Setting points and dwell

Trotter1414

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Apr 20, 2018
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ok first off new to site And boating. Hi to all.
I am working on a 1989 sport craft 1900 sprint br it has a omc 4.3 that came out of a 1990 four winds it’s not a roller motor it has flat tapets not sure what the deal is on that one that’s a different topic and a oms out drive which I pray that I have adjusted correctly per the manual. Took boat out twice last year after putting in the motor that I bought. due to the other engine had a crack block and that’s how I bought the boat with bad engine. All did good when I took it out. Now start of a new season and performing maintenance.
question is I have the new points set to .019. Now after start up and engine warmed up I worked on the dewell. The dewell is at 29deg book calls for 39 deg and the points are at .010 now and the timing is set to 6 deg before top dead center. Does this sound right. If I try to get 39 deg the points would probably be just about closed all the time. I am I missing something. All of this is done on the muffs.
 

Lou C

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Nov 10, 2002
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Something is not right, I set mine at .018-.019 and its usually in spec. Keep in mind that point gap and dwell are inverse. So if your dwell angle is too small, your point gap is too big, you must be at more than 0.19 for it to be as low as 29*. I try to set the gap at the high end this way as the rubbing block wears it will stay in spec longer. Book says 39* plus or minus 2* which means you can be as low as 37 or as high as 41.
The best and easiest way to set points is to get a remote starter switch and hook it up to your starter, take off the cap and loosen the point retaining screw just enough to move the point plate. Be sure to ground the coil lead coming out of the center of the coil. Crank the engine over and watch the dwell meter, you can get it real close this way. Then check it again with the engine running.

Also if the 4.3 came out of a 1990 Four Winns it is a roller motor, they switched to the roller cam in '87 or so and my '88 4.3 for sure is a roller cam. This pic is from when I replaced the heads and head gaskets, see the retainer in the cam valley, that's for roller lifters. The flat tappet engines do not have this...
 

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Trotter1414

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Apr 20, 2018
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Ok I will do that. On the roller part I can see the top of the lifters through the valve cover and they do not have the lifter retainers on them the lifters are round At the top where the push tubes are. Thank for the reply
 

Trotter1414

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Ok this is what I got and it was my bad. When I did the dewell I was looking at the 8 cyl. Scale and the 6 cyl. Scale is on the bottom of the dwell meter. Now by going by the 6 cyl. Scale the dwell is at 39 deg. And that is with points set at .010. When the points where set at .019 the dwell was at 28 deg. Does this sound right. I still need to do the procedure stated above to see how that work. But is .010 on the points sound about average after setting the dwell.
 

Trotter1414

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Apr 20, 2018
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Ok performed the dwell procedure stated above I still come up with the same thing where the points are at .010 and the dwell at 39 40 deg. Ok so has any Buddy have check what their points gap after sitting the dwell. Or how much out of adjustment point gap is normal after setting the dwell to specs.
 

Trotter1414

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After researching .019 point gap on gm engine it is a dwell of around 30 deg. I feel That the 39deg dwell is not Achievable with the points set at .019 +or- .002. Now setting at .019 then it is achievable shooting for a dwell of around 30 deg dwell. Could the manual Be incorrect on the 39 deg dwell becouse .019 point gap does not represent 39 deg of dwell.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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file the points before you attempt to set them. use your wifes nail file or use a points file.

always file your points.

then follow process in post #2.
 

Lou C

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Also make sure if you are setting the gap with the engine off that the dist cam is really on the high point so that you are setting them to the max they can open
 

Lou C

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Meaning that, if you are not really on the high point of the dist. cam and setting it to .018/.019, then when the cam turns to the high point, your gap is really quite a bit more, which would explain your excessively low dwell reading. Keep in mind that your dwell angle is the # of degrees the dist cam turns with the points closed, to fully charge the ignition coil. Then when the points open, the magnetic field in the coil collapses and the high tension current is discharged. If your dwell angle is too small due to a point gap that is too big, then your spark will be weak. If on the other hand, your point gap is too small and your dwell angle is to large, it will tend to burn points prematurely.

