Victor Mike gets a new exhaust (Eventually)

By Jim Small

My Zodiac had clocked up some 150 hours in the two years prior to last summer and the exhaust system supplied by Zenair was beginning to show signs of corrosion as it was made from mild steel. Remedial welding for brackets falling off or general sloppy fit had been carried out over the last couple of years and so thought had been given for some time to make stainless steel replacements. By September of last year yours truly was all fired up and well into construction of a Vans RV6A and didn't really want to be bothered with such a mundane ongoing maintenance challenge. First thoughts centred around drawing the exhaust up on the computer and seeing what it would cost to have the said item made professionally thus allowing the project in hand to proceed without hindrance and still being able to fly the Zodiac in the meantime.

Enquiries to the development shops of the large exhaust manufacturers in Blackpool came to nothing but one company suggested trying a local firm that made exhausts in small batches for a local car manufacturer. SORTED I thought. I presented the drawings and "no prob" was the reply a deal was struck and cash changed hands for the company to procure the necessary raw materials, a promise of 10 - 14 days was agreed so trying to be helpful I made an alignment jig and removed the exhausts from VM and let them have them as samples to make things simple.

After ten days I rang and was told "haven't started yet, still waiting for one of the tubes". Another ten days went by and a call this time revealed that the tube still hadn't arrived but were promised the next day. A week later I arranged to call to check on progress, an exceedingly rough approximation of an exhaust was reluctantly presented for my comments "this isn't what you are hoping to supply is it? " I enquired "oh no this is just a mock up to check developed lengths etc". A large bell began to ring in my head telling me to abandon this outfit immediately, but no we pressed on. The revised promise was for a further two weeks, enquiries at this time suggested that they were a little busy with their usual work but mine should be ready in a weeks time. Again I rang on the agreed day "we hope to have them finished Thursday". Thursday came and went together with a further three Thursdays.

That bell was getting louder and louder and by now I could stand it no longer. I rang and said I would be there tomorrow to collect the exhausts in whatever state of manufacture and would finish them off myself. I omitted to say earlier that I had promised to have a second set of exhausts made for a friend with a Zodiac so was expecting to collect the embryonic forms of two sets of exhausts, four items in total. My arrival prompted a rather sheepish partner of the firm to present various bits of scrap and one half of one exhaust which bore little dimensional similarity to my drawings or samples, with quality of welding that a five year old could have improved upon. I kept my cool loaded the junk, together with the raw materials, into the car and left, I saw no point in raising my blood pressure any further with an argument.

So here we were six weeks on and back to square one. The exhausts had fairly tight bends in inch and one eighth tube and I felt the easiest way to tackle these, without specialist machinery, was to obtain ready made elbows and cut out the required portion of tube. A mornings telephone calls revealed a company in Bamber Bridge who supply such items for the dairy industry. I arranged to call and collect the next day, the company specialised in the supply of stainless tube, fittings and STAINLESS STEEL WELDING to a very high standard required by the Milk Marketing Board. I arranged with this company to supply them with tacked up exhaust systems for them to finish weld on my jigs at a most reasonable hourly rate. Two visits were necessary to complete the exhausts and these were to my complete satisfaction. Three weeks from my abortive visit to my first supplier and I was ready to install my new sparkling and beautiful exhausts to my flying carpet, I was beginning to suffer withdrawal symptoms.

The day dawned when the exhausts were to be ceremoniously installed to the 912 engine. Earlier in the year a number of service bulletins had arrived for the 912 and one suggested an inspection of the rocker arm shafts for wear. With the exhausts off it seemed like an excellent time to do this little job as well. By now the aircraft had been unloved for some ten weeks and when I removed the exhausts, thinking it was only going to be for a week or two, I didn't bother to inhibit or seal the engine in any way, FIRST BIG MISTAKE.

On inspection of the exhaust ports on the head of the first cylinder I saw a small pile of ash deposited on the lower port wall. I brushed this out and noticed that around the inside of the ports, carbon was flaking off with the slightest touch, this was evident in each exhaust port. I brushed all of these deposits away and proceeded to turn the engine onto TDC to carry out the rocker shaft check, the engine felt different, a little tight perhaps. Further investigation revealed that one of the exhaust valves was sticking in it's guide, a liberal application of WD40 freed the culprit but still the engine didn't quite feel right.

I performed the check on the first rocker shaft and all was well. I buttoned that cylinder up and proceeded to turn the engine to TDC on the opposing cylinder. As I approached TDC things certainly didn't feel good; the prop stopped just short of TDC and wouldn't budge. I was reluctant to force the engine over TDC and had a cup of tea and a think. My thoughts centred on the sticking valve; had some of the flaking carbon in the ports dropped in between seat and valve head? Was the piston now hitting the valve head? Sitting drinking tea was not going to resolve the problem so a quick call to Dave Masterson gave me the approval to remove the cylinder heads for a butchers.

The problem was immediately apparent with the removal of the first head. The carbon that had detached itself from the exhaust ports had also detached from the cylinder head and piston crown and deposited itself in a pile in the bore. The piston moving along the bore had compressed the carbon into a solid mountain shaped lump between head and piston therefore not allowing the piston to go over TDC: similar deposits were found in each cylinder. The heads were taken away and stripped, the carbon removed from the valve stems, ports and cylinder head, all of which effectively fell off the surfaces with ease. The valves were reground and the heads re-assembled with liberal lubrication. Almost four months after removing the exhausts for replacement I was back at Blackpool with Dave re-fitting the heads and exhausts, a day or so later VM was doing what it was made to do.

So what lessons can be learned. Firstly trust your instincts and if you are not happy with a supplier or service offered, question their integrity and seek recommendations. If any bells start ringing walk away (not sure about wedding bells). Secondly don't neglect your engines health, nurture it, cuddle it and put it properly to bed if you have any reason to think you will not be using it for some time.

This engine had 150 hours from new, serviced to the book using correct oils, antifreeze and always run on 100LL, why the carbon was reluctant to stay where it should I haven't, a clue.