Topic: CB750K Engine Seized

[78CB750K Cafe]

Hello all,
This is my first “problem post” so bear with me please:
I have a ’78 CB750K that I’ve been working on for over 2 yrs now.   My best guess is that it has not been started in over four years.  About 2 months ago, I took a pressure washer to my engine and frame to clean them up.  I covered all the intake/exhaust ports and stayed away from assorted other opening in the engine to be sure I would not get water in the engine, but about a week after pressure washing, I found I could no longer crank the engine.  Up until then, I had been able to crank/rotate the engine using the kick starter with my hands, but it is no impossible to crank.
So far as a solution, poured diesel fuel into all cylinders and it slowly drained out of all but one cylinder, the cylinder on the far left as you sit on the bike (sorry, don’t recall the number).  After this, I put ATF in that cylinder and continued to let it soak, periodically trying to crank the engine via the kick starter, but to no avail.
Following this, I put the engine back in the frame and hooked up the chain and attempted to “rock” the bike free, but this didn’t work either.
My next course of action is to disassemble the top end and try to free the cylinder by hand.  The service manual directs that you rotate the engine to line up certain valve train components in order to remove them.  Here are my concerns:
1. If I cannot rotate/crank the engine, can I properly disassemble the top end?
2. Does the head/valve cover have to be installed and fully tightened in order for the engine to crank?  I ask this because it is not “fully installed and tightened” it is only resting on the engine.
3. What recommendation do you all have as far as freeing the piston once I get the top end off?   I saw one fellow recommend taking an impact driver to it, and that seems needlessly violent.  I’d like to keep everything fairly intact/in good condition so I can get this thing back together and running.
Sorry, for the long post, but I want to include as many details as possible, please respond with any guidance/encouragement/ominous first-hand experience.
Ron

[mikeawish]

Just by chance is the bike in "N" Neutral.

[KingCustomCycles.com]

I have broken loose engines that have sat for over 15 years and returned them to active duty with good compression and no oil consumption.  It can be done.  What I have learned:  The kick starter provides very little leverage, the electric starter can be used if it is tapped for short periods to bump the engine and not held stalled for long.  The bolt under the points cover is the end of the crankshaft and provides direct pressure but is fragile.  I have rocked them back and forth with this bolt and the rear tire with the bike on the center stand to free them.  A propane torch may also be used to heat the cylinder block to loosen things.  I have used ACF-50 which is an aerospace corrosion dissolver in the cylinder to free them.  I hope this helps, and keep us posted.  Mike at KingCustonCycles.com

[kghost]

Just so you know Mike....ACF-50 is a corrosion inhibitor not a dissolver

[78CB750K Cafe]

Just by chance is the bike in "N" Neutral.

I've tried freeing the bike both in and out of neutral.  I can spin the output gear in nuetral and the gear locks up in 1st and 2nd gear.  The cluth will also engage/disengage, so I know it's not the trans/clutch.

[KingCustomCycles.com]

The ACF-50 factory rep at our last Inspection Authorization Conference ( Aircraft Mechanic) described it as entering the pit of corrosion, chemically neutralizing the corrosion, and forming a shield to inhibit further interaction with oxygen and water.  I think the penetrating action, and resistance to forming waxy residue or varnishes are excellent for all sorts of bike lubrication tasks including stuck cylinders. 

[HondaMan]

Just by chance is the bike in "N" Neutral.

I've tried freeing the bike both in and out of neutral.  I can spin the output gear in nuetral and the gear locks up in 1st and 2nd gear.  The cluth will also engage/disengage, so I know it's not the trans/clutch.

78:
It does sound like rust in cylinder #1 (that's the left one as you sit on the bike  .)
Since it is recent rust, and not 10 years' worth (like the one I just tore down), you can probably get it free without damage by removing the head and using a 1x2 or 2x2  board and a hammer on the piston, preferably a 'dead blow' type hammer to transfer maximum torque with the least blows. The torch heating might work, but without getting an eyeball on the amount of rust in there, it could be hard to judge whether the walls are significantly torn up or not. These kinds of rust attacks often cause rapid ring wear, especially if the engine is a K3 or later with the 3-piece oil rings: these rust quick, and deeply. And, they are thin, so they don't shear rust well, which translates to oil burning problems shortly afterward. Normally, I would remove the cylinders in this situation and hone them, install new rings, and reassemble with new gaskets, so everything comes out oiltight.

[78CB750K Cafe]

Just by chance is the bike in "N" Neutral.

I've tried freeing the bike both in and out of neutral.  I can spin the output gear in nuetral and the gear locks up in 1st and 2nd gear.  The cluth will also engage/disengage, so I know it's not the trans/clutch.

78:
 you can probably get it free without damage by removing the head and using a 1x2 or 2x2  board and a hammer on the piston, preferably a 'dead blow' type hammer to transfer maximum torque with the least blows.

I'm sure the 2x2 and hammer technique will work, but as I stated in the original post, the Honda service manual calls for an alignment of the cam shafts prior to disassembly, and if the engine cank crank, I can't align the cam shaft. 

