Dirt Rider . Net Text Version Home
Pages: 1
426,& others cam shaft tip (or may be not)
(Click here to view the original thread with full colors/images)
Posted by: eunos---------------------
Forgive me if you`ve heard this before, but I`ve only been a member for 1 month.
I recently stripped the head on our 426 and mentioned to a nephew what I was doing (He`s a race team manager and ex 24 hr endurance racer) He advised I refit the camshafts without the valves to see what happened! I was intrigued, but did what he said. Intrigue turned to pure disbelief. The camshafts would hardly move,3times I removed them and refitted them doing everything by the book still they hardly moved.When I spoke to him again he infomed me this had always been a common fault with the bikes they raced and releasing the shafts was good for about 4/5 BHP.Needless to say I followed his advice and lapped in the camshafts.
The procedure is to use fine grinding paste on the plain journals apply finger pressure to the caps initially and start to turn the cam wheels in a back and forth motion moving the wheels about 1/4 turn every few moments. Gradually the bolts can be torqued down whilst still lapping to about 4ftlbs. Don`t continue until the shafts spin free, stop when they will spin about 1 turn with 1 finger,because they free off slightly when the head is torqued down.Finally don`t forget to wash off every trace of grinding paste or it will destroy the engine in a few seconds. We tried our 426 this weekend after carrying out the above and the difference is amazing, the bike just wants to keep revving and is much crisper off the throttle.
I would like to know if anyone else has had this experience.
Regards, Kevin.
Posted by: sfc crash---------------------
how many hours did you have on the 426 prior to this? did you say"good for 4/5,"as in four fifths, or as in four to five, cause i gotta tell ya ole buddy, getting 4 hp more outa the 426 merely by lapping the journals, well that sounds amazing.:think
Posted by: eunos---------------------
Hey sfc did`nt mean to mislead you there the four to five BHP came from the endurance racing FZR 750. The 426 has about150 hrs on it.Man if I could increase the power like that I`d be selling the info not giving it away.
Kevin.
Posted by: Natester---------------------
Kevin, thanks for the info. I'm in my last semester in college, so I'm riding a two-smoke, but a YZ426/450 is in my future, so I save all these tips. At this rate, my YZF should be pretty bada$$ when I'm done. 
Posted by: sfc crash---------------------
ok eunos, ya never know, ya might be the mulla eunos wahdi ahla 426,
ya never know. i'm taking my wr 426 to jeremy this weekend to have him work his magic,then when i get it back it is time for the bk mod, yz jetting, maybe cam timing, i'll take a look at the cam shaft then. 
Posted by: eunos---------------------
Good luck sfc let me know what you find. Hey Natester put all the tips in a book you could have a best seller.
Lurve the new smiley
Posted by: SFO---------------------
I noticed the same friction in my cam/journal interface and was able to get the cams to spin free by tapping the ends with a babitt hammer. It seemed the cams wanted to sit over a little.
Mike @enginedynamics is a big fan of honing the journal id larger, as it is also a problem to gall this interface.
Be extremely carefull torqing your cam caps.
Posted by: eunos---------------------
Thanx sfc i did`nt try the hammer trick, maybe I could`ve saved myself a lot of work. I was very careful torqing down,P.S. who`s Mike@engine dynamics?
Posted by: will pattison---------------------
what nobody has said, and what yamaha or the magazines certainly haven't admitted, is that the friction can be severe enough to cause the cam gear on the intake side to slip on the shaft. the real bear is that when it only slips a bit, your engine mysteriously has insufficient compression and may not start at all, and there is no obvious phyisical evidence of a problem. a trip to a dealer will probably result in lots of unecessary parts replaced and lots of down time. a new cam is about $140.
yes, i know all this from both first and second hand experience.
wp.
Posted by: SFO---------------------
I heard about from a wiseco guy after I did my 426 Gore bigbore.
I was putting the falicon gears on so I didn't apply but I know that powroll offers welding and reindexing as a service.
