Dwell and timing
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Boat Maintenance
Forum Discription: Discuss maintenance of your Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=34819
Printed Date: December-21-2024 at 10:41pm
Topic: Dwell and timing
Posted By: SWANY
Subject: Dwell and timing
Date Posted: October-24-2014 at 9:05pm
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Call me a young blood, but I need a crash course in checking and setting dwell. I've Never owned a vehicle that I needed to check it or timing. Heck I didn't know what a dwell meter was till last week. Best way to set up the meter? run the boat or just crank over? I just did a cap,rotor,condenser, points, oil on the distributor cam, plugs and wires. I think I have a decent Idea on how to set the timing but could use a run down just be sure. To adjust the distributor advance it looks like maybe a 7/16 bolt that I loosen to move the distributor? I've check all over the site but there's no explanation from start to finish. Maybe something to go in the FQA? Thank you for taking the time to respond! |
Replies:
Posted By: 8122pbrainard
Date Posted: October-24-2014 at 9:53pm
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Joel, When you changed the point set, did you set the gap? That's the starting point for dwell. The gap is what sets dwell. BTW, a 7/16 bolt for the distributor? That's pretty big!! Did you mean a 1/4" bolt which would have a 7/16" hex head?  ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: SWANY
Date Posted: October-24-2014 at 10:06pm
| Guess that's my starting point, I didn't set the gap. Just pulled off the old and put the new on. I'll post a picture of the bolt when I can get to my computer, but its a big bolt at the base where the distributor goes into the block.... |
Posted By: Orlando76
Date Posted: October-24-2014 at 10:10pm
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Pete, if we're going to get technical, isn't the distributor bolt a 5/16-24 with a 1/2" head?
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Posted By: 8122pbrainard
Date Posted: October-24-2014 at 10:38pm
On what engine? ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Orlando76 wrote:Posted By: davidg
Date Posted: October-25-2014 at 2:34am
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Once you have gapped your points to the right spec (you may want to call Discount Inboard Marine to check for correct gap and dwell), you can use your dwell meter to dial in the dwell. I know when I used to do it, I would have to make slight adjustments to the gap, to bring the dwell in. Going from memory, I think it was in the ballpark of 27-33 on the dwell. And, again, going from memory, I think the gap was .017" for the points, but, do a web search, or call skidim for the correct #s'. To set your timing, you are correct. Loosen up the bolt that holds the distributor down. Move your distributor in slight increments to the left or right to get it set. I like to make a chalk mark on the counterbalancer at 10 Deg BTDC. You can dial it in from there to whatever the spec calls for (or where the engine seems happiest). Tighten said nut down when done. I believe I normally just use 10 Deg. for the timing #. |
Posted By: SWANY
Date Posted: October-25-2014 at 10:53am
| As far as setting up the meter what is the best practice? I've read to get the motor up to normal running temp and check or pull all the plugs and just crank over for a reading. Why would I pull the plugs? Do I need to pull off and plug any vacuum lines? I should note even though mine is an 87' I have an 86' distributor. 351. Can't imagine there's really many differences in that 351 over the years as far as distributors and functions. |
Posted By: Nautiquehunter
Date Posted: October-25-2014 at 11:19am
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With the dist cap and rotor off you will have full access to the points. Hook up your dwell meter to the negative side of the coil. Crank the engine and take a dwell reading make adjustments to get the dwell to spec. To increase dwell you decrease point gap.To decrease dwell you increase point gap. After you get it to spec put the cap and rotor back on and check it running. You must set the dwell before you set the timing . |
Posted By: davidg
Date Posted: October-25-2014 at 11:53am
| Also, you shouldn't have vacuum advance on that distributor. If not mistaken, I think all boats are mechanical advance. |
Posted By: 8122pbrainard
Date Posted: October-25-2014 at 12:35pm
Dave, You're not mistaken. The distributor should be a mechanical advance marine. If it isn't, then it's most likely an automotive and a potential bomb! ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: phatsat67
Date Posted: October-25-2014 at 12:58pm
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All marine engines have no vacuum advance. Ford dwell should be in the 26-28 degree range. .16-.18 on the gap. I always shoot for .17 to start out. You need to have the distributor loose so you can rotate it around the points cam to set the gap at the highest open point on the cam. That is where you get your gap reading. Mark where the distributor was before when it ran the put it back there for the initial start up before you set the timing after your dwell is properly set. The best instructions for dwell using the starter is to pull all of the plugs so the engine cranks at a higher speed while measuring dwell. Make sure your ballast resistor is functioning properly or else you will over heat the coil or burn up the points prematurely. Don't forget to lube the points cam with the provided lube and make sure to lube the advance mechanism as well as ensure proper unobstructed movement of that mechanism. Also put a few drops of oil down the middle of the dizzy shaft where the little sponge sets on top. This lubes the internal movement on the shaft itself for the advance. ------------- |
Posted By: SWANY
Date Posted: October-25-2014 at 2:34pm
| Thanks for the responses. So set the gap loosening the points bracket/hold down and set dwell by adjusting the whole distributor? |
