View Single Post
Old 11-18-2012, 07:01 AM   #49080
Beastly Adventurer
mcma111's Avatar
Joined: Jul 2007
Location: San Francisco,Ca.
Oddometer: 12,923
Originally Posted by ReferJohn View Post
with Flatfenders recent timing chain issues i now am riding paraniod-kind of.

1. what causes a timing chain to jump? besides backwards motion in gear.
and how can i prevent that?

2. what are the symptoms of a timing chain that has been jumped
will the L still lift the front wheel in 2nd and 3rd and perform the same or will you be able to detect it right of way.
Thanks for helpful insight and advice

Since I am at work I have plenty of time to reply to your inquiry.

This is based on my '91 XR600. I used to go riding in Mendocino National Forrest and there were many times that I would get stuck going up a hill and I would walk the bike back down using the front brake and also the clutch while the bike is in gear. I would have both feet on the ground as to not fall over so the in gear/clutch bit was actually the rear brake. I can remember letting the clutch out and the engine winding backwards and I never had a problem with the cam chain jumping no matter how I punished this bike.

Now as to the why and how of a jumping cam chain. It all comes down to the tensioner. The tensioner has a one way clutch in it. If the clutch rollers develop a flat spot or the shaft is worn then there is the possibality that the tensioner will not be exerting pressure on the chain guide and under certain conditions the chain can jump or skip on the cam gear. How to prevent this from happening?? Don't ride your bike. If you ride your bike you wear out parts. No ride = No wear. Simple.

Same bike. Now as to having the cam out of time. A couple years ago the engine did the standard oil starvation bit after an oil change. Upon tear down I found that the last time I was in the engine I had installed the cam one tooth advanced. The bike always started up just fine and had loads of power so what does this mean? It's a friggin HONDA!!! If the cam is advanced you get the cam timing coming in more on the low end. Retard the cam timing and you get more top end. Change the cam timing a bunch of teeth as in a bad tensioner/chain skipping and you get valves that are hitting the piston.

There you have it. Send BEER.
Steve in SF

58 R26
79 R100s
91 R100gs

87 Harley FXRS-SP ~ 06 KTM 625 SMC ~ 72 Honda CB750/915cc ~ 92 XR600/654cc ~ 95 XR650l/675cc ~ 03 CRF450r ~ 05 CRF450x ~ 02 XR650l/675cc ~ 86 YZ490 ~ 93 YZ80 ~ 93 XR650l Project

mcma111 screwed with this post 11-18-2012 at 07:36 AM
mcma111 is offline   Reply With Quote