Honda ATV Forum banner

1 - 20 of 25 Posts

·
Registered
Joined
·
16 Posts
Discussion Starter #1
I'm new to these forums, and hoping I can get some help. I have a 2003 400ex, I bought it over the summer. It has run fine since I bought it up until last week.

While driving it on some pavement, it suddenly died, and the rear tires locked up. I was able to start it right back up, and continue riding, only to have it happen again 5 minutes later. Since then I have not been able to get it started again. It turns over and over, but the engine won't fire. No popping or grinding or any weird noises, just won't catch.

Things I've tried to diagnose the issue:
-Bump starting: tires roll when popping it into gear, makes normal engine noises, but hitting the throttle has no effect, rolls to a stop and is dead.

-spark plug: my first thought was that it wasn't getting a spark, so the plug was bad, but I put in a brand new one, still nothing. I tested to make sure it was getting a spark and there wasn't an electrical issue elsewhere (grounded it against the engine) and it has a strong spark, while turning over.

-carburetor: I thought it might not be getting gas properly, so I cleaned the carb (was already pretty clean though) and made sure gas was properly flowing through the fuel line. Gas I am using is new, hasn't been sitting around.

air flow: checked the filter, removed it and tested, still nothing.

oil: oil and filter changed a month ago, still looks good.


That's all I've got at this point. I'm good with tools, but I haven't been doing this for that long either, so I was hoping someone might have experienced a similar issue and could point me in the right direction as to what might be wrong. Any help would be much appreciated, thanks!
 

·
Premium Member
Joined
·
2,608 Posts
It sounds like an engine seize secondary to overheating or lack of oil pressure ..... probably not what you wanted to hear.

What do you have for compression in psi tested with the throttle held wide open while vigorously cranking?

Rick
 

·
Registered
Joined
·
16 Posts
Discussion Starter #3
Unfortunately I haven't checked the compression yet, I don't have a tester for it. I can try and get one in the next couple days, but in the meantime, I'm confused how it could be an engine seize (sorry I'm not an expert with this stuff). I was under the impression if the engine was seized, it would be unable to turn over, or the tires would be locked when in gear, but it doesn't have those symptoms. Also I have 3 400ex's, and of all of them, this one runs the coolest, never had any overheating problems.

If it is seized, what do you think would need to be fixed / replaced?
 

·
Premium Member
Joined
·
2,608 Posts
Seizes occur due to expansion of the piston in the bore due to overheating and lack of oil or oil pressure. Basically, the piston scrapes the cylinder until it seizes and then the engine cools down and things fit once again ...... for awhile.

Then the process often repeats itself due to the underlying cause not being fixed. Oil coolers get blocked with sludge, oil pump chains get derailed off of the pump sprocket, oil screens never get serviced and become blocked with clutch friction disk material ...... yada yada yada.

My 2006 Foreman had a badly plugged up oil cooler inside the internal plumbing - not the cooling fins. The previous owner eventually grenaded the piston at high rpm and destroyed the top end, crankshaft and just generally wore everything out. It was, an East Texas naval gun boat, a mud bike very poorly maintained. You should have seen the muck at the bottom of the crankcase, not to mention the metal chunks picked out of the carb and elsewhere. I picked it up and rebuilt it all and spent four hours flushing that oil cooler piping. It took hot water, detergent, and Coleman fuel to finally get the sludge and tiny bits of aluminum removed and finally blow clean into a paper towel.

My guess is that you will need a split the cases rebuild though some could be tempted to only do the top end. Only doing the top end is usually a false economy that does not fix the underlying causes.

Rick
 

·
Registered
Joined
·
16 Posts
Discussion Starter #5
Ok so my understanding of seizing is correct, but I was unaware that cooling down could alleviate the symptoms. Also I just had my brother do a compression test for me, and he said it was 140 with WOT which seems reasonable to me.

What doesn't make sense to me, is that when it died the second time, it didn't have any trouble turning over right away (which I would think it should if it was seized) while it was still hot.

Now that it's cool, shouldn't it be able to start again? or are you suggesting that it got hot, seized, damaged other parts, and now the inability to start is due to damage it took when it seized up?

I guess what I'm getting at is, even if you're right about the oil being the initial cause, I should be able to FIX something to get it started again, whether something happened to valves, or timing, or whatever else? It has compression, spark, and fuel, and it turns over, but refuses to fire. What would I fix to get it to start? Obviously I'd look into the oil after to make sure it doesn't happen again.
 

·
Registered
Joined
·
377 Posts
140PSI is perfect. I would say that engine failure probably isn't your issue.

After you try starting it for a bit, is the sparkplug wet with fuel? Have you checked the valve lash to make sure they are adjusted properly? Does the carb bowl fill up with gas?
 

·
Premium Member
Joined
·
2,608 Posts
I would look at timing next because 140 psi should be plenty. At a hundred psi is where I do minibike top ends, all things considered.

Will it try to start if you use just a little starting fluid / ether? I do not use starting fluid often but it is a useful diagnostic tool. Too much can wash oil off the cylinder walls.

Rick
 

·
Registered
Joined
·
16 Posts
Discussion Starter #8
I did try the starting fluid, and I got no response whatsoever.. not even a pop or anything from the engine. First I sprayed some into the spark plug hole, and then screwed it back in and tried. Then I tried spraying some through the intake, still nothing.

