Would you run the engine with this broken exhaust valve guide

I have a '78 Z1R that hasn't been run in maybe 15 years?  I took the exhaust off maybe 5 years ago and just happened to notice that one of the valve guides was missing a small piece.

I asked my dad about it (this bike was his) and he basically said "don't worry about it!"  But I'm having trouble not worrying about it.  What do you folks think?  Do I need to pull the head and have it redone?  And if so, where should I send it?  

It also looks like the valve seal is bad, based on what the other valves look like.  

 

I wouldn't run that, it looks like carbon buildup from a leaky valve seal  has smashed the guide away, the whole area needs a good clean up...

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I wouldn't run that, it looks like carbon buildup from a leaky valve seal  has smashed the guide away, the whole area needs a good clean up...

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X2.

Good reason and excuse to tear the motor down and refresh it. Sooner or later, the guide gonna scratch the valve anyway. Fix it before it does more damage.
 

The actual missing piece isn't a problem as it doesn't affect the valve stem support.
Many guides get cut back further than that when porting has been done.
Continuing to run it like that won't do any harm but the wet stems and carbon build ups means it's due for a clean up and new seals at the least.
If the bike runs fine though its not in any danger of anything major happening.

 

I would also be worried at the potential damage the broken piece did before it’s exit, fingers crossed none at all but it would be a reassurance to know.

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The actual missing piece isn't a problem as it doesn't affect the valve stem support.
Many guides get cut back further than that when porting has been done.
Continuing to run it like that won't do any harm but the wet stems and carbon build ups means it's due for a clean up and new seals at the least.
If the bike runs fine though its not in any danger of anything major happening.


 

If that piece has been fbroken by carbon on the valve forcing it out, there's a chance that the integrity of the rest of the guide, at least the underside , has been compromised.
Personally, I just wouldn't risk it. Much cheaper to fix it now than after it fails... That's my way of thinking anyway..

Carbon build up doesn't cause chipped guides.
There is no opportunity for carbon to build up on the part of the stem that constantly sweeps the guide.
I've seen this many many times and the most likely cause is excessive guide wear and bellmouthing at the broken end which allows side load from the stem on the guide in the same plane ( fore and aft ) as the sweep of the cam lobe or a fracture of the guide on installation.
The black varnising further up the stem indicates excessive valve to guide clearance but will not build up more than the clearance allows as it is constantly wiped when running.
In the current situation it is clear that it's been like that a long time and unlikely to cause any other issues apart from the on going wear and oil usage.
It's clear that ideally the head ( and probably the whole top end ) needs a overhaul but the chipped guide on it's own doesn't pose an imminent problem and the bike could be run for years like that if you wanted to put up with it.



 

wrote:

Carbon build up doesn't cause chipped guides.
There is no opportunity for carbon to build up on the part of the stem that constantly sweeps the guide.
I've seen this many many times and the most likely cause is excessive guide wear and bellmouthing at the broken end which allows side load from the stem on the guide in the same plane ( fore and aft ) as the sweep of the cam lobe or a fracture of the guide on installation.
The black varnising further up the stem indicates excessive valve to guide clearance but will not build up more than the clearance allows as it is constantly wiped when running.
In the current situation it is clear that it's been like that a long time and unlikely to cause any other issues apart from the on going wear and oil usage.
It's clear that ideally the head ( and probably the whole top end ) needs a overhaul but the chipped guide on it's own doesn't pose an imminent problem and the bike could be run for years like that if you wanted to put up with it.




 

I understand, but I still think  there's the risk, without cleaning and having a good look, that the guide could be weakened further up, if the guide has excessive wear, and it looks like it does, it would blow smoke and use oil anyway, maybe I'm over cautious but either way I'd fix it...

To each their own, but if that engine was mine, I'd tear it down and fix the head.  The valves look loaded with carbon anyway.

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To each their own, but if that engine was mine, I'd tear it down and fix the head.  The valves look loaded with carbon anyway.

 

I agree that it's probably the right thing to do.  But I really don't know where to send it.  It seems like it would be cool to have some porting done while it's off, but I don't want it to get messed up.  How do I find someone who actually will do it right and end up with a real improvement?  Now that Larry is gone, who is the second best?

At the moment I don't have a shop to work in, but I'm hoping to have something set up later this year. I figure I could pull the head and send it out and have it ready to go back on once I have space to work again.  Once I figure out where to send it...

wrote:

wrote:

To each their own, but if that engine was mine, I'd tear it down and fix the head.  The valves look loaded with carbon anyway.


 

I agree that it's probably the right thing to do.  But I really don't know where to send it.  It seems like it would be cool to have some porting done while it's off, but I don't want it to get messed up.  How do I find someone who actually will do it right and end up with a real improvement?  Now that Larry is gone, who is the second best?

At the moment I don't have a shop to work in, but I'm hoping to have something set up later this year. I figure I could pull the head and send it out and have it ready to go back on once I have space to work again.  Once I figure out where to send it...

Take this for what it's worth, but a big KZ already makes more than enough power to get a sane person into trouble, so why bother spending several hundred dollars for a minor increase in power via porting?  On my bikes under rebuild, I do some mild pocket porting to knock off the sharp edges and blend casting imperfections, and then call it done. 

I've got some Neeway cutters that I've used for several rebuilds, and they work great for cleaning up the seats.  I'm half way tempted to put them in rotation for guys interested in doing their own valve jobs.  The cutter inserts wear, so buying inserts may be the cost of rotation?

wrote:

Carbon build up doesn't cause chipped guides.
There is no opportunity for carbon to build up on the part of the stem that constantly sweeps the guide.
I've seen this many many times and the most likely cause is excessive guide wear and bellmouthing at the broken end which allows side load from the stem on the guide in the same plane ( fore and aft ) as the sweep of the cam lobe or a fracture of the guide on installation.
The black varnising further up the stem indicates excessive valve to guide clearance but will not build up more than the clearance allows as it is constantly wiped when running.
In the current situation it is clear that it's been like that a long time and unlikely to cause any other issues apart from the on going wear and oil usage.
It's clear that ideally the head ( and probably the whole top end ) needs a overhaul but the chipped guide on it's own doesn't pose an imminent problem and the bike could be run for years like that if you wanted to put up with it.

Yep I agree, that buggared valve guide isn't going to cause the engine to take a dump, but the engine must have done a ton of miles and needs a top end rebuild, at least.