I posted this on another forum. Can anyone help me out here?
This is my wife`s atv and was purchased new April 2010. Has 800 miles on it now and sat all winter in storage until this week-end. Got it out of storage and checked it over and all fluids were fine and she drove it one-half mile to the diner and it sat for an hour then drove it back and that was all she wrote. Started smoking out the exhaust and you could smell anti-freeze. Bike is still practically new, never been abused and never been hot or anything. No extended warranty. I am an auto mechanic by trade and I can probably fix this myself but is there anything I should be looking for other than a head gasket or cracked head on this particular engine? Are these engines noted for blown head gaskets or anything? There are bubbles (not a lot) in the a-freeze with the engine idling (at cold start-up) so there is compression going into the cooling system and the dipstick had water on it. Any tips or anything I should know on this 455 engine? Sorry for the long post but wanted to make sure I explained everything.
Thanks

 

cant imagine a head gasket on that machine but it sure sounds like it, motor didnt freeze up during winter did it? might also check water pump seal

 

Finally got around to looking at the atv tonight and the first thing I did was to check the compression and it was down to 50 lbs. so I guess the problem is the head gasket. At least I hope that`s all it is. The spark plug looks fine. BTW the owners manual says the compression ratio is 10.1:1 so is 87 octane good enough for it being that gasoline has a 10 percent ethanol content or doesn`t it matter? Just wonderin that`s all.

 

87 is what is called for on octane, but compression test isn't always accurate because of the exhaust detent lever keeping the valves slightly cracked open to relieve compression until the engine starts,then the lever moves back against stop on cam. Any seeping around head that you've noticed? ( can be a little tear internal though and not seep),I know you said coolant in exhaust and oil tank,possibly gasket but if is something had to have gotten hot I would think,was fan operating,hot light ever come on? Pretty well bullet proof engine,but any thing possible. OPT

 

There are no signs of external a-freeze leaks. Just how much should the compression be turning the engine over cold to check it? Will pressurize the cooling system tonight to see if anything shows.

 

Have you changed oil and filter,run engine with radiator cap off until fan comes on which will remove any air in system if present,then top off coolant,replace cap,top off coolant bottle and ride? I would try this before I did any thing major. If coolant still shows up in tank and exhaust,THEN you will absolutely know the top end needs to be torn down! OPT

 

Update
Just got done pressurizing the cooling system. Took the exhaust pipe off the head and then pressurized the system and there is water coming out the exhaust pipe port on the head.

 

You know what to do now,sorry since its a fairly new machine! Its not that bad a job though to replace a head gasket! OPT

 

Would you or someone on the forum here have a pic of the timing marks lined up for this engine and maybe an explanation with the pic about the timing marks.
Thaks for all the help!
Joe

 

Easiest way is to pull square cam plate on head(recoil side) Pull spark plug to make it easier,then pull recoil until cam sprocket index pin is at TOP CENTER of head. This is tdc. Remove valve cover,can then remove tensioner assy(just loosen 10 mm nut on end first,will have to later remove to push tensioner in) Remove hose to water pump,clamp off,remove hose to thermostat housing and clamp off. Remove thermostat cover and t/stat to obtain access to cam plate,remove round plate (cam is pulled out from the left after cam sprocket 3 bolts removed).Just let cam chain and sprocket lower down gently(don't pull recoil,keep at tdc. Remove carb and air box and exhaust. Loosen head bolts, may be a little cramped if you don't pull tank,remove bolts,then head can be lifted up.Make sure cylinder doesn't break its seal! This is how I've changed cams and head gaskets. The manual has another way showing the crank sprocket mark and how to time cam,BUT not necessary if piston is NOT moved! Remove old gasket,clean head and cylinder,install new gasket and head,then torque head bolts. Reassemble the cam from the left side(make SURE index pin at top center of head and pull up sprocket and place on cam and start the 3 bolts,then replace rocker arm blocks),hoses, install tensioner and push in tensioner spring and tighten 10 mm bolt to take up cam slack.Adjust valves to .006 intake and exhaust. Don't have the head torque in my head,others can chime in! PS lube up cam journals and after cam is installed line up cam sprocket on cam,then replace left cam cover so cam won't push back.
This might seem confusing,but a good manual will explain better! Others may be able to show pics also! Be sure to leave radiator cap off until fan kicks on to remove any air after cranking, then top off. This is how I did the 500's,I know the 400's are a little cramped, hopefully you will have enough room in the frame. Good luck, OPT