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Old 05-11-2013, 04:41 PM   #16
joexr
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Originally Posted by Valleyrider View Post
Yes, it was the cover of the Clymers manual. It's me from a magazine shoot at the old Orange County Raceway in Irvine Calif. Never knew that they were using me as a model!! No pay for it....
Thought so. I had a '77 GT500. Had the Clymer manual too , but I don't remember the cover. Cool.
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Old 05-11-2013, 05:58 PM   #17
baloneyskin daddy
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Are you sure the throttle isn't sticking wide open.
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Old 05-11-2013, 08:42 PM   #18
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Well I may have found the culprit. I pulled the cylinder, the gaskets looked good but I found this

 photo BFAE256A-820B-4AD3-89E1-2649C499DB08-20115-0000279922E856F8.jpg

 photo 79E9218A-C0ED-41F6-9D1C-704C3F5708EB-20115-000027992C5530D5.jpg

The top ring had a weird bend on the front of it, to the point where it didn't want to come off of the piston without some help. As you can see the piston has a matching bend. Other than that the piston didn't have any gouges or broken bits to it. The bend was on the very front, directly in front of the exhaust.

The cylinder didn't appear to be damaged however.

 photo 613CA229-DD4D-4E2D-A809-E18F62BB3453-20115-00002799761C8F20.jpg

That's a picture of the exhaust port, where the bent ring was. The spot on top is just an oil spot, you can see the smudge where it wiped away with my finger. No gouges or anything that can be felt with a finger. So maybe just a light hone and a new piston and rings (and gaskets obviously)?

The only thing that concerns me is a comment on another forum I posted on about the crank. It was pointed out to me that I neglected to change the 15 year old crankcase oil (stupid mistake) and possibly damaged the crank. How does one go about checking if the bottom end is trashed too? Since it's this far apart I'd rather make sure everything else is working before I put it back together. The connecting rod moves side to side about an 1/8 inch, does this indicate worn bearings?
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Old 05-11-2013, 10:07 PM   #19
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First, something went in or out the exhaust to do that kind of damage.
Do you have a strange rattle if you shake the exhaust pipe?
Some side to side play is normal at the piston end of the rod.
The important thing to look at is the crank end. Is there any discoloration of the rod? can you get any play if you lift the rod straight up and down with the rod at top dead center? If so, the crank will need freshening up/rebuilt.
The "Crankcase Oil" you refer to is not in the crank area. It lubricates the transmission. You should probably make sure it has the proper amount of oil in it, but it is not the cause or future cause of any crank issues.
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Old 05-13-2013, 12:15 AM   #20
Chunche OP
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Quote:
Originally Posted by Valleyrider View Post
First, something went in or out the exhaust to do that kind of damage.
Do you have a strange rattle if you shake the exhaust pipe?
Some side to side play is normal at the piston end of the rod.
The important thing to look at is the crank end. Is there any discoloration of the rod? can you get any play if you lift the rod straight up and down with the rod at top dead center? If so, the crank will need freshening up/rebuilt.
The "Crankcase Oil" you refer to is not in the crank area. It lubricates the transmission. You should probably make sure it has the proper amount of oil in it, but it is not the cause or future cause of any crank issues.
I believe the crank is ok, no discoloration, no play up and down. I did however get a chance to take a closer look at the cylinder, and I think you're right about some sort of debris entered the exhaust port. There's no rattle in the exhaust so I'm not sure where it would have come from. Could built up carbon cause such damage? Because there was quite a bit in the exhaust port. I also found damage to the cylinder wall that matched the damage to the piston and ring right above the port, so I'm going to take it down to a local bike shop tomorrow and see if it can be bored out, or if I'm looking at a new cylinder.
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Old 05-13-2013, 05:17 AM   #21
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Originally Posted by Chunche View Post
I believe the crank is ok, no discoloration, no play up and down. I did however get a chance to take a closer look at the cylinder, and I think you're right about some sort of debris entered the exhaust port. There's no rattle in the exhaust so I'm not sure where it would have come from. Could built up carbon cause such damage? Because there was quite a bit in the exhaust port. I also found damage to the cylinder wall that matched the damage to the piston and ring right above the port, so I'm going to take it down to a local bike shop tomorrow and see if it can be bored out, or if I'm looking at a new cylinder.
I think by rattle in the exhaust he meant the piece that went thru the motor is probably in the pipe now.
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Old 05-14-2013, 12:26 PM   #22
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Ok so I took it to a local bike shop, and can get it bored out for $62. He wasn't exactly sure how far they'd have to bore it out but I'm going to need oversize pistons and rings. Anyone know where to get parts for this bike? I looked on Wiseco's website and they have the pistons, in a few different oversizes but I can't seem to find bigger rings anywhere except a few random ones on ebay. I even went to the local yamaha dealership and they can't get any parts except the stock size piston and rings. Any suggestions on where else to look? I don't want to pay the guy to bore the cylinder only to find out I can't get the parts I need to put it back together
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Old 05-14-2013, 12:53 PM   #23
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The damaged ring was most likely due to a exhaust port that wasn't chanphored (sp) they probably didn't angle ground at the top of the port. If your tolerances are OK just replace the piston and rings.
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Old 05-14-2013, 08:28 PM   #24
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Originally Posted by WRW9751 View Post
The damaged ring was most likely due to a exhaust port that wasn't chanphored (sp) they probably didn't angle ground at the top of the port. If your tolerances are OK just replace the piston and rings.
On the cylinder wall, directly above the exhaust port, there is a gouge out of the wall that matches exactly the bent ring. So I can't just put it back together because of the damage. As far as I know this motor has never even been apart, so nobody did any work to the exhaust port
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Old 05-14-2013, 10:00 PM   #25
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wicked get!

i have one too! (1980) but its red. i think i like the blue!

B8es ngk spark plug, to answer an earlier post.

adjust the carb as per the book and she'll kick right up once you get that piston taken care of.

the oil lube will work. i'm experiencing it as we speak.

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Old 05-16-2013, 09:19 AM   #26
gloud
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Just search ebay on DT175 piston they are out there, you share a piston with the rare YZ175 and a few other bikes. (I used to have one and had to buy 2 pistons over the 2 years I ran it as a daily driver. (One was bad jetting) the big thing is to make sure the piston has the windows on the skirt. they are good little bikes. I would check your bottom end really good to make sure none of the
bearings or bits came loose. and change out the crank seals. (if you don't you will likly be sorry as you can suck oil from the right and air from the left , the air one will cause you to run lean.

Oh and a thought, make sure your reeds are intact, if one broke off it could have caused this problem. (the bent ring/dent)

gloud screwed with this post 05-16-2013 at 01:12 PM
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Old 05-17-2013, 09:36 PM   #27
Chunche OP
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Originally Posted by gloud View Post
Just search ebay on DT175 piston they are out there, you share a piston with the rare YZ175 and a few other bikes. (I used to have one and had to buy 2 pistons over the 2 years I ran it as a daily driver. (One was bad jetting) the big thing is to make sure the piston has the windows on the skirt. they are good little bikes. I would check your bottom end really good to make sure none of the
bearings or bits came loose. and change out the crank seals. (if you don't you will likly be sorry as you can suck oil from the right and air from the left , the air one will cause you to run lean.

Oh and a thought, make sure your reeds are intact, if one broke off it could have caused this problem. (the bent ring/dent)
I will take a look at the reeds, thanks. I did find some pistons and rings on ebay, and they're actually close (ish) to my house at a bike shop. So I'm going to go take a look at them next week to make sure they're not super cheap chinese junkers
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