YZ80 Top End Help

[RazBarlow]

OK guys,
I have a 96' YZ80 that I have just opened up the top end. I would like to get the piston dimension wear limits. Does anyone have a manual that shows the specs ? I have .004 in. difference between the bore and the piston. I think this is about max tolerance.
The bore is chrome or nikasel so I can't bore it larger. What do you guys do in this situation ? Do they make oversized rings for a stock piston ? Is that the route that you go, just buy a new piston and rings ?
Help me out here, as I am used to cylinders that can be bored.
The coating looks good as it isn't worn through into the aluminum.
Thanks so much,
Raz
Feel free to email me at dswebber@netins.net.

 

[Martin Cole]

A new piston kit may reduce the tolerance to within the specification. See if you can borrow one from a dealer/fellow competitor and measure the piston clearance and the ring gap. If it is still too much I'd suggest getting the barrel rebored and re-plated to take a larger piston from a YZ85. I can't give you the correct clearances because I don't have a manual. If you go down the 85cc route it is also likely you'll need to have the combustion chamber in the cylinder head enlarged to match the diameter of the bore. It's not a big job for anyone with a lathe.
If you don't fancy enlarging the capacity the other option is just to have the barrel re-plated to bring it back to standard bore size.
MC

 

[WaltCMoto]

Ive got the manual from a 2000 model YZ80.
The pistons specs are 1.8487-1.8493
The bore specs are 1.8504-1.8509
It says to measure the piston 3/4" up from bottom.
It also says standard clearance is .0016-.0018 and max clearance is .004
I beleive the piston is the same as yours, check an application chart to see if they are the same part number to be sure.

 

[Jasle]

cheapest way to go if you are out of spec is to just have your cylinder replated. you send your new piston in with he cylidner and the strip the old coating and put new in. it will tighten up the clearance problem.

 

[RazBarlow]

Where do you get them replated and how much does it run ?
Thanks,
Raz

 

[Jasle]

there are several places. US chrome and steel and Millenium are the two biggies that come to mind. About $150 to strip and recoat your cylinder. if there are huge gouges in the wall its about $50 more to weld the gouges up and re-bore it then plate it.
I've used Millenium a few times with good results. Others have told me they didn't have good luck. Eric Gorr from this site reccomends US chrome and steel. I just recently checked their prices and they are within a few bucks of Millenium. There was another guy with a new type coating advertising in the mags that has similar pricing but I forgot his name.

 

[RazBarlow]

Got the top end all put together. Now I would like to know the coolant capacity. Would anyone be so kind as to help me out with this ?
Thanks,
Raz

 

[WaltCMoto]

Radiator capacity is listed @ .3 US quart. Probley mix up a half gallon and put the extra in the car.

 

[RazBarlow]

Do you mean .3 US gallon ? .3 quart would only be 9.5 oz., I would think that just the hoses would hold more than that.
Thanks,
Raz

 

[RazBarlow]

I actually came up with about 18 oz. until it was full in the radiator, is this about right ? That is about twice as much as the book recommended.
Thanks,
Raz

 

[BDAY]

i have an old one that holds half a gatorade bottle.