Would valves or timing make sense for the way it's acting? I know how to do a quick valve adjustment (with a feeler gauge) but that's about it. I have no problem using a manual and working at it, but I just want to get some opinions on what I should put my effort into, since all the easy fix attempts have been tried.

scootstah, I ruled out fuel problems (in my mind) by trying the starting fluid directly in the cylinder and getting no response. The carb was also very clean, and had plenty of gas in it when I took it apart twice. Do you think I should revisit the fuel area? I have not done anything with valves yet.

Since you guys obviously have more experience than me, and I want to start with the most likely causes to avoid wasted effort, what direction do you think would make the most sense for me at this point?
 

·
Super Moderator
Joined
·
18,227 Posts
If you have determined good spark there is no reason it shouldn't at least hit on starting fluid unless the valve lash is incorrect. I would pull the inspection plug on the left case and align the "T" with the notch in the cover. Check your rockers and make sure they are loose feeling if not rotate 360° and check the rockers again. Which ever location they were the loosest is where you will make your adjustment. You can. Also plug the spark plug hole with your finger and bump the engine until the compression hits your finger. Then fine tune the timing marks. Set the lash to a tight .004 intake and .005 exhaust.
 

·
Registered
Joined
·
1,792 Posts
Im gonna guess that the timing chain tensioner is going bad and it jumped timing , thsts why it locked up. Now its out of time and wont start . Or valves are bent, but u said the comp test was ok. Stuff doesnt just lock up for no reason . If u do find it out of time, get a new tensioner or a manual one
 

·
Premium Member
Joined
·
2,608 Posts
I was thinking the same thing as ATVRIDER13. When it seized, all of that speed and energy had to go somewhere and I'll bet that it jumped timing. Soichiro Honda was smiling at you from that Great Sushi bar in the sky when he left you with 140 PSI of compression but I still believe you have an underlying engine seize problem even if you get it back into proper engine timing.

Rick
 

·
Super Moderator
Joined
·
18,227 Posts
Vapor lock..... acts just like a seizure... improper valve lash = valves not opening at the right time or enough creating an overload of gasses and causing a hiccup knocking off the engine check the fuel cap vent too . I would start with the valve train
 

·
Registered
Joined
·
16 Posts
Discussion Starter #15
Been busy lately, so I only recently got to trying to fix the issue. I took it apart and noticed a few things. Firstly, it seems like the previous owner did some modifications, at the very least it has a different cam and a manual timing tensioner. It wouldn't surprise me if it was also bored.

Anyways, the timing chain seemed a bit stretched, so I replaced it and made sure the timing was correct. Put it all back together, still wouldn't start. Wasn't really adding up, so I checked the compression on the engine again (my brother tested it the first time) and it was only 30psi. I tried adding a small amount of oil directly into the spark hole and checking the compression again, and it jumped up to 90psi.

So, to me that means that at the very least the rings on the piston got destroyed, because if it was a bent valve, the oil wouldn't improve the psi.

Do you guys agree with that assumption? And that being said, how much of a project am I looking at here, both in expenses and time? Could I just put on new rings, or is there a huge process, like getting the cylinder redone etc.

Thanks for all your help so far with this guys..
 

·
Super Moderator
Joined
·
18,227 Posts
Did you check the compression while holding the throttle wide open? If not retake the test... of so.... or your results are the same I'd say yes ... time for a build... you also could have a valve issue?
 

·
Registered
Joined
·
16 Posts
Discussion Starter #17
Yes this was at wide open throttle. So we agree that it's a problem with the rings? There could still be a valve issue, but if that was the ONLY issue, then I would assume the PSI would not have gone up to 90 with the added oil.

So how much is involved in this? Can I just replace the rings, or is it much more complicated than that? This is a 2003, I'm not looking for perfection, at this point I am just keeping it around for the occasional friend who will come over, so I don't want to drop an enormous amount of time and money into it if I can avoid it.
 

·
Super Moderator
Joined
·
18,227 Posts
You'll have to measure the cylinder you may can get away with a hone and a set of rings? You'll know when you get it apart
 

·
Registered
Joined
·
16 Posts
Discussion Starter #19
So I finally got a chance to work on this thing.. it sat around for a while.

Here's the update:
I tore down the engine, and the piston was pretty well chewed up, rings were destroyed, but the cylinder itself just had some aluminum residue, which I got off with acid. I rehoned it, measured, got a replacement piston (87mm), and rebuilt the top end.

So that all to went really well - it started right up. I do have another question for you guys though:
When this originally broke, the tires locked up while it was running. I figured that the destroyed piston explained this. Now though, even though it has a new piston and the engine runs, it seems like the tires are still locked up when it's in gear. Basically what I did was roll it down a steep hill, with the clutch in, and then pop it in second gear to see if the transmission was locked up in some way - and the tires just lock. I haven't tried running the engine and shifting into gear, because i'm afraid I'm going to destroy the rebuilt top end somehow.

Does it sound like something is also screwed up with the transmission? would it be a mistake to try and shift it into gear and drive off with it? Just trying to figure out what my next move is going to be.

Thanks in advance for any thoughts / advice you guys might have!
 

·
Registered
Joined
·
767 Posts
Did you split the cases and clean out the aluminum and all of the fragments? Are the rings 100% accounted for? Could have something jammed in there
 
1 - 20 of 25 Posts
Top