Do "jumped timing chains" really happen?

[Dave Young]

Edinmass, you nailed it exactly.  Exhaust valves number 5&8 were badly burned and wrinkled.  Number 7 wasn't a lot better.  Luckily, I didn't keep driving it and the seats don't look beat up at all.  They should clean up ok.  Thanks to everyone for all of your input.  I'm blaming this on my installation of the different carb and not paying close enough attention to the color of the spark plugs while I did my shake down runs.  The Zenith has an adjustable main jet and I moved it until she ran "the best".   Big mistake.

[hchris]

Yes good call indeed, however I think those valves have been going a lot longer than the 1500 miles you are attributing to your new carb and lean mixture.

 

I strongly suspect your diagnosis of poor running before the carb change, would certainly have been due to these burnt/worn valves. 

[edinmass]

Swapping over carburators is a popular upgrade/fix for many reasons. Unless you have an exceptional understanding  of stoichiometry and its relationship to carburation, you end up with poor results. Having a five gas analyzer to properly tune an engine is also a requirement when changing over carburators. I agree the problem with the valves probably existed before you ran the new carb. Very long story short, stock components restored correctly are your best bet every time.

Edited May 19, 2017 by edinmass (see edit history)

[edinmass]

By the way, replace all the valves. Those are two piece valves from days long gone by. Also, many people sell valves but they are not correct. Do a Rockwell hardness test on you valves, stems and heads, bet everything you find for sale is less than half what it should be. I would buy stainless blanks and have them machined localy. Drop your pan and clean it at the same time. Be sure to set up your distributor on a distributor test machine. It will run Iike new. Good luck! More photos please. Ed

Edited May 19, 2017 by edinmass (see edit history)

[F&J]

2 hours ago, wilbur said:

 on valves Exhaust valves number 5&8 were badly burned and wrinkled.

 

2 hours ago, wilbur said:

I'm blaming this on my installation of the different carb and not paying close enough attention to the color of the spark plugs while I did my shake down runs

 

I disagree on why... 

 

not bragging at all, but I am a life long mechanic, not a modern auto "tech". 

 

When looking in person at burned, warped exhaust valve: You need to know what you are looking at, for,  as a cause.  I cannot be there to look...

 

 Valve seat contact "spot" is normally 45 degree taper.  The Width of that "ring" of obvious contact showing as a shiny or cleaner ''ring" needs a close look .  The  width, if way too narrow...  causes lack of heat transfer from the super heated valve at point of being open with superheated exhaust flow, to the mass of the watercooled head or block (depending on OVH or Flathead). A narrow contact width is far less surface area to transfer heat.

 

Drag race engines have very narrowed contact area, due to enlarging the port size.  When opening the port further, you grind what is a 3 angle cutting of the seat.  The lowest cut narrows the ID of the seat at bottom, and also blends the path for flow,  Then the contact surface ends up quite narrow, but does not affect longevity of the valve, as it is not running long enough like a commuter car.

 

More looking..... to see if the valve appears to have suffered from almost zero lash when at running temps...there again, think... If the lash should be 20 thou, and it is at near zero, the valve imperceptivity has less time or duration of contact with the seat...to...transfer HEAT from the superheated valve.

 

There is more on valves, but trying not to "go long" here..

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Symptoms of incorrect mixture at carb in idle, mid range, and full throttle.....

 

We only really need to think about mid range when wondering if carb caused the valve damage.  Mid range is so easy to feel if it's WAY too lean,  emphasis on WAY too lean..

 

You will feel the motor "lay down" or feel somewhat loagy, or somewhat unresponsive, as you try to lightly accelerate from low speeds.  On a hand choke car...you would have a great advantage to know if midrange mixture is way off.  That would, in basic cases, be the main jet or jets if 2 barrel, to be too small for todays blends..or as in optional dealer installed  "gas miser jets".  You simply get the car up to that precise speed or load, where it lays down, and just gradually pull the choke a tiny bit more and more to see if the sluggish feel then goes to "WoWee".  If there is almost zero change at all, you have eliminated the biggest cause of mixture related valve issues,  It goes way more complicated, but the Carbking on here could get into the complexities of all of the carb "hidden" or unknown  properties/ systems....

, 

 

I worked on a guys 47 Ply woodie his wife owns.  He "let" me work only on his cheaper cars, and kept sending the poor running expensive woodie to an old time guy in Mass.  Towing costs and a $500 bill each time...he reluctantly "let" me work on it.  I met him at a show right before he asked me to fix it, I said "your description sound like wrong main jets"  He said NO WAY, I bought a NOS carb.  I said, do me a favor when you leave the show today, pull the choke out more and more to see if it turns into a rocket. He never did with some silly excuse, so as soon as I moved the car, it laid down in my LOT. I pulled it in my shop, pulled the carb top off, then the mainjet,.  I used jet drills to start small and then go bigger...First try it was 50% better just in my lot, then I hit it "dead on" the second time.  Took it out for a very long run because it was such a sweet driver with awesome zip.  He picks it up...maybe an hours labor fee...to drive the 45 minutes home with wifey following.  Hour later he calls...oh dang, what's wrong I thought... He says "you F'er (his normal speak), That dam car ran so sweet I pulled over to let her drive it the rest of the way".  Then he said it's not cool in todays world, but I want to drive back to you and give you a wet kiss  (er... no thanks)  No big impressive save in my eyes, I later looked up in my Dads old books from his 1950s repair shop, and saw a notation under that carbs settings, saying Mopar DID have economy jets for flat plains states..no hills.. That only confirmed my first impressions, from just HIS phone description. 

 

don't overthink these old cars, that's what I say to most owners.

Edited May 19, 2017 by F&J (see edit history)

[padgett]

ps if pulling the head might also consider hardened exhaust valve seats. Modern unleaded gas/alcohol mixes are very hard on valve seats and valves. Lead not only improved octane, it also acted as a top end lubricant.

[edinmass]

Lead didn't come into common use till after the war. The motor was designed to not have lead in the fuel. Don't install new seats, they are not necessary, and can only cause problems- I.E. falling out. Just do a regular valve job, removing as little as possible from the block. 

 

Adjusting mixture by thr seat seat of your pants is fine, if you know what your doing, and then be sure to always be on the rich side. Having a properly calibrated carburator for the application is where you should put all your effort. There are often fifty or more different factory calibrations for any particular carburator model, and they can vary widely from 200 to 500 cfm depending on the application for what it is being used for. Melting a piston or valve is common when people are inexperienced. Way too often people "just put another carb on it because the old/factory one is too expensive to find, get right, or just a plain lack of understanding of how stoichiometry works.

Edited May 19, 2017 by edinmass (see edit history)

[Spinneyhill]

Back to timing chains jumping a tooth. A story above reminded me of a friend working on a 1920s Hupmobile six cylinder. The pitch of one of the timing gears was different to the timing chain pitch and had been for a long time! The thing still ran fairly well but had worn the gear teeth to sharp, short points. It must have been pretty close to jumping a tooth or the chain actually falling off. The inside of the engine was lined with superfine metal powder in the oily gunk. It seemed he finally took it apart for a look because the chain was rattling a fair bit.

[F&J]

2 hours ago, edinmass said:

Don't install new seats, they are not necessary, and can only cause problems- I.E. falling out. Just do a regular valve job, removing as little as possible from the block. 

 

100% Perfect advice for that age of  "vintage engine", .....but it was not meant to be a statement for modern engines, which have much different valve requirements.

 

.

[F&J]

Just adding deeper info on valves on vintage engines like that prewar car..

 

When you take an older engine apart to inspect valves, the intake valve contact "ring" spot should be very shiny all the way around.  If you see that that one long area is not shiny, and darkened, that is what causes that strange misfire noise at the tailpipe if it has a properly maintained ignition system..  It is a very random skip noise, like Puh.....puh,puh.....puh.  The intake valve is occasionally letting a very tiny bit of the combustion, to enter the exhaust system.  However, it will never be enough to "burn" an intake valve.

 

The older the engine technology, the weaker the springs were, when it was new.  We have heard that a circa 1918 engine needed "head removal at 15,000, mile intervals, for decarbon and relapping of valves", and "ring replacement at 30,000 mile intervals".

 

The primitive fuels led to major carbon and soot buildup, aggravated by the primitive design of the rings and materials.  Being that the valve springs were quite soft,(a carry-over from the old hit/miss farm engines), and some normal oil burning from primitive rings,  it led to excessive carbon or soot buildup that prevented a perfect seal at that valve seat "contact area ring".  That carbon on that "contact ring area" of valve and seat, couldn't then be "pounded, crushed up, and dislodged" by such soft valve springs. 

 

 

[Mike36]

What am I missing here? Seems to me if the intake valve leaks even a little combustion, it goes to the carburetor, not the exhaust.

[cheezestaak2000]

i replaced a timing chain in my parents 1969 buick many years ago. the car had almost 200,000 miles on it, and it quit running while they were cruising down the road. i remember that job very well, i did it under a bridge by the C&D canel, took about 4 hours without any power tools.

 

[F&J]

9 hours ago, Mike36 said:

What am I missing here? Seems to me if the intake valve leaks even a little combustion, it goes to the carburetor, not the exhaust.

it is the faint miss fire as the result.  Backyarders often assume it is a random ignition problem and start replacing everything in the ignition system

[Dave Young]

Excellent advice by all.  Thank you very much. How does one confirm the Rockwell hardness of valves, and if they are found to be lacking, what can be done, and by whom, to make them harder?  I'm replacing all 16 valves.

[edinmass]

Wilbur - PM sent, check your mail. Ed

[Spinneyhill]

On 5/20/2017 at 3:53 AM, Mike36 said:

What am I missing here? Seems to me if the intake valve leaks even a little combustion, it goes to the carburetor, not the exhaust.

 

Just for comparison, I had a stuck exhaust valve in No. 6 and it popped through the carburetor. Actually, it blew back through the inlet valve when it opened and blew all the mixture in that end of the inlet manifold back out into the carb.. It ran but boy it was rough.