KymcoForum.com
Scooters - 125 to 300 => People 250 => Topic started by: hypophthalmus on July 06, 2017, 12:26:22 AM
-
So I was embarking on a 250ish mile trip. About 100 miles in, I loose power. I look down at the dashboard, and the engine was all the way hot (it was normal the entire trip). The radiator didn't feel very hot.
I let it cool down a bit, and start it again. The needle quickly goes back to the middle. I drive a few more miles, and lose power again. (Don't remember what the needle said this time).
Now it won't start. The starter motor turns, but it doesn't sound like it's cranking normally.
My best guess for what might have happened is I had a coolant hose loose (has a screwed clamp) for a few seconds by accident after I checked my valve clearances. Maybe it sucked in some air?
Thankfully the engine failed 3 miles away from a uhaul (expensive bringing it home though). It could as easily have been 20+ miles to the nearest town.
The engine oil looks pretty normal, but then this happened *very* suddenly, so I don't think it would have gotten much time to mix with coolant.
How should I proceed? Start disassembling and see what the head looks like?
-
If I did introduce air to the coolant that way, it went at least 600 miles of high speed riding before actually being an issue.
-
Describe sound when you try to start.
Miles, age?
Has the engine seized?
If not, shouldn't it start after cool down?
Can you burp air from coolant tank?
Compression still good?
Valve lash still normal specs?
Don't understand concern of oil in coolant, or vice versa. ...unless serious damage.
Keep talking to us.
Stig
-
18,000 km, 10 years old.
Now that it's cool, the starter is still running strong but the engine isn't making the turning sounds I'm used too. It basically just sounds like the starter.
I haven't tried turning the engine by hand yet. It'll be a bit before I get a chance to, since I'm going back out to where I was trying to in the first place... sadly in a minivan this time.
I'll try turning the engine and checking the valves once I get back. I'm not sure how to check compression, but if I figure it out I'll check that too.
Seeing the temperature needle on H right as the engine died has me worried the head gasket is blown, or worse.
Oh, and something that I forgot to mention is that the engine was making a very bad sort noise the second time it stopped.
-
Okay, I'm back now.
I had a chance to try turning the engine. It turns freely... too freely. It doesn't feel like it's compressing or expelling anything.
-
Okay, I'm back now.
I had a chance to try turning the engine. It turns freely... too freely. It doesn't feel like it's compressing or expelling anything.
Is there a spark plug in it's proper hole? In other words, did the spark plug come unscrewed?
Stig
-
The spark plug is still there. I can't turn it with my fingers, so it seems tight.
-
Some more thoughts/questions:
When the trouble started, it was shortly after filling up on gas. My first thought was that maybe the gas was bad. But then as it started to seem more serious, I decided that bad gas won't cause this sort of problem.... right?
The first time the engine stopped, the oil light on the dash board came on. What does this light actually mean? What triggers it?
The engine temperature is taken from the engine block, right?
-
I attempted to check the valve clearances. However, with the flywheel's T mark lined up with the line, there's a *huge* amount of play in the valves.
I'm also noticing now that when I turn it slowly, once in a while it seems to catch a bit. But not consistently, and not in the same place twice.
-
So that sounds like somehow the camshaft position became different from the crankshaft rotation. Although I don't understand why or how.
-
I hope I'm wrong, but you described perfectly a broken rod.. here's how to find out. Take the spark plug out. Get you a new or long pensil and insert it ,ereser end into the combustion chamber. Then turn the engine, by hand, slowly clockwise. If the rod is still intact you will feel it when it comes up to the pencil. STOP and remove the pencil NOW. If you continue to turn after contact you will break the end of the pencil off in the cylinder. Let us know what you find out.
-
Engineering seems to be similar on several types of machines so I will ASSUME it is similar to the DT and GTi. The oil light has two purposes: oil pressure and oil change. The pressure sensed in these machines is very low because of all the ball and roller bearings. When the engine stops with the key on the oil light lights. The oil light also lights up when the maintenance odometer reaches its limit. The engine temp sensor is on the block. Engines can stop and/or falter due to bad gas but not lose compression.
