71 knock/click Burned valve pics

P.S. Who did the valves/guides recently on your head ?

Its quite common for car guys to do the valve guides too tight, watercooled clearances are less that aircooled motors need.....

Only obvious thing to me not yet causing a problem are the taboo oil comma hole fatigue stress riser pistons you've lucked on on, so far. Only takes one to let go to make ya shy of why taboo forever more.

Otherwise noise evidence remains an interesting mystery that ain't mine this time, but could be anytime. i've have carb floats or manifold come loose on one side to run lean hot/stumbles but felt the effect and eventually accidentally found the reason, but didn't hurt engine to make mechanical noises. I couldn't see anything peckering the chamber so didn't inhale much to matter. I'd run those lifters again too. Cam does looked a bit more scuffed than burnish polished but quite usable a long time yet. Its possible I found out the hard way the bore blems than can't be felt can over the mereist re-hone finish can still allow blew by til worn in eventually 1000's of miles later,if ever. Last few times I've seen used rings the gaps were still staggered close to initial install, in case that's a clue sniff out on your lined up gap side. Carefully turn crank through a cycle to listen for anything lower down too, but highly unlikely. Did ya look inside TS case yet? Manual says every 5000 miles so just following instruction when all else fails.

Rohan said:

Those are the dreaded slotted type pistons ??

Click to expand...

But only if they are the fully slotted type. http://www.norvilmotorcycle.co.uk/techtalk34.htm

L.A.B. said:

Rohan said:

Those are the dreaded slotted type pistons ??

Click to expand...

But only if they are the fully slotted type. http://www.norvilmotorcycle.co.uk/techtalk34.htm

Click to expand...

I just took a look at them and noticed the slot doesn't follow all the way around.

I guess combat type...

So that being said, is there a chance this is a combat spec motor? I don't know how to tell.

worntorn said:

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

Click to expand...

Well I have not done an adjustment on the valves in a while since there has been no noise etc. I have not had the head off or serviced either. When you say "no clearance" you mean if its adjusted too tight? So weird as I noticed it loose at 1mm when I got the bike home and looked at it. Also the nut was tight so its not like it maladjusted by being worked loose. I may have to stare at it some more to find what went wrong.

iceteanolemon said:

So that being said, is there a chance this is a combat spec motor?

Click to expand...

Probably not, especially if the serial nunmber is below 200000.

All 750 pistons supplied from around mid-'72 onwards were the stronger "Combat" type, and, as they are +020" oversize then they are not going to be the original pistons.

yea the serial is 148021

If things look good can the barrel be blasted honed and I use the same rings? Or is that bad practice? Hate to have to buy something when I don't need to...

If you have it honed, I'd buy new rings. I mean how much are they?

Dave
69S

Slip the top ring off and check your ring gap. This should give you some idea on your discision.

If the gap is within spec then I might button up the cylinders without doing anything and return focus to the head.

If they are out of spec then you may want to get some fresh rings and give the bore a very light honing. If you end up getting new ring, be sure to check their gap also. File in as needed.

pvisseriii said:

Slip the top ring off and check your ring gap. This should give you some idea on your discision.

If the gap is within spec then I might button up the cylinders without doing anything and return focus to the head.

If they are out of spec then you may want to get some fresh rings and give the bore a very light honing. If you end up getting new ring, be sure to check their gap also. File in as needed.

Click to expand...

I know every time I have fiddled with pulling the rings I am close to snapping them. I don't want to snap one and be waiting for parts! I think I will take the following action...

number and remove the lifters
Take the cyl to the machine shop and have a light hone and blast the outside fins etc
find someone to redo the head and drop that off
order rings
wait.

I think the sound of the clicking was the rocker hitting the valve top. when it burned the valve could not seat and this created a 1mm gap and I'm thinking the clicking was that. Now how it burned is still a mystery, I still cant figure that out.

Any argument for ring brand? I see some talk about helolite, total seal, gapless? etc... I am going to be staring at the pistons to learn more history. Maybe there are markings I can identify them more than the bore...

GOOD GRIEF .

Look at the Hone Marks on the Barrel , if they havnt dissapeared , theyre still seating .
A well built Commando will take say 4.000 miles to free off fully . EGAD .

If your fuble fumbed , cut 3/4 in strips of thin plastic and slip four under the rings , to slide off .

If you have the thing secured , a palm ea. side of piston , and the thumbnails and fingertips raise the rings off . Presumeing the rings arnt catching / stuck in the grooves ( lands )
These are inspected for CARBON / Grit . Gee willickers , all smooth polished surfaces are seated . D F R P , on a fresh build. Unless its Crack testing .

YOU are looking for scratching / Galling / picking up . = torn surfaces .

same with rings , a seated / matched set are not going to use more metal seating . WEAR is obvious , but not in 10.000 miles .

Get a big magnifying glass and use a strong light ( Lamp 0 200 watt . ) for inspection . Rod Bolts would be the biggest bother , if you strip rods .
Read all the remove all burrs and sharp edges bit , and maybe polish . Should slip in with a firm fumb push IF ALIGNED .

And NO BEER untill youve cleared up AFTER working on it . Its not a pice of pottery . :mrgreen:

iceteanolemon said:

pvisseriii said:

Slip the top ring off and check your ring gap. This should give you some idea on your discision.

If the gap is within spec then I might button up the cylinders without doing anything and return focus to the head.

If they are out of spec then you may want to get some fresh rings and give the bore a very light honing. If you end up getting new ring, be sure to check their gap also. File in as needed.

Click to expand...

I know every time I have fiddled with pulling the rings I am close to snapping them. I don't want to snap one and be waiting for parts! I think I will take the following action...

number and remove the lifters
Take the cyl to the machine shop and have a light hone and blast the outside fins etc
find someone to redo the head and drop that off
order rings
wait.

