Author Topic: '79 IT/YZ 400 to 425  (Read 1158 times)

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Offline Devondan

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'79 IT/YZ 400 to 425
« on: May 04, 2013, 09:06:52 PM »
79 pistons are getting hard to find, I have a mate with a 79 400 which is on its last oversize.  Am I right in thinking that you can bore out to 85mm and fit a 77/78 piston to make a 425?  Any other mods that need to made like barrel gasket/spacer?

Dan
IT  400D - Trail riding
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Offline fatterhatter

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Re: '79 IT/YZ 400 to 425
« Reply #1 on: May 04, 2013, 10:12:15 PM »

its the same stroke as the 425 / 465 / 490 - the bottom end remained the same imho.

boring out the steel liner might make it prone to hot spots and deformation of the

barrel - best thing is to get a 425 / 465 / 490 barrel  .....if it doesnt work you can

still sell it on - whilst - overboring might wreck the barrel as well as losing cost for a rebore and

 piston - just my opinion ;)

i've not heard of the 400 taking a 425 overbore......




Offline 2fITy.J

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Re: '79 IT/YZ 400 to 425
« Reply #2 on: May 04, 2013, 10:19:26 PM »
There's something unique about the 425 barrel...from memory the stud placement differs by a few millimetres. They are not square to each other.



Cheers,
Chris.
A bike in the bush is worth two in the shed!

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Offline Martin I Henry

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Re: '79 IT/YZ 400 to 425
« Reply #3 on: May 04, 2013, 11:13:11 PM »
Mark started this topic back in the good old days, not sure if it may help or hinder !

http://www.yamahait.com.au/forum/index.php/topic,50.0.html


Dave R.

Offline Devondan

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Re: '79 IT/YZ 400 to 425
« Reply #4 on: May 04, 2013, 11:16:42 PM »
There's a number of threads out there, trouble is some have conflicting info, particularly about the interchangeability of the 400/425 barrel

http://www.thumpertalk.com/topic/427307-vintage-motor-mods-yz400/
IT  400D - Trail riding
74 Montesa Cappra - Racing
YZ250 H - Racing
Norton ES2 500 trials
Norton 250 Jubilee - Road
Norton 350 Navigator (in boxes)
Norton 350 Single M50 (in boxes)