Rotax Series-III Notebook

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Copied from Dix"s site

Guys that are currently running the 493 may already know some of this stuff... but, I'll throw out a few little oddball things to keep in mind about the Series-III 493 & 593 engines....

The first one isn't really that big an issue with the 493 & 593 that I've found... it's more a problem with the 600HO & 800 engines (they acutally use a smaller bolt)... but Y-pipe bolts can tend to rattle loose... & even using red locktite may not stop 'em from working loose... if you have that problem the cure is called a "Nord-Lock" washer...

Best source is your local Fastenal... they're expensive at over a buck each for just a washer... but, THEY WORK... a ton of BRP 600HO & 800 owners use 'em (including me) on the Y-pipes & it ends the issue of the bolts coming loose for good.

Y-Pipe Cracking - Again, not so much of an issue with the 493 & 593, but I have run into one 593 with a cracked one so it may not a bad thing to keep an eye out for... remember, a 2-stroke exhaust relies on pressure to function. (I actually have a 2002 700 sitting here waiting for a replacement as I write this)

Anyone who does their own piston replacements should know this already, but, when you assemble the cylinders on an engine, don't torque the cylinder bolts without the Y-pipe in place (I suspect some of the cracked pipes I see are the result of that during assembly) place the cylinders on & just finger tighten the bolts... mount the Y-pipe next... not tight, but just barely snug... now torque the cylinders down, & then finally tighten the Y-pipe.

Reed Valves - The condition of the reeds needs to be checked once in a while... if you have compression issues in one cylinder, don't be too quick to condemn the piston/ring.... check the reeds for that cylinder first... the individual reed petals aren't overly expensive... $20-25 ea... not a terrible idea to just replace 'em during a top-end job regardless of how they appear.

RAVE Valves - The RAVE exhaust valves need to be removed & cleaned every once in a while... if you seem to have issues with the engine at over 7000 RPM but it runs fine otherwise below that point, or if it's fine over 7000 but sluggish below 7K, suspect faulty exhaust valve operation... dirty, bad bellows, weak spring, etc,... usually just a cleaning cures it, but inspect the bellows while you're at it.... synthetic oils seem to do a better job of not mucking up the valve blades as quickly as mineral oils tend to... & remember, it matters which way the valve blades get installed... don't put 'em in backward.

TIP: Oven cleaner works well for cleaning... just make sure you completely remove the blade assembly from the valve when using the stuff.

Intake Sockets - The move to alky-blended fuels has raised havoc with the rubber intake sockets... an issue of becoming prone to blistering & cracking developed... now, this may not be as much of an issue using race fuels that don't contain alcohol... but, if you see any signs of blistering or cracking on the intakes toss 'em in the trash before they cost you a piston.

Intake Bolts - If you've removed the intakes more than a few times you'll eventually strip the threads in the mount flange of the cylinder... it's bound to happen... resign yourself to that fate right now... take one of the intake bolts to your local hardware store & grab a few that are about 3/8" or so longer (they're metric - can't remember the exact size off the top of my head) & a nut to go with it... then, when you strip out one of the bolt holes, just thread the longer one through while holding the nut on the backside of the mount flange of the cylinder... no wrench or socket required... the wrench flat of the nut will be up against the intake tract casting when you tighten the bolt.

Oil Pumps - The oil pump for the 493 AND 593 should have an "02" stamped on the pump arm... I noticed McMahan over on eFormulaCarFunnyPapers trying to sell "L7" as pumps for these engines... the L7 pump only lasted 2 years on the 593 (1999 & 2000) and 2 years on the 493 (2000-2001)... in 2001 the 593 got updated to the "L9" pump & the following year both the 593 and the 493 got updated to the same "02" pump. (which the 600HO also uses)

One more thing can also bite you in the asterisk about the series-III oil pumps... they wear out the inner bushing for the shaft... then the pump begins to bind & not fully return to the idle position reliably.

This has cost more than one Series-III engine sled owner an engine... what happens is that because the pump is not fully returning to idle reliably, the engine uses more oil than it should & the owner thinks the pump cable is out of adjustment, so he backs off the adjustment... I think you can see where this is headed... the pump is now out of adjustment at the WOT throttle position, & it's out of adjustment lean.

Some add a small light-pull "helper" spring attached externally to the pump arm to make sure that the pump returns to idle reliably... some have the pump modified to accept a small roller bearing in place of the stock bushing (done by DooTalk.com & F500.us member Brent Chwalek, AKA: "Bigwormskidoo")

Either way... before you back off that pump adjustment because you feel your oil useage is too high... make sure your pump is fully returning to idle position reliably first.

Pre/Post MY2003 Cases & Cranks - The cases & crank PTO end were redesigned in 2003 to eliminate the PTO end inner seal... as such the 2000-2002 model year cases & crank PTO ends are not interchangeable with later years... you can however use the 2003 360-watt mag & flywheel on a 2000-2002 engine & vice-versa just fine.

Details on this here...

1999 "Intro Year" 593 - The 1st year 593 (MY1999) cases & cranks are not interchangable with ANY other year 593... the center seals are different... however, same deal as above holds for swapping any other year's NON-RER mag & flywheel... works just fine.. details on the exact difference is in the same link above for the 2000-2002 differences.