Get It Right
After a while, if you work at it, you find yourself getting better and better at riding your watercraft. You may even start racing with your friends. A little effort, and before long, you find yourself in the Expert class, racing a Limited machine. You do pretty well, and you want to move up to a higher level of performance, say, National-level racing, or maybe even taking a shot at qualifying for the World Finals. -Why not? So you go for it.
At this point, you need to make very careful decisions when selecting your engine's powerband, as well as choosing which aftermarket parts to use, such as which impeller, ride plate, jet pump nozzle, steering system, etc.
If you choose correctly, you'll be rewarded with long-lasting performance, a good sense of accomplishment, and success. Unfortunately, however, this isn't the case in every performance modification venture - sometimes, you end up regretting every single selection. How do you avoid this expensive disappointment? Shop around. Attend as many races as you can, and talk to every one you can once you're there. Talk to the racers and the mechanics, note the performance of their equipment, track the failure rate of certain parts and equipment, hang around the pits, and watch the work being done at the trailers. If everything's going well, a quality builder won't hide anything; in fact, they'll be happy to show off their product and workmanship. Don't push it, though, trying to find out about experimental parts or R&D work. And bear in mind that builders dedicate lots of time and money to develop new products, and that if those experimental products fail, you shouldn't hold that against the builder - only through trial and error can successful products be developed and proven in extreme conditions.
Time has passed. You've done the research and you're about to spend a considerable amount of cash to build a fire-breathing power plant, using parts that have been promised to deliver arm- wrenching power: the smooth-talker behind the parts counter is trying to sell you 'a new ignition that's 'guaranteed' to burn every drop of petrol in the combustion chamber; a head mod that's going to deliver more power than you've ever experienced; a heavy-duty starter to crank it all up; the biggest carburetors on the market, to deliver as much juice as possible to the engine; and cylinders ported to 'secret specs, giving them an extra-special exhaust and high-and-mighty raised transfers.'
But don't be so quick to write out that check. Remember, if it sounds too good to be true - it is. The most important thing you can do is to bring in as much knowledge as you can as to what you want from your modified engine. A good builder needs this information to help create an engine that will perform to your specs, not someone else's. If the guy behind the counter doesn't seem to care about what you expect from your machine, or how you plan to ride, then you need to find another shop.
Also, you should always find out if your potential builder will be available to answer any and all questions you may have regarding the setup, the break-in procedure, or anything else. If he's not, then you can bet you'll be having lots and lots of unanswered questions.
Once you find a builder who'll answer all your questions, who asks you the right questions, and who will be there if you have any problems, then you're halfway there. At this point, you'll have a mechanic who's 100% dedicated to building you a strong motor; you need to be 100% dedicated to knowing what's going on with his setup. If you don't follow your tuner's instructions to the letter, then it won't be long before you'll be making more trips to the shop (and the local cash machine) than the local ride spot.
To help you know what's happening under your head, here are a few basics.
An engine's efficiency is related to many factors, such as a properly designed exhaust system coupled with a port time area designed to operate at a specific rpm range, and even the combined weight of the watercraft and the rider. In addition, the intake system's flow rate has to agree with the engine's fuel consumption to produce maximum power. A properly set up combustion chamber requires the correct dimensioning of squish thickness and area in order to work in harmony with the compression ratio, which is determined by the octane rating of your specific blend of gasoline at your chosen rpm range and squish velocities. Mechanically sound parts, such as a true-running crank, proper cylinder bore size, healthy pistons, rings, bearings, and connecting rods, make up a total package.
A lot of horsepower is lost due to excessive mechanical friction. When building an all-out race engine, special attention must be devoted to inspecting the alignment of the crank, connecting rods, and pistons in respect to the center line of the cylinder bore. Cases must be flat and parallel to the crank's center line, within 0.002". The front bearing journal must be in line with the center bearing, and the rear bearing within 0.002". The size of the bearing retention holes in the cases must be smaller (by 0.001") than the outer diameter of the crankshaft bearings. If any of these are over the limits, it's a good idea to re-machine the lower case and then line bore the bearing holes to the proper dimensions.
The top of the lower case must be flat (within 0.001'), as must the bottom of the cylinder. The top of the cylinder has to be flat, and parallel with the bottom. Cast iron sleeves should not protrude below the cylinder top. I recommend against lapping any surface on a lapping plate - due to the fine finish produced, the gasket may not stick to its surface, and this may result in gasket leakage, especially in the cylinder-to-head area. For best results, the top of the cylinder and the head-mating surface should be machined using a single tool with fly-cutter techniques. If a metal gasket is used, it must be coated (very lightly) with high-temperature silicone or copper spry.
An over-compressed engine could begin to bend its connecting rods as time marches on. When water is introduced to a combustion chamber, you can end up with a serious problem, sooner or later - due to hydraulic lock, the connecting rods may become bent out of shape, resulting in friction on the sides of the pistons and extreme pressure on one side of the lower and upper connecting rod bearings.
If the engine becomes submerged, take the spark plugs out, rotate the watercraft toward the exhaust side. Once the craft is on its side, rotate the engine by hand several times. Only then should you bump the start button several times. Make sure to attach the spark plug wires to a ground when blowing water out (unless you'd like to meet your maker a little earlier than you expected). After all this, start the engine and get it nice and hot to displace all the moisture from within. Its a good idea to spray some storage oil through the carburetor when the engine is idling; this is added insurance against rust which will damage delicate engine parts. Little rusty spots don't show their true ugliness for some time; little by little, bearing damage will progress to the point of engine meltdown - don't let let this happen to your pride and joy.
George Grabowski HPT Sport USA