Dropping valves

[isaac]

So this hasn't happened to me but sounds VERY impending based on head noise that's ratcheted up in the last few weeks. I've stopped riding the bike because of it. It seems to be an epidemic with these bikes considering what I've been seeing.

The evidence:

1) A few dropped valve stories on this site, even cases of the same bike doing it a second time later after a total rebuild.

2) A quick search of craigslist or ebay shows quite a few bikes that "need a piston and head" or "blown engine"

3) You just plain can't find a used cylinder head or piston for these things, but you can find used blocks, cranks, connecting rods and everything else all the time.

So what's doing it? I'm already midway into a teardown on my bike to find out. So far I'm not finding any parts that are loose and shaky like the ominous, growing rattling sound I was hearing would indicate, though at 12,500 miles parts of the exhaust cam lobe and cam journals show wear, but not exactly severe. Nothing feels loose to indicate serious wear up top. I do know this bike has had some issues where the head makes noise until the first time I ride it above 5,000rpm or so to bring oil pressure up enough to seemingly feed the head better, and that problem is getting worse.

That said, the bike doesn't burn oil, which would be indicative of serious valve guide wear or failure. It doesn't have leakdown issues from the valve guides when it's sitting, so the valve guides must be getting oil. That said, it'd have to be some serious issue to wear guides in only 12,500 miles.

So what's causing this? Has anybody really looked into it? I've heard of other engines having issues where the valve would literally stretch the stem until it just snapped at some point, sending the valve down into the cylinder and causing a total write off. But I haven't seen any discussion of it here, aside from the occasional story where somebody had it happen, everybody says "that sucks", and they either junk the bike or buy a new head and piston.

Any ideas?

[raul10141964]

the GZ come from factory tune to pas emissions, and the only way to do that with thees carburetor is set it to run lean.
a lean running engine will run hater that normal putting a lot of stress on the exhaust valves

[ovilc88]

All I know is that when it happened to me (dropped a valve). The stem broke at half point and fell in...u know the rest of the story. I feel the valve spacing gets thrown off to easily to quickly. Valve clearance can make a world of difference. Unless you decide to go for Ferrera valves made to specs for GZ250 that would be more durable, but way over budget $$$. Wouldn't really be worth it to get them. I don't really know what causes the breakage, the flaw may be more than one that contributes to this downfall of GZ250 engines, the Achilles's heal so to speak.

[isaac]

Good info so far.

Well today I finished removing the head, and everything in there looks fine, which is baffling. There is a little bit of wiggle to the one exhaust valve I've pulled in the guide, but very negligible. The stem and keepers and spring seem fine, but who knows. There's a ton of carbon on the piston at 12,500 miles, which makes me think I'm running safely rich. The cam has light wear on the journals and more wear on the exhaust lobe, but none on the intake. I may have been running these valves sliiightly tight but not by much. Like I said, this thing seemed to have a problem getting the oil pressure into the head until after I got it above ~5,000rpm the first time while riding it.

Two very odd things that make me wonder about this thing's build quality: There are 6 nuts holding the head down - 1 in each corner and one in the front center under the fins and one in the back center under the fins. The one in front was just plain missing, and the front right corner was less than finger tight. The rest came out normally. The head gasket shows no sign of why this thing was leaking oil from there, which it clearly was because the engine's pretty dark on the left front and left side.

[isaac]

Problem found: So I was looking over the head again today trying to figure out what the deal was with the rattling at certain rpm and throttle positions that had made me take this thing apart in the first place, when I figured out what it was: One of the exhaust valve seats had come completely loose and had been jingling when the exhaust valve was open. Had it continued doing this, it likely would have eventually cocked sideways in the bore and bent the valve then maybe broken the head off. at that point both the valve head and the seat would fall into the combustion chamber and carnage would occur.

