Some pics from Brian R, vids from Jake, and Instagram random.

@chinonthetank hill climb #readingdirtbikegetaway

A video posted by Nate King (@natemking) on May 30, 2015 at 5:06pm PDT

Getting cocky on the IT and starting basically on the hill. Fail.

A video posted by chinonthetank (@chinonthetank) on Jun 6, 2015 at 5:13am PDT

@chinonthetank

A video posted by Brian Robert Radke (@brianrobertradke) on May 30, 2015 at 5:18pm PDT

The benefits are:
– Lighter engine
– 6 speeds vs 5 speeds
– Overall more solid engine
– Parts availability are better (Wiseco makes piston kits for $100)

Well this got me pumped so at some point last year I picked up this 1981 MX 175 cheap with a solid motor, no title, and a bit rough around the edges. It was perfect candidate for the motor swap. However, after a few hours of disassembly and attempted reassembly the motor doesn’t swap over clean. Motor mounts kinda line up but more importantly the chain line is about an 1/8″ off so basically it would need all new mounts to correct everything. So the swap is possible but currently more work than I’m looking to invest in it. I had to try it for myself and this post is for anyone (probably few but..) who has thought about doing this.

MX motor piston is still standard bore which is good.

MX cylinder head

Motors side by side. DT175 left and MX175 right

MX motor in the DT with just the bottom right bolt engine bolt.

DT motor in the DT

DT will stay stockish for now. I have an early model MX175 exhaust that I’m going to try and fit on. Supposedly a power upgrade but we’ll see.

So so much damn fun. Little 2 strokes are the best.

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

It took some work to get it back on the road but I was able to do for about $200 and I made my goal of having a pit bike for Mid-Ohio which ruled. Since then, I’ve put ~400 (hard miles) on it and now it’s in need of some work to keep it running the rest of the year… and to make it better than Ed’s CT175.

As it started in May 2013. Full post HERE.

Back on the lift as it looks now. Just a little beat up.

Disassembly

Top end came off without any issues. I wish had a hose to wash the bike down before working on it.

The head is going to Mar Automotive to get cleaned and honed. I can’t seem to figure out what size the piston is based on the numbers and it needs to be replaced but Mar should be able to tell me what size piston I need to buy.

It looks like the timing was off at one point before I owned it since the piston shows signs of melting through a little.

My engine has always had a rattling noise that I’m going to try and fix so I’ll be going through the different tolerance checks. The crankarm free play should be between .4mm and .6mm. Mine is unfortunately measuring at .7mm but I doubt this is the cause of the knocking. I don’t plan to get that deep into splitting case and replacing washers and bearings right now since I don’t have the tools or experience of getting into that.

I mocked up a MT125 Elsinore front wheel from Chris F. I really want to run a 21 dirt wheel and this one will work with some modification and it came with a decent dirt tire. I plan to copy Dan’s brake mount solution he posted awhile ago on Greasy Gringo. That and turning a simple spacer should make the wheel work.

Next up: Engine reassembly

All were 69-71 era, piston port motors, before Yamaha really knew what dirt bikes would become. And all were relatively about the same dimensions, just different weight.

Lately I’ve been regretting buying my 71 CT1 since it’s lacking the newer technology compared to the late 70’s. I really wish I had bought a 78-82 dt175 instead; way better suspension and faster.

Regardless… I’ve been looking at ways to make mine better from a performance and suspension standpoint and after finding all these cool images, it gives me some solid inspiration. Some of these bikes below are badass! This is what I’m thinking:
– already have pod filter and jetted carb
– GYT expansion chamber exhaust
– aluminum rims. small front hub. no front brake
– plastic front and rear fender
– smaller front gear. bigger rear gear
– front end from a YZ or MX
– maybe take all my lights off and put a number plate on it

Yamaha had a power kit from the factory called “GYT”. (Genuine Yamaha Tuning)

You could walk into a Yamaha dealer in 1970 and get a new piston kit / carb / gear / exhaust (all yamaha parts) to make it go faster. I’m trying to find some of this stuff on eBay but its super rare.

FYI – the hot exhausts were:
– GYT
– hooker
– DG performance
– torque engineering
– bassani
– moto tech

Check out the map below. Zoom in/out to see it all.
As far as I’m aware, these are the only locations to ride dirt bikes. None are legal. All are sketchy, and be prepared for someone to probably try and mug/stab you or call the cops.

• A – kenzo trails
  I rode back here all weekend. It’s awesome. Super sketchy though. Watch out for booby-traps and someone trying to mug you.
• B – airport trails
  Has anyone actually been back here? I went there yesterday, and now there’s a big fence. It has an electric open gate portion which was open, so we went in real quick. I heard this is the most sketchy, ghetto spot in philly. Is it shut down now?
• C – fairmount mountain bike trails
  There’s really only one or two trails. Basically you’ll ride through it… pop out and then go on your way. Don’t expect to spend too much time back here I don’t think.
• D – river road trails
  I haven’t been back here yet, but I heard it’s good? Anyone know?
• E – wissahickon fishbowl trails
  This used to be crappy mountain bike trails behind the baseball field down in the bowl like area. It’d be fun to hit this up again.

Also… watch this video below. Philly cops don’t / won’t chase dirt bikes if you run away… Just saying…

Read this article too.

Pumped it came with the original rack. These go for way too much money on ebay.

The 175 came with some big upgrades for 2-strokes in the 70’s including a reed block (the piece between the carburetor and engine).

The head has 2 spots for spark plugs (2nd spot has a cap on it in the pic) incase you foul a plug you can just pop the cap onto the other spark plug and keep riding.

Yea, the tank is shitty inside and needs to be sealed with some Caswell.

This was just the beginning of the electrical mess on this bike. I unwrapped a section with speaker wire and Pepboys crimp connectors… gross.

Rear wheel needs some new spokes and a truing.