1982 GS650GL. Loud banging sound. Possible valve problem.

[Guest]

Hello, forum.

I recently replaced the transmission on my 1982 GS650GL. You can see the thread here. http://tinyurl.com/ld86h63

After finishing the work, the bike ran great for about two weeks, then all of the sudden one day I heard a light "tang tang" sound under load. As I was 15 miles from home, I decided to turn around. During the ride home the sound got louder and louder until it got to the point that it was so loud it sounded like something was going to explode and I began to lose power to the throttle, so I pulled over and had to come back with my truck to get my bike home.

A mechanic is telling me a valve may be stuck in the down position and the sound may be the piston hitting the valve, which may explain the sound, and loss of power due to lack of compression. I'm going to take the engine off the bike again and take off the head to see what's wrong. Or I may just try to get the head off while leaving the engine in the frame. That would be less of a hassle, but I'm not sure if it would work.

I'll keep you all posted on what I find out.

[Steve]

It is very possible to remove the head (and cylinders) with the engine in the frame, but before you do that, check your valve clearances.

If you have a valve that is stuck open, there will be a LOT of clearance.

By the way, if the piston has been making noise hitting a valve, I would bet that the valve is bent, keeping it from closing on its seat, leaving plenty of valve clearance.

If all the valves have proper clearances, verify proper cam timing, then try a compression check before removing the head.



.

[tom203]

Yes, verify cam to crank timing, maybe the cam chain tensioner failed (or couldn't move) and that " light tang ,tang" turned into more interference.

[William Groebe]

Thanks for the input, fellas.

I'll get back to it tonight and let you know what happens.

[William Groebe]

Didn't get a chance to do any work on the bike last night. I almost forgot that the NLDS game was on, and I had to watch my SF Giants take down the Nats. Or more accurately, I watched the Nats hand the game away to the Giants with some very odd and clumsy plays and pitches. But we'll take the win. Go Giants!

Back to motorcycle tinkering tonight.

[Steve]

'Tis a sick mind, indeed, that allows a silly NLDS (whatever that is) game take priority over some GS wrenching time.

At least have a TV in the work area, if you need to keep track of it.

.

[William Groebe]

I checked the valve clearances, many of which are too tight.
Ex - 1=(-.04mm) 2=(.06mm) 3=(.04mm) 4=(-.04mm)
In - 1=(-.04mm) 2=(-.04mm) 3=(-.04mm) 4=(.05mm)
(I typed -.04mm by anything that was under .04mm as my smallest gauge is .04 so I can't get an exact reading.)

I removed the head. I pulled out the shims and found a piece of hard plastic under the #3 intake valve bucket. This could definitely be messing with my valve clearance, right?




I'm tempted to replace whichever shims I can, put the engine back together and fire it up to see if the sound is gone now that I've removed the piece of hard plastic. But I may take the head to my mechanic to have him pull apart the valves and check inside for damage. I don't have a valve puller tool or I'd do it myself.

Here are some other pics just for reference.

[eil]

Heard a rumor that a valve spring compressor can be made with an 8" C-clamp and oxygen sensor socket, both available from Harbor Freight. I have both of these but haven't put them into action yet.

A valve spring decompressor can be made with a deep-well socket and a hammer.

[William Groebe]

I was in a hopeful mood yesterday and decided to see if the bit of plastic was causing the valve to hit the piston, so I put the bike back together and fired it up this morning. Alas, the engine is still emitting a loud banging sound. I think the sound may actually be coming from the crankcase. Looks like I'll be diving back in to the engine. yippee!! (sarcastic exclamation)

Eil. Thanks for the advice on the home made valve spring compressor. I'll try your method out this week.

[Toasty]

PVC works too and is easier to cut if you don't have the proper tools. Just glue a big washer on top.

[William Groebe]

I brought the head to the shop. They didn't take the valves out, but pretty much flatly said it isn't a valve problem. There are no indications of damage on the valves, nor are there any markings on the pistons from hitting the valves. I may take apart the valves later if I don't find any problems anywhere else.

So I am digging deeper. I took off the cylinder and pulled on each piston to see if there was any play up and down, which there shouldn't be, and found that my number 4 rod has up and down play in it. Each piston head has a little side to side play, but as far as I know there shouldn't be any up and down play in the rod. Not good. Gotta bust open the crankcase again. Yay

Side note. In pulling off the cylinder, I should've been more careful, as I tore the gasket. Oh well. I'm learning as I go. I'll keep you up to speed as I go back into the crankcase.

[William Groebe]

Well, I've definitely got a loose rod. I don't know anything about crankshafts, so I'm going to have to do some research. I'm not sure how it became loose, or what happened. When I did my transmission repair, I left the crankshaft alone.

There is a bunch of metal shavings in the bottom of the oil pan. Looks like the rod was wearing down the round part of the crankshaft next to the rod, whatever that part is called. I'll call it the round wheel thingie. The round wheel thingie on either side of a rod is supposed to have a rough texture on it like this


But the sides of the round wheel thingie next to the loose rod is worn smooth like this.

I think this is where all the metal shavings came from.

This seems really bad. Like I said, I've got to do some research. Lame. I was all ready for the Indian Summer riding season.

[tom203]

What a drag! You'll need a new crankshaft as yours got damaged by failing rod bearing. Honestly, at this point, I'd consider a whole other bike. Not sure about your area, but in northeast, one can scoop a low mileage/low cost bike with simple problems like carbs and electrical - easy stuff compared to what you gone thru. I admire your persistence at digging away at this critter but I think she's not interested in helping.

[recycled64]

There are many of these available on Ebay, especially from this guy. This is the configuration you want, with the rods still in place. It IS an 81, however, AFAIK, the only difference is in the bearings, if you look up 'crankshaft' page on Parts Outlaw, OR, better yet have the factory manual, it explains it all. Now you're gonna get into bearing clearances and the use of Plastigage, etc, a fairly involved process. The 'thingies' (HARrumph), lol, are called crankwheels, sometimes flywheels, etc. Watching your posts, and your lack of fear in taking things apart, something tells me you'll be fine, just maybe a little extra patience. In fact, if they had a yearly award on here for 'Best New Guy', you'd get my vote. Carry on!!

http://www.ebay.com/itm/1981-suzuki-gs650-gs-650-sm40-crank-/230525286197

[William Groebe]

tom203, thanks for the advice. I'm still thinking I'm going to try to fix this. My goal is to get this bike running, and learn whatever I need to learn to do it. I'm using this bike as my motorcycle school. I'm sure there will be a point when I will have to call it quits, but I'm still feeling motivated to get it running.

I found an 82 crank on ebay for $85 http://www.ebay.com/itm/290613867561...MakeTrack=true
I'll buy some plastigage and, if necessary, some new bearings.

One question I have though, is how did a rod come loose? Somehow there is play in the rod even though the rod nuts are tight. What gives?

Oh well, on to ebay. Hopefully I'll get it back together in the next week or two.

And thanks for the encouragement, recycled64.