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buildabike

1998 yz400f build/restore

34 posts in this topic

I picked up a 1998 yz400f recently.  I was looking for a project bike to fix up and flip.  Well resell and hopefuly not actually flip but ya never know. This will be my 3rd bike rebuild.  Last winter I did a frame up on my beloved 1995 xr250r which I bought new.  I then tackled a crf230 that had melted down a piston.  Here is what it looked like when I picked it up.  Engine was totaly froze up but I thought I would take a gamble on it.

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Tore the bike down and found that the rod was froze to the crank.  Which of course trashed the pistion and cylinder as well.  There was a lot of metal floating around but after cleaning and inspection the trany looked to be in good shape.

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Edited by buildabike

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The trick to your idea is keeping your costs well in check.  YZ426's like the one I bought go for around $1100 and I'm not sure the 400 is worth any more.  

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After some research on TT decided to make the 400 into a 426.  I was going to have to replace the crank, rod, piston, and cylinder anyway and turned out that I could get the 426 parts cheaper.  Found a 426 crank on ebay but when it arrived turned out to be a yz125 crank instead.  Bummer.  But found another and was pleased to see it in great condition on arrival.

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I was disapointed that I could not just take the cylinder to my guy and get it bored.  This is my 1st experiance with a watercooled mx 4stroke bike.  But I did find a good deal on a new 426 jug and pistion kit.

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I have some concerns about getting my money back out of this project.  Looks like I will be into it for 1300 to 1500.  I might have to take a loss on it but I should get most back and putting these bikes together in my spare time had proven to be rather theraputic for me and I am learning a lot about how these things tick.  Got the crank in and lower end together.

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Got the pistion and cylinder in place.  So much bigger than the small bore play bikes that i have been dealing with.

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I have had a lot of luck using the nylon brushes to clean the motors up.  They come in 3 differnt grits.  They last longer than the wire brushes and put a decent shine on aluminum.

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The head cleaned up good.  I remember looking lustfuly at the pics of this motor in dirt bike magazine when this bike first came out.  The 5 valves looked so exotic to me.

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Trying to keep cost down so just used a rattle can on the frame.  Decided to spray it with aluminum instead of trying to match the Yamaha blue.

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One of the cam chain guides was on the verge of breaking.  I hope there arent a lot of those little suprises.

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Got the swingarm all polished up and attached.  I decided to buy a weighted flywheel for the bike.  It came with a large capacity tank, 18 inch rear wheel , and an overflow tank for the coolant.  When I got the weighted flywheel in I found that the one on the bike was actually heavier.  The numbers on the one on the bike indicated that it was from a 426 which are suppose to be lighter than the stock 400 flywheel.  So it looks like someone put a modified weighted 426 flywheel on the bike.  Should be a good woods bike when its done.  Thinking about hanging on to it for a while if I am able to handle the extra power.  Quite a step up from my old xr.

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One of the cam chain guides was on the verge of breaking.  I hope there arent a lot of those little suprises.

 

If you don't like surprises, do yourself a favor: Get a new OEM cam chain and throw your old one far away. 

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The old cam chain did look a lil suspect so I did buy a new OEM one.  I always am a bit nervouse when timing a bike.  This was my 1st double cam so it was bouble the nerves but it looks right.

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Got the swingarm all polished up and attached. I decided to buy a weighted flywheel for the bike. It came with a large capacity tank, 18 inch rear wheel , and an overflow tank for the coolant. When I got the weighted flywheel in I found that the one on the bike was actually heavier. The numbers on the one on the bike indicated that it was from a 426 which are suppose to be lighter than the stock 400 flywheel. So it looks like someone put a modified weighted 426 flywheel on the bike. Should be a good woods bike when its done. Thinking about hanging on to it for a while if I am able to handle the extra power. Quite a step up from my old xr.

Where did you find the flywheel weight? I've been searching high and low for one for my 426 and can't find anything....

The project is looking great by the way. I'm digging that silver frame.

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Where did you find the flywheel weight? I've been searching high and low for one for my 426 and can't find anything....

The project is looking great by the way. I'm digging that silver frame.

I still have the other weighted flywheel.  I put it on ebay but havent had any takers yet.  It's a 400 flywheel but should bolt right up on the 426.

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Making progress.  Got the shock cleaned up and back on.  Wish I could afford a revalve on the suspension.  Also tore the carb down for a good cleaning.  Was not able to to see any numbers on the jets.  Not sure how the jetting will be affected by going from the 400 to 426.  With a cleaned up air box and sub frame it's looking more like a bike.

 

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Here are a few pics of the weighted flywheel that I decided not to use.  I should have took some pics of the other wheel that is in the bike.  From the numbers it is from a 426 but it is actually a lil heavier than the wheel in the pics which is from a 400.  The wheel in the bike is missing the marks that show TDC which leads me to beleive that a stock 426 wheel has been modified.  It is curious.

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What a difference some fenders and wheels make.  Looks like the tripple clams came from a wr250.  I am thinking a 97 model from the numbers.  Now I am wondering if someone put the wr forks on too.  They did some aluminum welding to attach the number plate bracket and looks like a good job so someone along the way did some work on the bike.  Got the wireing cleaned up and on along with the radiators.  Cleaned up the protapers and squeezed on a new set of oary grips. 

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