YZ490 Piston

[yamaico]

Can anyone tell me what the difference is between early and late model YZ490 pistons? The part numbers are different but the bore size is the same. Is it windows vs cutaway in the back, gudgeon pin height, gudgeon pin diameter, ring land positions?
Thanks,
Pete.

[hotdog1975]

IT pistons have the window/port in them YZ pistons have the cutaway.

Early YZ490's were side port & later models centre port, but I am unsure if the ring locating pins changed position because of this..?? someone else can hopfully clear this up.

gudgeon pin height, gudgeon pin diameter - I'm pretty sure these did'nt change.

[Viper666]

I always check wiseco because they just go by years where as yamaha may very well have different part number for different model even if the same piston suit. An obvious one might be they tried just one ring on a model then changed again.
YZ125 perfect example. 1976 to 1982 all can use the same piston kits but yamaha list about 4 different types depending on the model. Same with conrod kits. Yz125 & DT175, IT175 all use the same kit (Year depending) but list 3 different kits.

Wiseco says they are different, look at the ring gap. It may be that it will foul on a port. The cranks are the same, they all use a 465 conrod so I would say, as above, ring end fouling on a port or port timing. They use a different base gasket so that suggest the porting is different.

Viper666




YZ490 1982-83 87 87.00 478M08700 $199.46 3425TD S277 W4055 B1014
x 87.50 478M08750 3445TD 1983 $18.09
82 88.00 478M08800 3465TD CW18 $40.15
88.50 478M08850 $219.42 3484TD
89.00 478M08900 3504TD

YZ490 1984-90 87 87.00 PK1817 $249.82 546M08700 $189.57 3425TD S277 W5286 B1014
Pro-LiteTM x 87.50 PK1818 546M08750 3445TD $40.15 $18.09
WR500 1991-93 82 88.00 PK1819 546M08800 3465TD CW18
Pro-LiteTM 88.50 PK1820 $268.79 546M08850 $208.54 3484TD
89.00 PK1821 546M08900 3504TD

[2 shocks]

Hey Neale, you know they're a piece of crap, buy yourself a 490 Maico 


Mr Maico #54

[lms6201]

for center port i think the stop pins are in slightly different locations , only a few mm ,as the cylinder has a different porting pattern ,wiesco make the prolite for the centerport ,i don,t know what the diff it is ,mabey as the name suggest,s , all other dimensions are the same  they use the same rings , pin ect , it same as yz 

[yamaico]

Thanks for the help everyone. I think I will just source an '82 - '83 piston rather than take the chance. Either that or just throw the piece of crap away and get a 490 Maico.

[jimg1au]

hi
checked usa yamaha parts list against my yammaha zedder program looks like 1983/84 are only interchangable with themselves.
checked usa ebay the pistons for sale state the same 1984 to 1990wr500 the same but 1983/84 different.also wisco kits same 1984/90
and 1983/84 different part nos.yz and it use the same piston in wiseco
check this out

http://motors.shop.ebay.com/i.html?_nkw=yz+490+piston&_sacat=&_trksid=p4506.m270.l1313&_sop=10&_odkw=klx&_osacat=0

[yamaico]

Thanks Jim,
I had an opportunity to buy later model pistons at the right price, but I'll just stick with the correct model, rather than take the chance,
Pete.

[jimg1au]

pete
its proberbly just pin placement if you can get both then you can see what is needed to convert the later piston
just a thought

[EML]

On another subject, does anyone have an exploded view of a GT80 crankcases from a workshop manual so I can get my little booger bake together correctly and any hints/tips to make it all go well-there are always little tips that you pick up and I don't want to find out later that "you shoulda done that before you did this"