I think the sound of the clicking was the rocker hitting the valve top. when it burned the valve could not seat and this created a 1mm gap and I'm thinking the clicking was that. Now how it burned is still a mystery, I still cant figure that out.

Any argument for ring brand? I see some talk about helolite, total seal, gapless? etc... I am going to be staring at the pistons to learn more history. Maybe there are markings I can identify them more than the bore...

Click to expand...

The blasting of the outside takes a serious effort. The porcelain like finish is tough to remove. Just sayin'.

If the gap is within spec then I might button up the cylinders without doing anything and return focus to the head.

Click to expand...

2nd above, as each new hone is less good clearance remains and ring sets made to standard bores, so may be hard to source rings you can file gap back as opposed to gap ya can't close up. If pistons ain't rubbing the gasket sticking up past it like a Combat's and not redlining much then likely fine to put back a long time. Ya see how easy to dig in deep so if current ring don't seal for smoke or blow by then can spend labor of loving re-doing the bores and rings.

Might suspect and inspect valve seats for all of us to judge too.

Looks like a bit of wasted time and effort. That your bike ran well before the valve burned indicates that it will run well again after the burned valve/collapsed spring is replaced.

Something came loose and it sucked air into the intake tract, leaned out and burned a valve. When a valve gets that hot it can warp a bit and not seat all the way, which is where your extra clearance came from.

Get a new or good used Ex valve and a good used set of springs, kiss all the seats with a 45 degree stone and put it back together. You are changing the springs because when an exhaust valve gets that hot it overheats your spring and it loses tension and collapses, which may have even let the valve kiss the piston a bit.

Find out why that cylinder leaned out and fix it and you are done.

I went through this exact same thing with one of my old Nortons when a carb bolt came loose and it sucked air, swapped in some good used valves and springs and it is still running fine after a dozen or so years.

Check if valve is bent. If you can see daylight all around it then it is maybe being held open - Stuck in guide due to being bent, or partially seized in guide because of not enough valve to guide clearance. I used to do my own but last time sent it to someone who knows what they are doing (Leo Goff). (Because I didn't know what I was doing even though I thought I did.) Very easy to F-up the guide bore in the head by driving the guide out without scrupulously cleaning off all the carbon even though you heat it up properly per the book. The good guys machine out the old guide. Check that pushrod for straightness too.

Harley sells a good black paint for the cylinder barrel. I agree with avoiding honing. My standard cylinder bore has 37K miles on it. Wears like iron.

Russ

Is it the camera shot, or is there metal all smeared over the stellite on the lifter? My lifter faces are smooth as, any metal on there smeared on will lift valves off their seat, accentuated by rocker ratio. If the lifter surface is not smooth, whilst you have the barrel at a machine shop, get them to surface face the stellite, and maybe the cam surface needs close scrutiny?
HTH Richar

iceteanolemon said:

worntorn said:

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

Click to expand...

Well I have not done an adjustment on the valves in a while since there has been no noise etc. I have not had the head off or serviced either. When you say "no clearance" you mean if its adjusted too tight? So weird as I noticed it loose at 1mm when I got the bike home and looked at it. Also the nut was tight so its not like it maladjusted by being worked loose. I may have to stare at it some more to find what went wrong.

Click to expand...

Yes, if the valve was adjusted too tight it will cause the problem you have. This the most common cause of an overheated or "burned" valve.

Glen

worntorn said:

iceteanolemon said:

worntorn said:

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

Click to expand...

Well I have not done an adjustment on the valves in a while since there has been no noise etc. I have not had the head off or serviced either. When you say "no clearance" you mean if its adjusted too tight? So weird as I noticed it loose at 1mm when I got the bike home and looked at it. Also the nut was tight so its not like it maladjusted by being worked loose. I may have to stare at it some more to find what went wrong.

Click to expand...

Yes, if the valve was adjusted too tight it will cause the problem you have. This the most common cause of an overheated or "burned" valve.

Glen

Click to expand...

Well I want to get the head looked at at the same time as assess any damage and replace as necessary. I put the word out and ended up cruising by Dean Collinson's place to try and make contact. The bike has some history with him and he is in the area so I was in the neighborhood and just stopped by. Hes a great guy and offered to "have a look"... I am going to bring it by next week and he will give it the attention it needs. I also emailed Bill Bibbiani and he emailed back to give him a call for a reference. I have been wanting to get in touch with locals but never got the chance till now. I think if I was doing the head work on many bikes it would be worth the tools etc but for just mine I will farm the work out and get someone into it with more experience.

I will however put it back together and all that.

What if after your intial work , the push rod(s) werent seated in the lifter(s) properly, but once you ran it and the rod (s) seated, this would explain the 1mm gap after the noise went away.
When I replaced the head on mine last week, I turned the motor over by hand via the back wheel and in 4th gear, plugs out, and head bolts loose, heard an audible click and then nothing after the next few rotations. This indicated that the push rod was seated and then checked all valves were opening and closing, then tightened head down, torqued up and then set the tappets. Re torque this week on a cold motor after a few short runs.
Just a thought for your intial problem.
Regards Mike

Perhaps I've been lucky, but the times I've installed the head, I've always tightened the head down while making sure the rods were seated correctly by turning the engine over while tightening and looking up in there. You certainly can't see the bottom seating, but you can see the top. But you can feel the bottom without the head down. An unseated rod would not be a good thing, and can even bend or break them from what I've heard. I've never heard any clicking or strange sounds while installing the head and the adjusters seem to do their work fine. Then I do a check after the first run and maybe after 500/1000 miles or so, then regular service if nothing is out of order.

I'm betting something was wrong from the get-go. I too let someone else do the guides and head work. Leo did the last one.

Good luck with it.

Dave
69S