Timing moves

Classic short-frame models

Re: Timing moves

Postby chuckthebeatertruck » Fri Jun 05, 2020 8:12 am

I've been playing with a Morris MRA retardable magneto cap on my flathead.

It uses a TINY eccentric cam to shift the points in relation to the rotor cam. It's an unbelievably small eccentric, but shifts the timing up to 20 degrees. Surprises the heck out if me how that tiny shift in the position affects the timing.

Point is, check your points stud and points block. Static timing isn't dynamic running and you're consistently 10 off. Seems too consistent to be a coincidence.
chuckthebeatertruck
 
Posts: 86
Joined: Thu Jun 22, 2017 1:11 pm

Re: Timing moves

Postby Ferrous_Head » Fri Jun 05, 2020 8:42 am

The steepness of the dome isn't a problem. I have use piston position indicators for years. Dial gauge type the easiest and best
In any case, whatever one you use at this stage you are merely confirming that what you think is true, is true. Or not.
I expect that if you use am indicator you will see a solid line in the middle of the window, as you should.
After you have started and run the engine and checked the timing, if the timing HAS changed, that solid line will no longer be in the middle of the window.

You will find the engine runs reasonably well if it's within 5 degrees of optimum.
45 degrees BTDC may not, in fact, be optimum for your particular engine. There are several factors that come into play for the "optimum" timing on an engine. The quality of the fuel for example. Your engine was originally set up to run on leaded 100 octane "super" fuel. My guess is that you haven't had access to that for years.
"I know only too well the evil that I propose, but my inclinations get the better of me."
User avatar
Ferrous_Head
 
Posts: 384
Joined: Tue Jun 06, 2017 5:36 pm
Location: Australia

Re: Timing moves

Postby wz507 » Fri Jun 05, 2020 12:03 pm

To back up to your fundamental observation that the timing is perpetually changing, are you measuring it with a timing light or statically via continuity? If you are using a timing light are you suggesting that the timing mark is correct (centered in the hole) at some point with the motor running and that timing drifts thereafter with more run time?

Would seem to me the easiest thing to do at this stage is put a plastic plug in the timing hole and see where the dynamic timing is actually occurring with a timing light. If you don’t see the TM, rotate the mag to center the timing mark in the hole and observe to see drift while running.

In my mind there is no difference at all between observing a timing mark and observing a piston position since they both occur at the same place every rotation.
User avatar
wz507
 
Posts: 356
Joined: Fri Dec 11, 2015 9:13 pm

Re: Timing moves

Postby Otis » Fri Jun 05, 2020 12:51 pm

I have only checked it statically and that should not change after a short run time. I’ve been mixing non ethanol 90 octane with low lead non ethanol 100 octane aircraft fuel to about 93-94 octane so the fuel is as close as I can get to what the engine was designed for.
Otis
 
Posts: 123
Joined: Sat Apr 21, 2018 6:42 pm

Re: Timing moves

Postby wz507 » Fri Jun 05, 2020 1:20 pm

Otis wrote:I have only checked it statically and that should not change after a short run time.


I agree it should not change, but rather, behave itself and stay put. That said, I'm still curious in the dynamic mode if the TM were centered, via mag rotation, with the engine running, how much the TM flips about in the timing hole or if by some chance it is relatively stable in the dynamic mode and stays where it should start after start?
User avatar
wz507
 
Posts: 356
Joined: Fri Dec 11, 2015 9:13 pm

Re: Timing moves

Postby Ferrous_Head » Fri Jun 05, 2020 5:55 pm

those flywheels are the pre amf 900 wheels.

on these wheels:

the single line is 45 deg btc front cyl. this is the orig factory advanced ign timing setting.

the double lines are 15 deg btc front cyl. used to set retarded kick start timing.

the dot is tdc front cyl. not used for any ign settings.

Find TDC on the front cylinder. Rotate the engine backwards until the single slash appears. If you measure the piston at this point it should be 11/16ths down.

I'm NOT trying to tell you how to suck eggs here but you need to be sure that the timing mark you are using is the correct one. It is not unusual to find engines that have flywheels other than the stock ones that came with the engine.
It is also possible that the sprocket shaft has spun. If the sprocket shaft can move the timing mark will move.
But the piston position will always remain the same.
"I know only too well the evil that I propose, but my inclinations get the better of me."
User avatar
Ferrous_Head
 
Posts: 384
Joined: Tue Jun 06, 2017 5:36 pm
Location: Australia

Re: Timing moves

Postby Otis » Fri Jun 05, 2020 5:57 pm

What is the dynamic mode?
I pulled the mag again today and I noticed the adapter plate had a fair amount of slop in it. It would make sense that if the pinion gear and adapter plate were worn, things could change considerably. Now with a new pinion gear and it only changing a small amount I’m going to try the early fixed (not able to retard) adapter plate and see if it stays constant. If it does I’ll source a better correct adapter plate.
Otis
 
Posts: 123
Joined: Sat Apr 21, 2018 6:42 pm

Re: Timing moves

Postby thefrenchowl » Fri Jun 05, 2020 5:59 pm

If I want to double check meself when timing 45 deg front cyl ignition point on a Sportster, I look at the rear cylinder....

If it's in exhaust mode and at TDC, it is indeed 45 deg before TDC on compression stroke at the front cylinder...

; O )

Patrick
Flat Head Forever
https://web.archive.org/web/20071011184353/http://www.harleykrxlrtt.com/index.htm
I'm the one who has to die when it's time for me to die so let me live my life the way I want to...
thefrenchowl
 
Posts: 611
Joined: Sun Jun 28, 2015 4:33 pm

Re: Timing moves

Postby wz507 » Fri Jun 05, 2020 6:36 pm

Otis wrote:What is the dynamic mode?


With the engine running.
User avatar
wz507
 
Posts: 356
Joined: Fri Dec 11, 2015 9:13 pm

Re: Timing moves

Postby Ferrous_Head » Fri Jun 05, 2020 7:09 pm

Ferrous_Head wrote:How is the mag mounted ?

It should have the manual advance/retard setup. Is that still on there or have you gone to a "fixed" magneto ?


This is the first time you have answered this.

If the advance/retard system is in place timing is controlled by the left hand twist grip. At the very least even if the wire isn't installed the magneto can be moved by hand. If your not turning the magneto to full advance when timing it, your not timing it correctly.
You can tighten to nuts to fully " the magneto in the fully advanced position if you don't want to be able to retard it for starting.lock"
"I know only too well the evil that I propose, but my inclinations get the better of me."
User avatar
Ferrous_Head
 
Posts: 384
Joined: Tue Jun 06, 2017 5:36 pm
Location: Australia

PreviousNext

Return to 1957 to 1969

Who is online

Users browsing this forum: No registered users and 14 guests

cron