i might buy a 98 300ex from a friend. it is not running now and only spins over really fast. i am sure it's a timing chain. before it stopped running, it was tapping from under the cam cover. we think it needed a valve adjustment too. or maybe that was the timing chain slapping but who knows. i am going to open it up before i buy it. if the timing chain broke then would that bend the valve if they hit the piston or is this motor a non interference engine. has anybody broken a timing chain on there bike and what was you experience. thanks.

 

hi it does sound like the timing chain has stretched (not broke) if it broke the motors done for it streatched. it bent the valves and ruined a piston on top of buying a new timing chain it wont start b/c the piston is ruined and the valves are bent if anyone of those go wrong the motor wont run

get a new piston(about $100 or something) all new topend gaskets(40 TO 50 IM THINKING)

TIMING CHAIN ($100) I KNOW

vALVES (ABOUT 100 TO 150)

HAD THE SAMETHING HAPPEN 2 BE WITH MY BIG BORE KIT I DODN'T CHANGE THE TIMING CHAIN AND IT STRETCHED. LUCKALLY I KNEW WHAT WAS HAPPENING AND STOPPED IT BEFORE THERE WAS DAMAGE!!



good luck

I WOULDN'T GIVE HIM ALOT FOR THE 300EX AT ALL NEEDS ALOT OF WORK WHEN I GOT IT I WOULD SEND IT OUT AND GET A BIG BORE AND BIGGER VALVES THATS THE BEST OPTION AND A NEWW TIMING CHAIN

OH AND A CASE GASKET B/C YOU HALF 2 TAKE THE CASE SIDDE OFF 2 GET THE TIMING CHAIN OFF!!

ALOT OF WORK!! YOU BETTER KNOW WHAT YOUR DOING

 

well i took the valve cover off and found that it is one of 2 things. a stripped out lower timing gear of a bad keyway. i just hope it is not the keyway, it may have scared the crank up a bit if it was that. it has great compression so piston is ok. i will check the valves still though. he said i can have it for 1000. it's got gators on the rear and some nice tires up front,cobra exhaust, i think the jet kit is still on it. the plastic has seen better days but i can live with it. he said i can give him some money, take it home and pay the rest later. i am first going to tear into it some more before i decide. i priced the chain and it is 65 bucks not including the 10 percent discount that is offered on in stock items.

 

hate 2 tell you this but i was going 2 get the lower gear for mine 2 be safe but its like 300 bucks b/c they dont sell just half the gear its half the crank!! and then you half 2 go get the new one pressed on and alot of trouble!! if i was you get new valves and a new crank!!! and timing chain and new cam sprocket 2 be safe!!!!!


a 1000 bucks is alot for that fourwheeler!! but hey go for it but you better know how 2 work on it!!!oh dont forget the gasket set for the topend and the side cover!!!!

hope this helps

 

1000 for a 98. i don't think that is too much. i offered 800 though and he wouldn't take it. 300 bucks for that, i will check on it and if so i probably will just pass and fix my xr500 blaster head and woop his yfz450. there is an 85 yamaha tri Z 250 two stroke 3 wheeler that is in imaculate condition for 1000. but i don't think that is any better of a deal.

 

I would check the prices at servicehonda.com. Your cam chain price is pretty good. Think I paid 75 there, dealer is about 120. Both valves there were about $50 if I recall. Not that bad. It will bend the valves but forget replacing the piston if it just has a couple nicks in it. Not worth the expense for that on a 10 year old utility quad IMO. Not sure how you can tell the lower gear is stripped. I just did this on a 96 trx300, no way to see it. Maybe the engines are different, dunno. Only to see that was to pull the side cover and clutch. With the chain loose it'll slip aver the lower gear pretty easiely.

A grand for this quad might not be to bad if everything else is ok. I'm a fix-ur-upper guy to. Buy them cheap and fix them up.

 

the reason i think it is a bad timing gear or keyway is because i can pull the cam and chain tight and it still doesn't move.it barely turns when cranking it over and not holding the cam.

 

Interesting, I guess it could happen but I would see it as rare unless the engine was really moving. The valve is the easiest thing to bend so it's the first to go, then the engine dies very fast.

Here are a couple pics from the 96 300. Maybe give you an idea. I would pick up a shop manual.

Rob

pic 1
pic 2

 

well it has good compression, when i put my finger in the hole, it gets pretty hot from the compressed air. i found the problem and luckily i do not need a new carnk or sprocket. the chain got too loose and fell off of the lower sprocket. the sprocket has plenty of teeth left on it too. i am getting it tomorrow and will have it going by the weekend with a new timing chain and chain tensioner.

 

Uhhh yep I believe I mentioned that. Been there done that. I would NOT replace the tensioner if I didn't have to. If I recall they are costly. Plus if they work then there is no need. If you can wind it up and it'll spring back then it's good to go.

Assuming that you checked the compressioned with it timed properly. The first time I worked on the 4 wheeler pictured it only jumped a couple tooth. Compression still showed ok. Also I'm guessing you have a manual for this. There are 2 marks on the flywheel pretty close together, be sure you get the right one. It's a T if I recall. On the cam gear the 2 dots go even with the case. Doublecheck this, I'm going from memory of about 6 months ago. My manual is at home.

Glad to see you getting out cheap. Now a grand for this ATV is looking pretty good!!