dutbite

Member
Oct 10, 2004
3
0
valve recession & dust

this seems to be the forum with the more knowledgeble people so that´s why I post my questions here:

I live and work in Portugal and offer guided offroad trips.

Currently I own 6 KTM´s, five are 2003 EXC models. On all these EXC bikes I replaced the inlet valves and on one bike also the cilinder & piston rings after one year(my first year).

The foam filters used in todays dirtbikes doesn´t seem to get rid off the finest particals.

I pinpointed the cause to the fine claydust (powder) that destroyed valve and in a lesser way the seats. On all bikes the rings were also beyond specs.

I´m familiar with the correct cleaning and oiling methods, I use Twinair products. I use a standard, oiled filter + dry dustcover + skin. I make sure he filterholder is in the right position.
Still dust seems to pass the filter from the moment I start the engine and ride in dusty conditions.
I know this because there´s a fine layer of dust covering the flame arrestor mesh wire on the filter side.

I spend the last few days browsing forums and widen my knowledge. I learned a lot about valve materials and combinations of materials.The emphasis is put to the tuning of the engine and little thought has been given to airfiltering in the documentation that I found about tuning.

My question(s):
is there any info to the size of the smallest particals that are trapped by a foam filters on the market today?

Can anyone point my nose in the right direction concerning better filtering methods (if they exsist)?

where can I find info about the theories of airfiltering?

--------------------
I
am aware of the fact that lifespan of the engine is not the biggest isue when it comes to dirtbikes. Nevertheless I hope to find a way to overcome this problem.
High power output is not my goal. Durability is what I´m looking for.

Adriaan, spelled my username (dustbite(sic)) wrong, found out too late....
 
Last edited:

lukey

Member
Feb 21, 2004
2
0
Here in Australia we have a huge problem with valve recession on the four strokes. Particuarly due to the size of the dust particles, Australia is one of the oldest continents around and from what ive read we can get down to 4 microns which is pretty fricken small. Add to this the last couple of years have been drought and you get heaps of very fine dust and some big problems. Ive been reading up on this as well and the filter Yamaha ships with the WR450 (im assuming they will all be similiar) is good down to 8 microns. Uni filter make a very good filter but is very expensive and is the dual stage design, this design is great in theory with the outer layer catching the big stuff and the inner doing the small stuff... However the big stuff is easy to stop so the damaging dust (the fine stuff that laps your valve seats for you) is already halfway through your filter. Ill leave it to you to draw your own conclusions but ive decided to go with a good thick single stage filter and the airboot dust has all but disappeared.

Hope this helped a bit
BTW we have not long had the crf250x released over here, they brought 3 or 4 over pre release for some guys to race in a big enduro and i think one just barely finished, they all had zero valve clearance fairly quickly. In fact there were comments made that the motors looked a lot like vacuum cleaners on the inside they had that much crud through them. Of course honda said "this has never happened before" and sent people over to check it out. They ended up blaming Aussie dust and poorly suited air filters.
 

TM-Frank

Member
Dec 15, 2000
325
0
I have made some good experiences with these PC Filterskins. I soaked them with engine oil and installed them before the start of a three hour race on a MX track which is also very dusty in summer, with very fine dust. Nothing came through
They are somewhat hard to install on some bikes. Don't know about KTMs.

http://www.pcracingusa.com/filterskins.php
 

arjay

~SPONSOR~
Nov 19, 2002
222
0
Hi - there's an article about filter prep in Australasian Dirtbike.

http://www.adbmag.com/magazine.php

The advice they give is to go with a single stage filter and to prepare it well. They suggest a three bucket system. One - clean turps, two - more clean turps then squeeze it out and fully submerge the filter in filter fluid (bucket three) Squeeze out as much as you can then re-install. Sounds like a good system, and quicker because there's no drying time.
 

Studboy

Thinks he can ride
Dec 2, 2001
1,818
0
Another thing that you could do since it seems to be near impossible to filter out all of the dust, would be to coat the inside of the airboot with a thin layer of high temp grease and hopefully it will catch some more of the fine dust. Wipe it out every filter change, and you will be able to tell if you have been getting excess dirt through the filter.
 

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