Going to be replacing the head gasket...

[Ted J]

I'm going to be replacing the head gasket on my '04 YFZ450 soon here. I think the last owner had gotten it hot the last time it was rode and it's sat for a year now.

I figured while I have it apart I'd obviouslly check the piston and wrist pin to make sure it's okay and I'd also make sure there is no play in the connecting rod and crankshaft bearings or at leats to the best of what I can feel that is. Have a few questions:

1. Beyond replacing the cylinder gasket and the cylinder head gasket, is there anything else I should do while I have the top end off?

2. Should I just go ahead and replace the piston, rings, and wrist pin right away while I have everything apart? Or if they seem tight, and not loose just leave them in there and maybe just do the oil mod? (leads into the next question)

3. I'm thinking about doing the '07 Oil mod. Can be done after I get the top end together and make sure it runs okay by running it some to make sure there are no leaks after the head gasket replacement, right?

4. Is the oil mod required? I plan on taking this 4 wheeler trail riding and maybe some smaller jumps and some MX track riding. Please know that I am not going to go fast on the MX track, just enough to maybe get some small air. I plan on running the motor hard though, I like to go out and tear arse and want to not have to worry about the wrist pin not getting enough oil. On the flip side though if the type of riding I'll be doing doesn't justfy the oil mod then that will give me more to think about.

Thank you in advance!

[jshtex]

If it is an 04 and hasn't had a top end (piston and rings) then I would recomend replacing them just to be safe. I could show you pics of what happens if they let go. We run our bikes hard and normally I would replace the cylinder, piston and rings once a year. And I still had one go....

While your in there you should also replace the timing chain, they are cheap and I don't go in without one.

Check the valve clearance and as long as you can shim it into spec the head should be ok. If you can't get small enough shims then it may be time for new valves (intake usually first and the clearance will tighten up as they wear) and a seat job in the head. It isn't cheap but definatly cheaper than a rebuild if you drop a valve. Another thing that is cheap to replace is the valve springs. I haven't ever heard of a problem with them failing but like I said they are cheap.

If you think it got hot and hurt a head gasket, you should probably check the cylinder and head both to make sure they are not warped.

As for the oil mod, well I would send your cover off and have it machined for the 07 mod and get the kit to install it. As for wether it is needed or not, there is a reason the engineers at yamaha put it on the 07s.

[Ted J]

When you say run your machines hard I assume you are revving it out a lot? I plan on trail riding this machine and was maybe just going to pull the top end off, inspect the piston and if it's okay just put the gaskets on and run it for a bit and maybe sell it.

I plan on running it hard at times but that's mostly going to be running it hard just when coming out of corners and the such. Wondering if I could just get away with running her as is type thing if I don't ride it to hard on the trails and only rev it out sometimes and run it in the midrange most of the time type thing.

[jshtex]

If you have access to tools to actually check the clearance on the piston and cylinder then you might be able to keep the ones you have. But I would at least put new rings in. I think you could have a failure of a piston even in a bike that was just trail ridden occasionally if it got to far out of spec.

Good luck with it. :)