Confused about Tomas Timing being only 1.5 mm BTDC

I read the Tomos manual and find that timing on my 99 Tomos with CDI is supposed to be 1.5 MM BTDC . Why is my Puch running so well with timing so different set at 15 mm BTDC ? This is confusing.

Re: Confused about Tomas Timing being only 1.5 mm BTDC

todd amundson /

Because if you were running a puch set at 15mm before top dead center you’d be riding in reverse. It’s probably at 15 degrees before top dead center that your looking at.

Re: Confused about Tomas Timing being only 1.5 mm BTDC

Overpriced Parts /

> Bill Donati Wrote:

> -------------------------------------------------------

> I read the Tomos manual and find that timing on my 99 Tomos with CDI

> is supposed to be 1.5 MM BTDC . Why is my Puch running so well with

> timing so different set at 15 mm BTDC ? This is confusing.

Newer Tomos Have electronic retarding ignition Not 100 year old points ignition

Re: Confused about Tomas Timing being only 1.5 mm BTDC

Dirty30 Dillon /

> Bill Donati Wrote:

> -------------------------------------------------------

> I read the Tomos manual and find that timing on my 99 Tomos with CDI

> is supposed to be 1.5 MM BTDC . Why is my Puch running so well with

> timing so different set at 15 mm BTDC ? This is confusing.

Because the 1.5mm BTDC in the Tomos manual means 1.5mm of piston travel, and the Puch is obviously 15mm BTDC measured on the flywheel.

Boom, easy to answer

Re: Confused about Tomas Timing being only 1.5 mm BTDC

Tweaker trash /

> Dirty30 Dillon Wrote:

> -------------------------------------------------------

> > Bill Donati Wrote:

>

> > -------------------------------------------------------

>

> > I read the Tomos manual and find that timing on my 99 Tomos with CDI

>

> > is supposed to be 1.5 MM BTDC . Why is my Puch running so well with

>

> > timing so different set at 15 mm BTDC ? This is confusing.

>

> Because the 1.5mm BTDC in the Tomos manual means 1.5mm of piston travel,

> and the Puch is obviously 15mm BTDC measured on the flywheel.

>

> Boom, easy to answer

Smoke weed ever day

Re: Confused about Tomas Timing being only 1.5 mm BTDC

So when setting my Tomos Do I set it at 15 BTDC on the flywheel? It seems lik I have some conflicting answers above. BTDC is Before Top Dead Center no matter which way the flywheel turns

Re: Confused about Tomas Timing being only 1.5 mm BTDC

Dirty30 Dillon /

> Bill Donati Wrote:

> -------------------------------------------------------

> So when setting my Tomos Do I set it at 15 BTDC on the flywheel? It

> seems lik I have some conflicting answers above. BTDC is Before Top

> Dead Center no matter which way the flywheel turns

You want 1.5mm BTDC measured by a piston micrometer. If the OD if the flywheel is 360mm like Bosch, than you can use 15mm of flywheel movement.

And to correct, direction does matter concerning before top dead center. Otherwise it's after top dead center.

Re: Confused about Tomas Timing being only 1.5 mm BTDC

Hydra,

I realize that there is a right or left side of TDC where the timing mark should show depending on the direction of spin . What I meant is that TDC is in the center

no mater which way it is spinning. But thanks for the Info. I did not realize that Tomos was referring to the amount of piston travel rather than the degree of flywheel spin. I have timed a lot of vehicles back in the 50's when I first started driving and it was always amount of flywheel spin.

Re: Confused about Tomas Timing being only 1.5 mm BTDC

Kind of crazy that Tomos would use piston movement rather degree of the flywheel movement. I have timed a lot of cars and motorcycles over the last 60 years but never seen any manufacturer use amount of piston travel as a reference for timing.

Re: Confused about Tomas Timing being only 1.5 mm BTDC

> Bill Donati Wrote:

> -------------------------------------------------------

> Kind of crazy that Tomos would use piston movement rather degree of the

> flywheel movement. I have timed a lot of cars and motorcycles over the

> last 60 years but never seen any manufacturer use amount of piston

> travel as a reference for timing.

A lot of motorcycles and mopeds use mm btdc for timing, including Puch. It just works out that the Puch flywheels are 360mm around and that equates to .1mm of piston travel per 1° of flywheel rotation

Re: Confused about Tomas Timing being only 1.5 mm BTDC

> Nick MBC Wrote:

> -------------------------------------------------------

>

> A lot of motorcycles and mopeds use mm btdc for timing, including Puch.

> It just works out that the Puch flywheels are 360mm around and that

> equates to .1mm of piston travel per 1° of flywheel rotation

Wait, is that right? I know the degrees of crank rotation works out to the millimeters around the flywheel (so 16 degrees of crank rotation can be marked at 16mm along the flywheel), but I have some chart I printed out years ago that shows the piston at 1.03mm below TDC at 16 degrees BTDC and not neatly corresponding at any point except 0 and 2 degrees.

Re: Confused about Tomas Timing being only 1.5 mm BTDC

> Nick MBC Wrote:

.1mm of piston travel per 1° of flywheel rotation

NOPE that is not true, its a slider-crank mechanism so the piston travels less per degree as it nears TDC and more per degree when the crank is at 180 deg on a log-scale.

you have to either do the math and calculate it with trig using the dimensions, or use a timing chart. These are on the wiki or out there for most brands, i always print them out and put them in the 3 ring binders that i have manuals in for all my bikes.

https://www.mopedarmy.com/wiki/Ignition_Timing_Chart_for_Puch

1.5 mm of piston travel in a puch/tomos isn't 15 degrees, its closer to 19 deg. 1.3 is about 15. the reason timing is done this way is because its easy on 2 strokes where the spark plug hole goes straight into the piston. Lots of people that work on old two strokes have ignition micrometers or you can use a set of calipers stuck down the plug hole. I usually use the mic to set TDC and Firing marks then i mark them on the flywheel. As long as you are using the key in the flywheel you can always check timing quick and easy with a timing light.

Re: Confused about Tomas Timing being only 1.5 mm BTDC

Well thanks for correcting me, guess I've been recycling misinformation I've read before

Re: Confused about Tomas Timing being only 1.5 mm BTDC

> Nick MBC Wrote:

> -------------------------------------------------------

> ... guess I've been recycling misinformation

> I've read before

I bet you're the first person to ever do that . LOL

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