Honda TRX ATV Forum banner

1 - 20 of 22 Posts

·
Registered
Joined
·
19 Posts
Discussion Starter #1
Ok so i picked up an 03 400ex and the guy said the one way starter clutch needed to be replaced. So i did that and got it going. I took it around the house parked it and then 10 minutes later went back out and started it let it idle and then it made a clunk noise and shut off. So I figured the one way went again. So i just put a new one in and it doing the same thing as when i picked it up. You go to start it and it just spins. The motor doesnt even try to crank over. I am at a lose and cant find any answers. Anyone have any ideas?
 

·
Super Moderator
Joined
·
3,342 Posts
When you say you replaced the starter clutch, what parts did you replace? Just the one way clutch, the clutch and hub or the clutch, hub and starter gear? It's also possible the flywheel key sheared and the flywheel is just spinning on the crankshaft,
 

·
Registered
Joined
·
19 Posts
Discussion Starter #3
I replaced the bearing and hub it goes in, both little gears and i replaced the flywheel key.
 

·
Super Moderator
Joined
·
3,342 Posts
You should have replaced the big gear with the hub that runs inside the clutch (part # 28110-HN1-A70) and the clutch hub (part # 28125-HN1-003 which includes the one way clutch part # 28126-HA7-673), but that would not explain the "clunk" when it stopped running. The clunk could have been the engine turning backwards when it died which would lock the starter clutch and try to turn the starter motor backwards or the starter clutch may have locked when you started the engine which would keep the starter motor spinning and possibly damage the starter motor/ Just have to do the diagnostics and determine the problem.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #5
I put a whole nother bearing and hub in than the one i replaced originally. I think the clunk was when i first put it back i didnt put it on right and the big gear and flywheel were barely together, but now it is. I do now that when i put a ratchet on the flywheel there is compression. So the only thing i did not replace is the big gear. The guy did give me another starter with it. Would it be worth trying to replace that?

The other thing i know about this four wheeler was that is was bored out and piston was shaved. Thats what the guy told me. When i did get it running the valves tapped bad so i new i needed to and adjustment. Thats all i know about this thing.
 

·
Super Moderator
Joined
·
3,342 Posts
Well, I think the guy you bought it off of was an idiot. I am an experienced mechanic - I am self employed and have run my own shop for over 40 years. If the machine were mine, I would tear it down, check the piston to cylinder clearance and check the lower end of the rod. There is absolutely no need to "shave" a standard piston and high compression pistons are shaved to lower the compression for a variety of reasons. I would be quizzing the previous owner as to why the piston was shaved. Typically it costs about $200 per piston for shaving, so I don't believe it was done unless the PO was serious about racing.

If the big gear was not replaced, the hub that locks up in the starter clutch may be worn down to the point it is slipping. Sometimes if put the engine in gear and roll it backwards a little, it will lock the starter clutch and spin the starter backwards, then sometimes it will crank the engine normally once or twice more. Might try that and see what happens.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #7
I think the guy before the guy I got it from did the work to it and he was a mechanic. I ordered a gear a little bit ago. I didnt wanna spend to much on this thing. I got it for $600. When I get home I will try to put it in gear and rock it and then try starting it. I was thing\king the same thing you said about the hub on the gear being worn down last night cause there was a small groove in it.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #8
So i put it in gear and rocked the thing and tried to start it and it was the same. I then marked the bolt with white out and hit the start button and the mark was in the same spot. Im going with the big gear 8s worn down and slipping like you suggested. Also would the neutral switch habe anything to do with this?
 

·
Super Moderator
Joined
·
3,342 Posts
If it's not in neutral you have to pull the LH lever to get it to start in gear - test the switch by finding it (usually on the LH side above the shift shaft below and in front of the counter shaft sprocket) and with the key switch on, use a test wire to connect the wire going to it to ground. If there is two switches, one is for reverse and the other neutral. If you ground one and the reverse light comes on check the other the same way. If one light comes on but the other does not, check the bulb then start checking the wiring. The hot wire goes to the light and the switch grounds it to turn it on. If neither light lights, check the battery, fuse and key switch. The red wire at the switch goes to the battery through the fuse and when the switch is on it connects the red wire to the black wire.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #10
The neutral switch wire just keeps going in and out thats all. i have to go order a new wire. im pretty sure my problem is the big gear behind the flywheel. i will find out tomorrow when it comes in.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #11
So i tore apart the top end on this 400ex and i am thinking the timing chain popped off. Should you be able to freely spin the timing chain?
 

