The Troll was off the road for most of last year due to problems with its kick-start, steering and gearbox. The guys at The Vespa Shop got her fixed up smartly once I'd finally tracked down the replacement parts. I must admit that it felt strange riding her after so long. I found myself struggling again to remember which side was the gear change and which was the brake! One thing I did notice though was the engine was very spluttering and smoky.
A major part of the problem is the quality of the reproduction exhaust (May 2009 - http://www.heinkelscooter.blogspot.com.au/2009/05/running-in.html). Reproduction exhausts are available from a number of suppliers such as http://www.ost2rad.com http://www.sausewind-shop.com and other vendors on German ebay. The original exhaust was made from a long extruded tube that wrapped around itself much like a paper clip. All the seams in the original exhaust were welded making it very robust. The reproduction exhaust however was constructed of several interlocking pieces, making it much easier to manufacture but requiring a larger number of joins. None of these joins are sealed.
Shortly after I began running in the Troll in May 2009 the exhaust began to leak. The leaks were small though and a smear of sealant was enough to plug them. But over time it seems the exhaust has warped under pressure and heat and basically every seam was spewing gas, coating the sides and underside of the scooter in black soot. When parked, black oil residue dripped from a dozen places.
So it was time for a backyard repair. The exhaust was surprisingly easy to remove. A single bolt holds the exhaust to the footplate and a compression ring joins it to the exhaust pipe. It was positively filthy. The component parts were easily dismantled by removing two bolts at the front of the exhaust and all were given a good wash in degreaser.
The chrome came up well and all the soot was removed. After drying off I reassembled the parts. They are generally badly fitting and required a very liberal smearing of exhaust sealant around every join.
It was a bit of an effort to get the exhaust back on - these things are always easier to remove than reinstall - but I was pleased with the result. Although it hasn't completely solved the problem - there are still a few minor leaks - it's working much better than before as most of the exhaust is going out the back end, as it should. Next weekend I'll give her another good run and see if this has improved the performance. Maintaining pressure in the exhaust is critical to obtaining the correct compression in the engine and a leaky exhaust will substantially degrade the performance of a two-stroke engine.
One more point. I normally use Silkolene synthetic two-stroke scooter oil in all my machines. I find it works well and is low smoke. On a whim however I tried Valvoline racing two-stroke oil, which sold itself as a performance product with low smoke. In my experience to date it hasn't quite lived up to that claim. Maybe it is a better product and I've just used too much but the Troll now looks and smells like an archetypical East German machine, trailing an enormous cloud of blue smoke behind it. I'll give it another crack when I get to the bottom of this tank but if it doesn't improve I'll be saving the Valvoline only for East German car rally's!
Some footage from a German IWL scooter treffen.
Update 4 March 2012
I took the Troll out for a series of runs to test the resealed exhaust. I was pleased to note that the repairs provided a definite improvement on performance. The engine was a lot quieter and much more grunt. It was easy to run her up to 70 kph and I could feel that she had more in her. I should also mention I cleaned the carburetter.
That said though, the exhaust still leaks, but not as badly as before. Of course the leak is on the seam at the top of the exhaust where it bolts onto the floor plate so I'll need to remove it and reseal it again.
Since cleaning up the exhaust last week it's been easier to find where it is still leaking. If it can't be sealed up I might consider welding all the joins to solve the problem for good.
The Troll ticking over... just.
Update 10 March 2012
This weekend I removed the exhaust and re-examined the seals. The seal under the mounting bolt had completely opened up again.
I filled the exhaust with water to precisely locate the leak. The still shot doesn't quite do it justice but water pretty much gushed out of the seam on the left hand pipe.
The leak was far to serious for a smear of sealant so it was out with some exhaust tape. It's an unattractive but last ditch solution. After reinstalling the exhaust I took the Troll for a long ride to cure the silicone tape. I'm afraid I'm not convinced it has actually worked as there is already a long run of black oil along the edges of the tape. I think it's time to look for a replacement.