Cam/top-end Rattle?

[Guest]

Maybe you guys can help me out here.

I have an 81 gs650gl. It's a 16-valve DOHC model. It was laid down at speed, then patched back together, then sat, then I bought it and have been resurrecting it.

It's running, after I cleaned the carbs. I did not replace all the o-rings, but I will in about a month.

I have noise in the top end of the engine. It's worst when cold, and sounds literally like a rattling. I took the bike to the shop to get the carbs balanced and the valves adjusted. I realize I may want to get the carbs balanced after I replace all the o-rings...
Anyway, the noise is present under 3K rpm and is worst when decelerating. It doesn't sound like valve tap from a single valve. More of an intermittent tap noise - but it's semi-frequent when running at constant speed and more frequent when decelerating. It's quite loud under 2K rpm and causes me some worry.

I've looked through the forums, and I didn't see anything jumping out at me as a cause. Any suggestions or known issues I haven't see?
I noticed the cam chain tensioner seems to be an issue, and the valves are probably out of adjustment. When I acquire a vehicle, I assume that service hasn't been done, until I do it.

Ok, break's over. Back to calculus...

William

[friedshrooms]

oh you said top end yeah what he said, its most likely with the valves. Maybe they weren't adjusted properly?

[BassCliff]

Hi,

The GS650GL is an 8-valve motor.

If you're sure it's a top end rattle I would first suspect the valve clearances. Let's hope the "lay down" didn't knock a shim loose. But I like to run my valves on the loose side of spec anyway. "A slappy valve is a happy valve." Maybe a cam journal is loose? Another top end rattle could be caused by a loose cam chain. The chain could be stretched out of spec or the cam chain tensioner could be out of adjustment and need to be reset.

I wish you well with "the shop" working on your bike. Keep us informed.


Thank you for your indulgence,

BassCliff

[WilliamGLX81]

Ah, you are quite correct, Sir. It's "dual overhead cam" only because it has separate intake and exhaust cams. 8-valves for the win!

We'll see what happens here. I was just worried about grenading the motor somehow. That would be very unpleasant at this point.
So would a shop doing something stupid to it though...

We'll see. Valve adjustments are outside what I want to learn to do right now, and carb balancing exceeds my equipment for now. Both aren't needed all that often, so I'm hesitant to heavily invest time and money into them at this point.

If I get told it's not something that's going to destroy the motor, I'm not sure if I'll have them adjust the valves, or teach myself this summer.

Thank you foryour indulgence. I mis-stated some facts.
William

[tkent02]

If I get told it's not something that's going to destroy the motor, I'm not sure if I'll have them adjust the valves, or teach myself this summer.

I wish you well with "the shop" working on your bike. Keep us informed.

Don't worry about destroying the motor, the shop will likely destroy it for you.

[Nessism]

Having that shop adjust the valves throws a red flag. They may not have had the proper shims and just threw in what they had on hand. My local shop sold me Kawasaki shims first when I started working on GS's saying they use them all the time on GS's, only the Kawasaki shims are smaller diameter and rattle around in the bucket (not good).

I'd check the valves and cam chain tensioner. Assuming everything checks out, I'd just ignore the noise.

[WilliamGLX81]

Wow, hate towards the shops. Why so much?

About the only reason I take any of my machines to a shop is if there's special/expensive equipment I don't have, or there's something way beyond my skill set, like adjusting dwell on points (don't have them) or adjusting the valves, or balancing the carbs.
When I thought about it, I realized I just assumed it was something beyond my skills. After thinking about it more, it seemed like a loose cam chain is the only sound that really fit. Could have tightened that myself.

Anyhow, they said the cam chain was not tensioned right, so they tensioned it, and the noise is "pretty much gone".

I suppose we'll see when I pick it up Thursday. Rain today, work tomorrow.

[Big T]

Experience

Because most motocycle techs today have no idea how to actually work on a motor of this vintage. They will generally tell you that they won't even touch it, because it's too old.

A GS valve adjustment takes some time and then shims generally have to be ordered. Ask them what clearances they found and how many shims they changed.

[BassCliff]

Wow, hate towards the shops. Why so much?

Hi,

It's not hate. It is fear and trepidation. I have read literally hundreds of stories on this forum where a "professional" mechanic has really messed up somebody's motorcycle. A lot of shops won't even touch a bike of this vintage. Granted, there are good mechanics out there who really know how to wrench on these classic bikes, but they seem very few and far between. For this reason I have been acquiring the tools necessary to do my own valve checks, carb syncs, etc. My bike has never been in a shop since I've owned it. About the only thing I haven't done is mount a tire. That's because I get near internet pricing and free mounting and balancing at a great local motorcycle establishment. And I'm just that lazy.

