Heat Shrink Sleeve
Nonsense Or Ingenious Boxer Tuning?

First of all: Sorry about my bad English, if you are able to understand German texts you should read the German version of this description.

The idea was based on a description on the Website http://www.mot-technik.de/bmw/umbau/zstecker.htm. The author of this page describes in detail (with some pictures and physical formulas) that he realized electric discharges through the isolation of the spark plugs connector to the cylinder ribs on his BMW bike. He made some tests with the “ColorTune” (a transparent spark plug) to optimize the adjustment of the engine and realized these discharges. As a solution for this problem he suggests to use a additional isolation of the spark plug connector.

Someone had posted this link last autumn in the very popular German boxer forum (www.boxer-forum.de) – and after this there was a very long discussion about it. Although the first reactions (..”nonsense”..) haven’t been very positive some guys made some tests - and nearly all of them reported very positive results (".. engine starts better..", “..more power in low revolutions..”, “..better Sound“).

Because of these positive reactions I also made the decision to make a test. The best way to increase the isolation of the spark plug connector is to use an additional heat shrink sleeve over the connector.

These special heat shrink sleeve is rather difficult to get. The sleeve must fulfil the following conditions:

·        an operating temperature of more than 150°C  (I have used a sleeve with 55 to +175 °C)

·        a disruptive strength of at least 25 KV/per mm

·        large enough to fit over the spark plug connector (I have used a sleeve with a size of 25.4mm / 12.7mm)

For example HF cable (www.hf-kabel.de) in germany offers such a heat shrink sleeve under the part number 10860 (type KYNAR®) - unfortunately only in pieces of 1,22m. You needs approx. 16cm for two spark plug connectors, the minimum order quantity is thus enough for 7 motorcycles.

The usage of heat shrink sleeve is very easy.

First remove the plastic trim strip on the valve covers. To pull off the sparkplug connector; there is a little black plastic tool in your tool kit. With this plastic tool it is really easy to pull of the spark plug connector. Hook the tool under the top of the plug cap and pull straight out.



After this you can start with the isolation of the spark plug connector: Put the heat shrink sleeve over the spark plug connector:


The whole shrinking process can be done in 5 minutes. You need a “hot air pistol”. Just put the heat shrink sleeve over the spark plug connectors and start the shrinking process by heating the sleeve with hot air. It will take about 30 Seconds to have this work done.

The result:

I think the engine of my cruiser works better now. I think my cruiser is now more powerful at low revolutions. It is now possible to accelerate from 50km/h (only using the 5th gear) to top speed without problems. And I think that the sound changed a little. But maybe this is only an illusion ? You should try it by yourself to make a decision if it works or not.