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Question about points

D

DWester

Regular Contributor
I just bought a new set of points for my merc 350 distributor and when installed, the composite foot that rides the cam is a pinch to long and won't let the gap get small enough. Can a guy just file the foot down to make it fit or will that mess with the integrity of it? The reason I ask is, if I end up with a spare that is the same, I'd like to have an option if out on the water. I was thinking of just filing it down, smooth it off with some emery cloth, then lube it up good. What do ya think?
 
The points I bought are from the same place as last time and has the same box and numbers as the first set, which fit correctly. They look identical, just a tiny bit longer foot. Can we say China.
 
Docksidemarineservices said:
If you cannot find the correct points, which are available. You can modify them. Remember, you are setting dwell not gap.
Click to expand...
I'll ditto Chris on this one. Point gap is an estimate only of correct dwell angle. Set dwell, not gap!

I'll also agree that if you can successfully remove the right amount of material from the cam follower, I see no reason why the correct dwell can't be achieved.

Here's a 4 cylinder engine distribtor.
Out of 360* rotation, each cylinder has 90* in which to saturate the coil (points closed), and to collaspe the field (points open).
Of that 90*, the dwell angle will be the portion when the contact pionts are closed.
Your V-8 must do this within only 45* each cylinder.........., so the correct dwell angle becomes even more important.



ignition-system-points.gif


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Docksidemarineservices said:
What brand parts are they?
Click to expand...

They were Napa Chris.

RicardoMarine said:
I'll ditto Chris on this one. Point gap is an estimate only of correct dwell angle. Set dwell, not gap!

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Click to expand...

Since the 60's, I've always set my points with a feeler guage with good success. I do have access to a dwell meter that I could hook up and see what I get. Maybe I'll be running a little better. There's no instructions with it so how is it hooked up and what should the reading be with this motor? It's a 1978 Merc 350.

Thanks you guys. Always appreciated,

Darol
 
yes you can file down the rubbing block on the contact set. but first see what your dwell is. your dwell setting overrides what the gap setting is. also, don't forget to apply a small amount of lube to the distributer cam.
 
Darol, pay no attention to point gap. As said, gap is an estimate ONLY of correct dwell angle.

Your dwell angle wiill be approxiamtely 29* to 31*.
Please varify this by seeing your OEM specs.

And remember that when dwell angle is changed, BASE advance (as well as progressive advance) changes also. Meaning that you will need to re-check/set timing.

And just as an FYI for you:
BASE advance is BASE advance. We fire up and idle on BASE advance only! It must be close, but it is rather meaningless in the large scope of things.
The more important aspect of ignition timing, will be your progressive and TA (total advance).
If your distributor advancing mechanism is not providing the correct progressive and TA, then you'll be leaving power on the table.

Again, see your OEM specs for this.


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Thanks Ricardo. My first option for info always starts here and usually gets resolved here. I feel like I'm on the right track now anyway.
 
Well, I warmed the motor up as recommended and shut it down. It calls for me to take the cap and rotor off.
Then connect the green or red wire of the tester to distributor side of the coil and the other lead to the negative battery post. As instructed, I also disconnected the coil wire from the distributor cap and grounded it. I started the engine, ran it long enough to set the dwell to 30 and shut it down. Then put everything back together and it wouldn't start. It back fired, popped and quit several times. I then took the new points/condensor out and replaced them with the original set and the same thing happened. The spark is weak when I manually break them. What's going on. This thing ran great before doing this "DwellTest".
 
I'm not sure Chris. This was my partners boat till he died and then I ended up with it. I've had it for 5 years now. Is there something that I did that would cause a possibly weak coil to go bad? Would a defective coil cause these symptoms?
 
There's a 2 1/2 inch, round item that looks to screw into the manifold directly behind the coil and to the port side of the distributor that has a wire going into the harness that's included to the coil. Is that a ballast?
 
DWester said:
I started the engine, ran it long enough to set the dwell to 30 and shut it down.

This thing ran great before doing this "DwellTest".
Click to expand...

First I have a few questions.
How did you set dwell with the engine running? If this distributor has the window for accessing an adjustment screw, it's an automotive distributor.

Did you have the dwell meter set for 8 cylinders?

And ditto Chris' questions!

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I'm sorry you guys. I wrote that wrong. I CRANKED the engine over to get the dwell.

