1955 AJS Model 20

[oldbikedavey]

Angular measurement of piston position via the plug 'ole requires doing a bit of trig to compensate for the angle , or the setting will be miles out.
Best just find tdc with a dial-gauge equipped plunger, then employ a timing disc.
If the engine is out, and on the bench, fit and time the mag before the head (s) go on.....

 

[Seadog]

Fit a timing disc and then, to findTDC, approach from before TDC until you reach a mark that you've made on a rod poked down the plug hole. Record the angle. Remove rod then go over TDC, reinsert rod and turn the engine counter-clockwise with rod in place until you reach the mark again, read this angle on the disc. True TDC will be half way between the two figures.

 

[Cobbler]

I made a “tool” for finding TDC using a spark plug body drilled through so a thin rod could slide through. I wanted to check some timing marks, I was surprised how accurate you could get it if you took your time.

 

[Robotstar5]

Most of my old engines are side valve so the plug is offset from the bore which means I have to take the head off to get an accurate BTDC measurement on the piston.

Sparkplug hole on the right and cylinder on the left.

 

[Matchless]

Quick hijack if no one minds! whilst we have a few motorcyclists looking at this thread I would like to ask if anyone has a Lucas magdyno spare under the bench! the ideal is from a twin cylinder so it has plug lead outlets each side but a twin magnet version from a single cylinder could be modified for what I need, attached is a picture of they style of thing, I don't have much this new in my stocks of motorcycle bits, most are covered wagon type or earlier!

 

[Rannsachair]

Quick hijack if no one minds! whilst we have a few motorcyclists looking at this thread I would like to ask if anyone has a Lucas magdyno spare under the bench! the ideal is from a twin cylinder so it has plug lead outlets each side but a twin magnet version from a single cylinder could be modified for what I need, attached is a picture of they style of thing, I don't have much this new in my stocks of motorcycle bits, most are covered wagon type or earlier!
View attachment 448533

@zeppelin builder may have a suggestion.

 

[Robotstar5]

Quick hijack if no one minds! whilst we have a few motorcyclists looking at this thread I would like to ask if anyone has a Lucas magdyno spare under the bench! the ideal is from a twin cylinder so it has plug lead outlets each side but a twin magnet version from a single cylinder could be modified for what I need, attached is a picture of they style of thing, I don't have much this new in my stocks of motorcycle bits, most are covered wagon type or earlier!
View attachment 448533

If you do Facebook there's a group for vintage magnetos on there - https://www.facebook.com/groups/349645382440054

 

[Matchless]

It would be for this, sold it to a mate to part finance the Routemaster Bus............... 1934-35-36 Matchless X4 34 chrome edge mudguards because I like them, 1935 engine, 1935-6 foot change 4 speed BAP because that is much nicer to live with against the 4 speed hand change Sturmey Archer box, my mate is not used to hand change bikes.

 

[Matchless]

If you do Facebook there's a group for vintage magnetos on there - https://www.facebook.com/groups/349645382440054

Thanks, just applied to join, I have around 30-40 magnetos. some are complete, some even work, but nothing like the one I need!

 

[Matchless]

Most of my old engines are side valve so the plug is offset from the bore which means I have to take the head off to get an accurate BTDC measurement on the piston.

Sparkplug hole on the right and cylinder on the left.

View attachment 448531

I would drill and tap a smallish hole above the piston for timing, probably only after removing the head for the third time!

 

[Robotstar5]

I would drill and tap a smallish hole above the piston for timing, probably only after removing the head for the third time!

One of my engines already had a factory made hole above the piston and someone had made a plug out of an old bolt with a screwdriver slot cut in it.

So I found a nice brass bolt that looked a lot better

 

[oldbikedavey]

Just realised that, having twin -plugged my B.40E -ish enduroid, that a vertical measurement can be effectively taken.....

 

[Rannsachair]

All assembled the other night, not starting, plugs out and no spark!

Finally got a look at it today and found a small points shaped piece of cigarette paper stuck between the points

Removed and started first kick!

 

[Matchless]

The Rizla anti theft device!

 

[Cobbler]

All assembled the other night, not starting, plugs out and no spark!

Finally got a look at it today and found a small points shaped piece of cigarette paper stuck between the points

Removed and started first kick!

Going back when cars had points, I heard several recommendations to clean points with a slip of paper, tried it but got caught out with fibres or varnish off the paper stopping the spark, all looked clean but no sparkie. Put it down to experience & disregarded it as bad advice, took them out & did the job properly.

 

[Rannsachair]

Done about 40 mile test run, all good.

 

[RichardM]

You used to be able to buy files for points, long time since I have seen one though!

 

[Robotstar5]

You used to be able to buy files for points, long time since I have seen one though!

You can still get them - linky

 

[Eric the chicken]

I seem to remember making a device with crocodile clips a small lamp and a battery to pinpoint the precise point at which the points opened..I wonder what happened to it. Mind you it wouldn't be much use tome now as I have nothing with points!

 

[Cobbler]

I seem to remember making a device with crocodile clips a small lamp and a battery to pinpoint the precise point at which the points opened..I wonder what happened to it. Mind you it wouldn't be much use tome now as I have nothing with points!

You could do it with a transistor radio as well, leave it on medium wave between two stations & you can hear a click as the points open. I used to do it that way when my cars had points, last one was a Volvo 245 of about 1980.