I have made several posts regarding my rough running 1954 stock Merc and am wondering if it could be a timing chain issue.  I have zero experience with timing chains but have a basic understanding on the function.  The engine was running good, I lugged it out in second gear as I was pulling into my driveway, killed the motor and it sort of "humped up" like they do when stalled.  I have diagnosed and repaired/replaced all of the normal tune-up stuff.

What are the symptoms of a jumped chain?  And, more importantly, how can it be checked without an actual tear-down visual?  I have a good, old-timey, mechanic working on it now but he has limited experience with Y Blocks.  My pea brain says to crank to #1 TDC and then look at # 1 intake and exhaust rocker arms.  Please don't laff - I've never been in this territory!  Car has been down for over a year and my frustration level is to the moon...

Man! You are bringing back some old memories for me.  When I was a kid the timing chain jumped on my '56 Ford Victoria.  This happened when I was revving the engine and my "Coat Hanger" throttle linkage stuck wide open.  I was making $1.10 an hour bagging groceries and I had to pay a mechanic to fix it.  Yikes!

My advice is to seek help from an experienced mechanic. All V8 engines work pretty much the same.   As you know, you first must find TDC in cylinder number one. You could use the timing mark, but you don't know if it's correct as the damper may be wrong as well. A mechanic will use a piston stop.  When the piston is at the top and both intake and exhaust valves are loose, you are at TDC of the compression stroke.  At this point, the distributor rotor should be roughly pointing to ignition terminal one.  It is possible someone could have installed the distributor out of position. If not, the front of the engine must come off to verify the timing chain condition. 

A jumped timing chain is fairly rare on a street car unless it's been abused like mine was. If the motor has a bunch of miles, it is most likely stretched and worn. I would start with a timing light to see what's happening. You could have anything from bad timing, bad wires, an out of phase distributor, vacumn advance problems, carb problems or ignition problems.  All hard to diagnose without working on the car itself.  I understand your frustration.

A quick and easy way to check the chain is this:  take off a valve cover.  Turn the engine by hand and watch #1 or #6 exhaust valve (depending on which cover you removed).  Watch as the valve closes, and when it is almost closed, the intake valve of the same cylinder will start to open.  When both valves are equally open, verified with a straight edge across the valve spring retainers, the timing pointer should be within about 10 degrees of TDC or 0.  If off more than 10 degrees, there is a problem with the timing chain. 

John - "The Hoosier Hurricane"

How do I search the forum for info on setting up the timing chain on the gears?  I remember previously reading that there is a specific number of chain link pins between the marks.

This is on Ted Eatons website
https://eatonbalancing.com/wp-content/uploads/2015/09/Rollmaster-timing-set.jpg
stuey

stuey, thanks for the link.  Just what I needed.  Yesterday, with the help of a good, old-timey mechanic, we reinstalled the newly rebuilt '55 4V carb after a minor tear down, inspection, and air blowout, re-installed the fuel pump after a bench test, re-set the low-speed jets and timing, started the engine and it ran like crap, as before.  Much exhaust popping and blowback at the carb.  Loosened the dizzy hold-down and advanced the distributor nearly 50 degrees!  Ran like a top!!

Timing chain inspection next...  More later.  

Perhaps the timing mark on the damper has moved.. That happened to me. The outer ring moved.. 

56 Vic, B'Ville 200 MPH Club Member, So Cal.

Thanks again for the input, previously checked all indicators for timing - dizzy properly set with rotor pointing to #1 on the cap, #1 cyl. at TDC on compression (finger in the plug hole trick), timing pointer pointing at 4 degrees, #1 cyl. valves closed (visual at rocker arms).  Pulled the front of the engine off to inspect the timing chain and gears.  With the engine set up as above, the crank gear mark is at approx. 3 o'clock (there are nor corresponding marks on the chain anywhere) and the cam gear mark is at approx 9 o'clock.  The repair manual says that the marks on the crank and cam gears should align with the respective marks on the chain, which, as I just stated, doesn't have any marks whatsoever.  The manual also states that there should be about 1/2 inch side play on the chain, which there is.

 the motor has about 3,000 miles on it since major rebuild, don't know if the chain/gears were replaced as the rebuild was about 35 years ago and tthe motor kept in storage until 2013.

Looks like I should rotate the cam gear to to 3 o'clock, remove the chain, rotate the crank gear to 3 o'clock, and re- set the chain at 12 link pins of separation.  OR maybe I should buy new gears and chain, assuming that they will have the proper markings, and install at 12 pins.  Probably, with a worn chain and gears, it might just jump again (assuming that it has jumped).  Would the motor even run if it jumped 90 degrees?  Keep in mind that I had to advance the dizzy about 50 degrees to get it to run correctly...

More help please!

If your cam timing is correct it should be possible to get the gear marks to line up with 12 pins in between like shown in the earlier link. I am not certain whether that would happen with #1 at TDC on compression or not. I would suggest rotating the crank until the crank and cam marks are both near 3 o’clock and verifying the 12 pins before removing the chain—this way you can know for sure whether your timing jumped.

Before teardown, did you check compression? Valve lash? If the engine likes really advanced timing that suggests a very slow-burning mixture (lean, possibly?)

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Stating the obvious here but have you checked the valve lash yet?

With only a ½” of slack in the chain, it’s unlikely that the chain has slipped a tooth.  A cranking compression test on the engine would help to also verify that the cam timing is correct and at the same time give a quick indication if the engine is suddenly having issues on a particular cylinder.  For the 256 engine, I would be looking for at least 130 psi for the cranking compression give or take 10 psi.

A verification of the cam timing can come from observing that the intake and exhaust valves on any given cylinder at TDC on the overlap cycle are equally open.  With the exhaust valve coming up and closing while the intake valve is going down and opening, the retainers for those two valves should be level with each other at TDC for the cam timing to be in the ballpark.  If the damper ring has slipped, then the damper will be misleading if using that TDC mark as an indicator.  If your particular engine does not have a rubber mounted damper ring, then the TDC mark on the belt pulley should be adequate for this check.

You don’t mention what ignition setup you have but that’s a good place to start once you have verified that the timing chain is indeed not the problem.  If you haven't performed a cranking compression test yet, this would be a good time to do so.

Lorena, Texas (South of Waco)