[Thumbdoctor]

Here is my latest project.
[attachment=35765TO_Piston.JPG]
[attachment=35766TO_Pist...close_up.JPG]
[attachment=35767:Head_close_up.JPG]
[attachment=35768:Cylinder...ose_up_2.JPG]

The subject is a 2004 600 Series III Rotax with good after-market pistons which made roughly 3500 kilometers with them and this resulted during a part throttle drive in the glades. The oil pump is new and adjusted the jetting is spot on. The only obvious external issue is a cracked Y-pipe. Together we will be rebuilding this motor over the summer months. This project will include correct building etiquette (no butchery or cave man techniques)and some known performance enhancements. Lets start with some expert guesses as to what happened and why.

 

[catdoo]

OK, I'll play I'll guess the wristpin circlip came out and took out the cylinder.

 

[Thumbdoctor]

OK, I'll play I'll guess the wristpin circlip came out and took out the cylinder.[/b]

BINGO

Wanna Guess why

 

[catdoo]

OK Simon, I'll guess again.....somebody was too cheap to buy a new one and used an old circlip.

 

[dooman]

I was going to guess right too . it is missing in the one picture. I think the second guess is right as well.

 

[Thumbdoctor]

Re using wrist pin circlip is a good answer but I believe the method of installing and type of circlip used are to blame. You may have noticed that these are not Rotax / Elko castings which employ a larger diameter wire with an anti - rotation loop at one end (this loop resides in the cut away adjacent to the wrist pin bore). The correct method to install the clips is to use a tapered tube installer or this usually happens. The OEM clips are more tolerant to being manipulated with pliers and screw drivers but the after-market ones don't. What usually happens in spite of the best intentions (experience too) is the clip looses some spring tension from being over tweaked at one end and begins to rotate in its groove. This takes a long time to transpire but you can always see catastrophic results. On this particular motor it took a few thousand kilos to happen. Piston slap and mild detonation (pinging) create the right vibration resonance to accelerate the clip rotation and eventually the groove in the piston cannot hold the clip. Some measures the manufacturers have done to reduce the instance of clip failure is to chamfer the ends of the wrist pins to apply radial force on the clip, bend the ends of the clip in wards, use Spiro-Lox type clips and loop one end of the clip as mentioned above. Some things to look out for when replacing piston(s) for this condition are:

1) Bent / twisted connecting rod small end
2) Missing needles in small end (should be 28)
3) Poor quality wrist pins that are squared off at the ends
4) Loose fit of pin in piston (piston should require warming to install wrist pin)
5) excessive piston to cylinder wall clearance causing piston slap
6) Overheat condition of motor (continually operating in marginal snow conditions allowing temp light to come on)
7) Use of incorrect tool to install clip into piston

When you inspect pistons during replacement some tell tale signs of miss installed clips are scratches on the piston around the wrist pin bore and the clips being polished on the outer circumference. Unless otherwise noted on the direction the circlip opening should be at 12 or 6 oclock position. The reasoning for this is at 8800 rpm the piston is moving at 40 ft per second on an average 55mm stroke motor so the mass of the circlip is enough to overcome its spring tension if installed side ways (9 or 3 oclock position). As you can see on the above photo the side of the piston that the clip exited has a very large clip groove hence the disaster.

 

[catdoo]

OK, next time we're in Cochrane you buy me a beer for guessing the first one right, and I'll buy you a beer for missing the second question.

 

[Thumbdoctor]

Next on the menu we have the Mag side. I popped the flywheel and what did I find...

