Well... the day started out well...

CoconutPete

CoconutPete

1979 XS650 Special
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I thought I had noticed a slights putter at low RPM 2 weeks ago when I went out for a ride, but it went away as she warmed up.

Today I noticed it again, left cylinder only. I put-put around town for a little bit and no change. OK, time to head home. As I get home I notice a very pronounced rattle which sounds like it's coming from under the right timing cover. Was definitely not there when I set out.

Needless to say no more riding today!
 
Pulled the covers (by the way it's so much fun to stare at the points with the bike running). I take back what I said... not side covers. It's in the center... I am thinking timing chain tensioner.
 
Could be timing chain adjustment, (would thing that would affect both cylinders), or it could be a loose adjustment nut on one or more of the tappets. that will affect the timing on one side or also look for damaged valve-stem end or the tappet
 
Good idea Skull. I'll be checking all 4 valves and the timing chain as soon as I can make the time. Probably onto the carbs / intake boots from there if I don't see progress.
 
Do your timing chain adjustment/check as the motor sits there idling. It's very easy to hear any effects the adjustment is having then. If adjusted too loose, the chain will make noise, much like loose valve settings. You can demonstrate that sound to yourself by loosening the adjuster way up, until the chain begins to make the noise. Then tighten it back up until the noise goes away but the plunger still moves in and out slightly. You want to have a little bit of in-out movement, maybe a MM or so, no movement means you've set the adjustment too tight.
 
5Twins: Plunger should go level with the adjuster though right? Not past it? Or are you saying that it should go juuuuuust a tad past it - that's where the MM comes in?
 
Well technically, yes, the plunger should not bounce out past flush and it's movement should be in from there. But that's not always the case, depending on wear of the components and the damper washer used. Sometimes it might bounce out past a hair or not even reach out to be flush. The small amount of plunger movement is what you're after, no matter what the plunger location happens to be.

I bought the supposedly "upgraded" rubber/metal damper washer from Mike's for my tensioner several years ago. This washer is 1mm thicker than the copper washer it replaces. That didn't allow my plunger to come out flush anymore. It was inset and that made observing it's movement difficult. This is a part Yamaha actually used on the later models but they compensated for the 1mm thicker washer by making the adjuster screw 1mm shorter.

AAQ6x3C.jpg


Nip8W9y.jpg


I eventually swapped on a late type E adjuster and am able to use the rubber/metal washer now.
 
Well.. I used this as an excuse to buy a timing light. I found TDC to the best of my abilities and it appears timing is right on and goes to the advance position somewhere north of 3K RPM.
Cam chain adjustment plunger does not appear to come out past the point it's supposed to.
Those valves though .. holy crap. To me the noise all of a sudden sounds obvious as hell. Maybe it's because it's idling in my garage.....
I'm pulling the covers now and I am going to try to teach myself how to adjust them. Luckily some of the threads on here are gold for that.
 
Stupid question: Do valves rattle because they are too tight or too loose?
Left exhaust seemed to be right at 0.006, but the right exhaust was way tighter. There is a youtube video where a bunch of people are commenting that their engine was the quietest at .002 for intake and .004 for your exhaust.

Haven't checked the intakes yet. I tweaked the right exhaust to be right at 0.006 also and fired her up and she stil has the rattle.
 
Valves usually rattle because they're too loose. Since you're new to this procedure, I have to ask - you didn't check both exhaust valves with the motor in the same position, did you? You can't do that. You can only do the valves on one cylinder (intake and exhaust) with the motor at T.D.C. on that cylinder's compression stroke. The valves in the other cylinder will be tight because it's not on it's compression stroke too, it's on it's exhaust stroke. You have to give the motor another full revolution and bring up to T.D.C. again to put that other cylinder on it's compression stroke. Then those valves can be adjusted and if you check back to the ones you just did, they will both be tight.

Use .006" for your exhausts, .003" for your intakes. 2 and 4 is too tight in my opinion. 4 on the intakes, although factory speced for some years, usually makes them rattle like hell.
 
5Twins: THanks. No, I did not check both cylinders on the same stroke - I luckily figured that part out ahead of time.

I need to check the intake valves, but dinner time w/ the fam called. I hope to get out there later.

I was going to pull the carbs, but now it seems like overkill, the valves all seem pretty accessible without doing that.
 
I was editing this post because my brain melted and I confused myself between metric and 'merican. Ignore what you may have read.

Here are the intake settings:

Left intake:
.003 / 0.08mm is the largest that fit through. I think the verdict is that the left is OK.

Right intake:
.005 0.13mm is the largest that fit through. Too big of a gap i believe.
 
Last edited:
Ok... last concern of the night before I call it a day.

Somthing was just bugging me about this even though I thought i had it buttoned up.

That d@mn cam chain adjustment plunger.... i'm not sure how it's supposed to act. I can't get it to show me any movement, no matter how I adjust it.

If I crank it all the way in - it doesn't move at all, even if I push on it.
If I back it ou, I can push it, but once I release it - it come back out and sits flush. When It was running I did also not see movement.

Is the goal to SEE movement with the engine running, just very little?

Sorry for all these (probably) repeat questions.
 
Yes, the goal is to see a little bit of movement on the plunger as the motor runs. It should pulse in and out slightly. The plunger is spring-loaded and the tight and loose sections of the cam chain running past the tensioner blade cause this pulsing. A tight section of chain running past the tensioner blade pushes the plunger out. A loose section of chain allows the spring to push the plunger back in. If you try the factory shop manual method of adjusting by rotating the motor by hand, you should also see the plunger move in and out slightly. If you never see any plunger movement, maybe you're missing the spring on the plunger? Here's what the plunger, screw and spring look like. You can pull these parts out to inspect them without any ill effects. There's no loose parts inside that would fall off or away. Maybe you should yank them out to make sure the spring is there .....

2hFvVVz.jpg
 
Ayup, that'd do it. No adjustment at all without the spring. When you screw the adjuster in or out, you're adjusting the tension on the spring which is what holds the follower against the cam chain.
 
Step 2: Best source to locate the missing parts? Based on 5twins picture, I believe I need:

- Spring
- Washer/damper (is it one piece?) Mikes sells a damper. I suppose this and the spring will make it complete?

Anyone out there with a spare parts engine (79 perhaps) willing to part with one?

If I need to order from Mikes I'm afraid I'll fill the kart with more stuff....
 

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