Timing under power and idle

[romantic comedy]

The specs I have (Robert Hess) are 0 degrees BTDC at idle and 17 degrees BTDC at 1800 RPM.

Thanks Neil and Shawn. That is what I have been using. I do remember Don mentioning the timing under power.

[ndutton]

We felt Universal's timing instruction left a lot of room for imprecision so we wanted to see how our boats measured up (not so good in my case) and how much difference being exactly on spec made. In my opinion even the factory's roll pin mark isn't that easy to use precisely.

[sastanley]

I know that all members on this forum are always in different 'phases' of working on their motors, but face it..with the last ones made about 1980, we are ALL working on our motors to keep them running.

Being in a phase to do this kind of stuff is FUN! It felt great to cruise for 2.5 hours yesterday with everything running and sounding great.

I will have to redo this entire exercise again when I replace the accessory drive, which is on my radar right as one of the next issues I need to address.

[JOHN COOKSON]

Well, I went down to the boat today. Marking the accessory drive pulley won't work for me because of poor\no access.
I went for "Plan B" and marked the roll pin and hooked up the timing light. With the engine warmed up at idle the mark was 1 to 2 degrees to the right of the timing mark in the flywheel cover. This means the timing is very slightly retarded?
It's been going round and round in my head which way to turn the distributor to bring the timing to TDC. Can't figure out. Help.
Rotating the distributor a micro smidgen in the correct direction should bring the timing to TDC. There is no way I can read the timing light and rotate the distributor at the same time like I would like to do.
Then again maybe I should just leave it alone?

TRUE GRIT

[ndutton]

Your timing light indicates you're slightly advanced so you'll need to rotate the distributor body clockwise to correct. You also might consider Tom's window in the flywheel cover to establish a mark on the flywheel perimeter. I don't have the dimensions right now but I estimate it will provide about 8x more accuracy than the roll pin.

[JOHN COOKSON]

Thanks Neil.
The plan is to get the timing as good as I can by myself. Then the next time my brother in law comes to town I will have him help me get the timing set exact. One of us can read the timing light and the other twists the distributor. In the mean while I'll explore the modification to the flywheel cover that Thatch mentioned.
Once I get this squared away I want to make sure I'm getting the full 17 degrees advance. Seems like a good way to monitor the advance.

TRUE GRIT

[sastanley]

John, does your timing light have an advance dial on it? That is the easy way..or someone better at math than me can calculate what 17° is on the accessory drive for a 2nd mark.

I know that those of us with good side access to the motor are at an advantage, but maybe there is a way to clamp a pointer to the alternator arm or something and put a mark on the front face of the accessory drive.

A middle school science project method could be to use a protractor and make a mark on the flywheel cover, but of course this won't be very precise. - I'd use Thatch's tips/techniques here that Neil mentioned.

[JOHN COOKSON]

John, does your timing light have an advance dial on it? That is the easy way..or someone better at math than me can calculate what 17° is on the accessory drive for a 2nd mark.

I know that those of us with good side access to the motor are at an advantage, but maybe there is a way to clamp a pointer to the alternator arm or something and put a mark on the front face of the accessory drive.

A middle school science project method could be to use a protractor and make a mark on the flywheel cover, but of course this won't be very precise. - I'd use Thatch's tips/techniques here that Neil mentioned.

Thanks Shawn.
No advance dial on the timing light. (Rats)
I'll have a look see about putting a mark on the front of the accessory drive pulley and a pointer on the alternator arm. As I recall even if I could use the accessory drive pulley I couldn't get the timing light near enough or at the correct angle to read it.
Marking the advance using a protractor on the flywheel cover may not be the most precise method but should be better than nothing.
This project is still in the development phase. I haven't made any hard decisions yet.

TRUE GRIT

[ndutton]

Hopefully Tom will be along with a picture of his flywheel cover window. I think it's an ideal solution for those with poor viewing of the accessory drive.

In a recent email exchange Tom and I agreed on this point: Universal's timing mark (crankshaft roll pin) sucks. If using a timing light on the roll pin, because of the thickness of the pin (have you ever seen a timing mark ¼" wide?) and the very small radius it swings (have you ever seen a timing mark turn a ¾" radius?) you have considerable room for error. A very quick calculation shows the combination of roll pin width and swing arc gives a mark alignment zone of around 19° or 9½° either side of the centerline of the pin.

We have already done the calculations for accurate advance marks. On the accessory drive pulley it's 9/16" from TDC. On the perimeter of the late model flywheel it's a hair shy of 1 23/32" (1.706" to be precise). I could work on a dimensioned drawing of the flywheel cover window tomorrow if this sounds interesting.

[Wrsteinesq]

Maybe I'm just displaying my ignorance, but wouldn't it be possible to remove the cover plate from the flywheel and make a narrow mark on the flywheel? Wouldn't that solve the problems of too wide a mark on too small a radius?

And if that would work, why not bore a hole, or even if need be a slot, thru the cover plate, so the mark would be visible with the plate in place?

[ndutton]

Maybe I'm just displaying my ignorance, but wouldn't it be possible to remove the cover plate from the flywheel and make a narrow mark on the flywheel? Wouldn't that solve the problems of too wide a mark on too small a radius?

And if that would work, why not bore a hole, or even if need be a slot, thru the cover plate, so the mark would be visible with the plate in place?

That's exactly what Tom has done.

[Van_Isle]

The specs I have (Robert Hess) are 0 degrees BTDC at idle and 17 degrees BTDC at 1800 RPM.

Forgive me if I'm way off base here as I'm a newbie when it comes to this subject. However, I think what Robert Hess stated was 17 degrees at > 1800 rpm and he was basing that on a recommended minimum full-throttle RPM of 1800.

See here: http://www.cncphotoalbum.com/atomic4/faq/atomic4faq.htm and here: http://www.cncphotoalbum.com/atomic4/atomic4specs.htm

The timing curve has been published here (and I'm sure elsewhere on this site): https://www.moyermarine.com/forums/s...ead.php?t=2324, which indicates that advance continues to 21 degrees at 2000 rpm. The curve also indicates 17 degrees at 1600 rpm.

So given that wouldn't a better spot be the 21 degrees at 2000?

[Van_Isle]

Hopefully Tom will be along with a picture of his flywheel cover window. I think it's an ideal solution for those with poor viewing of the accessory drive ....
... I could work on a dimensioned drawing of the flywheel cover window tomorrow if this sounds interesting.

I'd love to see one ... this coming from a FWC guy with a pulley covering the roll pin and not so great access to the accessory drive.

[ndutton]

This timing study is Tom's baby so I'll wait for his conclusions. I appreciate your digging into other sources to add to the knowledge base and that is in part exactly why I cited my source.

After dinner I'll try to measure my spare engine's maximum advance with the weights against their stop for comparison. In the meantime, here's a picture of Tom's timing window flywheel cover (nicely done):

edit:
Timing advance measurement complete. With the weights extended to their stops I measure 18°.

[sastanley]

Here is an update from me using the accessory drive method for timing. With Tom's suggestions and guidance related to timing adjustments, I was able to set my timing at 750 RPM (I have an Indigo PCV valve installed, which sometimes leans things out..750-800 is as low as I can get it to reliably idle.)

I am running a 1st gen Indigo 10 x 7.4 prop.

The result at WOT today was 2,300 RPM....which is a full 150 RPM higher than it was after I dropped the boat in the water in early June.

Maybe if I add a sugar scoop on my C-30 to extend the LWL I might get some more!!?!?!