Dwell keeps changing which makes timing off?

[LAC_STS]

With the help of this forum I tuned up my dist (thanks Lou) installed a new coil and checked the carb over.


The manual says dwell should be between 27-31. So I had it at exactly 29. I then set the timing to 8 BTDC. Took the boat out and it has ran great. Put another 20 hours or so on it.

I checked the dwell again after the first trip after I did all this and I saw it was at 30. So I took the cap back off and got it back to 29 and tightened the screw that holds the points as tight as I could get it.

Then today I go out and it is running like crap, wont get over 4K RPM. I had an issue today with the fuel tank vent so I just replaced it with another one (hose, see my other threat). I got out the timing light and the timing had moved from 8 to 2 BTDC So, I checked the dwell and it was 33.

I took the cap off and the screw that holds the points is so tight I cant even get it loose. I was using the same flat screwdriver that I used to tighten it last time but I'm gonna have to get a wider one to get it loose so I don't break it.

So I don't see how the points could have moved with the screw so tight I couldn't loosen it to fix them.


Is there any other way this can happen besides the screw being loose? Because its for sure not loose.


Much thanks!!!

 

[Bifflefan]

Re: Dwell keeps changing which makes timing off?

The only thing that comes to mind is the part that rubs on the dist cam is wearing off for some reason. Did you put a little grease on it?

 

[rlbrooks99]

Re: Dwell keeps changing which makes timing off?

The only thing that comes to mind is the part that rubs on the dist cam is wearing off for some reason. Did you put a little grease on it?

Bifflefan is right. If you didn't grease the distributor lobes try doing that first. You may be wearing down the block on the points that rubs on the distributor. Don't use regular grease either, you have to use special distributor grease. There may have been a small packet with the new points, if not an auto parts store will have some. Put it on the tip of a small screwdriver and put it on the distributor lobes - just a little does it.

If not that maybe there is a problem with the mechanical advance sticking.

Welcome to the world of points distributors. Every car used to use them - and need them changed every 6000 miles.

 

[bruceb58]

Re: Dwell keeps changing which makes timing off?

If not that maybe there is a problem with the mechanical advance sticking.

That won't affect the dwell.

 

[LAC_STS]

Re: Dwell keeps changing which makes timing off?

I did grease the cam and the mechanical advance.

This distributor is pretty old but I did check the mechanical advance with my timing light.

The distributor kit I bought did not come with and grease but I went to an auto parts store and they told me to use dielectric grease so thats what I used.

 

[Fishermark]

Re: Dwell keeps changing which makes timing off?

You don't need dielectric grease for this - but if you used any grease at all I cannot imagine it would wear down that quickly.

Does the dwell vary much? Does the shaft have much side to side play in it? If so, the bushings may be worn leading to rough running and variable dwell and timing.

 

[LAC_STS]

Re: Dwell keeps changing which makes timing off?

Ok in my manual it says that if you check the dwell at idle and then at 3K RPM and the dwell changes more than about 3 degrees that the dist may be worn and needing replaced.

It also says that checking the advance will indicate a worn distributor.


I did both of these checks and both checked out ok. If I grab the dist pole with the cap off and try to see if there is side to side movement there is NOT any. But I CAN move the pole up and down. Its not much but I can move it.


But anyways thats what I was thinking is either somehow the points are moving of the dist is worn.

Actually, the points are moving. Because I can tell that the gap is smaller when the dwell gets off. When dwell goes up the points have gotten closer right?

What I did yes was I checked the timing. It said 2 degrees. I checked the dwell and it said 33. I took the cap off and stuck my feeler gauge in the points. It was a VERY tight fit. Not at all like I left it last time so it for sure got tighter. Then I tried to get the screw loose and could not.

So somehow the points did get closer (smaller gap).


thanks for all you guys help. I appreciate it.

So today when I go to the boat I am gonna inspect the part on the points that rubs on the cam and see if it is wearing.

 

[6meter]

Re: Dwell keeps changing which makes timing off?

Are your points pitting? I'd put a new set of points in. How many volts going the points? 12v will burn them up.

 

[LAC_STS]

Re: Dwell keeps changing which makes timing off?

Ill check if they are pitting when I go to the boat today.

I only have about 20 hours on the points.

When I changed the coil and was checking it out I had 7 or 9 (forget) V at the coil. I will check today again though.


Now that I know some more things to look for I will check the part of the points that rubs the cam to see if it is wearing, see if the points are pitting, check for play in the dist, and check the V at the coil.

 

[6meter]

Re: Dwell keeps changing which makes timing off?

7-9v is good

 

[LAC_STS]

Re: Dwell keeps changing which makes timing off?

Ok so today I went to the boat. I checked for sideways play in the dist. I can move it just a very small fraction of an inch up and down if I'm grabbing on the center pole that the cam is on. (cap off). I cannot move it side to side.

I took the screw that holds the points on off. It was on very tight. I took it to home depot and got another one and put it in and re gapped the points, checked dwell, and checked timing.

So well see if it was the screw but I doubt it since the other one was so tight.

Oh yea. When I was checnging the screw I noticed that the wire that connects on the same post in the dist that the condenser connects to then goes out of the dist (I think to the coil) that wire was only hanging on by a thread (at the post in the dist) so when I unhooked it it broke off and I re attached it to the post correctly. Don k ow if this would cause the point gap to change or not.

I also checked the points. They have about 20 hues on them but they still look new. No pitting or u even wear.

Guess well see how it goes from here.

 

[Aloysius]

Re: Dwell keeps changing which makes timing off?

Dwell is the angle the points are closed. Greater dwell time, more saturation of the coil, more heat in the points. As the rubbing block wears, the dwell increases. If you're that concerned, set the initial timing up a degree or 2 to compensate. Frankly, I never set initial timing..I mark total timing, and set it there. 34 degrees or more for SB fords or Chevies.

 

[LAC_STS]

Re: Dwell keeps changing which makes timing off?

Well I have put another 10 hours or so on the engine and the dwell as not changed. So I guess the old screw was not holding up any more.



Thanks again everyone.