71 knock/click Burned valve pics

Re: 71 knock/click left cyl 0lb comp!!!

i would agree with removing the head, safest way to eliminate multiple suspects. at that point you could pull the pushrods and make sure you didn't somehow gain enough clearance for the end to pop off one and be floating around tapping against the cam, which could certainly sound like it was coming from the timing cover.

Re: 71 knock/click left cyl 0lb comp!!!

Sounds like a valve got bumped and will not seat (bent). Didn't you just get the head done? Tight guide?

Check your timing mark and ALL the gearing in there along with the chain.

Re: 71 knock/click left cyl 0lb comp!!!

wow at first I was watching all the other posts roll by. I thought OK well its out there and we will see if a few others chime in. Now I look at its a flood of ideas! Awesome to see the community pull through with the ideas and tips.

As soon as I looked at the compression gauge and it said 0lb I was thinking aw crap the heads coming off. I think I will follow the consensus of "slow and methodical" and just start with removing the head and checking valves valve seats. If all looks well I will pull the cyl and look at the lifters.

Damn thing was running great too! The left pipe was not severely blued but the plug looked lean when I removed it.

Ill make sure and take pictures on this one so if there are findings that can help build our database with answers for the next person in my situation it will be that much easier!

I am getting a little beat taking that tank off so much lately though, its irritating especially trying to avoid nipping the paint. A few weeks ago I dropped a screwdriver on it and of course I had to remove it without tape on the neck so i gave it a nick there. Its stuff only I see does that matter? I wish I didn't see it! oh well, practice makes perfect!

Re: 71 knock/click left cyl 0lb comp!!!

pvisseriii said:

Sounds like a valve got bumped and will not seat (bent). Didn't you just get the head done? Tight guide?

Check your timing mark and ALL the gearing in there along with the chain.

Click to expand...

head hasn't been off, chain looked good, didn't look at the timing mark at tdc or anything though. only valve covers, comp test, timing cover, header off to look in cyl etc.

Re: 71 knock/click left cyl 0lb comp!!!

Re: 71 knock/click left cyl 0lb comp!!!

pvisseriii said:

Click to expand...

YUUUP!! that's the idea man.

Re: 71 knock/click left cyl 0lb comp!!!

Good luck I know how you feel. Got my 75' all done, motor was good (I thought) and then it started to smoke every start up so I thought i will do the guides. Now I am patiently waiting for my FullAuto head to arrive to go with my JS pistons/Carrillo rods and everything else Jim sells! Have fun.

Re: 71 knock/click left cyl 0lb comp!!!

If it is running lean it may have holed the piston.
Also could be a tight valve guide?
Was the valve adjustment off as in to tight or too loose?
If too loose it should still have had comp. If the pad falls off, the pushrod ought to get very loose, might run like crap but should not be down in compression.
Head gasket Ok?
Other possibility for ticking sound and no compression, could be a broken compression ring.They sometimes break but stay put, just need new rings and a light hone if thats the case.

Just some rambling thoughts.

Glen

Re: 71 knock/click left cyl 0lb comp!!!

dougmatson said:

Good luck I know how you feel. Got my 75' all done, motor was good (I thought) and then it started to smoke every start up so I thought i will do the guides. Now I am patiently waiting for my FullAuto head to arrive to go with my JS pistons/Carrillo rods and everything else Jim sells! Have fun.

Click to expand...

Yeah if I didn't enjoy this part of owning a old bike so much I would go crazy. I have a RC51 in the garage that I did a considerable amount of work on but it just doesn't have the soul of the Norton. I don't get excited to take that thing apart like I do the Norton.

I have been getting carried away with buying tons of stuff lately but when the heads off and other things I will try to restrain myself from getting all kinds of other non needed stuff.


I need to disconnect the carbs and I believe I will have enough room to roll the head off and see what we got!

Any good tricks to getting the head off? Last time I did it on the old 850 I cant even remember what I did with the rear bolt. I remember ruining a spanner though!

Re: 71 knock/click left cyl 0lb comp!!!

Looks like the left side exhaust valve is burned. I also placed a flashlight in the header cavity and the valve lets light in all around the circumference.




The cylinder hones look good still which is a good thing. I didn't know it so I checked the pistons and they are 20 over. That's also good news to me!





I just might get out of this without too much pain.

What is the consensus on the route of remedy? Last time I had an issue I just dropped the head off at the cycle place and told them to give it the works. Otherwise I don't have the tools or know how to regrind valve seats or any of that business.

