YZ 450 Tranny broke Major repair costs, Any advice for Engine repairs

My 4th gear went out. Now I think its time to do a major overhaul. Was hoping to get by until 05's came out but looks as if that’s not possible. Decided to keep for another year, since I just had the suspension redone 3 months ago (clutch too) and now must drop the cash for the engine repair. I need some advice from those of you that have either gone through this or are solid moto mechanics.

Since I have the whole bike apart. I decided to powder coat the frame and replace all of the plastics and other wear items. But what about the engine, since I am keeping it I want to do it right. I do not want to just fix 4th gear and then have something else break 2 months from now. What are the major wear items that should be replaced in a 4 stroke engine. Piston/Rings? Cam ? I might as-well do it all since I’m in there. Looking for good advice, thank you.

ive seen timing chains stretch too far skip time & destoy motors so i would always replace it.also a few oil pumps look pretty rough when taken apart and ive seen one set of pump gears crack.thats what i saw most often on the motors weve done.you need to go through the entire motor very thourouly making sure everything is in spec if you want a trouble free ride.

Thanks for the advice. Sounds as if you have seen a few of these. Is this something the average home mechanic can do or is this shop only stuff. If I took this thing apart would I be able to visually tell if something is worn. How do I check spec's? Do I need special tools. I am pretty good at putting all of these puzzle pieces together but have to admit I don’t know much about these things.

you would be amazed at how easy these engines are to work on. they made it as easy as possible, but i find getting the cam chain in and out is the hardest part. everything else just slips together. its easy to tell if things are worn. look for rounded gear dogs, bent forks and worn grooves on the shift drum.

use the manual, use a torque wrench and just take your time. you will need lots or room to lay everything out, label things if you want.

dont let anyone else work on your engine!

I have the hole 4 speed for sale if you need one :thumbsup:

Your the second guy today to post this same problem, any ideas why this has happened, what are the warning signs? How often do you use 4th and what kind of riding are you doing? I rarely use 4th on a track, just when I get off road a few times a year.

It may have been me both times posting 4th gear issues. I had some original questions and concerns and then from that and additional research I decided to attempt this repair myself. So I posted a different set of questions about this.

Anyway I pulled everything apart today, until I got to a point where I needed a crank puller that I didn’t have. (for the flywheel) Top end is off. I hope I can remember how to put that together….. So far that has been the only part that has scared me. I am unsure how to align the cam shafts and time it. I think I am going to replace piston and rings and have someone clean up the head (combustion chamber). It appears to be a bit crusty on the top. I may do the valves, don’t know why but since the combustion chamber seems a bit abused I assume the valves may need something too. Anyone have any comments on doing the lower crank bearing? Is it something that wears. I know on a two stroke it’s a good idea to replace the rod and bearing after so many hours or when the cases are apart.

Still haven’t even gotten into the gears yet. I see why it costs a grand to do a gear repair…

I just realized I didn’t really answer all of your questions. I ride MX tracks only. I race pretty consistently Vet Int... Since your from So Cal you should know the tracks I ride. I like the out door type tracks like Glen Helen, Cahuilla, I-5 and the like. At these tracks you get into 4th a lot. I cant say that 4th would be the primary gear however. 3rd would be the most used. When I ride the SX type tracks like Starwest, Ellsinore, Perris I doubt I get into 4th very much at all. But again I ride those tracks only occasionally. I had no warning signs. I was racing this Saturday and it kept feeling like I was missing a shift. I raced again Sunday and in practice I really noticed myself missing shifts and then started to pay attention. Went to a long straight and tested it and sure enough it would not stay in gear when in 4th,. However when in any other gear I felt absolutely nothing odd. I almost raced that day and figured I wouldn’t use 4th . Changed my mind in fear of doing major damage however..

How much do you want for them?

How about $250.00 that's less than 1/2 off

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