Ok, went to the dyno today to get a couple runs in on my new to me 1997 GSXR 600 with a 99 motor. Actual history is unverified. The tuner drew my attention to a slight knock in the lower end. It seemed to go away as the bike warmed up. We ran one dyno run and the bike seemed VERY low on power (75 HP). It also had a very large "hole" in the power band somewhere near 8,000 - 9,000 RPM. Then the bike banged with a HUGE backfire. Not your average rich running backfire. He said indications were that it was either VERY rich, or the motor had more serious mechanical problems. A second run was started without the air filter to see how how the curve responded. (A test for fuel mixture I guess). He got half way through the run, and felt uncomfortable completing the run, and aborted the run. I went over to the bike for a listen, and heard what sounded like backfires through the carbs. He had to draw my attention to it. It was clear that the bike was running VERY poorly. A leakdown test and a compression test are being done Monday morning. Anyone have any insight? Suggestions, or do's, don'ts? Thanks VIR is in 13 days
Sorry to say I hope you have a lot of $$ left on your C.C. with 75 hp you are down A TON so the least the motor will need is a freshen but with a lower knock I'm thinking you have more issues.
I don't profess to being an expert, but have significant experience on both 4 and 2 stroke engines. I try to be the optimist so here is a suggestion: 1. The bottom end knock while cold sounds very ominous, and the compression and leak down test is definitely the way to go.... 2. But sound can travel and the backfiring problem while possibly being caused by mixture or ignition, could be the result of improper cam timing. This will show up in the compression and leak down test, but before investing in a tear-down and rebuild, suggest you have your mechanic check the cam timing very closely. You mentioned that your not familiar with the history of this engine, and I am not real familiar with a GSXR 600 specifically. But...., if either Intake or Exhaust cam is one tooth out, with the piston to valve clearances as tight as they are in many of these engines, it could lead to catastophic failure or extremely poor performance. 3. Even if the timing marks line up, suggest that your mechanic check for slotted cam sprockets, they can slip or have been adjusted improperly to begin with. Proper cam timing (referred to as degreeing) can be a "Black Art" to some...it's not the process as much as it is knowing the degree settings you want to begin with. Hope this will save you some time/money on a teardown/rebuild. Don Nees
i have a friend with a GSXR that the cam slipped a tooth because of a loose cam chain and his bike ran like crap until it got fixxed. i don't know if that is your problem or not but for your sake i hope that's all that it is.
Cam chain tensioner If you find the cams timing out of whack you can probably blame the factory cam tensioner. They are spring loaded to take up slack with a ratchet to keep them in place. The factory ratchets will give up so you are at the mercy of the spring. An after market manual adjuster is the best bet in the future. Hate to suggest it, but if your oil pressure is low it would indicate the some of the lower bearings (rods & crank mains) have excessive clearance. They might knock but still run. As it warmed up the clearance would tighten up some causing the knock to be toned down.
Perfomance wise, I'd look at cam timing. Knock wise, I would cut open the oil filter and look for shrapnel, brass colored flakes from the plain bearings. Drill one small hole, and use tin snips to open the filter - this keeps shavings from the examination down. Good luck!
