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oof.

Can anyone tell if this is factory stuff? What do you guys suggest for a piston/size of boring?

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455 is the 74-75 MX175 model code...  you'll probably find a similar casting number at base of cylinder or near intake? (not always though)

When I saw the plug, I figured you had some water damage.  If you find any sign of corrosion in the bottom end, have the crank rebuilt now.  Just a little rust on the big end bearing rollers or pin will lead to failure quickly. 

Cylinder might be ok?  If not, check with Enduronut for a piston and maybe Bill Bune for a bore.

Welcome from NZ.
Does it spin over & if so how 'crunchy' does it sound. Let's see what's in there when the jug is off. I see it's on 66.50mm so second oversize in Yamaha speak or first over if it's a Wiseco piston kit. 66mm is std size.
Might be run-able maybe not longterm usable--i wanna here it run.
Then again i get some pretty dodgy things running but i'm not recommending following my lead--coz i'm lost haha. Just get keen to hear it run--then worry about the next step.
Is that carb new?. I'd better read the story fully sorry.
What is your Quad [atv] mine is a TRX300 'oldy'.

I appreciate all the replies guys....but there goes that idea :(

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You are looking at a piston (DT175MX will work) rebore, rod kit, main bearings, crank seals. If you want to keep and use the bike yourself, probably worth doing, but maybe not so if you want to sell it?

Oh haha [nervous laugh]. Won't be running by lunch time then [my favorite saying--running by lunchtime]. Keep us posted please if you carry on & rebuild.

Rod kits are readily available from Yamaha or aftermarket. Bill Bune can do cylinder and crank.  

If you decide on a piston from another model, carefully check where the ring end gaps are pinned...  You can often use other model piston unless ring end gaps will pass over transfer port (= bad).  You don't want to catch a ring end in a port.  

MX piston only only have one ring...  DT will have two...  but that's not a really big deal.  Might gain a little midrange power with two rings and lose a slight amount of peak HP.  

If you look close you can see the ring pin locations in this picture...  these are all pistons that will fit a 175.


Here's a 77-79 IT175 cylinder...  Yamaha used a wider rear transfer port and crowded the transfers farther forward...  There's a pretty big area between the ports to place the ring gaps


Here's a 78-81 DT175 cylinder...  smaller rear transfer and transfers moved towards rear.  Much narrower target for ring end gaps.  For example a IT175 piston will not work in this cylinder as the rings are pinned too far apart.


Top view of various pistons with pin locations marked.  (Flash washed out some of the marks)


Just something to keep in mind...  I'm not that familiar with the MX175 port arrangement...  you'd probably be fine with a DT piston...  it's prudent to check the end gap pin locations.








 

A few years back I was sent a Fantic motor, from a bike which had gone underwater when it was nearly new.

It seemed as though the original owner, had drained the water out, and started riding the bike again.

After a while, really bad noises started to come from the bottom end, and the bike was put into storage sometime toward the end of the 80s.

Fast-forward to around 2003, and it was listed on eBay and sold for very little money.

Turned out that all it really needed was new main bearings, most of the rest of it was like new.

Rebuilt it with new mains, and a new clutch pack, and fitted it into another bike, whose motor had failed big time.

It ended up running like a brand-new bike, and I would have thought had less than a 100 hours on it from new.

Awesome info thanks for all replies. Giving me a little hope. I want this to ride again but I cant spend a fortune to do it.

If you guys were on a budget (limited to amazon basically) what parts would you buy?

Looks like Bbune is $75 to bore and $100 for the crank work? Is that all thats needed in regard to machine work?

Ill try to get the piston out today, but obviously it looks like this is worst case scenario (story of my life hah)