Broken cam chain = bent valve

[hannibal]

A brief recap of what I've been dealing with (full thread here)... The bike died on me in November as I was coasting to a stop light. Opened the cam cover and found this:



I still couldn't turn the crank by hand and let it sit for the winter. I finally had time and nice weather and went to dig in more and found a broken cam chain. I did a lot of reading and with the help of this thread, I decide to pull the motor and open it up for a full inspection. I searched and found a post that said a GS650 motor weighed 150-160 lbs with the head removed. Figured a complete motor wouldn't be that much more lol. I got it off the bike and managed to carry it across the yard and up a flight of stairs. I would not recommend this as I had a few missteps where my life flashed before my eyes. I guess I'm still young enough to think I can carry 200lbs but not old enough to realize it'd be a BAD idea.

Got it in my place last weekend and now that I don't have to wait for weather or sunshine, I tore into last night. The first thing I saw was that the #3 exhaust valve was sitting lower in the head than the others. It looks to me like a bent valve that won't fully re-seat in the head.





I got the head off and noticed what looked like contact with the piston. Not bad but the carbon was broken off it that area.



I flipped over the cylinder head and noticed the #3 exhaust valve was much lighter in color than the others.



And it was definitely hanging down into the combustion chamber.





And view of the top of the cylinder in case you guys see something I missed



So it looks like valve hit a piston and got bent. I don't think there's much damage to the piston but I guess I won't know til I clean it up. Time to start making the valve removal PVC tool. Any thoughts? I know I have to change the head and base gaskets (scared to death of refitting the rings into the cylinder!). And I've read to change all the valve stem seals since I've come this far. Anything else I should be looking into?

Thanks!

[tom203]

Your first bike is not being kind! But on the bright side, you seem very ambitious. OK, one noticeable bent valve , maybe others. I didn't look at your main thread...... How's the overall condition of this critter? Is it worth doing this repair.. or move on to another bike with simpler problems?

[chuck hahn]

Good time to remove all that carbon from the pistons and any good valves. I think i would remove all of them and roll them in a V block or something similar that would allow you to roll them and observe the pans for wobble. Do the valve stem seal and all while she down. Be sure there arent any broke valve guides too from the hit.

[alke46]

What could have caused this damage? Anybody with an opinion please respond.

[chuck hahn]

Someone may have been in there at some point and didnt use red loctite on the bolts and they backed out. Jammed against the head and instantly seized the cams. Then the crank snapped the chain.

I also notice the are shiney allen head bolts..which is a clue that they were messed with. All the stock bolts i have seen and am aware of are black 10MM head bolts.

[Agemax]

yep, looks like the cam sprocket bolts walked out and jammed up. you should check to see where the bolts hit the head, make sure they havent done any damage.
Chuck, the sprocket bolts in both my GS motors are allen head bolts so they are probably stock, but as you say, not loctited in.
part number for new sprocket bolts is 07130-0610B, which are allen bolts

[John Park]

Is it possible to replace the bolts with hex head ones and the bend over lock washer plate that comes on some later motors? I seem to recall that there is [maybe?] some fundamental difference between the allen head cam sprockets and the later hex bolt type on a Twin, but can't remember what it was; gave my old cams away.

Good as Loctite is, a lock tab is visibly locked.

[Big Jay]

Is it possible to replace the bolts with hex head ones and the bend over lock washer plate that comes on some later motors? I seem to recall that there is [maybe?] some fundamental difference between the allen head cam sprockets and the later hex bolt type on a Twin, but can't remember what it was; gave my old cams away.

Good as Loctite is, a lock tab is visibly locked.

Suzuki bolts are hex head.

[rapidray]

Not all Jay!! The 16 valve 750s & earlier had allen bolts for the cam sprockets.
Ray.

[hannibal]

Allen screws on the cam sprockets as far as I can tell. They're black allen heads. As said earlier, my conclusion is the cam shaft bolts came out, stopped the cam, and broke the chain. Backed out bolts did score the head, but as far as I can tell I should be OK. Will post pics of the head damage soon.

I can remove all the valves and replace the seals. Don't have the tools for guide measurement. A 25,000 mile motor and I don't have the tools to replace a valve guide. I figure $300 is what I could spend on this motor to get it back to good. Any more than that and I should look for a replacement.

[Agemax]

Not all Jay!! The 16 valve 750s & earlier had allen bolts for the cam sprockets.
Ray.

and the 2v 750's and 1000's. the part number for the bolts even shows an allen bolt.

[Nessism]

Suzuki evolved those bolts over the years, on some models anyway. I suspect there must have been some history of breakage or backing out or they wouldn't have done that.

If that were my engine I'd pull the cylinder and bottle brush hone it and replace the rings. Pull all the valves and inspect and clean everything, then install new valve stem seals. Button up the engine will all OEM gaskets. It will cost a little more, but it will be worth it. The big question is whether or not to split the crankcase to install an endless cam chain, vs using a chain tool to peen over the pin with an non joined cam chain.

[hannibal]

With the help of some previous threads, I was able to break down the head. Got the problem valve out (had to tap on the stem to get it to fall out) and could see that it was definitely bent. Once I clean up the combustion chamber, I'll examine the valve guide for cracks.

Valve assembly


Valve seat






What do you guys think? And what do you use to clean up the carbon? A green brillo scrubbing pad and kerosene?

I found OEM valve seals for $20 and Vesrah vitron seals for $30. Is aftermarket the wise choice here? Should I look for an OEM valve to replace my bent one? I've found an aftermarket valve made in Oregon for $42 vs $50 for an OEM valve. OEM seems worth the extra few dollars here.

Still trying to decide what to do with the bottom end. I know I have to replace the base gasket, so I might as well change the rings. What's a bottle brush hone? And if I go this far, splitting the cases to install an endless cam chain doesn't seem to much harder (but I need to read more about this). Thoughts?

[Nessism]

There are tons of cheap OEM valves on ebay.

Part# 12911-45030 http://www.ebay.com/itm/NOS-Suzuki-G...VXvDFK&vxp=mtr

I'd take the valves to someone with a centerless grinder and ask him to dress them. This will tell you if anything else is bent while giving you a nice fresh sealing surface. After that take the valves and lap them into the seats to check the seat sealing surface. Compare against the spec in the book for seat width and decide if the seats need to be cleaned up with a cutter (most likely not).

Check enginehones.com for a hone. Read though the tech section and watch their videos.

[hannibal]

Thanks Ed. Unfortunately I need an exhaust valve and they're more expensive. Parts Outlaw has them for $45. Not too bad.

I've been reading and watching vids on lapping and honing. This is all new to me. I always thought lapping was recutting the valve and seat. I found this vid and it looks pretty simple. In the vid, he uses a brass wire wheel to clean up the valve (2:00) and around the valve seats (2:58). Is this recommended? Can I use a brass wire brush to clean the carbon out of the combustion chamber? I'm planning on buying that Gum Cutter he uses. And what do you mean by dressing the valves with a grinder? As for honing, that doesn't seem too scary either.

I made the mistake of adding everything up. The cost for base and head gaskets, O rings, 4 sets of piston rings, a new valve, valve seals, and the flex hone tool is about $370. Am I crazy for doing this?