Urban Myth Lore

[billyt]

Like many of you on this site I have been around the trials scene for over thirty years now.  

Heard many urban myths, street lore, snake oil, and some basic nonsense about mechanics of trials bikes, their engines, carbs and suspension.

In your opinion what are some of these myths and lore that are off the wall?

Love to hear your experiences on this topic.

 

 

 

 

 

[nigel dabster]

Paxau is an excellent mechanic.

Future bikes are much better.

[breagh]

I had this lad Tom Cholmondeley (Google him) at a wee club trial in the middle of nowhere.

Rumour has it his 4rt had a rifle mount on it.

Sadly he's passed away and no way will I take responsibility for him twisting his hip on section 4.

[taffe]

I could not think of any either.

Taff

[sirdabalot]

It isn't officially a crash or a 5 until you aren't touching the bike. 

[zippy]

"Cable clutch is just as easy to pull as a hydraulic clutch"

 

[sirdabalot]

It's true dear wife, the Gas Gas factory were so impressed with my riding that they gave me this brand new bike on condition that I signed the contract to do a trial every Sunday to promote their range. 

[cabby]

5 hours ago, breagh said:

I had this lad Tom Cholmondeley (Google him) at a wee club trial in the middle of nowhere.

Rumour has it his 4rt had a rifle mount on it.

Sadly he's passed away and no way will I take responsibility for him twisting his hip on section 4.

His trials story is the greatest never told  but don't go on his land whatever you do 

 

If you google him and trials, you'll not get what you expect 

Edited March 11, 2017 by cabby

[b40rt]

2 hours ago, oni nou said:

If you use a water-cooled piston in an aircooled engine it may seize up because of the tighter tolerances used on an water-cooled engine.

No, this is true. I read it on here so it must be ....

Edited March 11, 2017 by b40rt

[dan williams]

Not a lot of technical myths. A lot of ignorance of how things work but usually from people who are just new enough to not understand yet ( though I have my moments too ). Lot's of riding technique myths.

[elusivemite]

Buying a brand new bike will instantly make me a better rider. 

 

 

Reality. Fettling and setting up your current bike will probably reap far more rewards. 

Edited March 11, 2017 by elusivemite

[billyt]

1. 

    

   SUPERMOTORookie

   Member

   Joined:

   Oct 2, 1999

   Messages:

   5

   Likes Received:

   0

   I always had to run our YZ490 dirt track engines (same basic engine as the air cooled wr500) at about .006" piston to wall clearance when using forged pistons like Wiseco. We found the air cooled barrels distort so much when you run them hard, that anything less would cause the piston to tighten up on long straights. The bores just don't stay very round when they get hot so it takes extra clearance to keep everything working together. Big air-cooled engines aren't well behaved like the new water cooled stuff. It sounds like marbles in a coffee can when it's loose and cold, but it always worked well for us.
   
   It sure is a lot easier to go fast with the newer stuff .

    

   #2SuperMoto, Feb 27, 2006

[billyt]

I suspect freddy is pretty close. For example Porsche specs their 90mm (3.5433") piston to bore clearance at approx 0.003". This is on a precision engine that can survive on a racetrack off the showroom floor, it is also an air cooled cast aluminum cylinder with a coating and a forged aluminum piston both of high quality alloy content. Running a cast iron cylinder with an aluminum piston will definately need more clearance and it also depends on whether or not it's air or watercooled as the aircooled run a little hotter and tend to warmup faster. I remember my old stroker Ford Windsor, with street mufflers on you could hear the piston slap for a few moments til the pistons expanded.

Lose is like a worn engine an might smoke a little, too tight and the piston seizes or badly damages the bore, you decide. http://bbs.homeshopmachinist.net//wink.gif

------------------

[billyt]

This has alway been an issue. Motorcycle piston clearance vs American V8.

Typical Honda water cooled piston clearance is .0004 to .0015" new, service limit .002"

Have a cyclinder bored by a machine shop not use to those numbers it come back at .003 or .004". Already well past the service limit or more than twice the spec.

Typical air cooled Honda runs. .0004 to .0017" with service limit of .004"
Example 1986-1995 XR250 R .0006 to .002" service limit .004"


Wonder why some engines have piston slap cold ...........start with .005 or more for clearance.:eek1

[billyt]

I once heard you could use any piston from any bike.  Water cooled vs air cooled don't matter, a piston is a piston is a  piston. 

 

 

Edited March 11, 2017 by billyt