Ring a ding ding ding...two stroke Yammer. 1978 DT 175 needs rings a ding ding.

Okay, I get nostalgic about the "smell of a two stroke in the morning" and the sound...reminds me of the motocross track as a teen. (I somehow forget about all those broken bones, and still never winning a race...but alas...another story).

I don't know about you guys, but I go into motorcycle buying mode for no reason sometimes...I saw a 1978 DT175 enduro that looked pretty decent on Kijiji and just had to buy it. $160 sealed the deal. (pics attached)

Wasn't running and had very low compression (I did the thumb over the spark plug hole before buying it). When I brought it home and tested it properly it only had 40 psi (I wonder how it ran up to that point).

Drained the water...really, there was water in the crank along with some oil, and set about taking off the cylinder...so easy on those single cylinder two strokes!

I could see a lot of blow-by on the piston, so it's definitely in need of rings, besides the compression test results.

I was going to get a first oversize (.25mm) set of rings and clean up the piston. I have a three stone honer as well.

But, I thought...better drop in with the "guys" and get an opinion first.

Change piston? or not to change piston? I don't have a cylinder gauge (any work around to these expensive gadgets?).

Thanks in advance, I always welcome your advice.

Gord

 

We'd need pics of the piston to give a reasonable opinion. A pic of the bore would be nice as well.

Plan on changing the crank seals too. If they aren't leaky now they will be soon.

You can check the piston bore by checking ring end gap at three points along the bore. You'll use the relaxed outer circumfrence of the ring as your baseline for figuring the bore size, and use the change in the end gap as your measuring refrence (feeler gauges being the measuring tool). The only shortcoming of that method is that it's not very good at showing you if the diameter of the bore has gone egg-shaped.

 

Here is sled land we often use the term "2-smoke"

Nice find. I have a 2-smoke bike, too----a 1975 Suzuki GT750M (Water Buffalo) project. Only has 6k mi on it, has been parked in a garage since 1982.

Dave F

 

put some penetrating oil in the cylinder and work on getting it to run a bit. maybe the rings are just stuck

 

Check ring end gap, replace rings. I mean hell, if you are trying to make a daily rider out of it then go for the proper O/S piston and bore, if you just want it to run then re-ring it and move on. Crank seals are easy to get to, if and when they present a problem (over-revving and white smoking) then replace them, otherwise run it and let the seals swell back into shape with some usage.
Good luck, I love two-strokes.

 

Thanks K-moe, I love these little tricks. Makes sense, and I understand that it won't show if it's oval. That will give me an idea of what size ring I should order. It won't see much action, so if I can get away with keeping the piston that would be great.

I've attached pictures of the piston and cylinder bore.

 

I'd love to hear that one Dave!

 

I like the ultra cheap solution Polock! I would have tried it if I hadn't already pulled the cylinder off. Stuck rings are probably one of the reasons why the compression test came back so low

Thanks for yet another trick.

 

Thanks Hank,

You are spot on, I basically just want to get it up and running without spending a bunch of $ on it. I plan on getting it to the point of being road legal again but I won't be using it as a daily rider as you mention. It's just a keeper for the times when I feel like making some noise and smoke.

If I can get away without changing the crank seals for the moment, that would be great.

Gord

 

Looking at that bore, I'd say replace the rings and give it a try. And clean the carbon off the piston crown, big help.

 

Yes, I agree. No scores in the cylinder walls so it may be okay.

I'm headed down to my local Yamaha dealer later today to order some gaskets and rings.

Just have to free up the existing rings to get an idea of the bore size.

Thanks again

 

That looks very much like a soft-seize. Clean it up and run it, but watch your A/F and oil ratios. You might want to add a bit more lubrication to get some more life out of it.

 

Thanks for the note k-moe. It may have soft seized at one point, tough to tell.

I just pulled the piston off and worked carefully to get the rings off.

The rings were gummed in there really tight with all the deposits and crap. No free play at all, I had to pry them loose bit by bit, I was amazed I didn't snap them. I can't see how they had a chance to expand to seal the cylinder. Of course it could be that they just stuck like that after years of sitting in all that build up of crud.

I'll clean up the piston and the ring grooves tomorrow, enough so they can expand and contract, then measure the gap when I put it back in the cylinder. Too cold out in my barn tonight (one degree above freezing).

What do you mean by A/F?

Thanks again

Gord

 

Air to fuel ratio. Some people take "leaner = more power" a bit too far.

 

Aha!, thanks

I'm in the "running = good" camp I rarely look for more power, just reliability. I'll put it at the standard A/F settings once I get the slide unstuck from the carb so I can get it away from the bike to clean it.

I'm also cleaning up the autolube system at the same time, but I'll run premix first with a little heavier oil mix as you suggest.

 

Okay, thought I'd finish up with this thread. I bought a new piston and rings as as well as a gasket set. Total $56 on eBay (including shipping), I also bought an eBay Mikuni (I'm sure it's a knock off...) carb for $28. I'm amazed how cheap these carbs are. I had cleaned the original carb, but it needed gaskets and a float...a new carb was actually cheaper than a carb kit.

Threw it all together and fired it up. It went like crazy! plenty of power and a lot of fun. Very light bike with a great power to weight ratio. I love the way two strokes hit the power band...zippy, and leaves a patch of flying gravel every time I change gears (I live on a gravel road). eBay carbs are cheap and act cheap, but it's a simple solution...one day I'll fix up the original carb.

Alas, the fun came to an end this weekend...I'm thinking its the crank seal. I'll start a new thread on that as I've never changed one of these before. The advice I received here has been EXCELLENT! Good job guys and thanks again.

Gord

 

Oh, thought I'd post a picture of the bike...

 

Good looking bike. It looks like a new bike. Good work!

 

Thanks Lostboy, still a bit to do on it...but it's getting there

 

This is how we treated our DT175

 

Awesome !

I love it! Great ol' pictures Kickaha!

 

Was that thing ever on the ground? Love it!

 

When you jumped from the roadside into the section you couldn't launch real hard or the clothesline would take you out, the neighbours loved us