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1979 mx 175 resurrection from the barn

09 Jul 2020 08:12
timo
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1979 mx 175 resurrection from the barn #1
Hello, new to the site, but have noticed a lot of good information from helpful people. Recently retrieved a 79 mx 175 from my brother's barn. Several years ago he took it to one shop and then another because it didnt run right. The diagnosis came back that it needed new crank bearings. Recently, I put the top end back together. It had a stock bore wiseco. Cylinder looked and measured ok, ran a glaze breaker through it to get some crosshatch. Installed new 66mm wiseco rings since old rings had .045"+ end gap. New rings are about .020" end gap. I have decent spark on a b8es. Stock pipe was packed with a mouse nest that I flushed with garden hose. I cannot get a "pop" out of this engine!!!! I've put gas or premix in the plug hole, through the carb. I have not done a compression test, but it has a decent "feel" kicking by hand. I havent done a leak down test to verify the crank seals. Could the crank seals be so bad that it won't even pop with gas through the plug hole? I didnt see any oily drizzle on the stato side of the crank.

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09 Jul 2020 11:14
Grussell
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1979 mx 175 resurrection from the barn #2
Did you clean the carb thoroughly?

1978 DT400 (in progress)
1975 DT250
1976 YZ125C (in progress)
1976 YZ125X (in progress)
1976 YZ100C (in progress)
2018 YZ250FX (my race bike)
2010 Triumph America (my cruiser)

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09 Jul 2020 11:33
timo
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1979 mx 175 resurrection from the barn #3
Yes I did. There was a mud dauber nest thoroughly plugging the fuel inlet. Even with compressed air, it took some carb spray, tip cleaners to get it flowing freely. I did remove the pilot and the main jet, air screw. Sprayed through all the orifices. Installed yellow Tygon fuel line so I can see that I have flow to the carb. I put clear line on the fuel bowl so I can verify fuel level. Went home for lunch and did more kicking. No luck. Removed the baffle just to make sure it isn't causing a restriction. Originally, the kill switch/throttle housing was pack with a dauber nest, so I cleaned that but the switch would not ground the ignition system. I disassembled the switch and cleaned the contacts so I can ground the ignition and stop the engine when I do get it running. I did fill a spray bottle with premix so I could mist into the carb. Nothing. Had to get back to work.

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09 Jul 2020 15:43 09 Jul 2020 15:45 by RT325.
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1979 mx 175 resurrection from the barn #4
If you can't even get a fart out of it with fuel down the port or plug hole then you have a problem. I had a left crank seal blow right out & it wouldn't even go boo, but had been running well till it wouldn't lol. Had volatile stuff spraying through the open throttle inlet & nothing. So had to go looking--& there it was!!. mine was a YG5T but that's irrelevant. Other thing is--is the crank key for the flywheel in place. Maybe someone--shop--had it off & just fitted it back on minus the key. Remove the exhaust just incase its still "Moused" against the tail pipe internally. That reminds me of my "moused" RMX. Sorry i'll go back & read your story fully.

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09 Jul 2020 15:46 09 Jul 2020 15:56 by RT325.
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1979 mx 175 resurrection from the barn #5
sorry pics above split up my story a bit. Was meaning remove the exhaust to hear if you can any sort of response from it when kicking. Don't suppose it's flooded up & needs full song & kick or push around, but be sure the throttle is closing fully. I guess its cdi ignition & spark never looks great on those but if you can see it jump the gap then you wouldn't want a belt off it. Won't be compression if you can feel it reasonably on the kick start. My old stuffed TS125 has about 40psi at crank speed & can start it by hand when its warmed up--tried it just to see.

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09 Jul 2020 18:09
timo
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1979 mx 175 resurrection from the barn #6
Winner Winner Chicken Dinner!! Thanks RT325. I'm on the path of an ignition side crank seal. As I loosened the rotor cover screws, liquid (fuel) started draining out. I have 2 27mm flywheel pullers, but unfortunately I have the one with the smaller screw hole, so I can't get it over the crankshaft. Before I removed the cover, I removed the carb slide and sprayed fuel in there and gave it a kick prepared to choke it when it runs wild. Nothing. Loosened the exhaust pipe so it was hanging free of the port. Kick, nothing. That's when I removed the cover, and drained the fuel. Rain delay, were having a downpour in SE Wisc. And I need to get some tools from my jeep so I can counter bore the puller I do have with me. I do have new yamaha seals and bearings, along with a decent crank to install, but i want to get it running so i can diagnose the issues vs. 15 year old information relayed to me by my brother.

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09 Jul 2020 18:43
RT325
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1979 mx 175 resurrection from the barn #7
Yay, that's good. Sometimes i guess right haha. Flywheel pullers are cheap but not helping you on the spot. ya get yours bored out to do the job. We love pics & videos sometime if you're able to. Cheers.

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09 Jul 2020 20:21
timo
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1979 mx 175 resurrection from the barn #8
I was able to bore the puller to get enough engagement and get the rotor off. Stator plate screws were not too tight. The screws probably could have vibrated out. I was able to insert a pick and pop out the seal. The back side was fairly set-up, rotted, brittle. Not much sealing tension on the shaft. I do have pictures that I will post tomorrow. My phone was charging so they are on a camera. I assume: lube the shaft and seal ID with 2 stroke oil, clean and dry the seal bore, and then tap in seal with a PVC pipe driver. No yamabond on OD since seal is retained with stator plate, correct? Thanks again. Tips for attaching pictures gladly accepted. Tim

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09 Jul 2020 23:13 09 Jul 2020 23:17 by RT325.
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1979 mx 175 resurrection from the barn #9
Ok, on reading that i'm now thinking i may not have been 100% correct, because if it was still in place but not in the best condition then it should still run. So--if she still doesn't fart then wondering if it's blown the right side seal out as it can happen if it gets a belly full of fuel then given a hard kick & just hydraulics the seal out--which it could do to the mag side as well of course, depending which one is the tightest fit the case. Fit your new seal & see what gives. Might need to push it around with plug out & ignition"off" to get rid of fuel in the crankcase, & with the exhaust off. All guessing of course. Right side seal needs the clutch cover off to have a look. I just oil the seals to help them slide in. Should be a tight fit in the case so won't easily come out again. I oil the shaft bit too. Just what i do, but others may bond them in, no worries.

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10 Jul 2020 05:24
timo
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1979 mx 175 resurrection from the barn #10
Thanks again RT325. I hear what you're saying about "might/should run with a bad seal, but won't run with a blown out seal". I was surprised that there was excess fuel in the case so I must have a leaky needle/seat. It didn't drain the tank, but another issue to deal with. I did lay the bike on it's side, to drain the remainder. I'll install the new mag side seal at lunch and see what I get.

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