Excessive Exhaust Valve Clearance
While riding down a hill using the engine for braking the motor started tapping very bad. Shut it down and towed home. Took the valve cover off and the exhaust valve has around .125" of clearnce, intake has .006" as required. Locking nut was tight on rocker arm. The exh. valve looked like it was not as tall as the intake, so i thought the valve was bent. I adjusted the exh. clearance and checked compression, 75psi while adjusted and 180 psi with adjustment backed off. Looks good to me. I re-adjusted and put valve cover back on, started motor and it runs great. My problem is that the ajustment is all the way at the limit and I don't know what has moved to cause this instant issue. Can the lifter fail and cause this to happen? I've never been in the motor and it doen't have many hours on it. I'm scared to ride it until I find what caused this instant .125" clearance. Any help would be great. John

 

Not a Honda expert by any means,but on most four strokes this is really a gradual thing. The exhaust valves tighten up over time because of a combination of things. The valve seat itself can wear along with the face of the valve and also the "mushrooming" of the valve face itself,pushing the valve stem up.valve spring wear or collapse. Then you have to back out the adjuster more to get the correct clearance. This happens more on the thinner intake valves,but can happen. OPT

 

You have a worn cam lobe from a plugged oil pathway. You need a new cam and need to find out why oil stopped flowing to the cam. That's the only thing I can think of to give that excessive of clearance. When you said adjuster is at its max, that convinced me. Its common on the bayous and pretty hard to find a decent cam and rockers on ebay because of it.

 

Thanks for the input. I did check the valve clearance about 2 months earlier and they were dead on and required no adjustment. I may have misspoke above, I had to turn the adjuster screw down (clockwise) wich would indicate a worn cam. But I would think a worn cam would happen over time and not instantly. It also ran great after the adjustment. I will pull the head and cylinder and try to set up an indicator to check the cam lift.

 

You probably just didn't notice it.

Here are some pics of a bayou cam I was dealing with a year or two ago











It was same problem... adjuster was all the way down. We adjusted it and rode for 2 min and heard clicking again. Went to adjust it a 2nd time and found slop n thought "wtf". I knew something wasn't right. Turned out someone had put in a regular bolt on the oil line instead of a banjo bolt with the hole thru it (like brake lines have). That bolt blocked the oil from going to the head.

 

Oh, and the other cam and rockers in the pics are what I bought on ebay (the seller said they were good). Since I couldn't find anything decent on ebay, I ended up just welding the rockers and cam and grinding it down. It actually worked! I think its going on 2 yrs now.

 

Thanks for the pictures. This motor has push rods and the cam is in the bottom end of the engine. I hope I don't have to pull the engine out and apart. It will be a week or two before I can get back into the project.

 

Yeah I know. I rebored a 250ex, which is push rod, but can't remember if we could have gotten the cam out or not. I'm not much of a fan of the way honda does things anymore. Rockymountainatv sold me an oil filter for my 250ex, which doesn't have an oil filter! It seems your 250 engine wouldn't either. Honda isn't what it was in the 80s.

 

I mean your 350 engine. oops

 

350 Rancher has an oil filter..and if it backward or cheap oil filter it could cause an oiling issue on cam and transmission shaft....I have seen this on afew model..I also have seen cheap oil filter glue come apart on clog up oil holes...Than how cheap in an 3 buck filter anymore.... You can replaced cam on oil pump without splitting case just remove engine case covers..