yz 400 ?'s

[jmics19067]

can any one tell me the difference in engine components between 77-78 yz 400s and the 79 400?

everything appears to be similar in bore/stroke/ rod length ...external dimensions but yet the parts are different.crank pin different size ,crank webs and piston visually different with cutouts. Is the difference only in balancing on the components? My real question being can I stick a 78 yz 400 crank/rod/piston assembly inside a 79 case/cylinder?

 

[OnAnySunday]

>sigh< afraid the answer is, no.
From the sounds of things your in the same situation as i am.
I blew the top end of my '79 Yz400 and have been looking (off again / on again) for piston/ring set and rod kits for about 3 years now.
I dont remember exactly what the difference is, but i believe other than just the poting the bore/stroke and skirt length are different as well.
yea i know you can still get '77, '78 stuff but '79's are long gone.

check -w- speed and sport , or on e bay.

good luck Mr.Phelps, this tape will self destruct in 10 seconds.......... :worship:

 

[jmics19067]

ugh I was afraid of that hmm well back to the ole drawing board as they say

 

[OnAnySunday]

it might look grim, but dont give up the ship for good.
every once in a while ive seen piston / rings etc on e bay for sale.
trouble is i need a 3rd or 4th oversize.
(yea i blew it BAD!)
ive seen 1st and 2nds for sale, just not enough for my situation.
or ya could find a '78 engine that might fit???
or some other year??
Good luck to you.

 

[jmics19067]

Well I havent given up yet........... I will be just short of epoxying 10 weed whacker engines together before I do that ......

 

[VintageDirt]

Have you guys seen this place http://www.vintageyamaha.com/page10.html

 

[jmics19067]

thanks Vintage,


the 1980 IT 425 has the same bore as the 465's 85mm compared to the1979 400's 82mm bore
by just eyeballing my 400 piston against a 465 piston it appears the pin location is different,with the possibility of spacing the jug up to make up the difference. Now whether or not the 400's have enough liner to overbore that far is something I have to look into when I take a better look at everything.

FWIW the crank bearing/thrust washers and the piston bearing and retaining clips are common parts . The connecting rod length and the length of the crank pin are upto guessing at this point though

 

[Enduro_Nut]

yamatopdog.com
hometown.aol.com/vintageyz/index.prts.html

Try these guys out -
hope it helps

 

[ScottS]

If you can find 1st and 2nd over why not resleeve to original size ? then you would not need the 3rd or 4th over

Other option is to find a piston with the same pin height /diameter and resleeve to match that bore - maybe you will end uop with an oddball displacememnt but once you are over 350cc who cares, right ?

 

[2smoke]

My good friend still races his YZ400F 1979....there was a funny time at a grasstrack MX a couple of years back when they put him in the 4T class till we showed em the bike. He still flattracks it I watched him last year against 450's etc still managing mid pack finishes on the old beast. Point is he's been racing it solid for the last 3 years...he has to be getting piston's somewhere. If I can get onto him...(he goes Gold Prospecting out bush for long periods) Ill find out what he;s using and where he's been getting them.

Also look at DT400 pistons they were the same capacity ie 397cc....no?????...may just need a little shave off the skirt or something. Worth a look.