Topic: Top End Advice

[BrickWoll]

Hello All,

Chasing a leak on my '77 550K, I was advised to replace the pucks and side cover o-rings.  I decided since I was going to have the valve cover off, I'd just go ahead and do a complete gasket and o-ring replacement to the bottom gasket.

After getting the motor apart, I'd like some experienced advice on the state of my piston heads and valves.  They look pretty mucked up, but maybe that's common for a bike this old.  More concerning are the dimples in the face of the piston heads.  Is this by design or possibly the sign of a valve not seating properly?  Pics attached.

Appreciate any advice.

[bryanj]

The recesses are there for valve clearance

[BrickWoll]

The recesses are there for valve clearance

Thanks bryanj. Otherwise look as expected? Should these areas be cleaned before closing it up?

[PeWe]

Yes, piston tops and chambers look like a very dirty grill. Brush it clean.
Sure that valves,seats and guides are OK?

[BrickWoll]

Yes, piston tops and chambers look like a very dirty grill. Brush it clean.
Sure that valves,seats and guides are OK?

Thanks PeWe.  Brass brush good for heads and valve faces?  Unfortunately, I do not know how to assess whether valves are seated properly.  I'll research it in the manual, but if you have any tips I'd appreciate it.

Thanks.

[MauiK3]

Since you are there, check the cam chain tensioner, worth replacing at this point.
A valve job would be a good idea, be sure whoever does it knows these engines. Hondaman and a few others are the local experts.

[bryanj]

Changing valve stem seals at this point is a good idea as is lifting the cylinders to replace base gasket with O rings.
Put up a picture of the adjuster blade but unless its falling apart they dont often need changing.

READ THE MANUAL CAREFULLY BEFORE REFITTING VALVE COVER. If you dont you will bend valves, cost yourself a lot of money and have to do the job again.

[BrickWoll]

Changing valve stem seals at this point is a good idea as is lifting the cylinders to replace base gasket with O rings.
Put up a picture of the adjuster blade but unless its falling apart they dont often need changing.

READ THE MANUAL CAREFULLY BEFORE REFITTING VALVE COVER. If you dont you will bend valves, cost yourself a lot of money and have to do the job again.

Bryanj - the plan is to replace all the areas you mentioned.  As soon as I get the cylinders off, I'll put up a pic of the blade for eval. Thanks for the caution on the valve cover.  I'll research and follow the manual.

[BrickWoll]

Per the manual, the cam chain guide should lift up then 90 deg turn to remove.  It doesn't seem to lift high enough for the pegs to clear the grooves and spin.  Anyone had this issue? 

[bryanj]

I think you have to lift the cylinders to get that  out

[BrickWoll]

I think you have to lift the cylinders to get that  out

bryanj - it's definitely prior to cylinder removal in the manual. Regardless, I've loosened the cylinders enough to lift them and this doesn't seem to help.  The issue is the distance between the bottom and top pins is not long enough to do as the manual states, which is it should be a simple raise and turn 90 deg. There is no way that's possible on mine. Very frustrating place to pause on the teardown.

[bryanj]

In that case i would suspect the cam chain has dropped a bit and caused a loop jamming the bottom, its been a while since i stripped one, just got several to build!!

[BrickWoll]

Cam chain guide issue solved. The guide had significant cracking at the top. The result was that it was being bent to a curve that I don't think it's meant to have. Because it was bent over, the distance between the top and bottom pegs was reduced making it very difficult to lift and turn as the manual states. It finally came out, but it took some force. This was a disaster waiting to happen.  It looks like it could come apart at any time. Opening the motor has already paid off.

[DaveBarbier]

Regarding cleaning, clean what you can but don’t worry about getting it spotless. The gasket surfaces are another story. As clean and smooth as you can. Have the head and cylinders decked slightly is an option to get a nice smooth flat surface and you don’t have to spend time cleaning gasket material.

But if you are going to do it manually, the best thing I’ve found is a razor blade held completely perpendicular to the surface and scrape. It won’t gouge the aluminum and just scrape off the gasket. It will be slow going though.

[bryanj]

I have done a lot of these motors and never seen one like that, i suspect a po has done something wrong before

[PeWe]

If you have no plan to take everything apart to clean it.
Cover all holes on cylinder where the carbon can enter.

I cleaned my CB750 engine a few weeks ago.
Removed head and taped all holes. Not good if dirt enter the oil feed holes or return.

The center and most dirty part of the piston tops brushed clean with a small round metal brush on a drilling machine not touching the bores.

The dome sides close to bore manually with metal brush look like a big tooth brush, not scratching the bores. Upper carbonized part of bores cleaned with a cloth drained in WD40. Fine grit grinding paper to remove the hard carbon.

Brush will losen strands so very important to really cover all holes.
1,4 at TDC, then 2,3 at TDC or opposite. You need to help cam chain by hand when rotating crank so it will not lockup around crank.

I used a vacuum cleaner  to suck all dirt from bores before moving them. Again before removing all tape.
Before and after brush photos.

[BrickWoll]

If you have no plan to take everything apart to clean it.
Cover all holes on cylinder where the carbon can enter.

I cleaned my CB750 engine a few weeks ago.
Removed head and taped all holes. Not good if dirt enter the oil feed holes or return.

The center and most dirty part of the piston tops brushed clean with a small round metal brush on a drilling machine not touching the bores.

The dome sides close to bore manually with metal brush look like a big tooth brush, not scratching the bores. Upper carbonized part of bores cleaned with a cloth drained in WD40. Fine grit grinding paper to remove the hard carbon.

Brush will losen strands so very important to really cover all holes.
1,4 at TDC, then 2,3 at TDC or opposite. You need to help cam chain by hand when rotating crank so it will not lockup around crank.

I used a vacuum cleaner  to suck all dirt from bores before moving them. Again before removing all tape.
Before and after brush photos.

What a difference. That looks great! I've already taken the cylinders off, so it seems like a small step to remove the piston heads for proper cleaning. I was considering soda blasting the fins while it's apart as well.  Might as well get it all done.  I don't think the gunk between the fins has been addressed since '77.     

[BrickWoll]

I have done a lot of these motors and never seen one like that, i suspect a po has done something wrong before

Yeah - not sure what you can do wrong other than put it in upside down (which it wasn't). Too much tension on the chain over a long period of time maybe?


 

[bryanj]

More likely fitted it wrong, tried to force the chain on then fitted it right

[PeWe]

These old bike can have a long interesting history!