[attachment=35812:Flywheel.JPG]
[attachment=35813:Flywheel2.JPG]
[attachment=35814:Mag_seal.JPG]
[attachment=35815:Mag_seal2.JPG]

Yuk!!! the mag seal has vented (for the last time). This seems to be a chronic problem with Series III motors, the mag side has no way to vent pressure in the cavity between the two bearings and the outer seals. Fortunately only the out board seal leaks. When the inside bearing seal fails it ends your day quickly. The problem feeds on itself because excessive heat created by the stator on the mag side plus engine heat causes the Iso-Flex grease to expand. The grease that leaks into the flywheel accumulates all kinds of crap and sets the flywheel balance off and the vibration elongates the seal. Finally all the grease is gone and so are your Mag side main bearings. One big contributor to stator heat and eventually seal failure is over taxing your electrical system. Food for thought for you folks that install two 100 watt HID headlights on a 240 watt system. This is another argument for a temp gage to monitor engine overheat. In my opinion, when the idiot light comes on its too late and damage is starting to happen (like rings getting soft and piston pin clips loosing their tension)...did I mention installing wrist pin clips correctly.

 

[Thumbdoctor]

On the early ZX chassis with Series III motor pull starter failure was rampant causing no end to headaches. The root cause there (besides cheap design & materials) was heat. Heat radiated from the exhaust system and heat inside from the stator. The pull starter would fail and spit its guts into the flywheel magnets and take out the stator and eventually the mag seal...is there a pattern here somewhere.

My next pet peeve is the method builders use to measure squeeze band in combustion chambers. The squeeze band clearance can make or break a motor. The racing manual recommends and I'll quote "The squish clearance can be measured by inserting a piece of ROSIN core solder into the combustion chamber, rotating the engine through TDC, removing the solder and measuring the thickness of the solder. The solder should be inserted above and in line with the wrist pin. Measure the squish band on both sides of the piston as it may vary from side to side. CAUTION: Do not use acid core solder; the acids can damage the piston and cylinder". They seem to have missed alerting the public that using solid solder or alloy is a bad thing also...
[attachment=35818ents.JPG]
[attachment=35819ent_close_up.JPG]
[attachment=35820ent_close_up2.JPG]

The photos above demonstrate 2 reasons why I prefer to cc the combustion chamber volume. The first one being that solid or alloy solder doesn't compress accurately (dents the chamber and piston) giving false reading so base gasket selection is moot. The second reason is that you cannot be sure if the solder is positioned at the extreme edge of the squish band (the dents indicate that the solder missed the edge of the band by 4mm hence giving a safe squish reading). End result incorrect compression ratio, premium grade fuel requirement... END GAME detonation.

 

[XCR583]

Awsome post TD!! I will be following this closely!! Cody will have an awsome motor after you are done with it!!

 

[Thumbdoctor]

Like I always say...there's nothing that can't be buffed out with a little compound and elbow
grease. This piston is ready to be reused...

[attachment=35836:Buffed_out.JPG]


As a Paperweight LOL !!!


I managed to save the cylinder head by carefully tapping the high points down with a brass
hammer and smoothing out the damage. Although this may seem like an unorthodox repair.
The budget has made allowances for a High perf head in the future so spending money on a
replacement didn't make sense. The squish band needs to be straight and smooth to allow
combustion gases to reach the edges of the combustion chamber. Another method of saving
a slightly pitted head is to smooth it out and have a barrier coating installed.

[attachment=35837:Head_repaired.JPG]
[attachment=35838:Head_repaired2.JPG]

Getting back to the subject of Iso-Flex grease loss on the mag side. There is a way you can
recover the loss without tearing down your motor mid season. This is only feasible if your
inner seal is intact and your outer seal just burped out some grease without going totally dry.
Remove the flywheel and clean up the carnage left on the stator and flywheel
(brake cleaner will work). Remove the upper stator retainer bolt and add 5cc of Iso-flex
through the bolt hole with a syringe and primer hose. The cases have a relief cut into the
inside adjacent to the Mag bearing to allow grease to flow into the bearings. The next run
cycle the grease will melt and lube the bearing and life is good again. Don't forget to apply
Loctite red #272 to the bolt before you replace it. Be sure to service that seal in the next off season.