The good folks here have taught me just about everything I know about the GS and now I'm not hesitant at all to work on my own bike. I'll bet I've gained 10 years of experience in the three years I've been a member of this forum. What a great community.

Thank you for your indulgence,

BassCliff

[WilliamGLX81]

OHHHHHhhhhhh.

Ok, yeah, I think I get it more now.

These guys deal primarily with older bikes. They had 10-20 bikes that were for sale, or parts, or partially rebuilt most of the time.

There is at least one shop here I wouldn't take my bike to ever and they are the type you're talking about. It never even occurred to me to take it to that type of shop. That'd be like taking my 90 turbo-volvo to the dealer to get something fixed - NEVER happening.

Most of the mechanics there seem to be 35-50 and ride classic bikes.

They didn't check the valves, and I'd be glad to do that myself this summer. (Calc-based Physics2 test in the morning, two weeks, finals, and FREEDOM!).

At this point, it's tire mounting and... paint? And I want to learn some more about engine internals, but it seems... pretty straightforward, but labor intensive.

Shops have always been a last resort for me. I'm just still whiling away at the list of "things I haven't fixed myself yet". If I want something done right, I do it myself.
Everyone else is billing by the hour. Seems to always result in shortcuts... Like when the "electrical tech" "traced and fixed a short" on my car by connecting my right and left side running lights to the same circuit, blowing the 15A fuse, and swapping in the 25A fuse from my airbags...
Nearly all shops are not looking out for your interest, mkay?

Cool beans.
Hoping to pick it up tomorrow, if I have time

[almarconi]

About the only reason I take any of my machines to a shop is if there's special/expensive equipment I don't have, or there's something way beyond my skill set, like adjusting dwell on points (don't have them) or adjusting the valves, or balancing the carbs.

If you can take calculus based physics then there is nothing on a GS you can't repair or on your 1990 Volvo for that matter. Carb sticks cost about $60, to adjust valves all you need are feeler gauges, shims and Steves spreadsheet to do the calculations.

My 1990 Volvo 760 has 211k miles on it and I wouldn't take it to a mechanic to work on it either. They want 1k dollars just to do a timing belt, don't even think the cars worth that much.

[mike_of_bbg]

If you can make the sound occur in neutral and you suspect the cam chain, then get the bike to do it on the stand and look at the cam chain tensioner knob (below the carbs, from the right side). If you see it shaking while the sound is occurring, or if you can lightly lay a finger on it and the sound goes away (whatever you do, DO NOT TURN THAT KNOB COUNTER-CLOCKWISE WITH THE ENGINE RUNNING!!!), then you've found your culprit. The spring pulling the knob clockwise can get a little tired after 30 or so years and need another 1/2-1 turn of tension, plus the o-rings and seals can start to seep oil and generally just "get loose".

Rebuilding the cam chain tensioner takes about $10 in parts and one hour of your life - not inclusive of removing the carbs. The only tool that might not be in your most basic tool set is a 30mm socket to get the adjuster out. There's a link from BassCliff's site (the chewy nougat center of GS knowledge) to Mr. BWringer's tutorials including one on the rebuild. Or here's a direct link:

http://www.bwringer.com/gs/camchaintens.html

It is possible to remove the cam chain tensioner without removing the carbs (a known PITA particularly on the GS650s), but small and patient hands are called for And if you're going to remove the carbs to replace the o-rings anyway...

[WilliamGLX81]

*ahem* Got the bike back.

The noise went away. Well. The cam chain noise went away. The valves sound pretty good. These are solid lifters, right?
.....What's that test for rod knock? Wooden dowel into the spark plugs holes and check for play?

I appreciate your confidence in my skills. I'm sure I can learn to do it, I'm just busy and not making much money. I'd rather overhaul the brakes and suspension first.

But seriously. I think it might be rod knock that I'm hearing. It's only at specific engine speeds, and usually when decelerating a little, or coasting.
The bike rips and gets as before, but the power delivery is much more smooth and consistent. It also has better torque under 3K.

Bed time and ride in the morning.

So... what happens if I keep riding it and it's rod knock? Or piston slap? Am I going to throw a rod?

William