Can't advise you on the valve, but you must be wondering why it's burned. Here's what I did to get rid of those hateful nylocks on the tank studs. Once you get the bottom nut loose it's all finger tight.



Dave
69S

DogT said:

Can't advise you on the valve, but you must be wondering why it's burned. Here's what I did to get rid of those hateful nylocks on the tank studs. Once you get the bottom nut loose it's all finger tight.

Dave
69S

Click to expand...

I am indeed wondering why its burned.

power arc ignition
js flatslides mixture screw 1/4 turn out.

I thought it may be the carb adjustment but I cant understand why the other carb isn't failing the valve there.... The failure also occurred about 150 miles into the trip and this was the end of the day with not tons of speed just under 4000rpm on a level highway and the ambient temp was not super high either.

I am suspecting something had to have gone wonky to trigger the valve burning. I just cant put it together a the moment.

I do feel though I am making strides forward with the bike as a whole.

Earlier I was playing with the idle mixture screw a little bit since I was coming from 3200ft to the beach and back. I had a little fit of low idle at stoplights on the way back. This could be a clue or not. Could I still need to pull the barrels for inspecting the cam and lifters?

Maybe the failure happened there and the result of the failure was the burned valve?

I just went thru this myself. I purchased all the parts and tools, did it myself. Took all of 15 minutes. Pretty easy to do. Just follow the directions. So far working very well.
New guides and valves.
1972-combat-commando-t9840-135.html

iceteanolemon said:

Could I still need to pull the barrels for inspecting the cam and lifters?

Click to expand...

You're 90% there, for goodness sake. It would be a shame to go this far without validating this crucial aspect.

pvisseriii said:

iceteanolemon said:

Could I still need to pull the barrels for inspecting the cam and lifters?

Click to expand...

You're 90% there, for goodness sake. It would be a shame to go this far without validating this crucial aspect.

Click to expand...

OK then off with the barrels!

Ill be posting this one in a few minutes! Stay tuned!

Rider Biilie G, is the man to listen too on this, for me too. Can't just stop on first major obvious thing encountered, even if it all by itself could account for everything noticed, keep going to see cam, and lifters plus check big ends play and if anything nicked rod finish to alert might even part cases to clean stuff out the oil ways. Thank goodness all the parts are pretty neat objects to access and handle compared to the under hood of a small car work activity on moderns. My old ridding lawnmower is more desirable task to pull completely apart than just superfical stuff on my goat crashed and me bashed SV650.

What would make a valve burn and then not seal? What would a bunt stuck valve do to others things connected to yet unseen?

Ah, road side mediation both in the roar of freeways or not another being around but birds in the sun or bugs with moon light, wondering how this one will play out... again.

Familiar symptons...
Funny however you measured 1 mm clearance at the inlet, and apparently no excessive play at the stuck open outlet. You mentioned the left was a bit lean, that might be in comparrison to the right which could be oily. Hard to tell from the pics.
In my case it was the burned oil causing the valve to bind in the guide through just not enough clearance in there on a very hot day. A bad cilinder wall caused the oil to pass, slowly choking the guide, your barrel looks ok though as you say. Good luck.

The plot thickens. The story so far is nothing looks bad.

The lifters are healthy, barely any wear at all. The cam looks NICE. Lobes aren't looking like flaking or anything.

I do notice the barrels were spray canned a while ago while on the bike. The right side barrel looks to have a gouge in it. But when i run my finger over it there is no noticeable groove or anything. Other than that the barrels look pretty darned good.

I might just have them blasted and honed just because they are off.

Pistons are 20 over...

Oh I also notices the rings on the right cyl gaps are opposite and the left cyl the ring gaps are in line with each other. All the piston ring work I have done I make sure they oppose each other.

Before this valve incident I did a compression test and both cyl were around 170lb. It was really good healthy looking compression.

Stellite pads are in tact on the lifters btw....

Could it be the left carb was leaning out just too much? so weird since the needles are in stock position and the adjustments are in spec.

Check out the pics, I got the good camera out for this part...

cyl and rings

cyl and rings


stellite looking good...


stellite again


again...


cant seem to get a good angle on the cam lobes. I tried though....




If anyone sees anything obvious let me know!

Thanks,

Those are the dreaded slotted type pistons ??
As if after what you've just been through you needed to know that...

Get a 2nd 3rd and 4th opinion on that...

If the valve was maladjusted such that it had no clearance, then the engine run a fair bit, the normal result is a burned valve.

Glen