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UK mid 1975 XS650 motors
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xskev
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Joined: Jun 15, 2009
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Location: Scotland

PostPosted: November 1, 2009, 3:26 am    Post subject: UK mid 1975 XS650 motors

I have an 1975 UK XS650.it turns out that midway during 1975 on the UK motors Yamaha went to 533 connecting rods in their 447 motors then back to 447 connecting rods 1976 onwards.the 533 connecting rods are longer so different pistons were used the reason being they were supposed to hold TDC longer.i have got the motor stripped down as the previous owner didn't build it correctly.i need to get hold of some 1st oversize piston rings for the pistons but with the pistons being different than the norm as they are 256 pistons the piston connecting pin sits higher up in the piston they use a 1.5mm top ring also and i can only find rings for the standard piston from 650Central not 1st oversize.Speed and Sport had bought a load of XS650 parts so i will try them along with a company called Hastings who make pistons and rings.i would preferably like to go 2nd oversize if poss.anyone else had this problem or know of a supplier?.
Kev.

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despecial
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Joined: Sep 26, 2009
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PostPosted: November 1, 2009, 7:21 am    Post subject: Re: UK mid 1975 XS650 motors

- did i understand this right?

- you have a '75 xs which happened to be produced in both 447 and 533 versions
- but it has 256 pistons in it?
- so you have the 533 version thats had 256 pistons put into it?
...theyre both short skirt low crown - putting 256 into a 447 would lower the compression heaps...

- i have to ask myself why has this been done, the 256 conrod is 4 mm shorter than a 533 (6mm longer than a 447) and has a 22mm wristpin...have the conrods been swapped too?-number is cast on the side-if so the crank will be 256 also otherwise there would be problems with bottom end oil delivery...

- have a look at auto rings-i know the honda acura has the same rings as 447/533 with a 75/1.2-1.5-2.8, but this wont help you as the extra 2nd rings arent the right shape, but other hondas or toyotas too may use 75x1.5 top rings

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xskev
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Joined: Jun 15, 2009
Posts: 28
Location: Scotland

PostPosted: November 1, 2009, 9:29 am    Post subject: Re: UK mid 1975 XS650 motors

t
despecial wrote:
- did i understand this right?

- you have a '75 xs which happened to be produced in both 447 and 533 versions
- but it has 256 pistons in it?
- so you have the 533 version thats had 256 pistons put into it?
...theyre both short skirt low crown - putting 256 into a 447 would lower the compression heaps...

- i have to ask myself why has this been done, the 256 conrod is 4 mm shorter than a 533 (6mm longer than a 447) and has a 22mm wristpin...have the conrods been swapped too?-number is cast on the side-if so the crank will be 256 also otherwise there would be problems with bottom end oil delivery...

- have a look at auto rings-i know the honda acura has the same rings as 447/533 with a 75/1.2-1.5-2.8, but this wont help you as the extra 2nd rings arent the right shape, but other hondas or toyotas too may use 75x1.5 top rings

The connecting rods are 533's the engine number starts with 447 and the pistons take the 1.5mm top ring.

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