Top End Time!

[TIG88]

Hey guys, I think Im gonna go ahead and put a top end on my 03 yz450. It is all original inside. She still runs good and makes good power, but until it is warmed up, a blip of the throttle will give a little puff of blue smoke. Since it dosent do this if I leave the throttle alone for 1-2 minutes, Im assuming its the rings and not the valve guide seals, right?

I figure I will redo it with OEM stuff from the TT store. I know I need rings, piston clip rings, a piston, and a headgasket. I'll do the cam chain at the same time. Anything else I need?

Any tricks or words of wisdom before taking the plunge?

Thanks alot guys!

[KJ790]

You also need a wrist pin, a base gasket, a flywheel puller, and the right size torx head to remove the stator. The last two tools are only necessary if you change the cam chain, which I would definitely do. They aren't that hard to do, I'm gonna do my 450 this week as well, I'm still waiting for my cam chain to come. My only advice is when you put it together make sure you double check the timing after installing the chain tensioner. This is a common mistake. When the tensioner is installed it often reveals that your timing is off by one tooth on the intake cam.

[Two-Six]

Hey KJ what are you gonna do to your 450?

[KJ790]

Hey KJ what are you gonna do to your 450?

I'm throwing in a new piston and cam chain, I've got 60 hours on the one in there and it is winter so I have time.

[TIG88]

Sorry guys, but can I reuse my stock piston?

This will be the bikes first top end. Thanks!

[ajd187]

Sorry guys, but can I reuse my stock piston?

This will be the bikes first top end. Thanks!

On an all original 03, I would just put a new one in there to be safe.

[KJ790]

Sorry guys, but can I reuse my stock piston?

This will be the bikes first top end. Thanks!

I would put a new one in, the current one is 6 years old. You are already doing all of the work, why not use new parts?

[TIG88]

Roger that. Just making sure I wasnt spending 120 bucks on something that dosent need tobe replaced. Ordering everything tonight, thanks again

[grayracer513]

The problem with modern high performance 4 strokes is this:

In the old days, when cylinders were iron, and valves were steel, you could just let something run until it wore so much that it smoked and wheezed and ran bad, and figure out that it was tired. Loss of performance was about the worst of the risks. Once you got fed up enough with things, you could schedule the rebuild to suit yourself, and keep riding it.

But now, with the use of plated cylinders, hard coated titanium valves, and stuff like that, the engine will show very little wear or performance loss for a very long time until the plating/coating fails, the valves sink, the rings peel the walls out of the cylinder, the tiny little piston skirt breaks and the piston turns crossways in the bore, and stuff like that.

It isn't always nearly that dramatic, but the point is that it's very difficult to judge when an assembly that's part way through its useful life will come to the end of it, sometimes suddenly. If you don't wait 'til it breaks, you will be giving up an unknown amount of service life, and the expense that represents. But if you do let it go to the end, it may cost more, maybe a lot more, and it will almost certainly fail at an inconvenient time.

[jonova]

TIG88 how many hours are on your motor?

I rebuilt mine after 120 and the cyclinder still had the original hone (sp) marks in it, but the trans took a crap. Racing is hard on them.....

I had to put in new Ti OEM valves after about 250 hrs and the exhausts were the only ones that needed to be replaced. Once the Ti coating goes they will tulip in no time.

I'm not sure about the exact weights but the wiseco piston I think is lighter than OEM. That puts less load on the crank and increases longgevity of your bottom end. Greyracer might have exact weights for the pistons....

Good luck!

[grayracer513]

I'm not sure about the exact weights but the wiseco piston I think is lighter than OEM. That puts less load on the crank and increases longgevity of your bottom end. Greyracer might have exact weights for the pistons....

I don't have weights handy, but my experience is that most racing pistons are as heavy as stock, and frequently heavier. There is less likely to be much weight difference in aftermarket pistons and the OEM parts in a racing bike like the YZF, however, because the stock piston would be heavier than normal due to strength concerns, whereas a street cruiser might have weaker, lighter pistons to start with.

In any case, while a lighter piston would in fact reduce the inertial load on the crank and rod assembly, a significant weigh difference would upset the engine's balancing, which besides being annoying, also stresses the crank and bearings some. Most piston manufacturers try to make a product they are satisfied with that's close to the same weight as stock to avoid this.

[TIG88]

TIG88 how many hours are on your motor?

I rebuilt mine after 120 and the cyclinder still had the original hone (sp) marks in it, but the trans took a crap. Racing is hard on them.....

I had to put in new Ti OEM valves after about 250 hrs and the exhausts were the only ones that needed to be replaced. Once the Ti coating goes they will tulip in no time.

I'm not sure about the exact weights but the wiseco piston I think is lighter than OEM. That puts less load on the crank and increases longgevity of your bottom end. Greyracer might have exact weights for the pistons....

Good luck!

The guy that I bought it from was the original owner, and he would take it to a local track in PA, and ocasionally some mountain tracks. He said he managed to do this about 20 times a year. The bike didnt have much wear on it when I bought it, although the plastics were a little sore. 20x6=120. I multiplied this by 2.5 hrs per ride to arrive at 300 hours, which im 99% positive is overestimated. I have no idea how long the average day at the track is, lol. It could well be around half that. When I checked the valves they were all in spec with my old rusty feeler guages. I'm gonna recheck as soon as it gets warmer with a better set.

Havent ordered anything yet, would OEM be the way to go? The base gasket, is that the one that goes in between the bottom of the cylinder and case? Also, do I have to hone the cylinder?

And, on a similar topic, when is it a good time to redo the bottom end?

[KJ790]

The guy that I bought it from was the original owner, and he would take it to a local track in PA, and ocasionally some mountain tracks. He said he managed to do this about 20 times a year. The bike didnt have much wear on it when I bought it, although the plastics were a little sore. 20x6=120. I multiplied this by 2.5 hrs per ride to arrive at 300 hours, which im 99% positive is overestimated. I have no idea how long the average day at the track is, lol. It could well be around half that. When I checked the valves they were all in spec with my old rusty feeler guages. I'm gonna recheck as soon as it gets warmer with a better set.

Havent ordered anything yet, would OEM be the way to go? The base gasket, is that the one that goes in between the bottom of the cylinder and case?

And, on a similar topic, when is it a good time to redo the bottom end?

I'm going to say that is a large over approximation. An average day at a track is hardly ever over one hour of actual riding. many times I will go and bang out some laps and only put a half hour on my hour meter.

[grayracer513]

Havent ordered anything yet, would OEM be the way to go? The base gasket, is that the one that goes in between the bottom of the cylinder and case? Also, do I have to hone the cylinder?

Yes, yes, and yes.

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