Le Mans 850 flywheel ignition markings accuracy?

[Stevex]

I've got to the point of setting up the ignition on my Le Mans II renovation.
How accurate are the ignition markings on the flywheel?
I'm probably going to check the marking using a degree wheel, but how do I 'zero' the wheel to the correct starting position?
I've also decided to stick with the original points ignition for the time being; the timing chain is new and has a proper tensioner fitted and the points and advance springs are new as well. Any other advice out there please? Thanks.

[jacksonracingcomau]

I've got to the point of setting up the ignition on my Le Mans II renovation.
How accurate are the ignition markings on the flywheel?
I'm probably going to check the marking using a degree wheel, but how do I 'zero' the wheel to the correct starting position?
I've also decided to stick with the original points ignition for the time being; the timing chain is new and has a proper tensioner fitted and the points and advance springs are new as well. Any other advice out there please? Thanks.

Use a positive stop in spark plug thread
I made one from old plug, broke off porcelain and put an allen bolt in it with spacer to hold head down.
Put your TDC pointer according to S or D, then move piston away, fit stop, rotate till it hits, record angle, spin the other way till it hits, record angle.
Should be same ie 20 deg either side of TDC if it isn't, adjust degree wheel till it is.
Check both sides with stop.
When wheel is accurate, check marks

Only other advice, beware non orig points, there have been dodgy ones in past, marked Mareili is safe, branded Facet broke in action (long time ago but they all did it)

[canuck750]

Use a positive stop in spark plug thread
I made one from old plug, broke off porcelain and put an allen bolt in it with spacer to hold head down.
Put your TDC pointer according to S or D, then move piston away, fit stop, rotate till it hits, record angle, spin the other way till it hits, record angle.
Should be same ie 20 deg either side of TDC if it isn't, adjust degree wheel till it is.
Check both sides with stop.
When wheel is accurate, check marks

Only other advice, beware non orig points, there have been dodgy ones in past, marked Mareili is safe, branded Facet broke in action (long time ago but they all did it)

:

+1

Piston stop with a degree wheel will locate TDC with 100% accuracy, don't trust a dial gauge or the timing marks. Once you accurately locate TDC then you can check the flywheel timing marks, re-strike if necessary and paint the mark.

[Stevex]

Use a positive stop in spark plug thread
I made one from old plug, broke off porcelain and put an allen bolt in it with spacer to hold head down.
Put your TDC pointer according to S or D, then move piston away, fit stop, rotate till it hits, record angle, spin the other way till it hits, record angle.
Should be same ie 20 deg either side of TDC if it isn't, adjust degree wheel till it is.
Check both sides with stop.
When wheel is accurate, check marks

Only other advice, beware non orig points, there have been dodgy ones in past, marked Mareili is safe, branded Facet broke in action (long time ago but they all did it)

How far should the bolt protrude from the end of the plug when making a positive stop?

[PeteS]

How far should the bolt protrude from the end of the plug when making a positive stop?

Ideally the bolt should stop the piston around the middle of the stroke. Thats where the piston is moving the most for a given crankshaft degree as opposed to TDC where it barely moves for 5 degrees or so.
Its not right in the middle because it moves in a distorted sine wave due to the side motion of the crankshaft. It approaches a true sine function as the con rod length approaches infinity but is close enough.


Pete

[jacksonracingcomau]

Mine is about an inch under thread, stops piston around 20 deg BTDC
All I've use for 30 + years,

You can buy commercial stops but making from old plug is easy, can vary the length by putting longer bolt/spacer in .

[Stevex]

Well, I checked all my flywheel markings, TDC, initial advance and full advance. They were all 2-3° out. Nice to know that they're all spot on now that I've re marked them.
This is the rh pot's TDC markings, the double dot is the accurate one.

[canuck750]

How far should the bolt protrude from the end of the plug when making a positive stop?

The piston stop on the right was made from an old spark plug, as others have stated, grind off the porcelain, 6mm allan bolt through center, cheap and easy

[Stevex]

Yep, I made one from an old spark plug. I added a lock nut to the threaded end to make it a bit kinder to the piston head.

[Matt Story]

I'm picking away at assembling my motor.  Decided to check the accuracy of my timing marks.  Didn't see this thread, and didn't know better, so instead of using a stop, I put a dial indicator down the pug holes.  I 3D printed a plastic collet to thread into the plug holes and wedge clamp the shank of the indicator.

On each cylinder, I rolled past TDC, and noted the high point.  As expected, the dial barely moves around TDC.  I made a second pass, stopping about .001" before TDC.  Made a mark on the flywheel.  Continued to .001 past TDC, made another mark.  Marks were about 10mm apart.  Average position should be sure TDC right?

By this method, the factory marks are evenly ~2.5 degrees advanced.

Anything remarkable about that?  Anything wrong with my method?

Matt

[Dick]

I'm picking away at assembling my motor.  Decided to check the accuracy of my timing marks.  Didn't see this thread, and didn't know better, so instead of using a stop, I put a dial indicator down the pug holes.  I 3D printed a plastic collet to thread into the plug holes and wedge clamp the shank of the indicator.

On each cylinder, I rolled past TDC, and noted the high point.  As expected, the dial barely moves around TDC.  I made a second pass, stopping about .001" before TDC.  Made a mark on the flywheel.  Continued to .001 past TDC, made another mark.  Marks were about 10mm apart.  Average position should be sure TDC right?

By this method, the factory marks are evenly ~2.5 degrees advanced.

Anything remarkable about that?  Anything wrong with my method?

Matt

My only concern is the angle of the indicator to piston travel. Same goes for the dead stop, but that's just me. I prefer to over complicate and get in over my head. In this case, under the head.  :-\ :)   

[John A]

I personally have never seen a Guzzi engine with accurate timing marks from the factory . They are usually 2-5 degrees out, close enough so it'll run ok but not what I think is good enough.

[mtiberio]

...
Check both sides with stop.
...

why on earth check both sides?

[Chuck in Indiana]

why on earth check both sides?

It's a little cryptic, but I think what he is meaning is to check both sides by rotating it backwards after first contacting the stop.

[Chuck in Indiana]

I'm picking away at assembling my motor.  Decided to check the accuracy of my timing marks.  Didn't see this thread, and didn't know better, so instead of using a stop, I put a dial indicator down the pug holes.  I 3D printed a plastic collet to thread into the plug holes and wedge clamp the shank of the indicator.

On each cylinder, I rolled past TDC, and noted the high point.  As expected, the dial barely moves around TDC.  I made a second pass, stopping about .001" before TDC.  Made a mark on the flywheel.  Continued to .001 past TDC, made another mark.  Marks were about 10mm apart.  Average position should be sure TDC right?

By this method, the factory marks are evenly ~2.5 degrees advanced.

Anything remarkable about that?  Anything wrong with my method?

Matt

It would be interesting to check @ .050" each side of tdc. I would think it would be more accurate because the piston isn't moving much at .001". Probably a moot point, though..

[mtiberio]

It's a little cryptic, but I think what he is meaning is to check both sides by rotating it backwards after first contacting the stop.

don't think so, because 2 lines earlier he says this: "spin the other way till it hits"

[NCAmother]

My dumb question of the day, I've marked TDC on my RAM flywheel as it does not have marks with the cast pointer in the upper point of the case.  Do I need to re-install the transmission housing and mark TDC thru the timing hole?  Thanks!

[Chuck in Indiana]

My dumb question of the day, I've marked TDC on my RAM flywheel as it does not have marks with the cast pointer in the upper point of the case.  Do I need to re-install the transmission housing and mark TDC thru the timing hole?  Thanks!

How and where did you mark it?

[Stevex]

My dumb question of the day, I've marked TDC on my RAM flywheel as it does not have marks with the cast pointer in the upper point of the case.  Do I need to re-install the transmission housing and mark TDC thru the timing hole?  Thanks!

When I did mine I fitted the gearbox and transferred the datum mark position at the timing hole onto the engine case, then took the gearbox back off.
Makes transferring the new markings onto the flywheel a lot easier.
If you can't see the markings through the timing hole, how are you going to check static or dynamic ignition timing or know where TDC is, with the gearbox refitted?
In fact I've recently installed a lightened flywheel and gone through the whole process again.

[NCAmother]

How and where did you mark it?

I installed the ram clutch and followed the directions on setting up the flywheel arrows from the crank to the cast point on the engine.  When I degreed it in at TDC, the mark was were it was originally (about 1 or 2 O'clock.  I did the same on the starter (S) side.  So I'm guessing I should leave it at TDC at 1 O'clok, install the transmission case and mark thru the viewing hole?

[Chuck in Indiana]

I'd think that you could bring it up on compression ready to fire on either cylinder, and the flywheel timing mark should be looking at you if you pretended the bell housing was on there.

[jacksonracingcomau]

why on earth check both sides?

Sorry, been away
With positive stop on each cylinder

Cos not all 90 deg cases are 90 deg apart, I've remachined cases to get 90 but also timed accordingly to get 88 deg ones running right
Measure 3 times cut once, called blueprinting in the old days, correcting manufacturing tolerences.

Irrelevant to nearly everyone , close enough probably more than good enough

[Matt Story]

Per Chucks comment re: referencing the piston at longer displacements from TDC, I decided to make a piston stop from an old spark plug and scrap of steel rod.  By chance, it ended up stopping nearly exactly at + & - 45 deg from TDC.  This method proved that the factory marking error was even worse than measured with the indicator.  I am sure this is due to the limited piston stroke referenced with the indicator.  A full 3 degrees off, but consistent between cylinders.

On a side note, I had an excuse to use my newly resurrected used mig welder for the first time tacking the tool together.  I am pleased that it worked well, since it is an old bargain brand welder that was in a non working state prior to repairs.