Jump to content

Auto Decompression mechanism getting stuck

Recommended Posts

The weight gets sticky here and comes to rest in this position. I can push it in all the way to fully engage the decompression pin on the cam but it seems like the weight is contacting the face of the shaft that connects to the decompression pin/plunger. Everything works smoothly individually but as soon as I tighten the two Socket screws it does not engage smoothly. This all happened on my last ride. Any ideas?

 

IMG_6186.JPG

 

This is what fully engaged looks like.

IMG_6187.JPG

 

 

Share this post


Link to post
Share on other sites
I'd pull it out, check the pin inside the cam. Sometimes they shear off and yours might be trying to do that.

I have done that and can't see anything wrong, should there be play in the weights' axle when the gear is off?

Share this post


Link to post
Share on other sites

Not much. that's probably the problem. If the decompression shaft is getting bound inside the cam, that will definitely do what you're describing. Take the gear off, and pull off the weight and see if that shaft spins freely. If it's got debris in it somehow or there's a knick or ding in the cam or on the shaft, that could do it. There's very little force being applied there. It wouldn't take much to hang it up. The spring could be shot too.

Share this post


Link to post
Share on other sites
Not much. that's probably the problem. If the decompression shaft is getting bound inside the cam, that will definitely do what you're describing. Take the gear off, and pull off the weight and see if that shaft spins freely. If it's got debris in it somehow or there's a knick or ding in the cam or on the shaft, that could do it. There's very little force being applied there. It wouldn't take much to hang it up. The spring could be shot too.

I think I've pinpointed the problem. Everything moves well but as soon as I apply the spec'ed torque to the cam gear sockets the weight comes in contact with the face of the plunger pin and or the face of the what looks to be a bushing. See the picture of what I am pointing at. Should this be flush with the mating surface? Can the part with the threaded lobes move on the camshaft?IMG_6220.thumb.JPG.3db5b89982772b3bb295bed4d125529b.JPGIMG_6219.thumb.JPG.3e32d6e8a6d007b1abfacdbda78cdb14.JPG

Share this post


Link to post
Share on other sites

The flange is pressed onto the cam. If its moved inward, toward the bearing the spec is going to be wrong and it could drag. Or, what may be happening is the back side of the rod's radius is hanging up in the back side of the cam itself. Either of which, or both even could prevent the weight and that tiny spring from working correctly. It'd kind of late right now, but I'll go look at another cam and see how deep the flange is pressed on. 

Is there any kind of wear pattern in the back of the weight? Like where it may have been rubbing?

Share this post


Link to post
Share on other sites
The flange is pressed onto the cam. If its moved inward, toward the bearing the spec is going to be wrong and it could drag. Or, what may be happening is the back side of the rod's radius is hanging up in the back side of the cam itself. Either of which, or both even could prevent the weight and that tiny spring from working correctly. It'd kind of late right now, but I'll go look at another cam and see how deep the flange is pressed on. 
Is there any kind of wear pattern in the back of the weight? Like where it may have been rubbing?

Got it fixed! Took it to Lindsay Machine in Utah and he had never seen a cam Falange press on to the shaft but it had. It didn't twist on the shaft so he ground down the part that was causing the weight to hang up. It should be flush. Put it back together and runs great. Thanks for the help Shawn. IMG_6221.JPG

Share this post


Link to post
Share on other sites

Welp it just happened again, it moved in and about a 1/16" rotated.  Im going to repress it on and weld it.  Pretty strange that it moved for a second time but in such a small amount.

Share this post


Link to post
Share on other sites

Id make sure you dont have something else going on, like a bucket seizing in the bore or something. If the head is ok, Id just get a new cam. That one is beyond compromised.If it was a custom grind or something, I could see trying to save it, but if its just a stock cam...Use it for a paper weight.

  • Like 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×