The valve clearances are the alarming part. When you see the "T" in the window you should also see the cam sprocket two small holes lined up parallel with the top of the head. To show confirmation of timing there should be a third hole visible in the cam sprocket above center. Make one more crank turn if this is anything but described. Then the clearances should be whatever but not enormous! Timing has slipped if all these indicators are not met. Loose cam chains can cause this. The tip-off was the overly large clearances when the T was showing. Even if the cam was not in position, like on the exhaust stroke, the clearances should not be large. Another posibility is the clearances have not been set and they really got big but all of a sudden? Nah! Find why the valve clearances are big and that is probably the cause.
Karl
-
Sometimes the holes are mostly as described (but the small holes) aren't quite parallel. Sometimes it's about 180 degrees from that. It doesn't seem to be consistent (although I'm second guessing my memory of whether it was or not).
Actually, there doesn't seem to be *any* position where both of the rocker arms are close enough to the valves to be reasonable, though they do get there one at a time.
I used a thin, square offcut of pine since I had that on hand instead of a pencil. I was paranoid about not feeling anything and it breaking it off, so I kept taking it out. I never did feel anything, but eventually the engine stopped turning. I turned it backwards, and it stopped that way too. Eventually it started turning again, so I tried to feel something again The same thing happened, and it appears to be stuck that way.
I'm *pretty* sure nothing broke off. I guess an advantage to using a pencil is it'd be easier to tell... but the end of the offcut still looked cleanly cut.
-
I can't decide what to think of all this.
It's sort of shocking that the engine failed so badly, so suddenly, and without warning.
Was this all a result of accidentally allowing some air into the cooling system? Or was the sudden surge of heat a symptom of something else that happened? Is it just a matter of these engines not being able to withstand these sorts of long, high speed trips? Or something else?
Maybe this requires too much speculation at this point still.
-
Are the adjusters still on the rocker arms?
Karl
-
Yes. Still tightened down too.
-
Look carefully at the cam lobes. Are they smooth and shiny?
Karl
-
Yes, normally so.
-
Cool radiator when engine is hot = VERY BAD NEWS. No or little coolant in the system. Kaput!
Hopefully, this isn't the case.
-
I'm not sure. Besides the heat suddenly spiking, there hasn't been any cooling issues. And I don't have reason to suspect I've been losing coolant. I can check though.
The sides of the radiator were definitely warmer than the fins. I was thinking maybe there was momentarily bad circulation from some air (once I got it started again, the gauge plunged back to the middle of the range). Or maybe all the airflow was just cooling off the radiator effectively? I don't remember how it normally is.
-
Regardless of what was, or was not, going on previously with the radiator....."the very bad noise heard 2nd time engine stopped" seems to warrant opening the engine further. ?remove cylinder head?
Show parts to forum or scooter shop to get ideas of causes, possibility of repairs, etc.
600 high speed miles on a 10 yr old 250 .....oil lubricity or coolant system failure, valve settings, spark plug heat range, cam chain, come to my mind.
Hang in there,
Stig
-
All the pencil deal is good for is to tell you if the piston is still moving up and down. No piston movement = broken rod. Whatever caused the heat to spike could result in a broken rod. Once an engine gets hot enough, the piston can no longer slide in the cylinder and something has to give. I hope this is not the case. The pencil trick is just a quick and simple way to tell for sure without taking the engine apart. Since I'm the only one who thinks that's a possibility, I'll let this be my final comments. I wish you luck on finding the problem.
-
There's a lot more than 600 high speed miles on it. That's just how many high speed miles without incident since I accidentally left the clamp loose on the coolant hose for a few seconds.
But yes, engine disassembly seems to be in order.
Ole two wheels,
I think some miscommunication happened. I agree that a broken rod is a definite possibility, and I'm glad you mentioned it since it wouldn't have occurred to me. Although I hope that's not it, since it looks like I would need an entire new crankshaft, which are apparently quite expensive and presumably difficult to replace.
I understand the trick, but my engine seized before I could be sure if I felt the piston move. Once I get the head off, I'll be able to see it though.
-
All of us are standing by to hear what you find. To help as best we can.
Karl
-
Thanks, I appreciate it!
It'll probably be slow going, with limited time and a sprained wrist (from pushing the bike up a uhaul ramp I think, even with a helpful stranger's assistance).
