OzVMX Forum
Marketplace => Wanted => Topic started by: Yamahaha on October 23, 2012, 12:37:22 pm
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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
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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?
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I'm guessing you found the ow kit Brent, cheers
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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
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Hi Mark,
what is the actual bore size you will need. I have a piston to suit 82mm bore if that helps. Peter.
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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
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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
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82.00 mm standard bore size. Let me know if it helps.
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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.
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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...
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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.
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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.
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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
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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 ;D
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??? ??? ??? ??? ???
(http://i570.photobucket.com/albums/ss141/vmx-photo/IMG_0253.jpg)
:o :o :o :o :o :o :'(
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Yeah thanks Mark!!!! Didn't happen to get a shot of the 4th gear endo off the ski jump onto the main straight by chance? From what people told me it was quite impressive. I just remember my bum being where my head should of been!! ;D
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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
wonder how that worked out for him? I used one one afternoon of practice thinking that it would be better than using up my OW pistons and it was crap, put the OW back in before the next race.F models have 5mm longer stroke and a 7.5mm longer rod. If the bore size of the piston was all that mattered yamaha would have used the old D/E pistons in the IT425G and YZ465's,they dont.