The distributor DOSEN'T have an access for adjusting. It does have a 1/2 inch round screen on the side of the body that I would call a spark arrester. It is a Mercruiser distributor.
Before I did the dwell test, I had installed new points and condensor and the thing ran great!

If I could change my statement above I would, but the edit isn't available.

As far as the meter, it has three different readings on the screen. One for 8 cyl, one for 6 and one for 4. I was reading the 8. Maybe not the best grade meter out there, but it's what I have.
 
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You can check dwell with the engine running at idle.
Increase RPM a bit, and see if the dwell remains constant.

A worn upper disbrutor shaft bushing can cause shaft wobble. Shaft wobble will cause an erratic dwell once above idle RPM.

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DWester said:
There's a 2 1/2 inch, round item that looks to screw into the manifold directly behind the coil and to the port side of the distributor that has a wire going into the harness that's included to the coil. Is that a ballast?
Click to expand...

Silver or rusty with one wire coming out of it? If yes, it sounds like a repositioned condenser. You may have a ballast wire. You will want to check the voltage on the positive side of the coil with the key on, engine off, and the points open. Should be around 8 or 9 volts.
 
DWester said:
Before I did the dwell test, I had installed new points and condensor and the thing ran great!
Click to expand...
Unless something has changed since this, I think that you could safely out-rule a bad timing chain and sprocket set.

With the V-8 engine, you'll have 45* of distributor angle per cylinder.
Of this 45*, 30* (if 30* dwell is correct for your ignition) will be the angle dedicated to coil saturation, or in other words, dwell angle.
The remaining 15* angle is when the contact points will be open.

Perhaps try another dwell meter.

And again, increase the RPM some, and see if the dwell remains constant.
If not, then perhaps the contact spring is faulty, or the shaft is wobbling some.

Remember that you must re-set the BASE advance after a change to dwell is made.
Also check to see what the progressive advance is doing, and check this right up to point at which the mechanical advance discontinues advancing.
This will be your TA (total advance).
Your total advance should be "full in" no sooner than approximately 3K or 3.2K RPM or so.
See your OEM specs for this number.





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The resistance is done with a resistance wire.....doubt it is the problem.

If you set the dwell angle with a meter this time and not before and it ran good, then the only piece of the pie missing is the timing.

If you had set the gap with a feeler guage before with no issues and the timing was ok, when you do it by dwell angle then most likely the timing is out of spec...

Go back and try doing it the way you have always done it, see if the engine fires up ok. if it does connect the dwell meter and see what your reading is, report back with the info. also put a timing light on and see what your base timing is? report back with that also.

One more note, I am not sure as it has been a while since i used a anaolouge meter for dwell but you may have to ZERO it before use. How, i am not sure for your meter. I have and use a digital meter that works when cranking not many around that do this..........

When you swapped out the new points back to the old, did you also swap out the condenser? if not do that also...would not be the first time a new (bad) condenser was purchased.......

Here is the mercury spec from the manual for that year....
 
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Under construction. Going for more coffee, be right back.

OK... I'm back with a fresh cup.


Perhaps dwell angle can be looked at in two parts.
Let's say that there is a peak angle between when the points break, and when they close.
Let's take the 30* dwell angle, for example.
If the 30* was actually set to 32*, the points will be closed longer.
This means that they will break later to the tune of 1*.
(32* - 30* = 2*...... and 2* split = 1*)

That's a 1* ignition change at the distributor in the direction of retarding the advance.
So if I'm thinking correctly, a 1* change at the distributor, is 2 degree change at the crankshaft angle.

Most engines will idle just fine with a BASE advance that may be 2* too far advanced, or 2* too far retarded.
In fact, many will run at the higher RPM range with an advance that is 2* off in one direction or the other.

Note: not all replacement contact points will have the cam follower in the exact some location, nor will all replacement contact points have the same exact geometry.


Point being...... dwell angle would need to be pretty far off in order to cause a substantial change to the ignition timing, and the crankshaft angle is what we relate to for ignition advance.


This is not to say that we don't re-set BASE advance after replacing contact points, or after a change to dwell angle.


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issue is not 1 or 2 degrees of timing change based on dwell of a couple of degrees diffirence.

The issue is

we have no idea what it was before............lets say he was running a gap of .019" (maybe we dont know)
lets say timing was marginal, maybe 2-4 degrees BTDC, DOnt know if he knows what it was........

Install new points, set it at 30 degrees dwell, (not knowing if the meter is acurate or has been zero'd if need be,

ANSWER.... not a clue where we are now.....................

