Hello all,
My 1978 DT175mx has eaten a ring
As an almost-but-not-quite mechanical numpty, I intend to rebuild the engine myself.
The cylinder is marked and will need a rebore.
The marking is clearly visible and I can just feel it - it’s not gouged.
I believe the bore is plated, and am wondering whether it will need replating or whether I will get away with a rebore.
I think I have read that maximum bore oversize is 1.5mm and the marking is much less than that.
So I’m thinking replating will not be needed.
Does that make sense, or am I missing something?!
Many thanks,
Mike



 

Can you post a picture of the cylinder? I believe it should be a steel sleeve, not electroplated unless someone did some serious aftermarket work on it.

I only have experience with newer electroplated cylinders, and they don't get bored up a size, they get replated back to original size for ~$300 in the USA.

  

I have to say that I wasn’t expecting it to be plated,
but I thought i read that it was. But can’t believe everything on google!
Thanks,
Mike
 

Can be bored to 1mm over in 10thou steps so get 4 goes at it. See what is written on the top of the piston, but if can't be read [.25--.50--.75--1.00] then measure the bore. 66mm std size & from thereon up to 67mm. If ya not overly worried & just want to get it running you could get the alloy off somehow [i've heard of some acid process to dissolve it] i used to just scrape & emery paper it off then give a hone to make it look prettier than it actually is--but usable. Hope no alloy went down the bottom.

Well I'd wait for MarkT to chime in as he is the 175 guru, but I believe it's sleeved. Have a magnet handy? Whichever it is, the damage looks extensive enough to do a 1st over piston if it's stock currently or have it replated.

Thanks for that :-)
Where did that missing bit of piston ring go?
Probably out the exhaust port, but can’t be sure.
I was leaping to the conclusion that I should split the cases.
And do mains and crank seals whilst it’s apart.
Mike
 

Not plated. Just send it to Bill Bune or a good two stroke expert and get it done right.

You could just pull the motor and flush it with water followed by WD40, or as I did recently in a moment of laziness; I poured in some paint thinner, turned the engine over by hand, then sucked it all out with a shop vac. Took five cycles of rinse and remove to get all the visible metallic bits out, about half a gallon total.

Of course it would be better to do it right if time and budget are of no concern!

Did think about something like that!
But can afford the time ++
And hope rebuilding it will be an interesting / enjoyable experience (maybe one of those things one enjoys after it is done).
Eyeing up a TTR250 to fill the gap in the interim…
Mike

I think OEM pistons go up in 0.25mm increments up to 1mm.
Wiseco pistons go up in 0.5mm increments up to 2mm.
Give PJME a call they are a great outfit.