Engine is stuck!

[Kingrukus]

Hello everyone,

I am new to the forum but I have owned many a CB 750! I am about to acquire a 1974 all original with 8k. Been parked in a garage since 1986 and the engine seems to be stuck. Of all the bikes I've had I have never had to deal with this in the past so I need some help here. What is the best method of trying to free it up?

Thanks in advance!

[Beekeeper]

My 750 was parked and not started or moved from 1987 until summer of 2012.  When I finally decided to try to get it running, it was dry seized.  Per the Guru's here, I pulled the plugs, and put Marvel Mystery oil and let it soak for several days.  Put it in high gear and rocked it a few times.  I felt it break loose, so added more oil and let it soak a couple more days.  Rebuilt the carbs and got it started.   Lots of work on other systems, but she runs like the scalded cat she always was!  I would get some kind of assurances from whoever you got it from that nothing is broken as far as they know.

[Kingrukus]

Hey,
Thanks for the info....that is exactly what I'm going to try! I only paid $300.00 for it I can part it out for triple that if the motor is toast. I hope it isn't, she said it ran when they parked it there.

[Re-run]

A lot will depend on how it was stored too. Outside uncovered means good chance it wont break free and will need an overhaul. But from the looks of it, I assume it was inside. That should hopefully make it much easier.

[Beekeeper]

Thing looks in pretty good shape.  Did you get it broke loose?  I just ran through the valve clearances and am trying to decide what to do with the VC.  I wire brushed the peeling paint, and started light sanding with 600 grit wet paper.  Not sure that is the way to go, and am now considering finding a bead blaster or something to smooth things out and repaint.  The polishing idea is going out the window.

[Kingrukus]

Well, I poured the Marvel Mystery oil into the spark plug holes and let it sit for three days. When I went out and looked at it all the oil had leaked down into the crankcase past the rings. I assumed it was going to break free but it is still stuck. I know it went through the cylinders because I have the carbs and exhaust off and it didn't leak out from any of the valves....(well a little when I first filled it but most stayed in the bore). I refilled the cylinders and will try again in a few days! Anyone have a sohc 74 engine for sale that isn't stuck?

[LukeM]

Don't rush it.  Let the oil do its job.  Marvel Mystery Oil is very low viscosity stuff, so I would expect it to run past the rings after some time. There may be some issues elsewhere (like a dry bearing at the crank). Slow and steady wins this race.

Luke M

[mikeyboy1]

I went thru this w/a pair of 750's this winter.I had to put rings in.soaked in Marvel for weeks.plus some stuff I got from a guy in Canada which was "guaranteed" to free up rusted motors. it wasnt so much rust as the fuel had "fossilized" in there. had to pull the motors & do rings,carbs,etc. BUT it was well worth it!! I've got 2 bikes that run great for less than the price of a newer one.the brakes were totally shot on one of them,the other was good.the fluid had solidified !! rebuilt the hydraulics.great,fun projects that I ride every day.lots of great help here.these guys know their stuff.
like my Pops used to say--"dont be scared-go haaaard !! "

[LukeM]

You might also try PB Blaster.  It's a very low viscosity oil with some rust break-down compounds in it. If you can find it in a bottle vs. the spray can, you can dump a lot of it on stuff.  But the spray can may do the job as well.

This all is assuming the issue is stuck rings, and not something else like a stuck bearing or broken trans/chain or other stuff.

Luke M

[Kingrukus]

Is there any way to get the marvel oil into the bearings and valve train? I can move the rear wheel and shift the trans through all the gears. The clutch is functional so I'm sure it isn't in the trans. I would assume if the bike had oil in it all these years (it did) that the crank bearings would not be the issue either? I was thinking of just over filling the crankcase with just marvel and letting it sit for a few more days. Any idea how long this should take? Also, what is the best method for turning the engine over? Kickstarter, bike in high gear and pop the clutch or socket on the crank shaft?

I have watched a couple of youtube videos of a guy running diesel fuel mixed with marvel through the engine with a pump of some sort, in the bottom end through the oil lines and out the top through the breather port on the head. Anyone tried this?

Also heard of some stuff called "kroil" which is supposed to free up any stuck metal parts. Anyone tried this stuff?

I really need to get this unstuck so I can rebuild it and get it on the road!

[Beekeeper]

I climbed aboard mine and started rocking both forward and back in 5th gear.   I'm a load at 6'4 and a snicker bar under 300, so it probably gave up rather than having a toad like me bouncing back and forth on it.  After another couple days, I hooked up a weak car battery I use for charging model airplanes and let the starter crank it over.  It surprised me when it quickly built enough oil pressure to make the idiot lite go out.  After that it was just the time it took to rebuild carbs, master cylinders and calipers, fork seals, yada yada.  I've ridden the old girl into Idaho and Wyoming with barely a hick-up and put a little over 5,000 miles on it last year.  Definitely worth the effort.