Posted By: 8122pbrainard
Date Posted: October-25-2014 at 3:01pm
Since you missed it, once again, the dwell is set with the point set gap. The timing is set by twisting the whole distributor. Did you check to make sure you don't have an automotive distributor with a vacuum advance? ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: SWANY
Date Posted: October-25-2014 at 3:06pm
| Thanks Pete. Yes its a marine distributor. Just came to that conclusion that setting the point gap is dwell. My dwell reading is at 22. Calling it good put of frustration |
Posted By: SWANY
Date Posted: October-25-2014 at 3:22pm
| Nevermind, I knew that wasnt going to be good enough. Played with it and got the dwell to 26. |
Posted By: 8122pbrainard
Date Posted: October-25-2014 at 4:22pm
I was going to say something about getting the dwell closer but figured you would try and you did!  Now, onto the timing!  ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: SWANY
Date Posted: October-25-2014 at 7:12pm
Thanks again! Got the timing "set" in the driveway at 600rpms. Runs really nice. My timing light is a piece of crap, so I'll barrow a brighter one from a friend and check it again. Took the boat out, discovered couple more issues that need to be addressed eventually. But I noticed before I was ready to pull out it was idling at 900 rpms in neutral and when I put it in gear it's running at 600  Quick thought, why would there be oil sitting on top of the valve covers in the "rim"? Bad Valve cover gasket or oil cap? |
Posted By: phatsat67
Date Posted: October-27-2014 at 9:57am
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That's common. The oil leaks through the bolt holes on the old cork gaskets. Could also bee that the oil breather/fill gasket is leaking too. Look for traces of oil flowing down the valve cover from there. You will need a nice 1/4" swivel for a socket to tighten the valve cover bolts behind the exhaust manifolds. 600 in gear under way is fine. Pushing the trailer it should be 400-500. 900 is a little high out of gear but if a spring is week or the mechanism gets sticky that can happen. 100-150 rpm drop from neutral to forward gear is normal. ------------- |
Posted By: gtxragtop
Date Posted: December-27-2014 at 9:15am
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There is no need to set the point gap using a dwell meter. Set at .017" and your done. The use of a dwell meter is a good checking tool for those who have limited experience setting proper gaps with feeler gauges. I did not see it mentioned here but to set the gap, the points rubbing block needs to be placed on one of the high points of the distributor lobe. Make sure that the rubbing block on the points is centered on the high point. Once done, you need to add a very small amount of special grease. Some will say use any old grease but you do not want to use a grease that flows easily when warm as it can coat and destroy you new points. Again, a very small amount is needed. A spot the size of this "O" is all that is needed and it is typically placed on the points rubbing block where the block hits distributor cam. Look at the rotation direction of the distributor and place the grease (the very small amount) on the side of the rubbing block on the points where the rubbing block will wipe the grease OFF the distributor cam and get caught on the rubbing block. This will keep the rubbing block lubricated. http://www.summitracing.com/parts/maa-26015 You also need to verify that the mechanical advance in the distributor is working correctly. They often seize up or a spring breaks and then either the engine idles bad or the engine has no power due to lack of ignition advance. The best way to check is when the points are off. Gently hold the rotor and twist the rotor clockwise. Does it rotate? If not, try twisting counter clockwise. Does it rotate? If not, the mechanical advance is seized and and at this point your better off replacing the distributor. Some will say.... pull it apart, remove and clean off rust and lubricate all moving parts but it has been my experience that the removing of rust allows the distributor cam lobe assembly to no longer have the tight tolerances to the shaft as designed and your point dwell will jump all over the place as engine RPM is increased. You may also see that using a timing light, that the timing advance is jumping around. Either way performance and idle quality will suffer. Assuming that when you rotated the rotor, it easily moved, no let go of the rotor. The advance springs should quickly snap the rotor back to the position you started turning the rotor from. Do this several times. Check to make sure that it fully snaps back. If it is behaving this way, then your distributor may be fine. As an earlier poster mentioned, remove the rotor and you will see a piece of felt in the center. Place 5-6 drops of synthetic oil on the felt to lube the lobe assembly to shaft. ------------- 1996 Ski Nautique GT40 Worcester, MA. |
Posted By: 8122pbrainard
Date Posted: December-27-2014 at 9:28am
Dave, I've been setting dwells with point gaps for 40 years. I posted that fact and ended up being criticized!  ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: gtxragtop
Date Posted: December-27-2014 at 9:42am
