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bakeyz426f

yz426f help blown engine

63 posts in this topic

i just bought a 2002 yamaha yz426f and the motor locked up on me. i took it to a dealer and they said the timming skipped and a valve broke and ruied the piston and damaged the crankcase. wondering if this is worth fixing. it was bought new in 2005 so it hasnt been rode to long. at the dealer they said these bikes have a poorly built motor is this true. is this bike not worth fixing and do they have to be rebuilt a lot. a could not find an engine for sale any where. also wodering if a wr426f motor would fit on my yz426f. i bought it for $2100 and only rode it twice before it locked up. it was a huge dissapointment for me and want to get back out ridding. any advice would be much appreciated. the dealer told me they wanted about $5000 to fix and i felt like crying like a baby.

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Ummm. You need a new dealer. That one is ripping you off.

The Yamaha YZ400/426/450 engines are awesome. They are not a problem engine by any means. They are easy to work on (if you just have some mechanical skills and a descent set of tools). You just need to get the shop manual for it. Check the stickies at the top of the forum for links to the shop manuals.

Parts are readily available for these bikes. Four strokes can be a bit pricey to fix (when compared to a two stroke), but the Yamaha engines are very robust and powerful.

Get it fixed (do it yourself and save $$$$$), do the recommended maintenance, and you will have an awesome ride.

There are a lot guys on this site who have rebuilt dozens of engines and they can provide you with lots of help as needed. You only need to ask.

If you can post some pics of the carnage, it could also help determine what went wrong and what you need to replace.

Don't fret, it is fixable.

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And yes the wr engine will fit. Dont go back to that dealer either. I work at a dealer/repair shop and I know what it cost to fix things and 5000 is not even close. Even if you bought all new parts and paid a mechanic to fix it, it would be way under that. Look around on ebay and see what you can find for it. also its a good time to look at the bottom end to!

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do you know what tools i would need and i have a service manual that shows how to tear the bike down. do u think i would be better off repairing or buying another bike for like 1500 and using it as is or swaping out the motors. i have car mechanic that would probloy help me. i should of had him tear it down and tell me it was screwed instead of paying 300 bucks. i heard the crank case is hard to work on and thats what would cost the most is this true.

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It's going to be tough for you to accept, but the dealer is 180 degrees wrong. The YZF line is one of the most reliable, well built engines that exist, and they have a stellar record. They do not do well with neglect of regular maintenance, however, and I suspect you have a high hour engine with fewer than the needed numbers of oil changes and the original cam chain still in place after 4 years (since '05). It's unlikely, but there could be legal recourse against the owner if he factually and willfully misrepresented what you were getting.

Either way, doing the work mostly yourself, you could be looking at $2000 in parts. The bike is worth about $1700. Parting out the undamaged components, wheel set, suspension, etc., may get you some relief, and may be the wisest thing financially.

It's a great bike when it's all together, but so is another one that isn't broke for $1700.

I feel for you.

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i think its worth fixing because it looks almost new and it rode like a beast for the 2 rides i enjoyed before she locked up. it was faster than all of the 250 2 strokes a was racing around with. but do you think i woud be better off findig a new motor than repairing or would it be to risky you think.

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Do you have any tools as far as (Example): torque wrenches, feeler gauges, and various specialty tools for bikes? Also can you find anyone you know that works at a parts store to get discounts? I just rebuilt my '00 426 for about 650 bucks. thats from bottom to top due to a bad bottom rod bearing. Got a crank off ebay for 200.00 and everything else new from the shop with my discount. complete overhaul :thumbsup:

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no all i have is wrenches and sockets but my friend may let me use his shop. i been wanting to start tearing these things down. where can i buy tools

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what do think broke in the crank case i forget what the dealer said i havent picked it back up yet. there giving it back in pieces.

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when you are repairing your bike the service manual will tell you what tools you will need as you are going.

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do you think i would be getting in over my head even with manuals and maybe a little help from a mechnic and few people who have worked on bikes.

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no. its really simple if you take your time and do a little research as you are going. if you run into any bumps take a step back to re think things and get on here and simply ask. someone will know on here. trust me.

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ill try to get some pictures up of the engine in the next day or two and mabye you can help out along the repairs thanks for your help and advice really apreciate it.

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You can get a good torque wrench at Sears (Craftsman). Wait until they have a tool sale though or find a coupon online and print it out.

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Get your motor back from that dealer and never so much as call them for a spark plug again. $300 is a bit much for a tear down and inspect. a fair mechanic could pull the motor from the frame and completely disassemble it in under 2hrs. The fact that they said they are bad motors is another sign these guys should probably stick to working on Vespas.

I wouldn't buy a used motor unless you know the history 100%, you could end up right back in the same boat as you are now with a even lighter wallet.

Depending on what is truely wrong with the motor will help you decide if you should fix it or part it out.

You can do the work yourself, however I would hope that you have a fair amount of mechanical ability so you are able to get it done right.

Good luck.

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The bottom end may be gone due to the collision of the valve and piston - that is the usual outcome - so maybe they said crank/bottom end but didn't mean crank case.

Likely - what you'll need is a crank/bearings, piston, valves, maybe some head work and hopefully only a light honing of the piston.

You really don't need specialty tools - do some reading on here and ask questions as you go.

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The bottom end may be gone due to the collision of the valve and piston -
This may be true even when there is no obvious evidence of it, such as a bent rod, or roughness in the rod bearing. Having the rod bring the entire engine to an abrupt halt can cause the rollers in the rod bearing to "stamp" grooves into the crank pin. Even if these are not detectable without pulling the crank apart, if they exist, they will work the same way a small chunk of missing asphalt turns into a pot hole later. Be very discerning when you check the rod bearing.

BTW, the crank will be heat discolored around the crank pin. That's normal unless you see black.

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