A low-budget fix up of a beater 1974 DT 175 continues. As previously advised, I'll avoid the cheap Ebay Chinese pistons. However, I do see NOS standard 1974 MX 175 (455 series) pistons/rings available on ebay. Same 66 x 50 B & S. Same pin and top bearing per parts lists. Can someone confirm the 74/75 MX 175 piston will work in the 74/75 DT 175? Again thanks for any advice...

Sounds hopeful. So long as distance from pin centerline to top of the piston are the same--& likely is. Someone will know for sure & be along soon.

Per parts list...same rod...

I'm not familiar enough with the port design on the MX those years.  My concern would be where the ring gaps are pinned.  You want to make sure the gaps don't pass over a transfer port.  Pin(s) should locate ring gap between the ports. 

Some 175 pistons with pin locations marked on crown..   If you can find a pic of the MX piston that shows the locating pin location and it looks close to what you have you'll probably be fine.: Should check it though. 

 


 

Just FYI on the above....  You can use a 78-81 DT175 piston in a 77-79 IT175 in terms of ring end gap.  BUT, notice the IT175 rings are pinned farther apart...  transfers are shifted forward compared to DT.  So if you try to use an IT piston in a DT the ring end gaps will be pinned over the transfer ports...  not good. 

Ring end location/port snagging! I believe MarkT may have something there. In a previous post asking about standard DT 175 pistons, there were multiple suggestions of the ProX Blaster piston. No one suggested the available MX 175 piston...I'll assume for a reason? 

So...can someone with first hand knowledge of trying a "74 MX 175 piston in a 74 DT 175" confirm that it will...or won't work?
I appreciate the excellent advice always on this site.

There were probably no recommendations for the MX175 piston because of lack of familiarity, not because it doesn't work.  And you are looking for "standard" size which is a little unusual after all these years...  bores wear.  It's also probably why you are finding standard MX pistons cheap.  MX is a much rarer bike and almost nobody can use a standard piston anymore.. 

Enduronut might know or you can take the suggestion I made earlier...  compare pictures online with your piston and port arrangement. 

Here's a couple I found of 74-75 MX and DT pistons

 
 

 

Your photo of the MX piston is the best I've seen. I'll take the DT piston and try to "mirror" the MX pin locations onto it to see where they fall in relation to the ports.
Many thanks...

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The 455 MX pistons, are the same as the 443 Enduro pistons . . . except for their ring package (grooves) . . . and, holes drilled for wrist pin oiling
The ring locating pins are in the same position.
Go for it!  

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Many thanks to those that took the time to offer advice (including posting photos) on this topic. This is the 2nd time I've used this Forum for help on an old beater Yamaha fix up...and both times the replies have been just what I needed.