Topic: Head gasket issue: CB750

[Tugboat]

You can see it there in the middle - 9mm long x 5mm deep chunk of head gasket is missing on the left side of my motor. I know this will eventually need to be replaced, but would it help to try and get some gasket goo in there from the outside?

[Tugboat]

Also, this motor runs fine other than this and the ubiquitous valve cover gasket leak. So what's the least I can get away with when I go to change the head gasket? Hone, rings - sure. Replace valve seals & lap in valves? Anything else I should consider?

[phil71]

There's no point in putting goo in there. If the head gasket were actually leaking, there'd be evidence of a blow out there, and there isn't. You have to remember that the actual sealing surface for the combustion chamber is a steel shim o-ring. That little chunk has nothing to do with that.

[lucky]

Also, this motor runs fine other than this and the ubiquitous valve cover gasket leak. So what's the least I can get away with when I go to change the head gasket? Hone, rings - sure. Replace valve seals & lap in valves? Anything else I should consider?

You did not tell us how many miles are on the engine.
Before lapping the valves I would take the valve springs off and check valve wobble in the valve guide. Lapping a valve with a worn out guide could make things worse.
You have to remove the valve retainer anyway to put in new valve guide seals.


I would check the rollers in the cam chain tensioner to see if they are crumbling into pieces.

[Tugboat]

There is actually evidence of blow-by there. I cleaned it up to get a good pic. Dark black stuff, not "just oil" like my valve cover leaks

So I guess that's my real question.. as long as this leak is not affecting performance on the #1 cylinder, can I just live with it?

As to the engine itself: it's a replacement '77K motor on my '76F frame. Got it on ebay last year for a couple hundred.. had been sitting under a tree - on a bike - in upstate NY for about 20 years. I'm guessing that the gaskets just dried up, ergo the failure here. Supposedly only 11k miles on it.

[phil71]

It's not blowby. A compression breach would be a whole different ball game. If it runs fine, leave it alone. If you want it to stop leaking oil. pull it apart.

[chewbacca5000]

It's not blowby. A compression breach would be a whole different ball game. If it runs fine, leave it alone. If you want it to stop leaking oil. pull it apart.

+1 here.  Wish I hadn't pulled my 72 apart.  It smokes due to no valve seals on the exhaust and 1 piece oil rings.  Not worn guides.  Now I am pulling my hair out.  Get some enjoyment out of it then give it the works HD studs, resurfacing, .5 over bore, and a Serdi valve job.  I love Serdi!

[Kickstart]

You can see it there in the middle - 9mm long x 5mm deep chunk of head gasket is missing on the left side of my motor. ...

That's not a chunk missing.  I believe my head gaskets have that same notch in them (not in the garage right now, but I recall seeing them on each side of the engine when I removed the head on my project bike).

Also, I don't think that's a lot of oil... I've seen worse oil leaks around the head.

I agree with others... leave it alone for now.
If you must replace the gasket (more importantly, the head o-rings and the pucks underneath the cam towers) I would wait until it gets colder... enjoy riding in the fall weather first. 

Many years ago I decided I "had" to replace the head gasket for the same reason... I rushed putting it back together in order to have it ready for a long weekend ride with friends.... in the process a very small piece of gasket material fell into the left side oil passage.  That tiny piece of debris clogged the oil orifice in the head and the left side of the cam/rocker area was oil starved.  Bike stalled out 50 miles into the ride.  Killed my engine.  If you do this... take your time and be meticulous.

[Tugboat]

Thanks for the advice. I did a compression test when I got home from work: 140 140 150 155. Will keep an eye on it to make sure I'm not losing compression and jut replace my Oil Tampon when it gets nasty.

[phil71]

You know how far that divot is from the actual combustion chamber sealing surface? Short of someone using an icepick and a hammer right at the chink in the armor (can we still say that?) you're not going to be losing compression anytime soon.
  Keep up on the oil and ride it like you stole it.

[Cabilao]

had the same problem with my Z900. If no blow out or loss of power,leave it like it is. I did more than 3000km with my Bike without problems. Than i change because of other problems.

[dhall57]

You can see it there in the middle - 9mm long x 5mm deep chunk of head gasket is missing on the left side of my motor. ...

That's not a chunk missing.  I believe my head gaskets have that same notch in them (not in the garage right now, but I recall seeing them on each side of the engine when I removed the head on my project bike).

Also, I don't think that's a lot of oil... I've seen worse oil leaks around the head.

I agree with others... leave it alone for now.
If you must replace the gasket (more importantly, the head o-rings and the pucks underneath the cam towers) I would wait until it gets colder... enjoy riding in the fall weather first. 

Many years ago I decided I "had" to replace the head gasket for the same reason... I rushed putting it back together in order to have it ready for a long weekend ride with friends.... in the process a very small piece of gasket material fell into the left side oil passage.  That tiny piece of debris clogged the oil orifice in the head and the left side of the cam/rocker area was oil starved.  Bike stalled out 50 miles into the ride.  Killed my engine.  If you do this... take your time and be meticulous.

I agree. No piece missing. My 750's are the same, must be way it's designed. Do a search on paper towel trick. This will solve your problem until it gets much worse.

[lrutt]

1/4" cotton rope from Ace hardware really does the trick once it's cleaned up in there. Been running that on my 78 750 for 3 years now, replace yearly, no problem. Oil doesn't leak out past the rope. Just jam it in there with a screw driver. You can't even tell it's there unless you really look for it.

[Tugboat]

LOL That's what I meant by "oil tampon"! A couple of weeks ago I had an actual tampon shoved in there, but you know what? It wouldn't fit all the way in there and finally fell out when I was on the interstate. Maybe I needed a slimline one? Ladies?!

[phil71]

I use maxipads

[Sdsbassist]

Great idea!

1/4" cotton rope from Ace hardware really does the trick once it's cleaned up in there. Been running that on my 78 750 for 3 years now, replace yearly, no problem. Oil doesn't leak out past the rope. Just jam it in there with a screw driver. You can't even tell it's there unless you really look for it.