[attachment=35839:Mag_feed.JPG]
[attachment=35840:Mag_feed_close_up.JPG]
[attachment=35841:Stator_side.JPG]

 

[trailblazer]

Like I always say...there's nothing that can't be buffed out with a little compound and elbow
grease. This piston is ready to be reused...

[attachment=35836:Buffed_out.JPG]
As a Paperweight LOL !!![/b]

You crack me up Simon.

Thanks for the great thread.
The pics are awesome.

Jeff

 

[Thumbdoctor]

Whoever said the devil was in the details must have owned a Series III Rotax. I was giving the reed boxes a careful inspection
and noticed the general gnarly appearance of the petal tips and held one up to the light to do the seating check. I always check reeds this way
to make sure there's no belt debris holding the petals open. This motor had experienced a cold seizure this season and subsequent
piston pin exit stage left so I thought it prudent to put everything under the microscope. I could see quite a gap on one of the outer petals
so I dissembled the valve:
[attachment=35860:Reed_inside.JPG]
[attachment=35861:Reed_Valve.JPG]
[attachment=35862ebris_in_cage.JPG]
[attachment=35863ebris_close_up.JPG]

There is a minute shard of aluminum wedged into the valve's seat stopping the reed petal from fully seating against the delta box. I imagine
it had been there for some time as the framework of the box was showing signs of reversion (melting) on the frame and the one next to it.
Can't say enough about checking and double checking everything after a catastrophe. A reed that leaks this badly can cause some part throttle
lean issues. I thoroughly cleaned the Box, delta and petals using an ammonia based kitchen cleaner (easy on rubber components hard on carbon
build up) and didn't like the condition of the petals. They are quite eroded around the edges and don't provide the best seal. This being a 12 frame
/ petal design having a small leak in each petal adds up substantially. The frames will have to be dressed with 2000 grit wet or dry and I'm going
to flip the petals and use the undamaged outsides. The manufacture recommends replacing the reeds once a year. I don't think there are any published
life cycle for reeds but I don't want to have a motor ingest a set to find out. The petals don't do much damage but the sudden lean out and subsequent
burn down does damage the pocket book.
[attachment=35864etals.JPG]
[attachment=35865etal_close_up.JPG]

 

[jacqui583]

Wow. something so small can cause so much aggravation.

Jeff
(Disguised as Jacqui. LOL)

 

[dooman]

nice post Simon. something we need more of.

 

[Thumbdoctor]

Here's why you should get your own cylinders re plated and not accept an exchange:
[attachment=35879:Cylinder_crack.JPG][attachment=35880:Cylinder_crack_2.JPG]
[attachment=35881:Cylinder_crack_3.JPG]
This barrel fell victim to the dying piston's swan song. Enough force from the piston pin
clip being carried down to the bottom of the barrel severely cracked it. IMHO it should be
scrapped. Sure a machine shop can weld it and fill in missing material but it will be only
50% ~ 75% of its original integrity. Electro plating will further embrittle the repair. Try to
get your own uncracked jugs re plated instead of a quick exchange or buy new. To chance
having the bottom of a barrel drop out at full pull (8000 rpm) will break plenty more parts.

 

[Thumbdoctor]

OK we have the reeds cleaned up and the worn petals flipped over. I sent emails to Moto Tassinari enquiring as to what their opinion
was on flipping petals which show erosion. I gave them two weeks and 2 emails. Still no reply soo I am going to keep the reed petals
reversed and thats my story and I'm stickin to it !!!

[attachment=35935:Reeds_clean.JPG][attachment=35936:Reed_inside_Clean.JPG]

Nice and clean and as photo 2 indicates the petals are air tight. The best method for getting the petals to seat is to wet sand the
frames with 2000 grit wet or dry sand paper on a piece of 1/4" plexi glass (to assure straightness). The area at the base of the
petals is the most important because it controls the static tension the petals apply on the cage. There is a balance to establish
here as to how tight the petal tension can be:
1) Too tight means more crankshaft duration to pull the reed open and start the inlet stroke (Better mid to WFO throttle)
2) Too loose means more crankshaft duration to build enough crankcase compression to close the reed against the cage
(Lean mixture, low end burble and elevated hot idle and poor low end grunt)

Now the tricky part is "just right" which means the petals just touch the cage (some faint light around the petals). The name
of the game here is intake duration (measured in crankshaft degrees). The whole theory behind aftermarket reed valves is
improved intake Vs crankshaft phasing, the lighter carbon fibre petals are both stiffer and easier for the vacuum / pressure
cycles to articulate resulting in 'Livelier throttle response). No great increases in HP / Torque just quality throttle response.

