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Hey guys. So I picked up a 1971 CB350 Wednesday with 1,912 original Miles. The bike is in incredible condition, however, there is no movement inside the motor. Kickstand stuck. And there is a visible edge to one of the valves seen right at the hole of plug when spark plug removed. Only on one side. (This is my first time posting so I'll attempt to attach a photo for reference.)

Wednesday my dad and I pulled the plugs and added Marvels Mystery Oil (MMO) in it to sit for a few days. On Sunday, we tried to free it up with no luck. I was prepared for the next step, to continuously pump 5 gallons of diesel fuel along with 9 quarts of MMO through the crankcase and out the valve cover using a water pump. At this moment it has been running for 28hrs. I plan to let it run through Wednesday (approx 3 days) and try to free it up again. Of course, my goal here is to free it up without having to pull the motor. If you have any suggestions it would be greatly appreciated. Excited to get this all original back on the road.
 

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Nice find by the info you've provided, glad you plan to keep it a survivor. While I think it's a novel idea to flush through the engine, I'm pretty sure it isn't going to run very well even if you get it unstuck. Valve stems on open valves can be rusted, rings are highly likely to be stuck in the ring lands, probably a pretty serious amount of rust at least in the cylinder that had the valve open, maybe both... getting it running will help you understand what it will likely need, but I can't imagine you getting away without a top end rebuild at the least if you expect any decent longevity from it
 

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Nice find by the info you've provided, glad you plan to keep it a survivor. While I think it's a novel idea to flush through the engine, I'm pretty sure it isn't going to run very well even if you get it unstuck. Valve stems on open valves can be rusted, rings are highly likely to be stuck in the ring lands, probably a pretty serious amount of rust at least in the cylinder that had the valve open, maybe both... getting it running will help you understand what it will likely need, but I can't imagine you getting away without a top end rebuild at the least if you expect any decent longevity from it
Yeah. It seems the obvious thing to do is to pull the engine and rebuild for the reassurance that it is proper to last for many years.
 

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Pull the alternator cover and put a wrench onto the rotor nut and see if you have any movement. I have had these engines seem to be locked up and all it takes is to move the crank and get the transmission meshing properly again.

I would suggest taking it easy on the kick starter to try and free the engine.
 

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Put it in an upper gear and rock the bike back and forth. May get lucky and get it freed up. Worked for me on a CL175 that was seized.
 

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Pull the alternator cover and put a wrench onto the rotor nut and see if you have any movement. I have had these engines seem to be locked up and all it takes is to move the crank and get the transmission meshing properly again.

I would suggest taking it easy on the kick starter to try and free the engine.
Hey. So, that was the first thing I did after two days of sitting with MMO in the plug holes. I opened the alternator cover and put a 14mm on the nut. Attempted to move it back and forth a little. No luck. Didn't want to put too much pressure on it with a breaker bar due to breaking the end of the nut off in the process. Really wish I knew how much pressure I could put on that thing without hurting it. I saw a method of where a guy put his in fifth gear and rocked the rear wheel back and forth in hopes of getting the transmission worked out that way. No luck there for me either. On Wednesday I will try both of these methods once again in hopes of freeing it up after three days of fluid running through it.
 

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Put it in an upper gear and rock the bike back and forth. May get lucky and get it freed up. Worked for me on a CL175 that was seized.
Yeah. I saw where another guy did this on YouTube. So far, no luck. Hoping for a better outcome in a few days.

By the way guys, I did not try to free it up using the kick. Never once did this sound like a decent method so I didn’t want to do harm by trying it.
 

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I have found penetrating oil spray effective. I have also used my electric heat gun to heat cycle the cylinders. You can boil the oil in the cylinders with a heavy duty heat gun.

I have put a 24" bar with a socket onto the alternator bolt but would suggest doing so with caution. I'd keep the engine in the frame until it is free.

Time is on your side then it will be time and money, money, money.
 

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I have found penetrating oil spray effective. I have also used my electric heat gun to heat cycle the cylinders. You can boil the oil in the cylinders with a heavy duty heat gun.

I have put a 24" bar with a socket onto the alternator bolt but would suggest doing so with caution. I'd keep the engine in the frame until it is free.

Time is on your side then it will be time and money, money, money.
Thank you for the helpful info. As you know, tomorrow is Wednesday and I will be tackling this project a little more. I would love to speak with you about your heat method, is this possible? Be way to do so?
 

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JWard re my heat method is pretty straight forward ..... a hair dryer isn't hot enough so a heat gun is what I use. Actually I have two but if they aren't on different circuits then the breaker flips. You can leave whatever oil you have soaking in the cylinder and direct the heat at the cylinder where you believe the piston rings are. I just point the gun at the front of the cylinder and watch for the oil to smoke, leave the spark plug out. You can heat up one side at a time. Let it cool down, try turning the crank via the rotor nut. Repeat.

Hope this helps. I'll send you a PM.
 

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A little update after some hours of working on it today: turned the pump off which was cycling diesel and MMO through it, drained it, attempted to break it free using the crank bolt - no luck, tried to rock it back and forth in 5th gear - no luck, heat method - no luck.... so I pulled the motor out and it is in the back of my car headed back fo Wilmington (NC) with me. It looks like I will be very carefully watching some videos on how to break the motor down and see what kind of damage it has. Wish me luck. (By the way, tomorrow-Monday I have a solid schedule so will not be opening the motor up until Tuesday.)
 

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Good call and your only course of action moving forward. It was worth a shot to free it up, but stuck as it is Ancientdad is correct. Even if you managed to get it to turn over it likely would need some work internally to get it to run properly. Keep posting, there are plenty of members here willing to help steer you along with it. Glad you are planning to keep a complete, good condition, original bike exactly that way. Good luck!
 
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