Wr 400 Blues

[Frostbite]

oh yes the bike was a little noisy compared to my last wr 400 ,also 2000 model it sounded to me like mabee the timing chain or in that area but more at idle when warm but its done that for two years since ive had it .my son reckoned it never made any strange noise when it siezed on him thanks for your help ,,,stu

In your first post you mentioned that the engine died, and here you mention that the engine seized. Knowing what happened when it first stopped running would help. did the engine lock completely while he was riding - jam solid and lock the rear wheel, or did it lose power very quickly, like standing on the rear brake, or did it stall?

[Frostbite]

hey guys am going to try what math said today, i will let u know how things go. has anybody got any ideas on why the timing marks do not line up with the top of the head? tdc lines up on fly

I don’t think I’ve ever seen the timing marks on a WR line up perfectly. Are the marks significantly off, or just not quite perfectly level? As the timing chain stretches the cam timing will change and the cam sprocket marks may not be perfectly parallel with the head.

[stumac31]

thanks guys ive been busy at work this week so nothins been done yet ,frostbite when the bike first stopped the engine died like a sieze up but my son was riding slow the rear wheel didnt lock up when it done it with me the same thing the engine stopped but not any noises it was just llike a tighten up not a clunk or anything , thats good about the oil in the case .i

[stumac31]

i have a few day off this week so am taking the two side casings off to check things in there ,,thanks for the help guys ill keep yous posted

[stumac31]

guys i took the side covers of today all i could find was very small shavings in the oil and on the oil filter no big chunks ,how easy is it to pull the head and barrel of ??? i think i might look there next..thanks stu

[matt4x4]

Stu,

I just thought I'd pass this along since I read it in another forum, someone was having the exact problems you're describing (piston locks up TDC),

Turns out their lower crank bearing was worn, somewhere along the line, the rollers stopped rolling, it started to wear them flat, once some had a flat spot, if they spun the wrong way, they actually jammed and locked the rod/crank and the motor had to be rotated in reverse to undo the locking effect.

I hope this is not your case, once you have the top end off, you should be able to determine if your lower bearing is punched before splitting the case.

Keeping my fingers crossed for ya that this isn't the case.

[Math]

I'm at work at the moment but I will try to come back to you tonight to give some advises to pull the head off. You can put the covers you've taken off at their place except for the magneto cover... leave it unmounted for the rest of the surgery.

[stumac31]

thanks matt sounds very similar i think it could be that ill find out soon.

[stumac31]

thanks math, there is a very helpfull post on this site ,a guy had stripped down his yz 250 and posted a step by step picture account it was very helpfull indeed,i checked the valve clearances they seem to be very tight could this cause a problem ?thanks.. stu,,,,,,

[matt4x4]

Tight valves usually cause starting/idling issues, and can grenade if too tight and/or a stretched timing chain or you're running your rpms up.

Definitely reshim those to spec. but before going to that length, I'd look for the lockup problem, only because reshimming may be a waste if you've got a bent valve or something else wrong with the top end like chipped/dinged piston.

I also feel that at this point your best bet is to drain the rad fluid out and disassemble the top end including cylinder.

Check the lower rod free play (up/down) carefully and in many different positions as well, I'd flush the lower bearing with plenty of degreaser or WD40 to wash out any oils in there so you can feel the real play on it, not the dampened play you would get with a nice coat of oil on everything. Feel for roughness while turning the crank/rod assembly.

[stumac31]

thanks matt im going to tackle the top end on monday the valves were .15 inlet .18 ex.stu

[stumac31]

guys i took the head ,and cylinder off this morning the piston is in good nik and no scratches on the bore,i think it may be the bigend bearing as there is a little movement on the bearing, im not sure how much it should move more sideways than up and down,i did notice on the crank at tdc there is a wear mark i dont know if this is normal,i think not! when i get my cammera working ill post pictures thanks ,,,,stu ,,,,

[Math]

You can check with the specs but sideways loose is quite normal. Try to pull and push and pull when at tdc and see. From what I've been told previously by friends who are good mechanics, there should be no slack at all.

[stumac31]

math when i pull the piston up and down there is a slight movement with a little clunk ,goin to the bike shop tommorro ill let u know what he comes up with the marks on the conrod are normal thank stu,,,,,

[stumac31]

hey guys just a short note ,i had a mechanic split the cases at long last not good the crank had siezed the big end bearing was going but not gone yet after closer inspection the bore was scratched piston the same cams worn chain stuffed just a big mess. i hope this will help anyone else with the same symtoms and also seems that i was using the wrong oil (fully synthetic)no good for wr,s major rebiuld coming up ,,thanks guys for all the comments keep it up

[wartsnuff]

hey guys just a short note ,i had a mechanic split the cases at long last not good the crank had siezed the big end bearing was going but not gone yet after closer inspection the bore was scratched piston the same cams worn chain stuffed just a big mess. i hope this will help anyone else with the same symtoms and also seems that i was using the wrong oil (fully synthetic)no good for wr,s major rebiuld coming up ,,thanks guys for all the comments keep it up

how many k on the bike again?

i did my first 3 oil changes with mineral oil...

then i switched to synthetic.. mobile 1 5w50 racing oil...

considering 90+ % of synthetic oil is base oil/mineral oil.. not sure i agree with the oil.

but thats just my 02 cents ?

sorry the bike is in piece's hope you are riding soon

cheers

Warts

[swede426]

I like the blend mineral/synth oil, best from both worlds.

Synthetic= not so sensitive to temp changes (more stable)

Mineral= sticks better to surfaces and does'nt flush away as easy as synthetic.

[stumac31]

gday guys .the bike has 5000 ks if you check the wr specs in the manual it does tell you what oil yamaha recomend (yamalube mineral15w50non friction modified ) i think my bike has ran synthetic since new acording to the guy i bought it from im not sure why synthetic shouldnt be used maybe some one can tell us on here,i used mobile 1 fully synth 15w50(i thought the best),thanks guy,,,,,stu

[stumac31]

oh just another little question does a yz 426 crank fit a wr 400 2000 i think i read it here but i cant find it again(yz crank is supposed to a lot sronger) thanks again guys stu

[R_Little]

oh just another little question does a yz 426 crank fit a wr 400 2000 i think i read it here but i cant find it again(yz crank is supposed to a lot sronger) thanks again guys stu

The 426 crank is the same except that it has a splined rather than keyed counterbalancer drive. To use a 426 crank then you need a 426 counterbalancer sprocket also.

The 426 rod has a larger small end bearing which is also good but then you need either a custom 400 piston with a larger wrist pin or a 426 cyl and piston.

since you piston and cyl is stuffed I'd go with a 426 rod piston and cyl...then you'll have a 426