From your experience, can I still disassemble the top end?

[slick68]

JUST WAIT WITH THE DAM HAMMER....LOL

go here

http://seizedengine.com/

it works like a dam

no hammer required..lol

[slick68]

the stuff is called "ENGINE RELEASE"

[Clyde]

Yes you can dismantle the engine without aligning the crank and camshaft.
This is only suggested to make the reassembly easier.
Undo all the tappet adjusters to reduce any tension on the cam, undo the sprocket bolts and release the cam chain from over the sprocket.
Then undo the cam bearing cap bolts evenly
If you have a manual it will show you how to set up the crank/camshaft upon reassembly. It is not hard at all.

You should try to get the motor to turn over before resorting to stripping it down.
How long have you left the diesel in the cylinder? A week is minimum.
I would keep using the back wheel to try to rock the crank loose.

[dustyc]

From an old thread:

I got the April/May edition of Machinist's Workshop magazine yesterday.
Another very talented Lloyd did an interesting test of penetrating oils where he measured the force required to loosen rusty test devices.  Get the issue if you want to see how he did the test.  But, I thought the results he reported interesting.  Maybe you will, too?

Pentrating oil  /  Average load     /  Price perfluid ounce
None             / 516 pounds       /
WD-40           /  238  pounds     / $0.25
PB Blaster       /  214  pounds     /  $0.35
Liquid Wrench  /  127  pounds    /  $0.21
Kano Kroil       /  106  pounds     /  $0.75
ATF-Acetone mix  /  53  pounds  / $0.10

The ATF-Acetone mix was mixed 1 to 1 ratio.

Cheers,

I have yet to try acetone and ATF, but maybe it will help you out.

[bryanj]

Valve cover does not need to be on to turn engine but head does;

If you cant turn the engine over to remove the cam sprocket bolts you can split the cam chain with a grinder and fit a new chain;

As you already have the engine out, which is the hardest part, are you going to de-leak it(gasket kit)?

In order to turn the engine easier remove the generator cover and use the bolt that holds the rotor on to try turning.

They dont normaly sieze that tight that quickly, is it possible some thing is mechanical jammed?

[KingCustomCycles.com]

Spark plugs out during all of this to eliminate hydraulic lock from water or oil?  I agree with the last post, they don't usually seize that fast or that hard. 

[HondaMan]

From an old thread:

I got the April/May edition of Machinist's Workshop magazine yesterday.
Another very talented Lloyd did an interesting test of penetrating oils where he measured the force required to loosen rusty test devices.  Get the issue if you want to see how he did the test.  But, I thought the results he reported interesting.  Maybe you will, too?

Pentrating oil  /  Average load     /  Price perfluid ounce
None             / 516 pounds       /
WD-40           /  238  pounds     / $0.25
PB Blaster       /  214  pounds     /  $0.35
Liquid Wrench  /  127  pounds    /  $0.21
Kano Kroil       /  106  pounds     /  $0.75
ATF-Acetone mix  /  53  pounds  / $0.10

The ATF-Acetone mix was mixed 1 to 1 ratio.

Cheers,

I have yet to try acetone and ATF, but maybe it will help you out.

Very interesting, Dusty!
I just took apart the first Hondaman Special engine, which was seized so badly from being open for 10 years that the cylinder wall on the #4 is grooved 0.5mm deep from the rust alone, around those 3-piece oil rings. It will have to be bored at least .75mm oversize to clean up. But, it was so stuck that even with the cylinders off the engine (rod hanging out in the wind...) and blocked up in the air, after soaking with everything listed above (except the last item), I had to DRIVE it out with a 2" pipe and a sledge. Usually only the 2-strokes that went thru a creek, then got stored for a year, were this bad: this was the worst single Four I have ever encountered, although I've worked on quite a few stuck ones.

&*: yes, you can get the cam out, like Clyde says. You just need a thin 10mm combination wrench if one of the sprocket bolts happen to be in the  bottom position, like this last engine of mine was: tricky to prevent dropping the bolt down the cam chain tunnel, but entirely do-able. 

[78CB750K Cafe]

You should try to get the motor to turn over before resorting to stripping it down.
How long have you left the diesel in the cylinder? A week is minimum.
I would keep using the back wheel to try to rock the crank loose.

I have had either diesel or ATF in that cylinder for 4-5 weeks.

Spark plugs out during all of this to eliminate hydraulic lock from water or oil?  I agree with the last post, they don't usually seize that fast or that hard. 

Yes, the spark plugs have been out.  I will take a closer look down the cam chain tunnel and around the valve train to check for any visible mechanical binding.  I guess something could have fallen down there, i.e. screw/nut/etc.

[kghost]

The ACF-50 factory rep at our last Inspection Authorization Conference ( Aircraft Mechanic) described it as entering the pit of corrosion, chemically neutralizing the corrosion, and forming a shield to inhibit further interaction with oxygen and water.  I think the penetrating action, and resistance to forming waxy residue or varnishes are excellent for all sorts of bike lubrication tasks including stuck cylinders. 