This makes me wonder if guys who've had a valve allegedly fall into the engine also had valve seat damage. That's something only the guys who've had a ruined engine can testify on. So did you have seats down in the engine too? It makes me wonder if this is an issue that's pervasive but the damage is always so massive that you can't tell what fell apart first and caused what damage.

If this really is a systemic failure of valve seats dropping into the engine, then this could happen to anybody. Mine I just heard coming because of a rattling/jingling noise in the engine under varying load that had progressively gotten more noticeable, so I tore it down before it was too late. I hope I don't have to have this thing machined for oversize valve seats or something because there's almost no room for it.

[isaac]

Does anybody know where to get valve seats for these things? I've checked parts fiches on multiple sites and nowhere in the cylinder head or cam/valves pages can you find a valve seat. The closest it gets is a valve spring seat, which of course isn't the right part.

It makes it seem like I'm going to have to buy a whole head just to get valve seats, which clearly are removable from the head. If it really is gonna have to come down to that it'd probably cost me less money to swap in an engine that doesn't drop valves whenever it feels like it. My only other recourse for rebuilding this engine would be going to a machine shop, having them turn custom oversize valve seats for me, then installing them. At that point I'd take a guess and say the price would exceed the cost of a junkyard motor swap, and I can say it definitely won't be the stock engine because I'm not putting all that time into a swap only to have it drop a valve the first time I ride it.

I've already looked into swapping a DR350 engine which seems like it'd be pretty straightforward, the only problem being that they seem even more notorious for dropping valves than the GZ250, if such a thing is possible.

[jonathan180iq]

Seems like you and The Goose are going through the exact same thing right now, you guys should share stories and see what you end up coming up with.

viewtopic.php?f=7&t=6665 (http://www.gz250bike.com/forum/viewtopic.php?f=7&t=6665)

[Goose51683]

Hey Isaac. Check out my post above. Right now I have a torn apart engine in my basement/shop. piston is hosed, I pulled the valve out of the top of it and I can see straight thru. I'm gonna guess that makes it hard to build compression. Ha

I was able to find valves, a piston head, and the entire cyclinder from a chinese site. I think it's called aliexpress.com Either way it's for a GN250 but I was reassured on here that it is the same engine. Unfortunately, it's like a 2 week wait for the parts so I'm down for awhile.

[isaac]

Hey guys, it's good to know others are working on this problem. That definitely sucks about your issue, Goose. It's clearly a valve drop. It's just a question of whether the seat let go first.

I'm very interested in how those parts turn out that you get from China. Check the valve seats to be sure they're secure. I'm wondering if maybe we can make these engines a lot more durable just by proactively installing oversize valve seats so that it helps hold tighter than stock.

That said, I'm also shopping around for other engines to maybe finally blow through the legends of guys who've made these bikes faster. I've already taken a look at a CB350 twin engine that seems to fit shockingly well. With every engine I've based suitability of fitment off of one metric: Where the transmission output sprocket sits compared to the engine centerline. In this case the CB350 output sprocket sits only 1/4" off from the GZ250. The bizarre thing is it actually sits 1/4" inboard compared to the GZ. That requires one of two things: either I move the rear sprocket inward by somehow reversing its mount and shimming it inboard, or I offset the engine placement, which is not my preference.

For the sake of expediency I'd of course prefer to just throw good valve seats into this engine and call it a day. Incidentally the other exhaust valve seat doesn't seem loose at all.

I just know I don't want to get rid of the bike. It's my first motorcycle that I bought about 10 years ago and even with all the others in between I've never let it go. That and I really like what I've done to it.

http://www.pbase.com/volvoisaac/image/149535173/large.jpg

I just can't give up on it.

[isaac]

BTW Jonathan I now realize that this thread is just an in-depth troubleshooting discussion so if you can move it to the troubleshooting subforum that's fine by me. More guys might see it there who also want to figure this out.

[jonathan180iq]

Good call.

Done.

[Goose51683]

Isaac,

Let me know what you find regarding any different engines that fit. Like my wife says, I enjoy the "tinkering" as much if not more than the riding so any new project I can come up with makes me smile.