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I meant to add... Ideally buy or borrow a timing light with a dial that allows you to change the delay time that the light flashes. On the timing light the dial indicated the amount of advance in degrees. On the vibration damper (assuming that on your engine this is where the timing marks are locate the notch in the damper. This typically is the TDC (Top Dead Center) mark or zero degrees advance. Use a small artist brush with a bit of white paint and put the paint in the groove. This makes it easy to see the mark with the timing light. There should be numbers and small lines on the damper OR on the metal part that the timing is reference to that show you the degrees of timing advance. With the timing light with the dial, set the dial to the number of degrees advance spec'd for your engine. 5-7 degrees "AT IDLE" is typical. Check the advance ONLY with a warm engine. Start up the engine. Does the paint in the notch line up with the timing reference mark? If yes, then the initial setting is fine. If not, you can use the dial on the timing light to see if the idle timing is too far advanced or retarded. Make the necessary corrections to get the idle advance to spec. The final step with this is done is to verify total ignition advance. This tells you that the mechanical advance is working properly. Ideally find the distributor specs for your engine. It is typically something like 34 degrees at 3500 RPM as an example. Knowing this, dial the timing light to the spec (say 34 degrees) and start the engine and increase RPM to 3600 RPM (ideally with a helper on the throttle) Is the white mark on the damper lining up with the timing reference? If yes, your distributor is working properly. Now go back to idle. Dial back the timing light to the idle advance number. Is this mark lined up properly now. If yes, then your distributor is behaving properly. Lets take an example where at 3600 RPM, the timing is off. Dial the timing light until the mark lines up. What does it read? If less than say 34 degrees then your not getting full advance and power and fuel consumption will suffer. If much more than 34 degrees, then either you did not set the idle advance properly or the distributor is advancing too far which can also rob power but worse, cause pre-ignition (engine pinging/knocking) which will damage the engine. ------------- 1996 Ski Nautique GT40 Worcester, MA. |
Posted By: gtxragtop
Date Posted: December-27-2014 at 9:54am
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Peter, Please accept my apologies. The intent of my post was not criticize using the dwell method of setting the gap but to state that it is not necessary. I also stated, as you will note, that checking dwell (assuming one has a dwell meter which most do not except us old timers) has several advantages as noted. Once one perfects the proper use of a feeler gauge, then using a dwell meter is not needed. I did find the use of a dwell meter on the old GM distributors what had the metal door on the distributor cap where with the engine running at idle, a small allen wrench would change the point gap and hence the dwell. With the GM distributors, I only needed to set the point gap by eye, then dial it it with the dwell meter. Much easier than the Ford and Mopars which required you to set the gap via a feeler gauge. ------------- 1996 Ski Nautique GT40 Worcester, MA. |
Posted By: 8122pbrainard
Date Posted: December-27-2014 at 10:01am
Dave, My post was not directed to you. I was agreeing with you that a dwell meter is not needed. It sure seems that you have lots of experience behind you. You're occupation is "NG". Were or are you a mechanic? BTW, for those who do not have the fancy timing lights, a degree tape on the dampner will serve the same purpose for checking advance. This of course is for externally balanced engine with a dampner! ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: gtxragtop
Date Posted: December-27-2014 at 10:20am
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I've loved working on cars and engines all my life. I worked as a mechanic when I was in high school starting at age 16 in a VW/Porsche garage. Through college I worked as a mechanic in a garage to pay for school. In my mid 20's we built and raced a 68 Road Runner at New England dragway for several years and were very competitive. I'm an electrical engineer by trade now and perhaps should have been a mechanical engineer. I still do nearly 100% of repair on our vehicles at 61 years old. A big part of my enjoyment comes from helping others troubleshoot engine issues be they mechanical or electrical. I still have so much more to learn. ------------- 1996 Ski Nautique GT40 Worcester, MA. |
Posted By: gtxragtop
Date Posted: December-27-2014 at 10:30am
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This is a good definition of dwell. (Not mine) The dwell time is the amount of time the ignition coil primary has current running through it. So in a points ignition system, it is the amount of time the points are closed. There is only current sent to the spark plug when the points open. So if the dwell time is too short, the current in the primary coils of the ignition coil has not been able to build up far enough so there is not enough magnetic energy stored in the coil to give a good spark. If your points gap is too large, then dwell time is reduced as noted above. If too small, then the points will burn and pit early. Remember to replace the capacitor when changing the points. If defective, points will burn and pit quickly despite the correct gap. ------------- 1996 Ski Nautique GT40 Worcester, MA. |
Posted By: SWANY
Date Posted: December-27-2014 at 12:31pm
| Thanks for adding to this Dave. Great info. I'm going to get a timing tape to check the advance better. |
Posted By: gtxragtop
Date Posted: December-27-2014 at 2:23pm
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Checking timing at idle and checking timing at full advance may be different on a fuel injected engine than a carburetor engine. On my 1996 PCM GT40, idle timing advance is checked with the SPOUT connector removed. Full advance at the higher RPMs is checked with the SPOUT connector in place. In a carb based engine that uses a mechanical advance distributor, both are checked without the need to touch a connector or jumper since all the advance mechanisms are in the distributor. I will note that I'm not familiar with many Fuel Injected PCM engines by Ford or GM. So idle timing checks should be done following the manufacturers steps. Full advance would always be checked with everything normally connected and verified against the manufacturers stated full advance at stated RPM. ------------- 1996 Ski Nautique GT40 Worcester, MA. |