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Nighthawk 650


ShawnR

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I bought this as a possible winter project bike on the chance that the engine wasn't really seized up.

But, the engine is really seized up. Cams will turn, but crank & pistons are tight and I haven't got them to move yet.

So, I am either looking for a decent replacement engine, or else selling the whole bike as a parts bike for someone who already has one, or parting it out myself. It does have a clean Ohio title in my name. Has a new battery and starter solenoid (from previous owner).

$400 as is.

Or, if someone has a lead on a motor, please send that my way. I would really rather fix it, but I can see making enough profit after crank/bearings/pistons to make it worth while.

 

 

1.jpg

2.jpg

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Looks like it's in pretty good shape otherwise.  My guess is with a little patience you could find a good used motor on eBay.  For an all-in investment of maybe $800, you'd have a pretty good bike.  Sure looks worth more than that to me, not that I really know anything.   I tend to get too emotionally involved in my project bikes and never seem to make a profit, but I'm a perfectionist. 

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 Have you seen inside the cylinders? Tried any PB blaster?

I'd love to have that bike.  My dad had an 80 or 81 that I rode back-and-forth to football practice on. It was the bike that I fell in love with street riding on. 

Edited by max power
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While you're waiting for someone to buy it, pull the spark plugs and dump about a half cup of ATF in each cylinder.  On the chance that the rings are gunked up/froze.  I've freed up a couple of motors like this.  After a week or two, change oil and try it.  Just a few bucks, might work.

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1 hour ago, JustinNck1 said:

+1 on soaking the cylinders. You might be able to get the rings to unstick if that's the only issue with it. I have seen ATF or Marvels Mystery Oil used.

You can also mix some acetone with the ATF.  About 40%-50%.  This mix is also good as a penatrating oil on rusty bolts.  Old Grandpa trick.  It is important to note NOT to spin the engine over until the crankcase has been thoroughly drained.  While the stuff (with or without acetone) is good for dissolving rust, broke down oil and other gremlins; it's death on a lubrication system.  Ask me how I know.

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The same color Nighthawk 650 (83) was my second road bike.  Was a great bike and it also cemented my love of two wheels.  As stated above, try to unstick the rings.  Seafoam is also very good option.  Make sure you leave the plugs out when trying to turn the motor after soaking or you will hydrolock the motor.

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l just filled the cylinders with the trans fluid / acetone mix and will let it soak over the weekend. The starter seems to hit pretty hard, but nothing moves at all. I've tried bumping the rear tire in gear since there doesn't seem to be any good place to get on the crankshaft to give it any pressure.

Still watching craigslist / ebay for an engine. I'm sure there are some sitting around where the bike is beat to crap, carbs gummed up and dead battery. I just need to find it.

Keep any suggestions coming.

Edited by ShawnR
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I would purchase one of these $17 borescopes you can use with you phone or laptop so you can actually see in the cylinder. They work amazingly well for the price paid and this will let you see if you should continue further on the suspect engine.  https://www.amazon.com/dp/B01H00AJB2?psc=1 

Marvel Mystery Oil also seems to be a favorite to free up stuck motors. You're lucky the bike has a center stand, place the bike in gear and rock the rear wheel back and forth to try and free the engine. YouTube video of a guy using this exact method on a old CB350 with success.   

 

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9 hours ago, motocat12 said:

, Dry Ice/crc freeze off spray, vinegar,coke, diesel, heat the head from the outside.

 

What if you heated a bunch of oil and filled the whole thing up to coat below the pistons? or turned the bike upside down?

Just my opinion, but I wouldn't try any of that except the diesel on an assembled enging.

1 hour ago, o-no-moto said:

My question is the bike looks super clean doesn't look like it would be locked up from neglect by sitting around. Is the timing chain unhooked to be able to turn the cams? 

 

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2 hours ago, redkow97 said:

how did someone kill a Honda engine????

When I picked it up, he said that the oil pressure light had "flickered" while at idle sometime, but is actually locked up while he was riding it.

I have had penetrating oil on the pistons for a week now and no luck. Cams and crank will wiggle just a hair, but pistons seem completely frozen. I'll probably pull the head next and start tapping/pounding/heating/cooling to see if anything works. If it is locked up this tight, it is probably toast.

Crank & rod bearings are close to $200 themselves, so I'm not seeing a rebuild being worth it.

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41 minutes ago, ShawnR said:

I have had penetrating oil on the pistons for a week now and no luck. Cams and crank will wiggle just a hair, but pistons seem completely frozen. I'll probably pull the head next and start tapping/pounding/heating/cooling to see if anything works. If it is locked up this tight, it is probably toast.

Crank & rod bearings are close to $200 themselves, so I'm not seeing a rebuild being worth it.

In the past I've flooded the cylinder through the spark plug hole to where I can rough measure where the top of the piston is relative to the surface of the oil.  Piston completely covered; I measure the next day to see if it's gone down any.  If it hasn't, I know it's stuck good.  If it's gone down, or if I can see the top of the piston I know it's hammer time.

Also, this is why I recommend ATF.  It has strong detergent additives.  It'll eat through grime, carbon, and other boogers that cause issues.  Penetrating oil; not so much.  Good luck Shawn.

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  • 2 weeks later...

Update: Pulled the head, cams & valves look good. Soaked pistons, heated & cooled, hammered with a block of wood on top of pistons and nothing gives at all. They are pretty close to the top & bottom of the stroke, so there isn't really much force towards rotating the crank to get things moving.

My opinion is that it is probably toast, so I don't have much to lose. I may pull the engine & try to split the case with the cylinders still attached. I could take each rod off of the crank and remove them individually then. I keep watching craigslist/ebay for replacement engine. This was meant to be a fix & flip so not a big deal if it gets parted out.

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Cylinders 1 & 4 from the outside looking in. No real scoring that I could see. I've melted a few pistons over the years (2 strokes) and screwed up cylinder walls, but these look pretty good. Middle 2 pistons are up close to the top so nothing to see.

 

1b.jpg

4a.jpg

IMG_20170101_213245.jpg

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