wilbur

Do "jumped timing chains" really happen?

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wilbur    12

I'm chasing a problem on my 28 Chandler.  After finally getting it running beautifully, an abrupt change occurred while driving and now I'm getting backfires thru the carb, hard starting, low power and heat.  This is a straight 8, dual point ignition engine.  It ran poorly when I got it a year ago.  Better carb, manifold fixes, vacuum tank, relined brakes, and other external improvements made her purr right along.  I'd say that I've put maybe 1500 miles on it lately.  After exhausting the usual diagnostics such as fuel and ignition, I'm left with the conclusion that the valve timing may be off as the result of the Morse chain being too loose and jumping a tooth on the cam.  Does this occur?  It seems so unlikely given the diameter of the cam sprocket.    It looks like quite a task to get at it on this car.  Luckily, I do have a new chain on the shelf for my other Chandler which I am I the process of rebuilding.  I'm not looking forward to this one.  I've got my Model T engine almost done, my T Pickup was next on the list for rebuild, and the Chandler "all done".   Funny how my 29 Model A just never seems to have ANY problems!  The dependability of the Model A is simply uncanny.  Too many cars for a guy who isn't retired!

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Owen_Dyneto    18

Yes, it can and does happen.  However, for every 100 times that someone has a problem and suspects that the chain has jumped, I'd guess that 99 of those times the problem was elsewhere.

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wilbur    12

Great odds!  My first plan of attack is going to be to pull the manifolds and head.  Then pull the  valve cover plates and check that the valves are in fact closing at the correct relationship to piston travel.  It's a bitch that I just put those manifolds on there with brand new, very difficult to find, copper clad gaskets.  The head is held on with studs... a million of them, and we know how difficult it can be to get that head to move upward when those studs have a death grip on the cast iron.  Luckily, I was able to get a few head gaskets last year from Then and Now Automotive and have them sitting on the shelf.

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39BuickEight    194

"jumped time" is a word I hear many people use to describe virtually any reason a vehicle isn't running correctly :)

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billorn    55

I havent seen it happen but I did have a 69 Caddy where the cam gear had teeth worn down to points and there was so much play in the chain that it acted like it jumped a tooth or 2. If you didnt have another gear to compare it to you might not see how worn it was because it was so even but when I got a new one it had square teeth not pointy and the wear was very visible.

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edinmass    272

Possible? Yes.  Do a compression check. You sure you don't have any sticking a valves.  If you have no stuck valves,  and then low compression ,  consider the chain.  I agree with the above.  It's very unlikely but possible.  A blown head gasket between two cylinders would cause the same backfiring symptoms.  We also explain overheating.  Take your time and be methodical. 

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Tinindian    319

If you have to pull the head, leave everything else on the engine, start it and run it for a minute, then loosen all the head nuts and start the engine again.  Usually juts firing once or twice will pop the head  loose. 

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capngrog    243

I know nothing about a '28 Chandler, so take my advice "with a grain of salt".  I learned the hard ($) way that a bad vacuum leak or a severely lean carburetor can cause an engine to act like it's off time, dropped a valve etc.  I would check that out thoroughly before tearing into the engine.  As another thought, is it possible that something has gone amiss with your distributor?  Is it possible to perform all the usual checks, such as compression, on a '28 Chandler?  I would think that if the cam timing is off that the compression would be affected.

 

Just my guess.

 

Cheers,

Grog 

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keiser31    974

Happened to my 1974 Plymouth Duster. I was going along, minding my own business when a guy ran into my quarter panel from a freeway offramp. The car was jolted so hard that the timing chain jumped.

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padgett    457

Well GM from 1969 to 1972 used in some engines (SBC was one) a fiber timing gear that broke. I made sure when I ordered my 72 Wagon that it had a steel timing gear (400-2bbl didn't, 400-4 bbl did). Had to pull the front cover to see but was obvious if had jumped time.

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PFitz    40

If the chain was loose enough to jump, you'd likely here is "hissing" as it rattles.

 

Does your 28 have a potmetal carb, or at least a potmetal venturi ?  With heat cycling and engine vibration a well running potmetal carb can go down hill quickly.  And they can fail either rich, or lean depending on where they develop internal cracks.  28 is right in the middle of the bad die cast era.

 

Paul

Edited by PFitz (see edit history)

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oily rag    23

I have had it happen with worn timing chains. 

I also the gear on the bottom of the distributor split on a 1970 Plymouth 225 six cylinder. that really threw the timing off.

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Bhigdog    912

Yup. 62 Pontiac. Jumped for no apparent reason....................Bob

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31 Caddy    108

Back in '74, I had a '72 Ranchero GT with a 351C. It had been running fine, and I was getting ready to go on a trip. Threw my bags in the back, and cranked it over - nothing but popping back through the carb occasionally - would not start although it had both spark and fuel. Confirmation of it having jumped time was that when number 1 cylinder was brought up to TDC, the distributor rotor was nowhere near to pointing at the number 1 position on the cap. Teardown revealed nylon ( or whatever the plastic like material was on the cam gear) broken off leaving small nubby teeth which the chain had jumped. I had shut it off not 30 minutes before. I suppose the torque of cranking it to start caused it to jump at that moment.

