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How far can you bore a TY175


jc2
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Hi , Ive got one with what looks like a yam mono 250 piston in it (69mm)with no spacer.

you can go as far as 70mm twinshock piston but it will need work to the gudgeon pin and skirt/barrel spacer to achieve port timing, and if you like your bike get a genuine yamaha piston even second hand with new rings and have it bored to suit.

plenty of pistons on US ebay and rings seem to come up regularly on UK ebay

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HI, so does the mono piston fit without modifications apart from the big bore ? if so this seems an easy way to get to 200cc as you could fit a mono piston plus 1mm to get to 200 ? or is it easier to fit the twinshock 70mm piston, dont think it would be difficult to make a spacer plate to raise cylinder to suit taller piston, might be a little trickier bushing gudgeon pin hole in piston to suit 175 little end (or am I wrong ?)

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I dont think your getting anywhere near 200cc with the mono piston (will have to look up the pie formula to be exact}and i havnt investigated the skirt area yet but theres definately no spacer. A well respected local rebore/engineering boffin who did quite a few in the day explained that the skirt on the twinshock piston did require a bit of work and the gudgeon pin was bushed to accomodate the difference in pin diameters.

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I think you will find the OD of the standard sleeve prevents going above 70mm bore (it sounded to me like you were asking about boring the standard sleeve bigger).

Bigger bores than 70mm are possible but only with a bigger OD resleeve and the maximum OD of the sleeve is limited by the location of the cylinder studs.

My TY175 is 72.5mm (bigger sleeve fitted) and the sleeve is very thin.

If money is no object then 72.5mm bore is possible but a 70mm bore would be much less labour cost.

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I've had a look about and the sleeve seems easy to get hold of.

This one here

The piston seems a bit harder, I can't find anyone who does a piston that big for a DT or WR200. I have found some big pistons for Yamaha Blaster quads which I believe is the same engine as a DT/WR but with an aircooled top end.

Not sure is these will work 72.5mm and 72mm Not sure on the pin size though?

Any tips?

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The 72mm and 72.5mm piston kits for the Blaster look very much like what went into my engine but I can't be sure they are the same. My piston uses Wiseco rings also. The pin size looks right in the photos, but if you have a doubt, why not just ask the seller what size the pin is? - and check the other important aspects of a piston swap like ring location pin positions, height from gudgeon pin to top edge and gudgeon pin to rear edge of skirt.

Beware while those piston kits and the sleeve look well priced, the main cost components in the job will be the welding and machining.

Cylinder head - weld up head nut holes and redrill to 8mm - machine head surface flat - machine combustion chamber to suit bore diameter - machine combustion chamber to provide correct squish and correct compression ratio. Make custom head gasket to suit bigger diameter bore.

Make or find longer cylinder studs to enable use of plain hex cylinder head nuts. My studs and nuts are from a Maico MX engine.

Machine throat of crankcases to suit OD of bigger sleeve (requires complete disassembly of motor)

Machine out old sleeve and prepare cylinder for new sleeve

Cut port holes (undersize)in GS1000 sleeve

Machine GS1000 sleeve OD to provide interference fit in cylinder

Fit sleeve to cylinder

Take ports out to match cylinder with porting tools

Bore sleeve to suit piston

Make custom cylinder base gasket

Other possible pistons to consider are KDX220 and TY250 twinshock. Don't know much about the KDX220 but the TY250 piston requires the gudgeon pin holes to be bushed smaller but being only 70mm will have a far less risky sleeve thickness than mine.

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On the same theme...

Saw a ty 175 that had been beefed up to 239 cc.. It did have a French " Rayner " barrel and head though.

Everything else pretty original although the black rims did look a little odd....

Handy little bike....

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Early DT175 motor is the same cylinder stud arrangement as TY175 motor. Late model DT175 has different cylinder stud arrangement but I have not yet measured up how big a sleeve can be fitted.

Rayer big bore cylinder photos I have seen look like a late model DT175 cylinder but modified to suit the TY175/early DT175 stud pattern.

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Yes I was only look at some pictures of the Rayer conversion earlier and noticed the DT head. Maybe using the whole DT engine would make more sense rather than having to modifiy the TY crankcase to suit. I'll have a look at the gear ratios and see who different they are.

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on this subject has anyone bought a 200 conversion from majesty yam site (Craig mowlem) were you impressed, is it a new liner job or just a big bore on the standard liner, it also says some mild port work is done, any more info on this kit much appreciated.

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