Author Topic: Ignition timing with flywheel 180 out  (Read 287 times)

Offline dogshome

  • Posts: 116
Ignition timing with flywheel 180 out
« on: September 02, 2020, 11:58:53 AM »
From the way the engine is running, I don't doubt that the timing is far off. However, she had the clutch fettled by BMW 30 years ago and they put the flywheel in the wrong spot. The PO has never touched the timing as evidenced by the totally unmarked fixings on the electronic ignition bean can.

This also means the mechanical advance hasn't see the light of day for 30 years either.

I've timed up several home-brew model aircraft petrol engine conversions so have a degree wheel and a plug stop. I've read Snowbums thread on this and it sounds good. Get to close to TDC, put stop in, find where it is, rotate the other way and set the degree wheel (bendy wire) stuck to the front of the alternator.

Then I'll put a paint mark on the flywheel through the bung hole for TDC and the same for 6 degrees. Ancient Gunson timing light then gets a go and we see what flickers where.

Question is, with 650 flywheel and 860 pistons (800 for cash) what sort of range of flicker can I expect?  :-?

I have no noise from the engine or gearbox when cold and just a little thunk-thunk clutch out and a bit less clutch in when hot. I've not balanced the 850 kit yet and will do that after a few miles. If the ignition is bouncing around though, I'd rather know.
肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O

Offline mrclubike

  • Posts: 1437
  • Jungheinrich Master Tech
Re: Ignition timing with flywheel 180 out
« Reply #1 on: September 02, 2020, 09:27:58 PM »
You should also mark 32 BTDC   to make sure your advance is working properly
Its more important to have full adv at 32 deg than it is to have your base time at 6 deg
(6+26=32)
 Not sure what you mean by "range of flicker"
1982 R65 running tubeless Snowflakes
2004 R1150R

Offline dogshome

  • Posts: 116
Re: Ignition timing with flywheel 180 out
« Reply #2 on: September 03, 2020, 02:13:46 PM »
RE:Flicker. When centrifugal advance and the timing chain/gear driving it are worn, the timing tends to jump or flicker between degrees. Lumpy Austin Mini with various mods even without worn timing gear tended to change from cycle to cycle at idle.

My light 650 flywheel is now trying to regulate a more brutish high-compression 860, so a bit more 'irregularity' due to power strokes is expected. Just how much  :-?

Yes I should have mentioned I intend to mark the full advance. If that one flickers, then (Houston) we have a problem  :D

I am seriously thinking of knocking up an electronic advance and crankshaft sensor. The electronics and programming with a modern Arduino clone are fairly trivial. If my bean can is rattling around and timing is flickering, then that will solve it.
肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O

Offline skippyc

  • Posts: 339
  • Shouldn't have sold them old bikes.
Re: Ignition timing with flywheel 180 out
« Reply #3 on: September 03, 2020, 06:44:46 PM »
Remember an electronic advance is actualy an electronic retard.

Offline Barry

  • Posts: 5014
Re: Ignition timing with flywheel 180 out
« Reply #4 on: September 04, 2020, 03:06:21 AM »
Even the points timing can have flicker of a degree or two, due to a small difference between the cylinders.  Careful positioning of the outrigger bearing plate can eliminate it almost entirely.  I find that easier to do when static timing and you can static time and electronic ignition using a simple test circuit. 

Full advance can be checked with a strobe but I have never found it it be wrong once static timing has been set accurately.  If there is a difference between static and full advance settings then when you have done it once you will know what that is and can offset the static setting appropriately.

https://robfrankham.com/hall-effect-tester
« Last Edit: September 04, 2020, 03:11:23 AM by bhodgson »
Barry Cheshire, England 79 R45

Offline dogshome

  • Posts: 116
Re: Ignition timing with flywheel 180 out
« Reply #5 on: September 05, 2020, 01:29:13 PM »
So the paper degree wheel glued on the front of the crank and bent pot-noodle lid with piston stop found what I wanted. The marks are definitely 180 out and I paint splodged the ring gear and clutch plate.

Idle is slightly retarded, probably 3 degrees. Full advance goes past 26 degrees by a similar amount.

From Snowbum site:
The marking for point of maximum advance on the flywheel (F dot or Z line) should be at 25 degrees before OT, tolerance of +- 2 degrees, through the 1977 machines, later engines were 26 degrees.

MRbikeclub, your value of 32 degrees total advance sounds what it should be and I need to advance the kit'n'caboodle a tadge. Iv'e never heard a ping as a 650, not given enough load on the 860 to know yet.

32 from TDC full advance yes???  :-?

Very little flicker or deviation and the mechanism gradually and smoothly advances as revs go up, so no issues there.
肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O

Offline dogshome

  • Posts: 116
Re: Ignition timing with flywheel 180 out
« Reply #6 on: September 05, 2020, 02:02:14 PM »
Don't bother replying  :)

I moved the bean can, it's mountings are now dead central and the timing is now spot on.

Also the £$%^&!!! thing is idling a new one. Cold engine usually wanting to quit until really hot. I'd got used to it and assumed that was normal. Wish I'd checked it earlier  ;D
« Last Edit: September 05, 2020, 02:03:09 PM by dogshome »
肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O