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Sorry, my english is not very good

If your timing wanders 4 degrees--get a new timing set, your chain has most likely stretched. This is also a likely source of your mpg problem.

The Cox Brothers (phone: 614-268-9920) sell a double-roller timing set if you would like to upgrade from the stock sprockets and chain.

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The "Silver Bullet"
87 Ram D150

Sometimes a worn distributor shaft will cause the timing to bounce around.
This would cause a rough idle.
Also, what is the total distributor advance? How much mechanical advance, how much vacuum advance does the pod give?

Here is some info on checking the cam "phasing":
My thinking is that you should re-check your cam timing at the valves, lets see how close your cam position is to a true "split overlap" setting. here is my "quick & easy" check process:

-Pull the valve cover, install a "degree wheel" or accuratly mark you damper.

-Rotate the engine to true TDCE (Exhaust Stroke) (TDC point with no "lash", both valves hanging open on "overlap")

-Place a dial indicator on the intake valve keeper. From TDCE (zero) rotate engine backwards untill the intake valve closes, (dial needle stops moving)"Over shoot" and come back to this point, turning clockwise to where the needle starts to move again, note this position in degrees.

-Move the indicator over to the exhaust valve keeper. Now continue to rotate clockwise, through TDCE and to the point where the exhaust valve closes. Note in degrees where ex. valve closes.

-Subtract the small number, TDCE to intake opening (intake Pre-TDCE opening degrees) from the total overlap number,(degrees both valves are open) the remainder, (exhaust Post-TDCE) should be 4-6 degrees less then the intake Pre-TDCE number. Example: intake opens 26º BTDCE, exhaust closes 22º ATDCE, (48º "travel" or total overlap) This would be a 2º advanced cam

If you see that the "split" is pretty even, with the intake opening a few degrees longer, then the cam position is OK. If the exhaust is staying open longer then the intake or if you see the intake opening more the 10º longer then the exhaust, you should re-degree the cam.

Note that these measurements are taken right off the valve "keeper" at the proper "lash" setting so we can see what the valve / engine really sees. (lash changes have a big effect on this test so be sure the lash is correct)
DD

My timing mark used to float about 3-4 degrees at idle. Then I built a distributor using a new housing and shaft assy. Now the timing mark is steady. The worn distributor, however, did not impact my gas mileage.

Mitch

Thank you

Distributor shaft was very good and everything there.
I have checked both advances, mechanical and vacuum, they were OK.

Today, Thanks to DD, I checked that "cam degree" (or whatever is correct word) .
Intake valve opens 48 degree BTDCE and exhaust valve closes at 25 degree atdce. With these numbers it's very easy to notice that the chain is set one tooth wrong.

TOmorrow i'll Change timing chain. Now it's late evening here in Finland. I'll finish my bottle of rhum and continue my battle of slant six when I'll woke up tomorrow morning.

if there is anything I should watch out when I change the timing chain. I would appreciate if You tell me that.

One thing is ... How do you check that proper timing ( " Cam Degree") when you'll change timing chain.

Doc, I Have still difficulties with this timing chain. Marks are correct but overlap is not even, there is about 20 degrees difference In all cylinders.
I think that valve lash is ok, but...

To be sure that chain is correctly adjusted, isn't it easyest to check degree where valve is full open?? I do not know what it should be. Ihave stock engine.

Joug

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Sorry, my english is not very good

One more thing, I've done this overlap test with cold engine. Is it ok?

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Sorry, my english is not very good

Your cam overlap results look good, I like it when I see that the cam has some advance. Did you check for slack (free motion) in the chain? How much did you see?

My guess is that the rough idle is something else and not caused by the timing chain. What are the cylinder to cylinder compression readings?
DD

Combression pressure was good and even. Chain lack was about 0.08" I think that it was not so bad.

Is that overlap really ok?? Intake opens, now with new chain, 37 degrees BTDCE and exhaust closes 18 ATDCE. This is similar Federal Mogul chain set than there was before.

I also checked Lobe centerlines( from valve keeper, many times and with many different lifts). Intake CL 101 degrees and exhaust CL 117 degrees. I think that this is not ok, but how much this has effect to the MPG's, rough idle, vacuum and mixture?

Change one tooth it allways change everything ~20 degrees. So its not possible to adjust that timing advance with chain and sprockets.

Joug

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Sorry, my english is not very good

Just to add my 2 cents worth, there is an easy test for a loose timing chain. Turn the engine to TDC, then use the fan (with a little pressure on the belt) to rock the engine back and forth. You can feel the extra tension when the slack in the chain is taken up and the cam starts to turn. By reading the timing marks, you can measure the distance that it turns "easy", that is, turn in one direction until you feel the resistance, note the position of the timing mark, then turn the other way and note that mark when you feel the resistance. The total distance between the two readings is the "chain slop". I have noticed that 5 degrees is about the most you want. I have seen the chain jump and pop holes in the pistons at 7 degrees.

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Chuck Rivers, Webmaster

Chuck. I have now new chain and sprockets. And with old set the lack was not too much (if i'm trusting haynes book).

But what You people ( who have more experience than I) think about those Cam lobe centerlines that I mentioned before.

Joug

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Sorry, my english is not very good