is a twist in the hose when the hose is pressurized :facepalm: . A drop of loctite would fix this.
Third the supplied pump head.
The EVA pump head is a big lump of plastic that works ok, but feels flexy when the locking lever is used and it's really big for what it does.

None of this is that big of a deal and most of it is personal preference at best or minorly annoying at worst, BUT IT MAKES ME NUTS. So let's fix it :shock: .

This is a standard SKS Rennkompressor...

This is my Rennkompressor after modification.


The gage replacement required recutting the threads in the pump base using 1/4 NPT tapered pipe tap to accept a standard industrial 160 PSI gage, the existing gage used an ISO straight pipe thread, no drilling required just run the tap in to convert to NPT. The replacement gage is a 2 1/2" WIKA glycerine filled 160 PSI process gage P/N 9767223.

The newly installed gage that you can actually read.


Next up was fixing the very annoying hose that kept loosening. This modification required drilling the hose port using a "Q" drill so it could be tapped to 1/8 NPT tapered pipe threads so it would accept a standard 1/8" NPT to 1/4" hose barb, as the supplied SKS fitting won't accept standard 1/4" air hose :facepalm: . The hose used was 1/4" 300 PSI rated industrial air hose, the fitting is a SSP 300 PSI rated hose barb, and the hose clamps are Oetiker.

The new hose fitting and hose installed.


The only thing left was to install the Kuwahara Hirame pump head which is an absolute joy to use and feels great in the hand.

The new pump head installed, with the EVA head for comparison.


Other minor stuff done was dissassembly and cleaning of the entire pump to remove the chips from cutting the threads, and to remove the factory grease prior to replacement with Dupont Krytox teflon grease, the thread sealant used was Loctite 569 Hydraulic thread sealant, and the air hose is retained by a trimmed toe strap.

This is a quality pump with old school construction that makes it very easy to upgrade or repair, I chose this pump for myself as I was looking for a tool, not an art object. It is well worth the price. I would recommend the SKS to anyone looking for a high pressure track pump

Best Wishes: Mike

 

[Apple Tree]

Extremely interesting article. Many thanks for sharing it with us.
I have a Renkompressor and it is certainly the Tiger Tank of track pumps. I have replaced the head with an SKS dual head with separate holes for Presta and Shrader valves. Although mainly plastic, it works very well and has proved reliable except it blows of the hose sometimes. I think this may be more to do with the hose end becoming deformed after a lot of use and can probably be solved by cutting it back to a fresh bit. The gauge is not brilliant but ok if you just want round figures e.g. 100 psi. There is a red hand you can set to show the pressure you are targeting. All that thread tapping sounds a bit scary but I guess you have the skills.

 

[Blackbike]

Extremely interesting article. Many thanks for sharing it with us.
I have a Renkompressor and it is certainly the Tiger Tank of track pumps. I have replaced the head with an SKS dual head with separate holes for Presta and Shrader valves. Although mainly plastic, it works very well and has proved reliable except it blows of the hose sometimes. I think this may be more to do with the hose end becoming deformed after a lot of use and can probably be solved by cutting it back to a fresh bit. The gauge is not brilliant but ok if you just want round figures e.g. 100 psi. There is a red hand you can set to show the pressure you are targeting. All that thread tapping sounds a bit scary but I guess you have the skills.

Hi Apple Tree,
Thanks for the kind words. It seems like most equipment reviews say things like "It's new and shiny and works great" and not "It works well but it was built to a price point and has a few issues you can fix and here's how". I looked at a lot of pumps before I bought the SKS and I absolutely agree with, and I will quote you "it is certainly the Tiger Tank of track pumps".
My OCD drives me to little projects like this, the Rennkompressor was designed in 1966 by Walter Scheffer, this pump has been in production for 50 years :shock: , that makes our pumps, the all time classic track pumps. I thought it would be fun to rebuild it using the best quality industrial components I could lay my hands on, I asked myself, what would Walter do, and followed my instincts.
Threading is really quite simple and is nothing to be afraid of. The hardest part is, drilling the hole where it needs to be. After that all that needs to happen is turning the tap on axis into the drilled hole and you have created a new home for a bolt of the desired size . A little practice on a piece of scrap steel and and you will find yourself bolting all sorts of handy stuff together. All you need to start, is a drill chart like the one shown below, this tells you which drill is used to cut your desired thread with the corresponding tap. Watch a few Youtube videos for the finer points and you're in business .

