Decompresion mechanism repair.

Message

Cdale_racer_669 · #11 Post by **Cdale_racer_669** » Wed Jan 12, 2005 4:16 am

i want mine rebuilt! give me a price:)

MX Quad Dad · #12 Post by **MX Quad Dad** » Wed Jan 12, 2005 4:49 am

Do you think it is possible the unbalanced cranks (viberations) played a roll in the early failures of some of these?

wistech · #13 Post by **wistech** » Wed Jan 12, 2005 6:22 pm

I know the early cams had a very small rivet holding the wieght on . The newer ones have a step machined into the backing plate to support the rivet. Vibration may play a role but I dont know how to prove that. It seems the ones that fail let the wieght move over enough to contact the cam cap and snap it off. I have seen many with the rivet still in the backing plate but bent halfway out . The wieght shatteres throwing pieces into the cam lobes wiping out the cams and sometimes jamming a valve open. You know what happens then.
I only have a limited supply of repair parts so I will only be able to repair about 5 more till new parts come in. Cost will be determined on how bad yours is. If it just needs hand fitting its about $30. Rivets are $5 . The screws are just a few cents.

cannondale27 · #14 Post by **cannondale27** » Thu Jan 13, 2005 2:34 am

Nice job Wistech.I would like to add that Timbomoose has tried making these weights and could have been a sucess if he had one tool which he doesnt have.If enough people give him the incentive to buy the tool then we can have better weights.We have to remember even though the piece is small it is quite complicated machining wise and has to be perfect.That takes time and money along with expensive equipment.Lets make it worth the effort.

comander420 · #15 Post by **comander420** » Thu Jan 13, 2005 2:41 am

I'd be interested as long as he did it while he still has my head and i was first

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Canniboomer · #16 Post by **Canniboomer** » Thu Jan 13, 2005 3:28 pm

Thanks much Wistech!!! Comparing same here now, since I have an old and new exhaust cam side-by-side, will post pic soon.
I can see the sideplay at the end of the flyweights, and will get worse with wear like you say... I don't like the "fix" of grinding away at the cam cap -- that's not a cure.... If any contact is made, something has to be getting loose beforehand, so the grinding of the bearing cap would only "delay" the inevitable destruction. Your intent to tighten clearances at the pivot will reduce the wobble, great diagnosis!
But for the fix method to reduce wobble, can we instead put an ultra-thin shim underneath pinhead?, and of a slightly larger OD than pin head?, to take up the "excess" clearance there? without the take-away hand grinding to shorten pin? The larger diameter of a shim washer would also stabilize the flyweight sideplay at the other end. The clearance of pinhead to bearing cap would be exact same, but if that is really a problem you could consider to grind slightly on the head of rivetpin when finished -- it looks plenty strong and thick there, and should be able to give up a few thousandths.... but hard to believe a properly set pin could
ever make contact with bearing cap -- the loctite and punching as you recommend probably already cures that with the unmodified pin.

????

Canniboomer · #17 Post by **Canniboomer** » Thu Jan 13, 2005 3:43 pm

Older better looking exhaust cam on left, with machined flyweight, newer version pressed metal on right. But you know my next question... what's with the wedgie on older cam between the lobes?, no longer there on newer camshafts?

Canniboomer · #18 Post by **Canniboomer** » Thu Jan 13, 2005 4:01 pm

Hmmmn, did that have something to do with the earlier cover-mounted cam position sensor??? lightbulb just came on! sorry...anyway, enjoy the pic... always learning on this site!
Magnificent thread Wistech!:clap:

Happyboy · #19 Post by **Happyboy** » Thu Jan 13, 2005 4:31 pm

Ding ding ding ding ding we have a winner!

wistech · #20 Post by **wistech** » Thu Jan 13, 2005 6:53 pm

I have not ground a cam cap myself ,its something I heard had to be done because it was just to close . The pin and the wieght are at the same hieght in relation to the cam cap. It will not cure the play anyway. Yep the lobe is for the cam sensor. The washer under the pin idea would work good to but then if the washer ever were to come loose it would be free to float around in the head. Filing the pin down is pretty easy if you measure the play before you take it apart . Heck we could have set of pins machined to different thicknesses and larger heads for super quick rebuilds. One other thing I have seen is the small silver pin on cam pivot have a tendancy to move out. Thats why I would rather just machine out the end of the cam to remove the cam pivot instead of breaking it off and installing a new one. I figure the ones that are still held in good will stay in .

I have recieved some pm's about some of you interested in making the wieghts. All I can say is go for it. Cannondales are all about us anyway and the more involved the better to improve these babies. Whatever you need just ask . :clap: