When Things Go Wrong!!!

[Slojo]

Jerry, All theses engines burn a little oil , they have no valve seals. Carb. is tuned well plug and pipes look good. And yes Rowe is or has closed their doors, retiring.

Cotton, I have looked all the parts over and with the perfectly clean fracture it would appear the valve is at fault. There is no other damage other than the seat impression and loose exhaust valve guide bore.

mcarver The valve springs, retainer and keepers look fine.

Cotton, The valve guide for the broken exhaust valve is loose and I could pass a .395" gauge pin through the .375 nominal hole size. On the other hand the intake valve guide was a close fit smooth operating and well oiled without nicks or dings in the valve margin or seat area. The intake seat was large and the valve seat surface on the valve itself was slightly unusual. I don't suspect any foul play with anything other than the exhaust valve breaking possibly aggravated by the unusually loose guide bore.

I to am aware of the English sabotaging our Panheads with those faulty valves. I have seen and heard of several of them breaking.

As far as a vacuum leak , that was way in its past and resolved. This motor would idle at an extremely low RPM and run smoothly through its normal rev range. Vacuum leaks tests have been conducted since the leak repair and non found.

Gary, This is a big deal to me. Yes it is repairable in my shop by me but time is a problem I have several projects in operation right now and more lined up so I don't know when I will find time to repair this motor (entire rebuild with hydraulic conversion for the lifters). This bike is my regular rider and it will be down for the rest of the year. Right now the Barber bike (1912 belt drive twin) and the Cannonball bike (1914 twin) are consuming all my time.

Duffey, These old low compression motors run fine on the same gas I put in my Town Car, (most anything). I have near 300,000 miles on the T.C. and it runs fine.

What we have is a very loose guide on an exhaust valve and nothing else is suspect as far as I can see. There isn't any galling on the stem so perhaps the valve wobbling around fatigues the valve stem. The break as clean as it is tells me other wise though.

joe

[BigLakeBob]

Joe,
Remember to check how the rocker arm makes contact with the top of the valve, if not correct it will wear out a new guide quickly. The arm may need redressed to make full contact throughout the opening of the valve. Bob

[Slojo]

Bob

I have not checked the strike point of the rocker to valve, my time is spent on other projects and unfortunately the 48 has taken a back seat. What I have checked is the rocker travel and feel. Both rockers have like new action and appear not to be a problem. I still maintained the valve is a faulty part even though the guide was so badly worn.

joe

[MeanGene]

As Cotten said, the valve is the victim, not the perpetrator. A very loose guide allows the rocker to push the stem out of alignment, causing the valve to contact the seat on one edge first when closing, every time, then slamming straight at the end of it travel, with the stem flexing a tiny bit every time- might as well hold the valve and hit it on edge with a hammer- sooner or later it's gonna break at the weld. Same thing that happens when a valve makes contact and gets slightly bent, it'll pound on that one edge until it fatigues from the flexing and the head comes off. Nothing wrong with that valve except it's been abused for a long time by a very sloppy guide- and that guide could have been sloppy since day one. The very wide contact pattern on the valve (all the way across, edge to edge, and wider than the width of the seat in the head) also shows that it was hitting on edge and then funneling in straight. Same problem occurs with hollow-stem, sodium-filled exhaust valves- they work very well unless the guides get sloppy, then they get pounded and fatigue, and the heads start coming off

[Slojo]

The confusing aspect, why is the intake valve guide so perfect and the exhaust valve guide so loose? I know the exhaust is under sever conditions when comparing the two yet I haven't seen a guide this loose. Also I don't know how many miles are on this motor, it was rebuilt prior to my ownership.


MeanGene "then slamming straight at the end of it travel"

Cam profiles prohibit the slamming of valves when closing, if the valve is wobbling in the guide it will hit improperly.


joe

[MeanGene]

It helps if you take the whole statement in consideration- "A very loose guide allows the rocker to push the stem out of alignment, causing the valve to contact the seat on one edge first when closing, every time, then slamming straight at the end of it travel, with the stem flexing a tiny bit every time". You obviously didn't get the gist of it, as you are determined to blame the valve. The valve stem is allowed to get out of alignment by the sloppy guide, which puts the valve head out of alignment with it's seat- which doesn't affect much in a relatively low-performance app like an early Harley, until it's time for the valve to close. Then the misaligned valve hits the seat in one spot on the rocker side first, putting it a momentary bind and causing it to flex a minute amount, before straightening up and aligning with the seat at the end of it's travel (the "slamming straight" that you chose to nit-pick and interpret your own way). I'm well aware of how cam profiles work, and also that there are very varied rates of opening and closing built into various cams and types of cams, and an early Harley probably has some of the gentlest profiles this side of a Briggs & Stratton- which is relatively useless info in this case. I work with flat tappet solids, flat tappet juicers, solid rollers, and juice rollers, and almost all of my stuff runs much more aggressive profiles, higher lifts and a lot more spring pressure than anything you're going to find in a panhead- some of my solid roller stuff is well over .700 lift and around 300lb on the seat. There are actually some racers running in the neighborhood of 1 inch lift, and between-round spring maintenance and replacement id pretty common. Some of my buddies who run NHRA Stock class have to use cams that "check" stock, as in they begin to open and completely close at the same time as a stock factory cam, but have extremely aggressive ramps and open and close the valves very quickly (and violently) requiring stout springs and components even though the cam doesn't appear to be that "big". The Super Stock guys get up into the .800 range and spin 8-9K, big dual or triple springs, titanium retainers and such- Thunderbolts, Hemi Darts and Barracudas etc. And the valves are high-dollar severe duty stuff from Manley, Ferrea, etc.- but you can still break them from abuse. An old high-mileage two-piece stock-type panhead valve being stressed and abused by a very sloppy guide is being asked to do to much

[Slojo]

MeanGene " You obviously didn't get the gist of it"

Thank you for your response and experience on this important subject.

Yes I did take the entire statement in consideration I just found it unnecessary to re-print or discuses all of it at length, you made your point and a good one. I do believe that the possibility could exist as you describe it.

Understand, there is no nick picking taking place here this is an open conversation between several people to better understand what went wrong.

Interesting as your post is with the high performance aspect in consideration this is still a stock 61" Panhead where speeds of 80 MPH are unusual and not sustained. I know the guide is important I can and do measure my assemblies. In all my years of building and ridding, outside of wearing out components this is my first and most severe failure so my experience with these events are at a minimum.

The valve broke off cleanly while sitting, idling waiting for a traffic light to change. Was it aggravated by the loose guide? Possibly. A better valve probably would have not broke. The valve stem exhibits no visual stress or fatigue characteristics near the fracture and until I dig the valve head out of the piston and inspect it a conclusion cannot be determined.

Once again the valve stem shows no fatigue just a perfectly clean break. /// When things go wrong shouldn't a valve stem bend not brake? ///, This is elementary engineering and part of the design criteria. Perhaps now you will understand why I blame the valve not the valve train for the failure

Other than the loose guide all other components appear to be in excellent condition.

joe

[T. Cotten]

Joe!

At risk of repeating myself, let me simplify my previous post.

If for some reason, the valve slows or stops in its travel,
something is going to hit it.

A piston can knock off the head off a valve in a hearbeat, but don't blame the piston either!

.....Cotten

[Slojo]

Cotton, Mean Gene

Just for conversation sake, Last week I spent some time with the manufacture who produced my 1914 Cannonball bike valves, intake and exhaust. These are Titanium valves and are of the two piece welded construction.

While in conversation with the general manager he displayed some valves used for testing welds. Although tests were not conducted under heat and operation of an internal combustion engine with rapid cycling they were non the less actual bench tests, not very scientific.

Test included flexing and bending valve stems to an angle greater than 90 degrees without weld failure.

In my 1914 Cannonball motor the guides were a little loose after the cross country run, I ran short of time when building the bike to properly addresses the situation. Making oversize valve stems to fill the freshly honed guide bore was a quick fix. The guide bores wore fast due to insufficient lubrication on iron guides.

When I returned from the cross country run I removed the valves and found the exhaust valves had dished .030", one valve was slightly bent. I attribute this to the constant accidental retarding of the ignition timing while at speed. A natural position for my left wrist appears to roll out the twist grip, retarding the ignition, over heating the valves, pistons, rods, oil and cylinders. With the excess heat and loose valve guides there was only deformation and not a fracture of the valves.

In the case of the 48 61" pan the loose guide aggravated a week point, a substandard valve. Did the valve hit something to cause it to break? Possibly yet the end result is still, a broken valve not a bent valve that is the failure of the valve and not the aggravator.

We can take a different prospective of what actually happened but the end result is the valve broke instead of bending, the cleanly severed stem still slides through the loose guide hole. I will inspect it later for any bend condition.

joe

[Slojo]

When I inspected the valve stem it was found perfectly straight. Inspection method conducted on a Starrett granite surface plate using a dial indicator graduated to .0005". There doesn't appear to be indication of any misuse or abuse to the valve remains. Without any indications of abuse a piston or intake valve collision is unlikely. If the valve broke from wobbling around in a loose guide it was a defective valve in my opinion. I will maintain the valve should not have broke. I will attempt to have more photos posted later.

joe

[c.o.]

Joe! It sounds as though you may have to wire in some sort of buzzer or shock type device on the left twist grip. A warning buzzer or a zap might get annoying but would cut down your chances of overheating....

[T. Cotten]

Joe!

You have an uncontestable arguement,
that a valve stuck at 90 degees would be preferable to a head coming off, as my photo example does not show the cylinder damage.

Kibblewhites for you, or nothing.

....Cotten

[c.o.]

[Slojo]

Cotton

Kibblewhites?

It is my understanding that Kibblewhites valves are of one piece construction, are they a good valve?

joe

[Slojo]

Joe! It sounds as though you may have to wire in some sort of buzzer or shock type device on the left twist grip. A warning buzzer or a zap might get annoying but would cut down your chances of overheating....

Cory

I think I will try to "flex" the handle bars a little wider, they are bit narrow and uncomfortable right now. This should solve the ignition retarding problem. There should be no shock treatment necessary.

joe