Topic: 1976 F Worn Valve Guides Question

[Jordonr]

I have a piston ring or worn valve guide question.  I have a 1976 F (47,500 miles) and oil is misting out the breather at a pretty good rate.  Oil mist is starting to cover the bike (and me) after a 30 mile ride.  I suspected worn rings so I did a leak down compression check:  90 psi on the supply side, 83-87 psi on the engine side - which is good, but I could hear and feel air leaking out an open valve tappet cap.  I could not hear or feel air leaking out through the intake runners or exhaust (carbs are removed as is the muffler).  I initially thought the rings were worn and the blow-by was causing pressure in the crankcase and forcing oil out the breather, but now I am not so sure.  The air leaking out the tappet cover makes me think the valve guides are worn.  Anyone have any experience with worn valve guides and or worn rings creating blowing oil out the breather?  I once read that replacing the valve guides on these old bikes is an expensive proposition, so I was wondering if someone has any estimation of repair/replacement costs and procedures. 

Thanks,

Jordon

[Inigo Montoya]

I guess it depends on how much you can do yourself. You will need to take the engine out of the frame and pull of the head. Valves would need to be removed. It is quite a chore and would cost a lot to have a shop do it probably. luckily I have not needed to do this yet.

[ZanVooden]

When I had my engine out (cb750 K8) , I took the head to a machine shop and had them pull the valves and replace the guides, as well as ground the valve seats and such.
Total cost was a little over $300. I provided all the parts including springs and valve guides (not included in the $300).
If its rings, they are fairly easy, in my opinion, to replace.
Either way, requires the engine to be taken out of the frame.

[Big Jay]

It is probably rings. You are probably hearing crankcase pressure coming up the cam chain tunnel and out the top.  The guides are probably worn, but I doubt you could hear air coming past them.

However, send the head to someone who knows about them.
http://www.aperaceparts.com/headwork.html

New guides are $73.08
http://cbrzone.com/sohc.html

Jay

[BlackMax]

Yea, I'd vote for rings, although an "F" with 40,000 miles will usually have valve guides big enough to slide a broom stick through. 

APE does a great job on the heads for a reasonable price; but if you're in a rush.....

[BeSeeingYou]

Yea, I'd vote for rings, although an "F" with 40,000 miles will usually have valve guides big enough to slide a broom stick through. 

APE does a great job on the heads for a reasonable price; but if you're in a rush.....

That is more a problem with the F2/3 bikes.  The 75/6 F0/1 motors should not have any more abnormal valve guide wear than the typical K bike motor.

[Jordonr]

Thanks for all the insight gentleman.  I know I have to remove the motor and open it up, I guess I will see what need replacing then.  Anyone have any luck in resurfacing valves and seats?  I would imagine the seats can be reground, but how about the valves?  As far as I know they are not exotic metal and should clean up as any other valve would - providing of course that the stems are not worn, but who knows.  Just what I do not need at the moment is another money pit, I seem to be able to spend everything I make without another project, I do not need additional help right now. 

In another thought, anyone have any good way to remove the motor besides with a hoist, which I do not have?  I was thinking putting a jack under the motor, removing all the bolts and the strapping two 2x4s to the motor and having a person on each side of the motorcycle grab the two ends of the 2x4s and try to tilt and lift the motor out of the frame. Sound like a plan or am I being sucked into trouble?

Thanks,

Jordon

[Big Jay]

Yea, I'd vote for rings, although an "F" with 40,000 miles will usually have valve guides big enough to slide a broom stick through. 

APE does a great job on the heads for a reasonable price; but if you're in a rush.....

We have pretty good turn around time now.

[Big Jay]

  Anyone have any luck in resurfacing valves and seats?  I would imagine the seats can be reground, but how about the valves?  As far as I know they are not exotic metal and should clean up as any other valve would -

You can grind the valves and remachine the seats after installing the new guides.  It is rare to see a 750 valve that needs to be replaced.

Jay

[bryanj]

Acording to Honda you SHOULD NOT regrind the valve seat angles or tips on the valves as the are stellite coated-----this does not stop you lapping them in with grinding paste(bit of a misnomer----really ought to be called lapping paste!!)

[Jordonr]

Thank you for the info, in the back of my mind I kind of thought there was something funny about those  valves.

Thanks again,

Jordon