I recently bought a 1997 Yamaha Big Bear. The electric start wasn't working. I found out that the starter clutch was shot. I drained the oil and quite a few metal shavings were in it. Once I saw this I flushed motor oil and gasoline through the engine until metal was no longer coming out. Since then I have changed the oil every five hours or so of operation. I still get fine metal shavings in the oil filter, although less each time. The motor still starts, runs and idles fine, but I'm starting to see a bit of smoke at start-up.

My plan is to perform a top-end rebuild and change out the starter clutch simultaneously. While the engine is opened up to perform these tasks I will thoroughly flush it out with gasoline and oil and compressed air.

I'm a novice at this kind of engine work so I'd like to avoid a complete rebuild?

Questions:

1: Will this plan do an adequate job of removing contaminates from the engine? If not, what would you advise?

2: Are there specific things I can check for damage while I have the engine opened up this much?

Hi Paul,

You have got the procedure down. I would recommend paying attention to how much air pressure you use to dry it all out...

Normally 50-75 lbs of pressure will clear everything out of the channels and groves, and not cause any damage to metal edges or seals that may remain in place.

While you have the top end opened up, here are a few things to keep your eyes open for...

Top of the piston- excessive carbon build up, or signs of scratches or uneven wear on the cylinder wall.

Head- check for any warping by laying a known good straightedge on the mating surface. Be sure to check all four compass points, north to south and east to west. Also check the points in between, like northeast to southwest, northwest to southeast.
If there is any variance, this would be the time to mill the surface just enough to remove the irregularities.

If you do need to do any milling, keep it to a minimum, since you don't want the valves hitting the top of the piston.

You should also check for any bent pushrods, or worn out rocker arms. (I don't remember which ones are used on your motor)

Since you have found shavings, I would also check the piston rings. The best way to do this is via a compression check before you remove the head. And then once again after you have cleaned everything up.

And whatever you do, make sure to use a new head gasket when putting it all back together. You can even check the head bolts for warping by using that good straightedge along the bolt body in a couple of spots.

If you plan on keeping your Big Bear, you might want to spend a few and get a repair manual for it. You can get one by following this link, and it will be able to answer any future questions you might have...

http://www.atv-411.com/yamaha-atv-repair-manual-7.html

Hope this helps, let us know how it all turns out...




Ride Safe. Ride Legal. Ride Again... Curtis

Thanks for the info.