All the theory in the world is of no importance here.

He clearly states it ran good before trying to set points with dwell meter.........

If this is true then only two things can be wrong,

1. new points or condenser are no good.........he did find an annomoly with the points

2. adjusting by dwell meter vs point gap caused a change in timing enough to cause no start or poor running.


I doubt anything else such as resistance or coil is the issue here, simply the method used and lack of doing it in a way that is repeatable each and every time. Again we have NO idea what his timing is.....bet it has never been checked and set by ear.......
 
DWester said:
The spark is weak when I manually break them.
Click to expand...

Weak coil.

Asking about the resistor because this is an older boat and maybe some where along the way one of the owners was not aware of the factory resistor wire that feeds the ignition system and piggy backed the system with a ceramic resistor.
 
Kghost...... I'm suggesting these as for conversation only.... as I don't want for you and I to get into it over this.
Fair nuff?


kghost said:
1... issue is not 1 or 2 degrees of timing change based on dwell of a couple of degrees diffirence.

The issue is

2... we have no idea what it was before............ lets say he was running a gap of .019" (maybe we dont know)
lets say timing was marginal, maybe 2-4 degrees BTDC, DOnt know if he knows what it was........


3... All the theory in the world is of no importance here.

4... He clearly states it ran good before trying to set points with dwell meter.........

5... If this is true then only two things can be wrong,

1. new points or condenser are no good.........he did find an annomoly with the points

2. adjusting by dwell meter vs point gap caused a change in timing enough to cause no start or poor running.


6... I doubt anything else such as resistance or coil is the issue here, simply the method used and lack of doing it in a way that is repeatable each and every time. Again we have NO idea what his timing is..... bet it has never been checked and set by ear.......
Click to expand...

1... If you site an incorrect advance as a potential for the problem, then how can you remove this from the equation?
kghost said:
If you had set the gap with a feeler guage before with no issues and the timing was ok, when you do it by dwell angle then most likely the timing is out of spec...
Click to expand...

2... See above.


3... And yet this theory may perhaps lead him to a conclusion.


4... Understood.

5...
1. No arguement there at all.
2. IMO, this is an assumption!
We have no idea as to his experience with a dwell meter, nor if the dwell meter is accurate or not.

6... Again, no arguement there.
He needs to be checking/re-setting his ignition advance each and every time he makes a change to the dwell angle.


DWester said:
The spark is weak when I manually break them.
Click to expand...
At what area are you looking at spark? Pay no attention to any arcing at the contact points for now.
Look at your secondary voltage spark output.
When viewing by color and at the spark plug gap, you'll want to see a hot white-ish/blue-ish spark.... not yellow-ish.

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And by no means should anyone be setting Marine Ignition advance by ear. :mad:
That would be a recipe for either poor performance (under advance, for example), or severe detonation damage (if over advanced, for example).

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DWester, how about helping us out here by posting what your BASE advance is being set at?

Have you checked to see if there is any excessive distributor shaft wobble?

Have you checked or tested the mechanical advancing mechanism?

Are you seeing a consistant dwell once out of idle speed RPM?

Can you post a few photos of your ignition distributor... under the cap, etc?


And as an FYI only, I'll suggest that you NOT fool around with anything else until this issue is resolved.
If the cam follower adjustment has not been an issue prior to this, I'd not mess with it at this time.
P of E.... process of elimination. Take one item, and one item only at a time. ;)



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Docksidemarineservices said:
Weak coil.

Asking about the resistor because this is an older boat and maybe some where along the way one of the owners was not aware of the factory resistor wire that feeds the ignition system and piggy backed the system with a ceramic resistor.
Click to expand...

Yes this is possible and i hope he can answer this, but again he states it ran fine before tune up parts change.........

Maybe he can chime back in and clarify/answer some of our questions/assumptions.

Too much unknown here.....

kinda sounds like a issue may have been created and now the backtracking begins.............

for all we know he may have a wire touching ground or again a bad condenser......maybe even a bad tachometer.......

keyboard diagnosis can be difficult.............lol
 
Yes, I can agree with you guys! I do tend to offer a bit more than what may be necessary.
My thoughts are, that perhaps not enough information may prevent a person from looking elsewhere.

You may disagree with my approach, but I've been thanked more often than not, for giving a bit more info than asked for.


And for the record, my key board has a built-in Internet Engine Diagnostics Center! :D :D


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