·
Super Moderator
Joined
·
3,342 Posts
No, the cam chain is driven by the crankshaft - there is a sprocket on the crankshaft that drives the chain - (working from memory here) the chain normally will not come off the crankshaft sprocket because the oil pump is too close to allow it to come off - if the chain is worn out, it may contact the top of the oil pump, wearing it enough to allow the chain to come off during service. You may just have to look down the cam chain well and manipulate the chain back onto the drive sprocket, or the chain could be worn to the point the lifter can no longer push the tensioner far enough to take up enough slack to keep it on the sprocket, or the lifter may not be functioning and taking up the slack, or there may be another undiscovered problem.

I worked on one that had a new cam chain installed by an out of state shop and had a lot of cam chain rattle. I found the "lifter" was fully extended (not normal for a new cam chain) - I removed the clutch cover, clutch, crank pinion gears and oil pump - found the anchor bolt for the tensioner was loose and about to fall out of the engine case. I tightened the bolt, retracted and installed the lifter, released the lifter and the chain again had proper tension.

The only way the chain will move without turning the crankshaft is if it's off the sprocket, the sprocket is broken or missing or the teeth are worn off the sprocket.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #13
Im hoping the sprocket is good on the crank. I have the head off it already and i am going to pull the jug when i get home. I really dont want to pull the clutch but i am probably going to have to.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #14
Now that i have the whole top end off how can i tell what it was bored out to? How can you tell if the piston was shaved?
 

·
Super Moderator
Joined
·
3,342 Posts
Measure the diameter of the cylinder in mm - 85mm (397cc) is standard, 85.25mm (399.5cc) is first over bore and 85.5mm (402cc) is second over bore - anything over 85.5 requires the installation of aftermarket pistons like Wiseco, Namura, Pro-X or the like. Wiseco is available in 86,87,88 and 89mm.

86mm bore makes it a 407cc, 87 = 416, 88 = 426 and 89 will make it a 435cc (commonly referred to as the 440 kit) To bore to 89mm the cylinder has to be sleeved with a special heavy wall sleeve or the original sleeve will break in use.

If the piston has been shaved, there are indications of milling and there will be no markings on top of the piston. Before a piston is shaved it has numbers and sometimes an arrow indicating the exhaust side of the piston either stamped or engraved into it. You will have to remove the carbon to see the markings (if any) by bead blasting, buffing, or heating (burning the carbon off) - I usually bead blast or buff. Also, if there's anything left of the rings, oversize rings will have a number stamped on the top side of the ring near the end where the two ends of the ring meet when installed in the cylinder.
 

·
Super Moderator
Joined
·
3,342 Posts
Looks don't count - take the top ring off the piston and put it in the cylinder about 1/2" below the top surface. Use a caliper, tin can, pop bottle, old piston or whatever you can find that will fit the hole to push the ring to square it in the bore and measure the ring end gap. You can have a new, but incorrect size piston in an engine and it will not run. It has to be right.
 

·
Registered
Joined
·
1 Posts
01 TRX400EX Not Starting

I just picked up an 01 400EX down the road and the starter spins along with the first two gears I can see behind the starter gear cover but haven't torn into it further yet. Hoping to get into it shortly here but was curious if there are any important "don't forget to do this" when I start on that side of the engine for a diagnosis? I have worked on/rebuilt snowmobiles my whole life but this is my first sport quad so looking for anything that might not be obvious pulling it apart for the first time.
 

Attachments

·
Registered
Joined
·
19 Posts
Discussion Starter #20
My issue was first the starter clutch one way bearing and now the timing chain popped off. The first thing i would get is a gasket kit.
 
1 - 20 of 22 Posts
Top