This Could Be The End!

[Jerry Hall]

F-Red:

Make a list of the components and specifications of you engine package.  If you do not know all of these specs. call you engine builder...he should be able to supply the info.

Piston clearance when the engine was assembled.
Piston to head clearance at the squish OD and at the squish ID
Volume on top of the piston at TDC.
Mfg. of Pipe and silencer, stinger ID and muffler ID where it exits to the atmosphere
Carb Mfg. size and jetting
Brand of fuel and octane of the fuel you were using
Ignition timing.
spark plug Mfg. and heat range
Port timings
reed valve
intake system and air filter
Radiator Mfg. and are there any inline temp guages or inline coolers?
Fuel to oil ratio

The above specification and components are what we call an engine package.  All of the above should have been engineered and tested to work together.  If any one of the above specs or components were not tested as part of the package, it could result in the failure you experienced!!!


What was the approximate outside air temp and cylinder temp when the failure occurred?

[jason323]

how many times was it starved out of fuel do to your float level being to low? the post in the carb section with pics the floats were way off.

[Langbolt]

Did Wossner ever get the weight down to an acceptable level ,  They used to be so heavy that I was afraid to use them in our healthy big Bore builds that turned a lot of RPM.

78.5mm Big-Bore Piston wights:

Wiseco - 296 grams

Wossner - 307 grams

BOTH Pistons have the "NEW" design features of the extra material beside the Piston pin Area towards the exhaust side to eliminate the cross linking issue.

[Jerry Hall]

78.5mm Big-Bore Piston wights:

Wiseco - 296 grams

Wossner - 307 grams

BOTH Pistons have the "NEW" design features of the extra material beside the Piston pin Area towards the exhaust side to eliminate the cross linking issue.

It is good to see the Wossner pistons went on a diet.  When LA sleeve first started selling the Wossner big bore pistons, I bought one.  The Wossner piston felt heavy when I when I held it in one hand and the old Wiseco on the other.  I got the scales out and they were over 50 grams heavier.  I sent it back and started using the ESR Wiseco pistons because I was afraid that the Wossner pistons would break the con-rod on that high revving 330 engine.

[All250R]

A lot is discussed regarding the piston lifecycle, but is it possible these relatively new ESR cylinders have a design flaws that are causing otherwise good pistons to interfere with the bore?

[fearlessfred]

I viewed a discussion on this a few weeks ago and one builder mentioned ring gap being to  tight and heat transfer from piston to cylinder via the rings.Jerry can you elaborate on this .

[Jerry Hall]

I viewed a discussion on this a few weeks ago and one builder mentioned ring gap being to  tight and heat transfer from piston to cylinder via the rings.Jerry can you elaborate on this .

Can you rephrase the question?  I am not sure what you are asking.

[dem3500]

i agree with the comment about waiting until you have the money to do it All and do it Right the first time. i bought a R with a used ESR 310 pv complete kit last fall. the bore was worn out. so i took it to my machinist for a new bore. i bought the specific ESR Wiseco piston and he followed all the Wiseco/ESR specifications that i got right from Eddie. even down to the clearance on the PV to the .000th. spark plug type, inital jetting, torque spec, break in......on and on. i have been riding it like it since early this spring and i am far from nice to it. point being, do it RIGHT and do it once! 2 strokes are easy! if you are having this many problems with a 2 stroke then there has to be something that your missing. maybe its not your fault. not trying to be mean to you my any means! but these bikes are so so so easy to work on and build. maybe the machinist your using doesnt know what hes doing. maybe there was some suggestion that you were givin that you misunderstood. DONT GIVE UP ON THE R!!! do some extra research this time. call Eddie, (hes hard to get ahold of but keep trying. hes such a wealth of knowledge and likes to help!) talk to your machinist/engin builder to make sure hes following the correct specs, double check EVERYTHING on your next build. dont give up dude! theres plenty of people that have been in your same situation and now have a good reliable R because they were able to learn from their mistakes and diddnt give up. knowledge is power but nobody is born with it!

[wilkin250r]

I viewed a discussion on this a few weeks ago and one builder mentioned ring gap being to tight and heat transfer from piston to cylinder via the rings.Jerry can you elaborate on this .

I wish I had seen this thread earlier.  My first thought was the obvious seizure, but seeing the vertical lines extending all the way to the top of the cylinder, my SECOND thought was the ring gap.

[Jerry Hall]

I also noticed the scoring streak from the top piston ring. When the ring gap is too tight there will usually be many lines around the whole circumference of the bore, but the lines are not usually as wide as the "ring streak" pictured.  

I frequently see the rings put steaks in the bores directly above the center bridge in a bridged exhaust port when the bridge has not been relieved and guys are not running enough oil in the fuel for their type of riding.  The center bridge in an exhaust port runs much hotter than any other part of the cylinder wall.  The excessive heat oftens kills the oils ability to lubricate, causing the rings to gauld where the ring is making contact with the dry unlubricated bridge.  The gaulding damages the ring and the ring damages any other part of the cylinder wall where it makes contact.  