[jonathan180iq]

Your wife is a very smart woman, Kemosabe.

[Goose51683]

You're right but I'd never let her know that :)

[Goose51683]

Anyone know a way to disassembly the valves without the special tool?

[alantf]

Your wife is a very smart woman, Kemosabe.

Wish I could say that about mine. :cry:

[Goose51683]

I'm not touching that comment! Ha!

[Goose51683]

Also, I figured out a way to remove the valves and reinstall them, unfortunately I didn't figure that our until after I had lost one of the half moons. Now I have to wait till Tuesday for the one bike shop in town to open up and hope they have one.

[jonathan180iq]

This might be a good time for you to tackle a How-To and let your knowledge benefit future generations of GZ riders :)

[isaac]

Eh, you just get a large sliding jaw C-Clamp (jaws at least 4") from a tool or hardware store and clamp between the valve face and the valve retainer at the back end, leaving enough room to use a combo of a magnet and a pin or tiny screwdriver to pull out the half-moon keepers. You have to jiggle it a little to get them free.

[Goose51683]

Lost one of the half moons, there isn't a Suzuki dealership for 100 miles and none and I do mean NONE of te other bike ships within an hour of me have one. So frustrating. All I need is one little half moon and I'd be back in the road.

Ahhhh!!!!!!

[Goose51683]

YES!!!! Found a half moon at a new father and son shop that mostly does
Scooters but they do some work on Suzuki bikes as well! You have no idea how thrilled I am right now that I can actually
Put my bike back together tonight.

[ovilc88]

Good luck :smile:

[Goose51683]

Keep sending that good luck. I need it. Got everything together but she's still not running.

[jonathan180iq]

You'll get it going. Now it's just a matter of ironing out the details.

[isaac]

Goose I'm really interested in your parts supplier. I'm looking for a source for valve seats that doesn't require I buy the whole damn head.

[Goose51683]

I used a site called aliexpress.com and I had to buy parts that were labeled as
Being for a GN250. Exact same engine from what I hear.

Either way I wasn't very happy with what showed up so I'd try to find somewhere else if I was you

[isaac]

What was wrong with the parts?

[Goose51683]

Both of the sections that had cooling fins had a fin that was chipped pretty significantly. Also one of the gaskets was ripped. Luckily I was able to use the old gasket as it was still in really good shape.

I should have returned it, and if I knew I'd be waiting weeks for another part I would have but oh well.

[Sciota]

Anyone know a way to disassembly the valves without the special tool?

Could be dangerous! but I did it with a towel over the head to keep flying parts in. I opened a number 10 crescent wrench a little outside the stem space . Then I gave it a whack with a 5lb hammer..... Not saying its the best way, but it worked on my damaged head on the second tap.

[mtbdrew]

So beside the chip were the parts compatible as advertised? Did you order the cylinder head assy and cylinder jug with piston?

For some background, my youngest son bought a 2002 GZ250 and the second week in the bike stopped running on the way home. After taking the cylinder head assy off found the two exhaust valves were missing their heads. Looks like the was a detonation in the exhaust port the force of which had embedded parts of the valve head into the piston top and shredded the upper surface of the bottom half of the cylinder head. Spark plug could not be removed. The front nut between the exhaust pipes was also missing and part of the gasses from the detonation had escaped between the two halves of the head assy. This completely blackened the screw stem and melted the plastic around the started cable.
Drained the oil and found no metal filings or bits. Rest of the motor now turns freely so hoping all is okay. Bike didn't come to a screeching stop and the piston was not seized in the jug. Have parts on order form Chinese supplier on eBay with same comment that should work.
Would really like to know what cause the detonation. Son said the bike was backfiring when he turned it off. The carb main adjust screw is turned all the way in which doesn't seem right to me. previous owner was running with over 2.5 quarts of oil and there was about another 0.5 in the breather box.

Andrew