Best Wishes: Mike

 

[Gazelleer]

Re:

Nice modification of an already great pump! The only thing I have to do every once in a while is replace the pump head rubber seal (€ 0,65). My over 30-year-old example has no clamping mechanism in the pump head, you just push it onto the valve.

However, you overlooked one essential thing in your excellent work. Cycling is a metric sport, therefore pressure should be measured in bar, not psi. This is very unfortunate because it means you'll have to replace the entire gauge...again.

I am aware of the fact that certain brands of tyres indicate pressure in psi as well as bar but for any serious riding the former should be ignored for being inaccurate.

 

[kaiser]

Re:

Top job! That new head looks very very nice.

 

[Apple Tree]

Cycling is a metric sport

Blackbike writes from the USA where Imperial is still very much in charge for everyday use by citizens - and long may it continue !!

 

[Blackbike]

Re: Re:

Nice modification of an already great pump! The only thing I have to do every once in a while is replace the pump head rubber seal (€ 0,65). My over 30-year-old example has no clamping mechanism in the pump head, you just push it onto the valve.

However, you overlooked one essential thing in your excellent work. Cycling is a metric sport, therefore pressure should be measured in bar, not psi. This is very unfortunate because it means you'll have to replace the entire gauge...again.

I am aware of the fact that certain brands of tyres indicate pressure in psi as well as bar but for any serious riding the former should be ignored for being inaccurate.

Hi Gazeller,
I like the pump head you described, I have a similar head on a old Silca floor pump that lives behind the seat of my truck to support away from home rides.
Thank you for bringing the need of a gauge replacement to my attention. Please excuse my egregious oversight of this matter, I have realized that a true metric pressure measurement is the common thread that binds all cyclists together.
In acting on an immediate corrective action I have made disturbing discoveries :facepalm: .

"The bar and the millibar were introduced by the British meteorologist William Napier Shaw in 1909, while he was the director of the Meteorological Office in London. The NIST includes it in the list of units to avoid and recommends the use of Kilopascals (kPa) and megapascals (MPa) instead".

If that wasn't bad enough, further research has revealed that the French invented the metric system and the bicycle.

"The term bicycle was coined in France in the 1860s. The first really popular and commercially successful design was French. Initially developed around 1863. The bicycle renaissance began in Paris during the late 1860s. Its early history is complex and has been shrouded in some mystery, not least because of conflicting patent claims: all that has been stated for sure is that a French metalworker attached pedals to the front wheel; at present, the earliest year bicycle historians agree on is 1864."

"Until 1875, the French government owned the prototype metre and kilogram, but in that year the Convention of the metre was signed, and control of the standards relating to mass and length passed to a trio of inter-governmental organisations, the senior of which was the General Conference on Weights and Measures (in French the Conférence générale des poids et mesures or CGPM)."

This leads me to my observation, that to be a true metric cyclist you must ride a Peugeot PX10, embrace the Huret or Simplex derailleur hanger standard, and inflate your tires in kilopascals, however when in England you may inflate your tires using bar...

These new discoveries have left me at odds with a course of action, I have consulted a metric Magic 8 Ball (made in China), the response was "Drink ONLY Single Malt Scotch".
So what should I do???

: Mike

 

[Gazelleer]

Re:

Oh my god, what have I done??!!... I opened Pandora's box! :facepalm:

Your well-researched reply made me realise that I can do away with almost my entire bike collection since all except my PY10 are built with Reynolds tubesets in Imperial dimensions :shock:

I think I need a malt now too... or two...

[off looking for a bottle of Talisker]

 

[Gazelleer]

Re:

N.B. this is the pump head on my 30-year-old SKS. I now also notice that the gauge dial is white instead of black on the old ones.

 

[chrisbeeching]

I have been fascinated by this post. I have an aged pump which looks identical to the last picture in this thread (thanks Gazelleer) but I have been unable to obtain a new main pump washer for it. Its internal diameter is 38.1mm. Does anyone have any idea of a source? After 30-ish years it’s the only bit to have ‘given up’ and as others have said, it’s a brilliant bit of kit. SKS are unable to supply so any help or suggestions will be very gratefully received.