Wanted: 1979 YZ 400 f piston and rings

[Yamahaha]

Need some help guys, following a engine malfunction at ravenswood viper on Sunday my YZ is in need of a top end rebuild. I need a 1st or 2nd oversize piston kit, the bike is still a virgin bore amazingly after all these years. They appear to be very scarce.. I can get a 426 OW kit but it means boring the standard barrel to death which I am not particularly keen to do.

Any leads or ideas would be greatly appreciated. MARK VIPER 73

[motomaniac]

only old stock , because they are an odd size nobody does aftermarket , there were some on ebay us recently .

where can you get an ow kit ? how much?

[Yamahaha]

I'm guessing you found the ow kit Brent, cheers

[motomaniac]

this will work if you dont want to go to 85mm bore ,the only difference is the piston has ports on the inletside instead of a cut away.
http://www.ebay.com/itm/1979-YAMAHA-IT400-1ST-OS-0-25-PISTON-PN-2X8-11635-00-00-/180533312816?hash=item2a089fbd30&item=180533312816&pt=Motorcycles_Parts_Accessories&vxp=mtr

[Billet YZ]

Hi Mark,
            what is the actual bore size you will need. I have a piston to suit 82mm bore if that helps. Peter.

[motomaniac]

Hi Mark,
            what is the actual bore size you will need. I have a piston to suit 82mm bore if that helps. Peter.

yer they are 82 mm , only 79 yz and it 400's

[Yamahaha]

Yeah 82 Pete, is it 82 exact or .25 or .50 etc bigger than 82? It was standard but now needs to be first maybe 2nd over

[Billet YZ]

82.00 mm standard bore size. Let me know if it helps.

[JohnnyO]

The 426 kit just uses the YZ400 D/E model piston. You can bore the F model out and use those pistons, it was a popular mod in the day.

[Yamahaha]

Does anyone know if using the 79 it 400 window style piston or the earlier 77-78 piston affect performance or port timing?? What a bugger of a model bike...

[motomaniac]

The 426 kit just uses the YZ400 D/E model piston. You can bore the F model out and use those pistons, it was a popular mod in the day.

no it doesn't . It is an 85mm bore but not the same piston. I bought Landmans spare OW stuff after he'd finished with the F.

[motomaniac]

Does anyone know if using the 79 it 400 window style piston or the earlier 77-78 piston affect performance or port timing?? What a bugger of a model bike...

The 79 IT is the same in every dimension except for the intake side. it will make the bike a bit less explosive like an IT and will also minimise the famous Yamaha rattle . It was a common swap back in the day .There is an article on a MX400B  with this swap in an early ADB .
The earlier 77/78   85 bore x 70 stroke piston will make your bike run like a gutless 250.
Its a great bike .You just have to get to know them.

[JohnnyO]

The 426 kit just uses the YZ400 D/E model piston. You can bore the F model out and use those pistons, it was a popular mod in the day.

no it doesn't . It is an 85mm bore but not the same piston. I bought Landmans spare OW stuff after he'd finished with the F.

What i'm saying is you can use the D/E YZ400 piston in the F, Gaythorne Yamaha ran them in Andrew Bailey's YZ400F in '79... Ask him

[D project]

Need some help guys, following a engine malfunction at ravenswood viper on Sunday my YZ is in need of a top end rebuild. I need a 1st or 2nd oversize piston kit, the bike is still a virgin bore amazingly after all these years. They appear to be very scarce.. I can get a 426 OW kit but it means boring the standard barrel to death which I am not particularly keen to do.

Any leads or ideas would be greatly appreciated. MARK VIPER 73
Told you someone would be able to help you out

[yamatragic]

 

 

  :'(