 

[Thumbdoctor]

Lets do a systematic approach to this build. I vote we follow the air path from the air box through the motor (air pump and out the exhaust. Since only the mods can alter the contents of this post my vote wins!!!

Mikuni TM 40 is a good choice for this application. In the bike world these are referred to as "Smooth Bores" because they can be fitted to both small and large displacement engines using the same 40mm aperture size with few associated air fuel mixture concerns and yet feed much more than their advertised CFM (air / fuel cubic feet per minute). High efficiency / RPM engines love to have little intake restriction hence good cylinder packing VE (volumetric efficiency).

Lets begin.

[attachment=35937:Carb_apart.JPG]
This is the beast (1/2 rack) and its innards. I will cover each part step by step and cover the thought process behind them. The spigot mounting flange on these units seem to react to the type of rubber Rotax chose for the intake boots. Actually some of the make up of rubber is acidic and corrodes aluminum in short order. The best advice is to clean and treat the boots as soon as you get your sled and if there are any signs of blistering on the outsides of the boots get em replaced if you still have warranty. For the non warranty folks.. look at the after-market because they are cheaper than replacing the BRP units. Back to the corrosion around the spigot flanges try to back out the carbs carefully and be sure to loosen the worm clamps all the way out. With the carb off vacuum out the reed boxes on the machine This is specially important if you service the carb before summer storage. I disassemble the carb completely and use a stainless steel brush on the flange corrosion then apply a film of white lithium grease to both the flange and inside the boot. A good coating of glycerine (vasaline) to the outside of the boots will protect the against the elements.
[attachment=35938:Spigot.JPG]

 

[Thumbdoctor]

After complete disassembly remove all rubber seals and gaskets. Thoroughly clean all
components then blow dry with compressed air (a shop vac on blow will do in a pinch). The first component we'll look at is the bowl screws. Photo 2 illustrates some build up in the seal recess which usually migrates up the bolt and into the main jet well.

[attachment=35939:Bowl_assembly.JPG][attachment=35944:Bowl_nut_close_up.JPG]

One thing I've observed over the years is this: Put an over sized fastener on any component an there will be the propensity to over tighten it! This observation is most apparent in the bowl retainer screws. Just because the size of the bolt is 17mm it doesn't require 100 lb ft of torque. The subsequent distortion to the main body causes the throttle valve to bind in its track and eventually wear off the Teflon plating. This is one contributor to erratic or elevated idle due to the worn valve not being able to modulate air entering mixing chamber.

[attachment=35943:Bowl_nut_tighten.JPG][attachment=35941:Throttle_valve.JPG]

The correct bowl screw torque is 17 inch pounds or 1/4 turn after bolt o-ring contacts bowl.

Next is the float assembly which has been simplified by making it modular (modular = $$$). Have a float go south or damage the O-ring seal will cost you $96.00 for the assembly so care is prudent here and getting the parts separately is not an option.

[attachment=35945:Float_assembly.JPG]

Clean this assembly with mild chemicals and air dry ASAP so the plastic parts are not damaged. BTW float level is fixed and non adjustable. The area that needs special attention is the well where the float assembly slides into, this area tends to corrode and accumulate debris which eventually ends up in the float needle and seat.

[attachment=35946:Float_needle_well.JPG]

 

[idooski]

Can I just come over and sleep in your shop so I can watch and learn? It would be so much easier than waiting for the next installment.