ATV rebuild question-General knowledge wanted

[maroonandwhite]

Hopefully some of you guys have experience working on ATV's and can answer this question.

 

I am going to buy an 06' Rancher from my uncle for a good price. They said the engine was locked up and needed a new one. I can't imagine for the $30 the shop charged him to look at it they really took anything apart though. The unit hasn't been dogged out or sunk or anything like that. Just riding in the back yard in the occasional mud hole probably.

 

My question is: What normally causes an engine on these ATV's to lock up? I haven't even seen the bike in person yet so I can't give specifics. I know  running it dry with no oil would possibly sieze the rings to the sleeve. I am hoping maybe something like a timing chain broke and has it seized.

 

It look's like a whole top end rebuild kit including boring out the sleeve can be had for under $200 so hopefully that is the most it would take. Looks like crankshafts can be expensive.

 

Any info or experience will be appreciated. Thanks!

[oldmustangjunkie]

Most likely, it was run out of oil.  I've owned numerous Honda atv's and 3wheelers (I currently own an 05 Rancher and 83 ATC 110) and the only thing I've seen that stops them is lack of oil and it would likely seize the rod and main bearings before the rings. A broken timing chain would keep it from running but not lock it up.

[maroonandwhite]

Well that is what I am hoping it is not! I have heard changing the cranks is a pain on these and can be expensive. Granted for what I have in it I can afford to spend a little but am hoping for an easy fix.

[oldmustangjunkie]

I noticed you live in the west side of TN, the mudhole zone.  I know you don't think it has been sunk, but it's a possibility based on geography, so a bent rod from water ingestion is possible.  Also, it's possible that the recoil mechanism got full of gunk, destroyed the crank seal and let the crud into the engine.  

[maroonandwhite]

Well if it was from anyone else I would say that is a possibility but I know where this ATV lives and is ridden. The deepest thing it has been in doesn't go over the rim. The son likes to tinker one stuff so maybe he let an oil plug out or something. I probably just need to wait until I pick it up tomorrow and take a look inside. From what they said it was running fine, they shut it off then later tried to start it and nothing. Locked up. That made me think something heated up then kind of bonded on the cool down. Am I way off here?

[oldmustangjunkie]

I'd expect the scenario you described to be the opposite--I had a friend with a Rhino and it ran way hot and locked up.  Once it cooled down (and the swelling decreased) it was able to run again although it was in need of a new top end.  But anything is possible.  Try to turn the motor over with a ratchet, going both directions and see what happens.

[maroonandwhite]

Yeah. Far as I know metal contracts when it cools so you'd think I could free it up. I'm hoping the piston may just be seized and a $200 top end kit will fix it. I'll get it apart this weekend and let you know what happens. Thanks for the help.

[runco]

25 years ago, I use to work as a small engine mechanic. There can be several reasons to cause a lock up: Engine was ran without oil, Engine was litteraly blown (hold the throttle wide open for a period of time), the spark plug was left out, and rain/mositure got into the cylinder and rust is preventing the engine to rotate, and this one, fuel was left on, fuel dripped into the cylinder, fuel leak then into the oil pan, and the next time the engine ran, the oil was so diluted, it seized the bearings when everything got hot.

[maroonandwhite]

Well I think I got lucky! I don't know how or why but one of the valve seats(intake) broke and got on top of the piston. All I need is a new head and a top end job! If all goes well I will be in this 4-wheeler for cheap.

[oldmustangjunkie]

Be sure and check all the valves and seats that weren't damaged and their clearances when you reassemble the motor.  If the seat wasn't a defect from the factory, the problem could have been caused by too tight clearances.

[maroonandwhite]

Yeah I think they were a little tight. I had to order a whole new head so it's all new so they should be in good shape. We will of course be sure to set them properly. Thanks for all the help.

[maroonandwhite]

Just to give an update I got the thing running last night. Finally got the newish head, bored cylinder and new piston, and the new recoil starter installed. We also had to put new seals in the rear end. It runs good but the engine does have some "tick" at the valves. We adjusted them three times with the engine in the correct spot so I know they are set correctly. I am going to ride it for a while and recheck them. The one way bearing is also bad so no engine braking. I plan on changing it down the road if I ever need to change the clutches. All in all I got a great little ATV for a killer price!