Odd knock... Camshaft end play?

[PointBlank]

Hello all,

I have a '79 425L that I have been going thru what seems like forever... But recently I got it assembled and shoved out the door for the season (so I thought).... The issue is I have a weird incremental knock that I cant trace down... It comes from the top end near the cam caps/cam idler and only appears once the bike has reached operating temp.

At first I thought it could be because I changed the tappets to a narrower thickness... So I changed back to the older thicker ones but now the sound is... more spaced out...

The best way to describe it is... *knock six times* (wait a couple seconds *knock six times*. It goes away once you rev above idle.

Im at whits end with what the problem could be... Here is the list of what Ive gone thru/checked in the past week:

Cam tensioner - Tested per bikecliffs/manuals recommended test
Cam chain - Mic'd most of the links out and they all appear to be relatively the same
Tappets - Changed to thinner... then thicker. Thinner is close to spec but a little loose. Thicker is way to tight.
Front chain guide - Checked for damage.
Rear chain guide/tensioner - Checked for damage.
Cam Chain idler - Checked for wear.

I measured the cam runout on the intake and exhaust as well and got .10mm on the intake and .18mm on the exhaust. Does this seem excessive enough to create the intermittent knock Im hearing?

I know that there aren't easy ways to fix that... So would I be better off developing a deaf ear to it?

Or could it be that the cam chain is starting to come to the end of its life? The bike has 16,000 miles on it and has had a rough life as far as I can tell. Great example being the DIY gasket on the bottom of the jugs restricting oil to the top end... And the extra quart of oil in it when I got it. But I did I gauge out the cam journals thankfully they are within spec. Actually really close to factory somehow.

If you guys have any thoughts on what else it could be it'd be appreciated. At this point I'm ready for it.

-PB

[Mekanix]

0.10 is the service limit for camshaft runout in the manual

I think this is your problem.

There are two ways to fix it.

1 like on bascliff's site, you can macnine a recess to install a piece of shim stock.

2 Find a source for washers that are thin enough to get you below the 0.10"

It should be (0.866)ID and maybe 0.946 OD.

Just something thin that fits over the cam and is the size of the shoulder of the cam.

I used head gasket shims for a model airplane engine but I'm sure there's lots of other places to get some.


.

[Nessism]

Can you post a video of the noise? Upload to Photobucket or similar and then post a link.

Some noise from a GS top end is normal, but it's hard to say for sure unless we can hear it.

[PointBlank]

2 Find a source for washers that are thin enough to get you below the 0.10"

It should be (0.866)ID and maybe 0.946 OD.

Just something thin that fits over the cam and is the size of the shoulder of the cam.

I used head gasket shims for a model airplane engine but I'm sure there's lots of other places to get some.


.

Im thinking I may lean towards the shim idea first since that seems like the cheapest option.

So the washers that I end up going with... Do they need to be anything special material wise? Will simple steel work or does it need to be brass? And the RC head gasket shims you used, is that something you bought in a sheet then cut down? Im wondering if I can find some sheet metal and cut out my own so long as the thickness is good.

As far as a video goes... I had this really great one that I shot before I tore the bike down (4th time this week )... But my phone decided that apparently I wanted a video without sound. When I assemble it for this next go around Ill be sure the damn thing is recording sound, even if only to show off the bike.

[Mekanix]

I'll try and find a link for you.

They are coper, brass, aluminum that range from 0.02mm and up

This is the idea.

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXMMT2&P=0

You could use one from a 0.18 or 0.21 size engine. Its just a mater of finding one the right size.

I'd say its the exhaust cam causing if in fact its the cam's causing the noise.

Maybe its more than 0.18 when Its warmed up.

[bwringer]

Wear ear plugs and ride.

It does sound a bit like cam end float, in which case it's harmless. My 850G makes a very similar noise these days, but only at certain temps. The noise stops once the engine has thoroughly warmed up in my case.

Assuming you've verified the tensioner is working correctly and inspected the cam chain (which I'm sure you have), button it up and ride it. It's just not worth the effort to eliminate a noise that doesn't hurt anything.

[7981GS]

Im thinking I may lean towards the shim idea first since that seems like the cheapest option.

So the washers that I end up going with... Do they need to be anything special material wise?

Bronze is your best bet.

Eric

[PointBlank]

Assuming you've verified the tensioner is working correctly and inspected the cam chain (which I'm sure you have), button it up and ride it. It's just not worth the effort to eliminate a noise that doesn't hurt anything.

So are there any ways to verify the cam chain is alright? Ive visually looked it over and measured the width of some the chain links. Is there anything else that I should be looking for?

I kind of suspect something may be going on with the cam chain simply because I had a facepalm moment when I was putting on the points (had to do some clutch work this winter as well). I wasn't paying attention and the chain bound in the bottom of the case when I torqued it down. It came loose when I backed it off but I'm wondering if I may have messed up a section of the chain.

I'm tempted to button it up and ride though. But only so long as I know the cam chain isn't the issue. To my understanding if those break on you when its running it can do some serious damage.

[PointBlank]

Well I figured I would give you all an update.

I ended up just saying the hell with it and reassembling it as is and lone behold its fine! ... After it warms up... I took it for a 30 minute ride and its just putting along like it was before I rebuilt it. Guess I was overthinking things as usual.

If I get a chance to record a video of it Ill post it just so others have an idea what it sounds like.

Now I just need to get this weird surging issue figured out. At about 3-4k it is slightly doggy and has very minor surges under load. I noticed a couple things like having a bit to much oil in it so I'm going to siphon that out then give it another shot. I doubt that's the issue though since its running crazy rich. So I'm going to be tinkering with the carbs tomorrow night.

Anyway thanks all for the help!

-PB-

[alleyrat]

Mine was doing something similar but it was the counter balancer bearing...it ended up toasting the case on the right side...