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TOPIC: DT 175C Is my Piston Toast?

DT 175C Is my Piston Toast? 08 Oct 2018 18:40 #1

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Hello,
New guy with a DT175. I have a bad crank bearing as I can wiggle it up and down a significant portion. I also have removed the engine and the head to reveal a slightly scored piston. So I have embarked on an engine rebuild. I have been reading a lot about others adventures with this hobby. I too would like to have the bike I wanted when I was a teen ager. So take a peek and let me know if.....
  1. If I need a new piston..
  2. Can I just get by with a Hone Job, I have a new gasket set
  3. Do I have to have DEET rebuild my Stator
  4. What about my ugly speedo

I don't want a full restore, I want to ride it. I want to teach my 14 year old daughter how to ride so we can go on adventures up at the farm.

I am sure I will have lots more questions ...maybe I should start a rebuild thread..
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1976 DT175 Not Running...yet
Primary Home Long Grove, IL
Secondary Home UP of MI
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DT 175C Is my Piston Toast? 08 Oct 2018 18:49 #2

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More Pics...
A good 20 footer pic
Carb issues
Looks like the base gasket was leaking
inside looked pretty good except for the sediment..
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1976 DT175 Not Running...yet
Primary Home Long Grove, IL
Secondary Home UP of MI

DT 175C Is my Piston Toast? 08 Oct 2018 19:12 #3

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Looks like you just need a normal cleaning and engine rebuild.
There will be a number on the top of the piston that will tell if it is standard or some oversize.
I am guessing it will take the next oversize unless the cylinder is badly scored.
I didn't see any stator photos. Unless it is damaged, I would wait until you have the engine rebuilt, see if you have spark, and then determine if the stator needs to be restored.
Most times, all you need is points and condenser.
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Yamaha@nc.rr.com

Where the Yamaha Enduro is still a current model...
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DT 175C Is my Piston Toast? 08 Oct 2018 19:26 #4

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The only reliable method to tell if you need boring vs honing only is to have the piston and bore measured to determine the existing clearance. I am certainly not an expert in this area but the scoring on the exhaust side of the bore may not clean up with a hone-only process. And if it did, it may push the clearance to where the cylinder would require boring. One area I do have ecperience in is piston skirt breakage on a 175 Enduro. This happened when I was a teenager. Fortunately I had just backed off the throttle and was nesrly slowed for a u-turn. The engine stopped abruptly and locked the rear wheel. A small part of the skirt ( I believe it was from below the piston's ports on the intake side) jammed the piston from moving. Fortunately I was going slow. For me and the engine. So, if your piston has reciprocated beyond it's service life, my suggestion is to freshen it up.

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DT 175C Is my Piston Toast? 10 Oct 2018 02:07 #5

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I'd guess you're in for a complete rebuild including re-bore unless the aim is just to get it running. With the play in the left main bearing just be sure its not spinning on the shaft which will groove it so a new bearing will still have play when pushed right home. Don't think those had that issue as by memory run a 6205 on the left side but might be wrong. Check the big end as best you can & flush it out then oil it & rotate it to feel & listen for roughness. Seriously think you're in for a complete rebuild job though. Love that model & shouldn't even mention but those reservoir shocks go with the reservoir facing forward. But if not original they might run into the chain guard fitted correctly--least of your worries, so get that motor apart!!, looks like it might've had water down the bottom or is it just old fuel plus oil dripped in from the oil pump & tank. Goodluck.
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DT 175C Is my Piston Toast? 10 Oct 2018 05:32 #6

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Thanks very much for the responses. Looks like a rebuild for this motor. I really look forward to learning how to rebuild a 2 stroke the best way I can. I have been reading a lot and bought a book by Paul Oleson on how to rebuild a 2 stroke motor. I do have a bit of experience with mechanical stuff as I own a 25 year old Range Rover so keeping that running and on the road has been challenging. I am happy to buy tools to measure and determine whether my cylinder is out of round etc and there is a lot of info here on the forum and other web places.

So now I need to get a piston & rings, which may be the most challenging part of this...at least for me

PISTON 1 O/S 0.25 443-11635-03-00


or this one...looks questionable and is a 2nd over 66.5mm I think


PISTON RINGSET 1ST 443-11610-10-00

Searches come up with little options or I can find rings for $100 a set and a maybe a piston for another $100..maybe that's just the price, just buy it and be done with it. I have seen pistons for sale in the UK that look like they are brandx...

Any comments on sourcing a piston & rings would be appreciated.

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1976 DT175 Not Running...yet
Primary Home Long Grove, IL
Secondary Home UP of MI

DT 175C Is my Piston Toast? 10 Oct 2018 08:30 #7

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Not sure what country you're in... still would probably be worth the shipping to send cylinder to Enduronut in the USA. He has a huge supply of pistons and rings in stock at good prices. a challenge can be getting the rings and piston to match as Yamaha had some design changes. It takes skill to properly measure and recondition a cylinder. Sending to Enduronut insures a first class job....

Another note is you really shouldn't be buying a piston until you are sure what size you need... and any good machinist will need to have the piston in hand before machining. What often happens is the machinist has to "guess" what it will take to clean up and true up the bore so without a stock of pistons they tend to guess large to be safe. This practice can waste a bore size or two! This is not a concern with Enduronut.

If you decide to have it bored locally, make sure the shop knows two strokes and that they adhere to the factory Yamaha clearance specs... so many shops "add a little extra" and you end up with a rattly job that doesn't last long. Port chamfering and bore cleaning are another two critical aspects of the job.

The 175's have a lot of piston options... for example in a pinch a Yamaha Blaster piston of the correct size works just fine if you trim the skirt a few mm to match the length of the original piston. Wiseco and probably Wossner make forged pistons... (if using forged, follow the piston manufacturer specs for clearance) Yamaha OEM is the best choice IMHO... just wanted you to know there are many available options.

One concern I'd have is the crank big end rod bearing... engine looks like maybe it took on some water. If the needle bearing got corroded at all it will fail quickly. at the very least do your best to inspect it and make sure clearance is within specs. Might be worth a crank rebuild while you have it apart? Rod, pin, bearing, washers, are still available from Yamaha or tons of aftermarket sources.

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1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

DT 175C Is my Piston Toast? 12 Oct 2018 17:53 #8

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Thanks for your advice, I sent a PM to Mr. Enduro Nut lets see what he says.....

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1976 DT175 Not Running...yet
Primary Home Long Grove, IL
Secondary Home UP of MI

DT 175C Is my Piston Toast? 16 Oct 2018 16:56 #9

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The EnduroNut says send it over..I can fix you up. So, I need to send it over to him..he was very helpful with his communication, thanks to those who pointed this new guy in his direction.

Now what about my crank?...my rusty crank? Where do I go to get that fixed?

I have read of this man..anybody have work done by him?
home.earthlink.net/~scloughn/id14.html

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1976 DT175 Not Running...yet
Primary Home Long Grove, IL
Secondary Home UP of MI

DT 175C Is my Piston Toast? 16 Oct 2018 18:42 #10

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Scott does good work... not sure if he does cranks or sends them out.

Bill Bune is another source many use.

I've used "Mr. Crankshaft" a couple times on my 175's and have been very happy with his work... very fast turnaround. Cranks came back true and engines run very smooth with little to no vibration.

Any bearing that gets rust on it will fail quickly. Replace it. Also never reuse the piston pin clips.

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1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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