1975 DT175B Rebuild | Engine Reassembly

I got the top end back from Mar Automotive all nicely cleaned, honed, and painted for $50. I really recommend these guys. They open at 7:30am which makes it easy to drop/pickup parts before heading to work.


I found an NOS piston and rings on Ebay for $130 which is expensive but it was the only option. My head is a stock bore of 60mm and Wiseco and Prox do not make an piston for it. There are plently of new pistons for the 1977+ models which are not compatiable because of the wrist pin location from the top of the piston. So, I was stuck having to buy expensive NOS. Came in some cool packaging though.


This is the best example I was able to find of the comparison of early vs late dt175 pistons. I might be completely wrong about this but there’s so little well documented info out there between all these different year DT’s.


Checked ring gap at .4mm which is within spec.


These rings have locating pins on the piston so and they have to be installed with the ‘V’ to accomodate that pin.


Lubed everything up with 2 stroke oil before assembling. The wrist pin and bearing I took off were worn out so I got new ones along with new clips. Another $40 in parts. After ordering from BikeBandit I found that Yamaha has a site: http://www.yamahapartshouse.com were you can get all the same OEM parts and it’s a little cheaper.


I used Hylomar to prep the copper head gasket.


Assembling a single piston 2 stroke top ends is dumb easy compared to 4 strokes. Torqued the head to 15 ft lbs.


I had a few different plans for making the 21″ MR125 Honda Elsinore front wheel fit my stock forks. The main issue is the brake sits 1/4″ away from the stock fork stop. To keep it simple, I decided to just extend the stop to fit into the brake.


Came out pretty nice. I’m a little out of practice with my aluminum welding so Rick did it for me quick. With a little file work it’ll look stock.


Next: Electric simplification

7 responses to “1975 DT175B Rebuild | Engine Reassembly”

  1. Carson says:

    Looking good! 2 strokes are stupid simple. You need to get some carbon reed paper and cut you some reeds for that thing. You’ll definitely notice and improved throttle response on the bottom end.

  2. Adam says:

    I put the Boyesen power reeds in when I first got running last year. I never ran it with the stock reeds but I like where my power band is at with these reeds.

  3. Ben says:

    Nice job. Saw the bike last night and the head looks so clean!

  4. Joel says:

    Hey are you going to post the Electric simplification
    i would love to see more

  5. adam says:

    Hey Joel, I’ll have that post up in a week or so. I’ve got the DT back together and been riding it a bunch. I wanted to make sure my electrics worked before putting it out there.

  6. Alex Caverly says:

    Hi Adam, I realize this comes years after the above post, but… did you ever publish a write-up on ‘Simplified Electrics’? I’m working on a ’75 DT100 with electrical issues and could use all the help I can find. Cheers.

  7. Chris Clark says:

    What jet sizes are you running? I have a stock 1970 with a pod filter as well but stock jets. Bikes you guys have are rad!

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