I think that the same phenomena mentioned above occurred on the bridge of the pictured cylinder between the main and auxiliary exhaust port.  There was aluminium transferred to the bore in this same bridged area.  This means that there was a time when the surface temperature of the piston skirt was over 1100 deg. F. I do not know of any lubricant that can provide lubrication when it is 1100 deg F.  The lubrication has to fail before aluminum can be transferred to the cylinder wall even though the piston was a press fit a few strokes before the seizure.

The friction from the press fit of the piston in the bore is what generates the excessive heat that causes the surface of the piston skirt to melt and transfer aluminum to the bore.

[wilkin250r]

To continue Jerry's thought just a little further, castor oil is about the best you could hope for in a seizure/overheating application.  It has excellent shear strength (meaning it doesn't get scraped off quite as easily as other oils), and if/when it DOES overheat and burn, it leaves behind a waxy substance that still has lubricating properties.

Now, that doesn't mean Castor is the "best", it burns dirty, gummy, and leaves behind a lot of residue.  But it generally IS the best in preventing a seizure if something goes wrong inside your engine.

[Jerry Hall]

..............Now, that doesn't mean Castor is the "best", it burns dirty, gummy, and leaves behind a lot of residue.  But it generally IS the best in preventing a seizure if something goes wrong inside your engine.

For me, castor oil has some very desirable characteristics that mineral and synthetics oils do not possess.  This unique quality does not show up in the conventional (falex test, 3 and 4 ball test, timkin test, etc.), laboratory oil test where the parts are swimming in oil.

There are many oils and additives that will carry more load in the above lab tests than castor but they do not burn well and many that do burn well produce an abrasive ash when they burn.  Oils that produce an abrasive ash when burned can be eliminated as candidates as being used as base stock in a two stroke oil.   The manufactures of the two stroke oils that show high load carrying capability in the above test that do not burn well usually recommend that "best performance" is obtained at ratios in the 32:1 to 100:1 fuel to oil ratios.  Make note of the words "best performance" which means best power not best lubrication is obtained at those ratios.  Oils that do not burn well do so because these oil molecules get in the way and slow the chain reaction in the combustion process.

The gummy brown waxy residue from castor oil becomes a high temperature lubricant at temperatures where most mineral and synthetics have turned to ash. This is what I like about castor oils.  The gummy brown residue from castor oil does not form on a part that is running cool. A part that is running cool does not need a very good or more lubricant.


The things I look for in a two stroke oil that will be subjected to the most extreme engine component heat and load condition are:

1.  The oil must mix well with the fuel at the temperatures the fuel will be at while supplying the engine with fuel.
2.  The oil must provide high load carrying capability at extreme temperatures.
3.  The oil must burn easily even at ratios of 15:1.  Remember that oil is a fuel and if it burns easily it makes the fuel a better fuel
 
An oil that burns clean is not a high priority for me on an all out racing oil, but an oil that can be run at low ratios is desirable.  An engine that is running on a low fuel to oil ratios (around 20:1) provides a little more "wetting" of the parts.  A part that has more wetting will have a wider contact patch for heat to pass from the hot parts to it's cooler heat sink.  

Intuition and physical test says a cylinder wall that has more oil on it provides a better ring seal and yields higher cranking pressure on a compression gauge.  I do not think that this is a valid point on a high RPM engine for running more oil in the fuel.  A cylinder wall that has more oil on it provides more surface area for heat to flow from the hot piston skirts and rings to the cooler cylinder wall.  


A better oil or more oil in the fuel would not have prevented the seized piston shown at the beginning of this thread.  This engine has some basic problems with the build, tuning, and or break-in procedure.  A better oil or more oil in the fuel in this engine build would have only added another 1/2 second or less before the engine seized.

[Sky]

I see this every week.  

I think that it is the engine builders/parts supplier DUTY to inform the customer as to what pipe, porting, head, carb, reeds etc. and starting point on jetting they should be using for a given engine package.  If the engine builder cannot furnish this information you need to go to builder or supplier that can. This knowledge only comes from expensive testing on the engine builders part. If you are following all of your builders recommendations for engine package components and tuning specifications and are still having problems....you need a builders that has done the necessary testing and development. A customer should not have to go through a handful of $150.00 pistons to work out the bugs that was in a engine package that was supposed to be already developed.  

Customers often shoot themselves in the foot trying to select their engine package components themselves rather than finding a builder and following his recommendations to a "T". I have some customers that do not listen to my recommendations and use the wrong pipe, porting, head etc.because they do not want to spend the money for the tried and tested components and do not understand the importance of using components that compliment one another.

AMEN Jerry. Thanks God for knowledgable and experienced men like you. Thanks for all you share with this site. Your insight and wisdom is not taken for granted.

[wilkin250r]

And THAT is why we love Jerry.  Good luck trying to find that kind of in-depth, technical explanation on Facebook...

[havinnoj]

And THAT is why we love Jerry.  Good luck trying to find that kind of in-depth, technical explanation on Facebook...

X2.  Nice to see you around here Wilks! :cool: