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Yamahondaha

WR400 Engine rebuild

13 posts in this topic

Let me first say that I really love this bike and I don't want a newer or bigger bike but I am to the point where I need to rebuild my 1999 WR400FL. I would like all the (friendly) advice I can get before I begin so if you can add your two cents please do... :applause:

I hear the small rod end is week but is there an after market fix? :banghead:

I have to chose between the nikosil plated cylinder or a cast iron re-sleeve. Has anyone out there used either one? I have heard that plating can ware off and send lots of metal filings into the motor. I have been told that the iron sleeve will out last the plating but it is heavier and less effective for cooling.

I have been told that the stainless steel valves are more reliable than Titanium and will most likely regrind them unless someone has better advice.

Will a stock auto decompression cam from a 426 or 450 fit the 400? I use the YZ exhaust timing so is there an auto decompression cam with the YZ timing?

Are the Flywheel weights different for different year 400's? Was the 98 heavier than the 99 or does the YZ have a lighter flywheel than the WR?

I got a 1998 WR400 motor off of Ebay for $600. Turned out the cylinder plating was worn through to the bare aluminum and it smoked like crazy.

My original plan was to use that motor while I rebuild the factory motor so I put my top end on the Ebay motor and got the bike up and running again.

I noticed after the first ride that the 98 motor does not rev out as quickly as my 99 motor even though the 98 motor was YZ timed and the 99 was WR timed, both had the gray wire cut and were using the same piston, cylinder and head.

I have a speedometer on the bike and they both seem to have the same transmission ratios but my 99 motor with the gray wire cut hit the rev limiter in less than 3 seconds into each gear, even without the YZ timing. The 98 motor will take 5 or more seconds before the RPM's "hit the wall".

It seems to me as if the 98 came with a heavier flywheel or the 99 came with a lighter one but they both look the same and have no added after market weight on them.

If there is some articles or other informational sources out there can you please point me in the right direction?... :lol:

Thanx

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I have had the cyclinder recoated it is harder than the iron sleeve as it is what the factory does in the begining with the iron sleeve you can have it rebored and honed next time and not have to worry about a large cost just about 40 buck if you bring them the cylinder than you have to buy the next size up piston

so if you plan on keeping it for a while it is a good option or you can buy a new cylinder for not much more than the coating coats i think it was 300 for the cylinder and like 245 for the coating out here where i am at

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The fix for the 400 rod bearing is to have a 426 rod/bearing pressed onto your 400 crank and then find a 426 cylinder. I know its not the answer you were hoping for, but it is an improvement on a few levels.

I would have the cylinder re-nik'd. Thats how Yamaha sent it out from the factory and I'm sure they would have gone with cheap iron plating if it were the better alternative.

You can get your cylinder punched, recoated and a piston/gasket kit for $350 shipped from Lukes Racing.

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The fix for the 400 rod bearing is to have a 426 rod/bearing pressed onto your 400 crank and then find a 426 cylinder. I know its not the answer you were hoping for, but it is an improvement on a few levels.

I would have the cylinder re-nik'd. Thats how Yamaha sent it out from the factory and I'm sure they would have gone with cheap iron plating if it were the better alternative.

You can get your cylinder punched, recoated and a piston/gasket kit for $350 shipped from Lukes Racing.

I have found a source on line that sells an OEM 99 WR400 cylinder for $250 I wonder if it is ready to role or if it still needs a hone? They have a piston for $80, rings for $20. That Luke's Racing package is looking good.

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The fix for the 400 rod bearing is to have a 426 rod/bearing pressed onto your 400 crank and then find a 426 cylinder. I know its not the answer you were hoping for, but it is an improvement on a few levels.

I would have the cylinder re-nik'd. Thats how Yamaha sent it out from the factory and I'm sure they would have gone with cheap iron plating if it were the better alternative.

You can get your cylinder punched, recoated and a piston/gasket kit for $350 shipped from Lukes Racing.

I want to keep the engine 400cc. My fear is that something else might fail at a quicker rate in the bottom end like the crank bearings. Besides, the bike is pretty frantic as it is. I am looking at ways to keep the rear wheel from breaking loose like a flywheel weight or something.

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I believe the 400 rod does tend to stretch over time.

You can get all your questions answered by contacting Rich at

Eric Gorr

I have called Eric and we talked for a few minutes about the best option for me, which turned out to be a re-sleeve. After talking to a neighbor who recommended a local guy.

I went with the local guy... sorry Eric.

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Hi, all.

I recently bought a '00 WR400 that will be needing a new piston/rings/rod/bearings.

(the cylinder looks ok, although it does have a scratch)

My question is (I haven't seen this covered elsewhere, sorry if I didn't search hard enough):

Do you recommend OEM or aftermarket parts? If aftermarket, any particular brand?

Anything else you suggest I should check/replace?

Crankshaft bearings? Any gears in the gearbox? (I heard of the problem with 3rd and 5th...)

Cheers,

PT

Yamahondaha,

I hope you don't mind jumping in here, but I think we can both benefit from it :applause:

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I've not done the mod yet, but "they" tell me that the 2003 exhaust cam (450) will give you auto decomp on a pre-03 WR. Also HOT CAMS does the same thing, but only for YZ timimg from what I've read.

Good Luck

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Hi, all.

I recently bought a '00 WR400 that will be needing a new piston/rings/rod/bearings.

(the cylinder looks ok, although it does have a scratch)

My question is (I haven't seen this covered elsewhere, sorry if I didn't search hard enough):

Do you recommend OEM or aftermarket parts? If aftermarket, any particular brand?

Anything else you suggest I should check/replace?

Crankshaft bearings? Any gears in the gearbox? (I heard of the problem with 3rd and 5th...)

Cheers,

PT

Yamahondaha,

I hope you don't mind jumping in here, but I think we can both benefit from it :bonk:

I don't mind.

The Cam chain is something to replace any time you tear into your motor. I would check the valve clearance before you tear it down and rebuild the head. I would replace everything you mentioned with the 426 parts. I was told by some very knowledgeable motor re-builders that you can bolt on the 426 crank,rod,piston and cylinder to a 400 motor (and 400 head with SS valves)with the drive gears from the 426 crank (the crank spline is different but the gear teeth are the same) and get the most reliable Yamaha super thumper motor ever made. I am still rebuilding my 400 with 400 parts and spent $1000 on it so I won't be testing the 426 idea for a while. I also purchased a 2006 Husqvarna TE510 with a plate for street use so I may sell the 99 Wr 400 this summer. I just sold my XR400 (also street plated) and someone is coming tonight to buy my 99 YZ400F, Im going to have to change my TT ID. Huskyha? Yamahuskyha?

:thumbsup:

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I don't mind.

The Cam chain is something to replace any time you tear into your motor. I would check the valve clearance before you tear it down and rebuild the head. I would replace everything you mentioned with the 426 parts. I was told by some very knowledgeable motor re-builders that you can bolt on the 426 crank,rod,piston and cylinder to a 400 motor (and 400 head with SS valves)with the drive gears from the 426 crank (the crank spline is different but the gear teeth are the same) and get the most reliable Yamaha super thumper motor ever made. I am still rebuilding my 400 with 400 parts and spent $1000 on it so I won't be testing the 426 idea for a while. I also purchased a 2006 Husqvarna TE510 with a plate for street use so I may sell the 99 Wr 400 this summer. I just sold my XR400 (also street plated) and someone is coming tonight to buy my 99 YZ400F, Im going to have to change my TT ID. Huskyha? Yamahuskyha?

:bonk:

Exactly what I did..... I broke one of my intake valves on my '99 400 and replaced everything with 426 parts. The valve wiped out the cylinder head which I replaced (400 head), I also replaced with all SS valves. Piston was wiped so I replaced both the cylinder and the piston with the 426 as well as the crankshaft. You would be remiss in not replacing the crank and the cam chain because you can't replace just the gear. The intake cam was bent so I went ahead and replaced both cams from Hotcams. I went with the regular exhaust cam (no auto decomp) and saved about half the price.

All said and done I'll have $1600 in the rebuild. Labor was avoided by doing it myself.

:thumbsup:

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Great thread!! I just happen to have my 400 apart and I’m contemplating what to do. I think I can get away with just new rings, valves and some work on the valve seats.

However, I sure would like a little more horsepower and the 426 parts sound appealing (possibly even the 444?).

My question is this; if I want to go to 426 cylinder and piston, is it necessary to replace the 400 connecting rod with a 426 rod? Does that require the 426 crankshaft as well? I’m a little lost here. Is the 400 piston wrist pin a different size then the 426 wrist pin?

Also, are WR & YZ parts interchangeable?

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I was told that the 426 rod will fit onto the 400 crank but it was suggested that I take a close look at the 4oo crank for wear. I hope I don't step on anyone's toes by posting this number.

Direct Phone Line for Eric Gorr

Call 1-630-289-5645

I'll be answering the tech line from 7am (U.S. CST) to 10pm Monday-Friday.

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