Edited by 31 Caddy (see edit history)

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wilbur    12

She did have the dreaded Schebler S-3 pot metal nightmare on it.   Now, she sports a 10 pound monster Zenith, all cast iron updraft and it made a world of difference in the drivability.  Lean on fuel was my first suspicion, as was the blown head gasket. Oddly, one plug is oil fouled.  The others are all very nicely colored.  The oil foul is a brand new change.  It's on number four.  One set of points in this distributed fires 4 of the cylinders and the other set of points fire the other 4.  I only did a compression check on the fouled hole, and got a respectable 50 lbs.  70 would be ideal.  I will test the remaining 7 before doing anything else at this point.  Thank you for the tip on popping the head.

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sfair    5

Many times you can hear this problem when cranking with the starter.

It will have a different lope/cadence/crank faster than it did before.

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wilbur    12

Fitz,   The flex discs that you made for the driveshaft on this car are superb.  It totally eliminated the driveline vibration that seemed to be be shaking her apart.  Many thanks for a job well done! 

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PFitz    40
12 minutes ago, wilbur said:

Fitz,   The flex discs that you made for the driveshaft on this car are superb.  It totally eliminated the driveline vibration that seemed to be be shaking her apart.  Many thanks for a job well done! 

 

Your very welcome, Dave. Glad to hear that's all it took to get rid of that vibration. 

 

 Like many other car and truck manufacturers, Chandler  knew that those flexible discs can absorb and dampen vibration and drive train sounds better than all-metal u-joints can.  Because of that natural dampening ability they are much more forgiving of less than perfect drive shaft balance. That's why many inboard engine boat builders and high-end European cars are still using flexible u-joints for propeller and drive shaft couplings.  

 

Paul 

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PFitz    40
45 minutes ago, wilbur said:

She did have the dreaded Schebler S-3 pot metal nightmare on it.   Now, she sports a 10 pound monster Zenith, all cast iron updraft and it made a world of difference in the drivability.  Lean on fuel was my first suspicion, as was the blown head gasket. Oddly, one plug is oil fouled.  The others are all very nicely colored.  The oil foul is a brand new change.  It's on number four.  One set of points in this distributed fires 4 of the cylinders and the other set of points fire the other 4.  I only did a compression check on the fouled hole, and got a respectable 50 lbs.  70 would be ideal.  I will test the remaining 7 before doing anything else at this point.  Thank you for the tip on popping the head.

 Ok, pot metal can be crossed off the list.

 

Oil fouled plug ?  As Edinmass suggested, I'd do a compression test before pulling anything apart.

 

 Is the spark healthy to that plug  ?  How old are the spark wires ? Are they in a metal loom, as was common practice then ? Do you have a  timing light (poor man's oscilloscope) ? If so, even if it's only 12 volt timing light you can power it with a modern car and just use the pickup leads on the Chandler.

 

Clip the pickup on each plug wire in turn, point the light at a surface that will let it be easily seen and watch the flash sequence very carefully. Are the flashes steady and evenly spaced .... or does it skip a flash now and then ?

 

Are any of the wires showing a quick double flash ? If so that's cross-firing - either a short from the insulation breaking down (can happen with high heat not just a break in the insulation - topic for another thread), or inductive cross-firing caused by the magnetic field of the wires being so close inside the loom. If it happens at the right time it can cause some of what your experiencing.

 

Paul

 

 

Edited by PFitz (see edit history)
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wilbur    12

It does have the metal conduit that all 8 plug wires run thru and I did suspect a cross fire situation as a cause of the chuffing thru the carb.  So, rather than pull the wires out of the tube, I swapped out the entire assembly from my other Chandler, cap and all and she ran exactly the same.  I used one of those neon spark indicators to show fire, but I like the idea of the timing light as it would be much brighter and easier to see.  She definitely sounds different when cranking.  Very inconsistent.  In the moments before the change occurred I thought that the water pump was making a strange noise so I pulled over and cranked in on the pump's grease cup and motored on.  I barely made it home.

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benjamin j    41

you said running hot was a symptom. firing at the wrong time like when exhaust vales are partially open will cause the heating up issue. loss of power means you have to give it more throttle than normal which in turn means more raw fuel into the exhaust. of course it could be the distributor moved of the timing chain jumped.  they are both fairly common issues.

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wilbur    12

The first symptom was much more throttle needed to power the car.  Then came the cuffing out the carb.  This distributor drives off of the generator shaft, which is the only means of adjusting the timing chain tension.  It might be possible that the chain jumped a tooth on the generator and not on the cam, putting the ignition timing off and not affecting the valve timing.  The road ahead is getting pretty steep!

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benjamin j    41
45 minutes ago, wilbur said:

The first symptom was much more throttle needed to power the car.  Then came the cuffing out the carb.  This distributor drives off of the generator shaft, which is the only means of adjusting the timing chain tension.  It might be possible that the chain jumped a tooth on the generator and not on the cam, putting the ignition timing off and not affecting the valve timing.  The road ahead is getting pretty steep!

ignition timing being off still means firing when valves are partial open.

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