Yeah they said that at mine too a few years back.

From experience I can tell ya that while it doesn't get waxy...it does congeal a fair bit.

[78CB750K Cafe]

FYI guys, I've spent the last few weeks trying difference techniques, so I'm down to breaking down the head and trying to break this thing loose up close and personal.

I tried diesel, ATF, ATF w/ acetone, ACF-50, rocking it back and forth...nada.  I'll let everyone know how it turns out.  Thanks again for all the insight.

[78CB750K Cafe]

okay, here's the results:

I was able to break the engine down and get everything apart.  I originally wanted to only take the head of, but as I was rocking the head and jugs, it was easier to get them both off.  Now that they're off the block, any advise on separating two?
I was able to get the piston from cylinder 1 out of the bore and take it off the con rod.  Overall, I'm happy with what I found.  There is definitely some corrosion within the cylinder, but I'm pretty sure I can clean it out of there once I get the head and jugs separated.  Also wondering if I should replace my piston rings on all my pistons.  Necessary?  Good thing to do while it's apart?  Let me know.
I was able to crank the engine with the kickstarter and everything seems to rotate smoothly, so I'd say that's progress.  Now all I have to do is put it all back together
Next question: Any of you recommend upgrading my cam/pistons while this whole thing's apart.  Keep in mind it hasn't run in a few years, so if installing hot cams will create a more finicky machine, I may shy away from that, just curious what your thoughts were

[78CB750K Cafe]

here's a couple more pics, one is of a mar I saw on all my pistons, I'm guessing it's from the intake valves being out of adjustment and travelling too far into the combustion chamber.  The other is what pretty much all my pistons looked like when I first got to them.  I've since cleaned them up.  The pic in my previous post is the inside of cylinder 1, and you can see what it looked like in there.  Some nasty looking corrosion, but I think I can clean it up.
Once again, I appreciate all your guys help, I'll keep you posted on further progress, probably in another thread.

[cafe750]

Ron,
Did you get the four screws underneath the rubber pucks on the head?
if not, that may be where they're stuck together. Those marks in the pistons are there from the factory, so that the intake valves don't hit the piston...

[goon 1492]

Ron,
Did you get the four screws underneath the rubber pucks on the head?
if not, that may be where they're stuck together. Those marks in the pistons are there from the factory, so that the intake valves don't hit the piston...

Yeah what he said  , and on that note those are some pretty clean pistons ya got there, and I would go ahead and get new rings, gaskets, and probably could do a little cleaning up in the ports on the haed. Not quite a "stage 1" but just tidy up a bit while your in there and if will give you more time to poke around, read, poke around, and learn alot more than you think. Hope you put all the right screws in bags or cups and labeled them, you'll thank yourself later, good luck.

[78CB750K Cafe]

Ron,
Did you get the four screws underneath the rubber pucks on the head?
if not, that may be where they're stuck together. Those marks in the pistons are there from the factory, so that the intake valves don't hit the piston...

Yeah, I got the screws from under those rubber pucks, I think the gasket is sticking them together. 

I also was highly organized with the screws/parts I removed.  I used those plastic drawers they sell for organized screws and labeled each drawer according to the part that's in it, i.e. cylinder 1 exhaust rocker arm, and so on.
Thanks again for the advise.

[grgjms01]

This is to Hondaman or anyone who has some thoughts. I recently aquired a 750k2 fr a couple hundred bucks. Single owner and everything is there, never been tken apart and not ridden since 1987. Problem: it sat outside since then. So long that the complete exhaust has rotted of of it. The motor is stuck obviously but crazily enough everything else looks really good and is a complete bike and im venturing into my first total rehab/rebuild. The gentlman who sold me the bike has 2 more 750k engines that turn freely. Would it be worth it to grab one of them from him and go with it?, as I plan on redoing the motor at 836 anyways?..Save the hassle of hard dissasembly..I havnt even began dissassembly, acquiring vehicle this weekend. Should I try to free it..wee what happens? Thnks for the input fellas.

[HondaMan]

This is to Hondaman or anyone who has some thoughts. I recently aquired a 750k2 fr a couple hundred bucks. Single owner and everything is there, never been tken apart and not ridden since 1987. Problem: it sat outside since then. So long that the complete exhaust has rotted of of it. The motor is stuck obviously but crazily enough everything else looks really good and is a complete bike and im venturing into my first total rehab/rebuild. The gentlman who sold me the bike has 2 more 750k engines that turn freely. Would it be worth it to grab one of them from him and go with it?, as I plan on redoing the motor at 836 anyways?..Save the hassle of hard dissasembly..I havnt even began dissassembly, acquiring vehicle this weekend. Should I try to free it..wee what happens? Thnks for the input fellas.

That's exactly the sort of "package" I look for, so I can build these 750 restos I'm doing. I'd sure go for it! In fact...if you don't, is he in Colorado, by chance?