After reading this thread, here’s my take on all of this.
1. A bone stock Blaster will run for hundreds of hours IF properly maintained AND ridden within the scope that it was built for. Yamaha built the Blaster as an entry level quad for beginners. Run chain saw oil, ride for miles on the road pinned in sixth gear, and clean the air filter once a year and all bets are off.
2. A Blaster engine in a slightly modified state (raised exhaust port, aftermarket pipe, air box mod) will require maintenance a bit sooner. The reason for this is simple. You just took a very poorly designed engine and made it quite a bit better. It revs higher and develops more cycles per operating hour.
3. A blaster engine in a slightly modified state (same as above) with a head redesign. This engine will require more frequent inspection due to the fact that the compression has been raised from 125 psi to around 160psi. The additional compression will give the rider a noticeable gain in performance but WILL put additional stress on internal engine components. These components include piston pins, rings, top end bearings, connecting rods, thrust washers, main bearings and lower connecting rod bearings.
4. Professionally ported cylinder with a redesigned head. Here’s the bad news boys…….You want power and every builder is delivering. Serious power comes at a price and I’m not talking about what you just paid me. Any engine placed in a high state of tune will wear faster than its bone stock counterpart. End of discussion. Check compression, piston clearance and the condition of the connection rod once a year. Gaskets are cheap…….I’m not. Piece of mind is priceless when you’re 15 miles in the woods.
5. My ride. 240 sleeved Yamaha cylinder, 5mm long rod, 4 mm stroked balanced crankshaft. I pulled it apart after 20 hours to do rings. It looked and measured fine. Changed the rings and ran it until it started making noise 100 hours later. It needs a Piston and a hone. I probably let it go longer than I should have. Keep in mind that my Blaster started life as a 15 HP piece of crap and now it eats piped Banshees for lunch. I take very good care of it and it gets the best maintenance that money can buy. I also beat it like a rented mule.
6. Top of the line drag Blaster. I can’t tell you how long they last because we don’t take chances with parts. Too much money invested. Ian has around 100 runs on his and we’ve changed the piston a couple of times. Everything else looks good.
You can’t measure an engines life by years. Hell, I can make one last for 50 years if the internal components stay lubed and I never ride it. An engines life is measured by hours. The more you build them, the more maintenance they’ll require.
I build a ton of YZ 125 and 250 engines every year. We keep a very close eye on the ones for our local sponsored boys. I changed Ben’s rings after 6 hours of him beating the living crap out of it. Every thing looked great. We ran a brand new top end for 25 hours and found that the stock Yamaha, cast piston skirts had worn .003. The bike still had great compression and wasn’t making noise. It was ready to blow up. What’s the lesson? Top level performance requires top level maintenance. A compression test is not the deciding factor when it comes to measuring wear of internal components. Fast means nothing if you don’t finish. Here’s the really bad news. Thinking of buying a four stroke? Your valves, timing chain, valve springs and piston are junk after 75 hours, if you’re slow and riding a stock bike. Get to the Pro Expert level and I’ll see you for a new top end every 40 hours and a full rebuild in about 100 hours. Break this rule and I’ll be watching you face plant over a 120’ triple jump. Very embarrassing in front of 1000 fans.
Ken