Draining the coolant was the first thing to do anyways. It was low, although not as much as it seemed.
I weighed what came out, and it works out to about 0.9 liters, when it's supposed to be 1.0 liters. It didn't come up to the neck. The reserve tank was also significantly lower than last I checked, and it had been stable for a long time before.
-
Also, having changed the head gasket on my van last summer, I'm appreciating how accessible everything is in comparison. And the incredible number of things I don't need to remove first.
A question: the manual is telling me to set the engine to top dead center before taking off the camshaft. Is there a reason why, and can I safely ignore that?
-
TDC on compression stroke makes it easier to put everything back in time.
Karl
-
I cant add much help here, but I'm pulling for ya Hypothalmus!
-
Karl is correct, of course, yet at this point, It's not gonna make a difference.
Most likely a complete engine tear-down will be required.
My question is, what is the quickest way to remove the engine unit from the scooter ?
redk
Oh, and sry to hear of failure, but this is what does happen to machines, eventually.
My guess is it will be far less expensive to get back into working condition than many other brands.
-
Thanks, Paul!
I didn't think the engine position would matter, but I didn't want to be surprised with something.
I'm going to try not to remove the engine if I can avoid it. But the engine/transmission/wheel should unbolt from the frame as one unit pretty easily I think.
I feel like it's too low miles and I've put too much care into it for it to be a reasonable fate. That combined with the suddenness is disconcerting when I want to be able to safely drive into the middle of nowhere, and expect to be able to get back.
As far as less expensive, I'm not sure. More common bikes might benefit from more used parts. And i've noticed that small Kymco parts (nuts, bushings, etc) are frequently more expensive. A quick search for instance shows used Silverwing and various V-Star crankshafts in good condition for significantly less. And it seems that you can buy V Star piston rods separately, which is much much cheaper.
-
I have opened up the engine. Unfortunately it looks quite bad.
The piston is at an angle inside the block with two valve-shaped indents. The valves also seem to be messed up and not fully seated. The rod seems to be in tact, but disconnected from the piston and bent at the same angle.
The worst part is that the back of the piston shattered, leaving tiny fragments of metal all inside the engine. I think this alone makes the idea of any sort of repair questionable.
So I guess the timing chain skipped.... somehow? Insufficient design? Still not sure why the coolant was a bit low, or why it got hot.
The head gasket looks pristine. I haven't checked anything for flatness.
-
There is not ONE WORD in the DT300i owner's manual about checking or retensioning the timing chain! I recall from my Honda days this being included. Anyone remember the interval?
Yep, the timing chain wore and got slack, timing jumped, valves started touching the piston crown and things got worse real fast! That's my guess on the sequence and I'm sticking to it!
Sorry to hear about the destruction. I KNOW you hoped for a different outcome.
Karl
-
Here's my understanding from my recent internet research:
The tensioner is supposed to be automatic. If it develops any slack, the tensioner pushes out more to compensate, but it can't retract.
I came across some motorcycle forums where it was high recommended to replace the automatic tensioner with a manual one, although I don't know if such a thing exists for our bikes. Apparently if the RPM is high, they might not be able "to keep up" (not really sure what that means?). I doubt that
Probably your Honda had a manual tensioner?
I'm supposing it could be a defective tensioner, something going on with the chain guides. I think I read that a stalled camshaft can also do it. Or a worn chain/gears.
I didn't see any clues as to what actually caused it though.
It's the shattered metal fragments that's really disappointing. Even with the amount of damage, repair is approachable. But don't think I could get out every last bit of metal fragments. And they might have damaged other components at this point already.
I'm not seeing any engines for sale where it wouldn't have to ship from Italy or I wouldn't have to drive to California for. I'm not sure if I should wait and hope that someone has one. Or try to part it out and save up for a new bike.
-
Been thinking more about this.
I disassembled the tensioner, and it looks fine to me.
The quality of the oil seems odd. I know I said it seemed normal in the beginning, but I meant it didn't look like it had coolant in it. But has a strange kind of burnt smell and looks unusually dark and possibly thick. Checking how full it was, at first I got nothing. After an odd delay, it went significantly over the gauge (although I'm pretty sure I didn't overfill it).