classic car forum header
Classic cars forum & vehicle restoration.
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
Register     Posting Photographs     Privacy     F/book OCC Facebook     OCC on Patreon

1912 Magneto timing
Post new topic   Reply to topic    Classic cars forum & vehicle restoration. Forum Index -> Electrical Restoration
Author Message
Rdover



Joined: 26 Nov 2007
Posts: 413

PostPosted: Mon Aug 08, 2011 9:21 am    Post subject: 1912 Magneto timing Reply with quote

After a recent failure, my magneto was rebuilt again and now I'm trying to get the timing sorted so I can get the car running in time for the Biggar Albion Rally this weekend.

Its a side valve with priming pots so I've 'found' tdc by leaving the primer on the front (No. 1) cylinder open and turing the engine until I hear the hissing (compression) stop. I check it is not on the exhaust cycle by putting my finger on the primer and feeling/hearing pressure.

At TDC (roughly) I move the flywheel back by 10deg, calculated by taking the circumference and dividing by 36 and measuring out. There are marks on the flywheel left by the original rebuilder which sort of line up with what I've found.

At this point I set up the magneto at Cyl 1 and set the points with the advance/retard mid way in the adjustment becuase I can't seem to either figure out or remember which way is advance nor which way is best for starting!

Problem. It wont start and I'm not even getting a puff or 2. There is a good spark (I still need to check all the HT leads, connections and plugs again). What I am missing or getting wrong?
_________________
Richard
Back to top
View user's profile Send private message
Rdover



Joined: 26 Nov 2007
Posts: 413

PostPosted: Mon Aug 08, 2011 9:31 am    Post subject: Reply with quote

just found this on http://www.magnetorepairs.com/tip1.shtml

Quote:

Find Top Dead Centre (TDC).
By adjusting the camshaft timing, set the LT igniter contact to break at TDC with any advance/retard lever set to full retard. Allow sufficient clearance on the ignitor adjusting system for the contact to snap closed. Say 1/32nd inch free movement after the contacts have closed.
Adjust the magneto timing such that as the igniter breaks, the armature pole is about 1/8th to 3/16th inch away from the carcass pole, having just left the pole in its normal direction of rotation.

If the system is fixed timing it probably makes sense to start as above to get the engine running. Then advance the ignitor break, and the magneto timing so that the relationship between the armature position and the igniter remains the same, until the engine kicks back on starting. In the case of my 1904 Berliet this is equivalent to about 40° maximum advance.


So
"advance" means making it spark closer to TDC
"retard" means making it spark earlier in the cycle

Starting should be attempted on full retard. Normal running should be on retard with an extra push coming from advancing the spark?

Or am I confusing myself even more?
_________________
Richard
Back to top
View user's profile Send private message
roverdriver



Joined: 18 Oct 2008
Posts: 1210
Location: 100 miles from Melbourne, Victoria, Australia

PostPosted: Mon Aug 08, 2011 10:34 am    Post subject: Reply with quote

'Retard' usually means later, that is, especially with a hand-cranked engine, a few degrees AFTER TDC.

When the engine is running, the spark is advanced so that occurs before TDC for best running results.

Hand-cranking with a spark occuring before TDC leads to broken arms!
_________________
Dane- roverdriver but not a Viking.
Back to top
View user's profile Send private message
Phil - Nottingham



Joined: 01 Jan 2008
Posts: 1252
Location: Nottingham

PostPosted: Mon Aug 08, 2011 6:23 pm    Post subject: Reply with quote

Good explanation!
_________________
Rover P2
Rover P4
Rover P5 & P5B
Land Rover S2 & S3
Morris Mini Traveller Mk2
Back to top
View user's profile Send private message Send e-mail
Rdover



Joined: 26 Nov 2007
Posts: 413

PostPosted: Tue Aug 09, 2011 4:17 pm    Post subject: Reply with quote

roverdriver wrote:
'Retard' usually means later, that is, especially with a hand-cranked engine, a few degrees AFTER TDC.

When the engine is running, the spark is advanced so that occurs before TDC for best running results.

Hand-cranking with a spark occuring before TDC leads to broken arms!


After several hours of trial and error I ended up hurting my shoulder (they are knackered anyway) and bashing my knuckles off the chassis when I lost grip. It was firing, sort of, and almost running so I'm close but it needs professional attention.

I've found a local classic/vintage repair place that can sort it out. They're going the whole hog and checking compression, finding TDC properly and setting the valves.

I may miss this weekend's run but its far better to have the car starting and running reliably so I can enjoy it without killing myself!
_________________
Richard
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    Classic cars forum & vehicle restoration. Forum Index -> Electrical Restoration All times are GMT + 1 Hour
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
OCC Merch link
Forum T&C


php BB powered © php BB Grp.