If the friction in the cam cap interface was to result in galling/seizing I would acknowledge it as the source for the press on camgear spinning but I suspect that there is a problem with the gear/camshaft press on interface.
Either the level on press fit or a heat issue and uneven expansion or the actual instalation process.
Posted by: will pattison---------------------
in each case i've seen, there was galling on the bearings. the scary thing is that it's even been observed on motors that have never been worked on...as in, should have come from the factory with the correct torque on all three intake cam caps.
wp.
Posted by: sfc crash---------------------
hey..enous, what the..i'm all for banging on stuff with hammers, bricks, beer kegs etc, but that was S F O that posted that...don't wanna take the credit for the first guy that "taps" his cam out'n thru the garage wall.:D
Posted by: eunos---------------------
HACKIT & WELD.
REPAIRERS PAR EXCELLENCE.
WE ALLWAYS USE STERILE HAMMERS.
Hey sfc thought you might like to try our new repair shop!
Posted by: will pattison---------------------
precision fabrication: beat to fit, paint to match.
wp.
Posted by: SFO---------------------
What has been your aproach to managing the cam cap galling issue?
Posted by: eunos---------------------
Question for either S.F.O. or Will.
Can you explain what you mean by the term "galling". Its not one we use in G.B. and I`ve not heard it despite 20 years + in engineering.
Thanks Kevin.
Posted by: will pattison---------------------
no surprise there..."spanner"-man.
galling: what happens to your liver when you drink to much warm beer and eat too many kidney pies.
seriously, i don't know where the term comes from, but it basically means that the metal has smeared. in the cases where i've seen it happen on these cam caps, there are only two alternatives that i know of. one is to buy a new head and caps for about $500. the more practical is to veeeerry carefully clean the surface of the aluminum with very fine sandpaper (600 grit) and finish off with lapping compound. it happened on my '98 yz 400 and i did the cheap fix. it ran perfectly for anouther 120 hours before i sold it.
wp.
Posted by: eunos---------------------
Hey Will
Thanks for enlightening me.
I think Yamaha are covering themselves by suggesting in the manual that camshaft/ journal clearance should be measured using Plastigauge.Not a lot of help if the camshaft caps have never been removed!
Maybe they would just like us all to take the bikes apart to check that THEY have screwed them together right.
Just thinking out loud, would it be feasible to weld the shaft to the gear?Tig welding should keep it cool and prevent stress fractures.
Posted by: will pattison---------------------
from my tig welding experience, i would say absolutely. if it were me, i would put 3 or 4 small spots equally spaced. just to be on the safe side, i would probably do each one separately with cooling time in between, and maybe even wrap the shaft in a wet rag. might be overkill, but safety is in never knowing.
wp.
Posted by: Scott F---------------------
Another definition of galling: When dissimilar metals such as steel and aluminium experience excessive heat and friction, the softer metal can adhere or deposit onto the harder metal. Or, as Will said, the aluminium can become smeared, scored, gouged, abraded, etc.
Posted by: sfc crash---------------------
what do you use to lap the journals, i mean what kind of tool and compound. i was thinking 8" grinder and pea gravel, but that might give too much play.
Posted by: eunos---------------------
Come on sfc you know we brits are renowned for our finesse and being subtle a 4" grinder and ba*ta*d (coarse) file are quite adequate.
Posted by: sfc crash---------------------
here's is my response,in deference to Rodney Fortne, a brit ex-pat,serving in 7th group spec forces, in my brittish accent,termed worse ever by ole Rod..."RIGHT! well then, very good"
Posted by: eunos---------------------
Latest update.
Thought you might like to know ,the bike was used in anger for the first time after the mods this weekend.Got 3rd place in experts 500 race, best result ever.
Text Version Home
vBulletin Copyright ©2000 - 2009,
Jelsoft Enterprises Limited.
vB Easy Archive Final ©2000 - 2009
- Created by Stefan "Xenon" Kaeser