Its too bad you cannot use a variation of the the Delco 'window' distributor GM used in the '60s and '70s on marine engines that still use points. This made adjusting points REALLY easy. The points mounting plate was set up so there an allen fitting that could move the plate slightly to change the gap with the engine running. So, you slid open a little metal window in the dist cap, inserted an allen wrench (we all had a flex one with a long flex piece) and just turned it with the engine running and the dwell meter hooked up. You got it right on the money the first time.

Keep in mind after setting dwell, you have to set the curb idle (500-600 rpm in gear in the water) and base timing (6* BTDC).
 

Maclin

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"Its too bad you cannot use a variation of the the Delco 'window' distributor GM used in the '60s and '70s on marine engines that still use points. This made adjusting points REALLY easy. The points mounting plate was set up so there an allen fitting that could move the plate slightly to change the gap with the engine running. So, you slid open a little metal window in the dist cap, inserted an allen wrench (we all had a flex one with a long flex piece) and just turned it with the engine running and the dwell meter hooked up. You got it right on the money the first time."

Old MoPar guy here, I still think that is cheating...:lol:
 

Lou C

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lol sometimes GM had a better idea ;)
though Mopar was the first one to go to electronic ignition in the early 70s, I think '72 or so.
I worked on a few cars with GM's HEI system and only had to replace the module, maybe once or twice over many years of use. It was actually a reliable system. Used to stick a spare HEI module in the trunk for long road trips.
 

Trotter1414

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Thank for the info. My first car was a Jeep with a amc 360 and the distributor cap had the window to fine turn the point with the dwell. And back on topic When I set the points on the high step of the cam now setting the dwell is to fine turn the adjustment on the points to get that more exact .019 due to you can’t eye ball the heel of the point perfectly right on the Peak of the point cam and in return that gives you the right time of opening and closing the point is that a fair statement . I find in my all 60 70 model Shop Manuals And found points set at .019 they only have a dwell of around 30deg Now if points and dwell run as the same I still don’t think a man can get the 39 deg as in the omc shop manual states.
 

Lou C

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Are you sure you're lookin at v6 and not v8 specs?
When I get home I'll pull out my dusty 1970-1977 Chiltons manual and check. But I've had this same engine 16 years and not had that problem!
 

Lou C

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Looked in it and it doesn't even list the 4.3's closest relative with a points ignition, the Buick 225 cu in V6 because it was used prior to 1970, AMC had bought the tooling in the '60s and used them in Jeep CJs due to the compact size (225 cu in or 3.8 liter 90* V6), When GM bought it back they had already converted to electronic ignitions. What I could find on the Buick V6 said the point gap was supposed to be .016: and dwell 29-31*. I'm not sure why there is a discrepancy but it may be related to the way the crankshaft throws on the 4.3 vs the Buick engine are situated to off set the vibrations caused by the 90* V6 design which is inherently unbalanced.
 

Trotter1414

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Very good point lol. I will get back to it and adjust on it till I can achieve the specs. Or something close. First I have to get done with this work week so I can back at it. Thanks for all the info. And for working on this with me.
 

Trotter1414

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Apr 20, 2018
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You know I my be putting to much stock in this old cam dwell meter I have I used to count on it . I will see if one of the guys at work has one to double check and compare mine to their meter.
 

Lou C

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When I run the boat up on the water hose I'll check mine and post back. Later this week I can get to it...
 

Trotter1414

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Apr 20, 2018
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Ok guys and girls thanks for all your help and being patient. I am at .017 with very minimum amount of drag with 39 deg dwell timing is set to 6 deg before top dead center on 93 pure gas. The issue was with my old dwell meter the one I borrowed from work Is the one I am going by since every thing fell into place like the manual. All I have to say if you don’t have good tools you’re going to fail every time. Once again thanks for your help
ps ready for the lake 😀
 

Lou C

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Sounds like you got it perfect! I've been getting about 4-5 seasons on a set of points and condenser. Pick up an Actron digital engine analyzer it will make your life a lot easier.
 

Silvertip

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Sep 22, 2003
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One last thing. Understand that dwell affects timing, but timing does not affect dwell. What this means is that if you change dwell you need to re-time the engine. Always set the dwell first, then time the engine. Distributors with worn bushings can create dwell/timing issues. Setting points with a feeler gauge and then checking dwell with engine running may produce weird response because of the worn bushings.
 
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