Topic: unstick engine or talk me down

[thelowmax]

I've got a lead on a cosmetically decent bike that has been barn stored for 20 years. It only has one minor issue. What does it take to unstick an engine? I know taking it completely apart will most likely be the obvious answer, but what are the possible issues I might encounter? What is the likely damage to the engine? Will the pistons need to be replaced? Is there a way to permeate it with lubricants to unstick it? Maybe some SOHC elfin magic? I'm not afraid to tackle a big job. I just don't want to dig a hole to throw my money in (If I want that I'll get a girlfriend ). If the pistons are shot, would this be a good candidate for a Big Bore upgrade?

I haven't made the purchase yet but I'm on the ledge with cash in hand. I would appreciate your advice and support. And I'm sure that I will carefully consider it after I make a mess of things .

[SOHC Digger]

Consider the bike as if the engine were completely missing.  If it's still worth the price to you, pick it up.  If you can salvage the engine, bonus!  If not, you still got something worth your money.

Seized engines can be something as benign as rusty cylinders or as malignant as a lower end roasted from lack of oil.  It's hard to say what could be the culprit, but a total teardown is most likely.

[Alan F.]

True, but by the same token...a little marvel mystery oil down the spark plug holes for a week or two followed by warming the fins gently with a propane torch, and gentle application of torque to the rotor bolt could just break it free. Worst case you'll have to tear it down after that, best case has happened many times to many members...all will be well and proven by a consistant compression level across all 4 cylinders. If all is well to begin with it can sometimes improve after a few hundred miles into a very happy engine that doesn't burn oil. It has happened.

But since you're in eastern Massachusetts, you're in a good place as far as owning a CB750 is concerned, there are quite a few esteemed members in this area. If you haven't yet joined www.nehondaguys.info please stop by. All is known, and very little is left to chance with these bikes.
Alan F.

[thelowmax]

I was basically looking at it as an engine-less bike but the over-achiever in me always wants more. I figure one more paperweight in the driveway will hardly be noticed.

I'm jumping into the deep end. Thanks guys!

[Terry in Australia]

The 50/50 Transmission fluid/Acetone mix is good for unsticking rusty stuff, and a couple of guys here have used it successfully to unstick engines. Tip some down your sparkplug holes at regular intervals for a few days and see if that doesn't work. (brush/spray some around your sparkplugs first, they tend to corrode into position after sitting for awhile and if you're not careful, you can strip out the threads)

It's easier than a tear down, not forgetting that even if you strip the engine it'll still be a royal PITA to remove the rusted cylinders off your rusted piston rings. Easy works better for me. Cheers, Terry.    

[Stev-o]

I "unstuck" my motor last month with ATF/acetone cocktail! It's easy and it works.

Read here -->>  http://forums.sohc4.net/index.php?topic=77533.0

How much is he asking for the bike?

[DavePhipps]

I used PB blaster in the spark plug holes once a day for 4 days or so.Turned the crank and and it broke loose. Watch out, as the fluid will shoot a good distance. I had one messy wall after that.

[Stev-o]

I used PB blaster in the spark plug holes once a day for 4 days or so.Turned the crank and and it broke loose. Watch out, as the fluid will shoot a good distance. I had one messy wall after that.

Mine shot 18'!! That's what I call a money shot!