Intro
A lot of the time on these forums the topic of timing is thrown around:
“My bike won’t start?” – “check your timing”.
“How do I detune my YZ250’s hit?” – “retard your timing”
“I’ve got detonation problems!” – “retard your timing”.
“I’m looking for more performance and am willing to run race gas” – “advance your timing”.
“I’ve just bought an aftermarket crank” – “make sure you check your timing as mine was 6 degrees retarded”

When should I test/change my timing, common reasons:
- To make sure it is set correctly because its easy to do
- You bought an aftermarket crank (set it back to zero degrees or otherwise)
- De-tune the hit when you get on the pipe (1 or 2 degrees retarded)
- To combat detonation problems (1 or 2 degrees retarded)
- You're playing with your squish/shaved down your cylinder head (only because this can cause detonation problems)
- Looking for minor performance gains and are willing to run race gas (1 degree advanced +) note: I am no expert on this, you should do your own research before considering advancing your timing.
- You can also use the process to check if your crank rod and main bearings are in spec. In theory, if there is any delay/free play in movement of the dial gauge when you rotate the flywheel then one of those is out is out of spec.


In this thread I intend to
- Explain how to put together a tool to check your timing using a dial gauge of FeeBay and an old spark plug
- Brief pictorial guide on how to test your timing
- What timing is


Build the tool

As you can see, its simply a dial gauge and an old spark plug I’ve chopped up and put on it. Works perfectly!

What you’ll need:
1. A dial gauge. I got mine for about $15 of FeeBay. No doubt its Chinese. Some people will tell you to stay away from Chinese and get a better quality one, that’s up to you.
2. An old spark plug.
3. A grinder or dremel to grind the metal lip off the spark plug ceramic. Pictures of this below.
4. A hammer and screwdriver.
5. A drill

Steps: (pictures of each below)
1. Grind the metal lip off the spark plug. This is what holds the ceramic part in.
2. Grind off the arm on the bottom of the spark plug.
3. Place the plug into something such that you can knock out the ceramic with the screwdriver and hammer.
4. You’ve now got your thread!

The next steps vary depending on the dial gauge you bought.
5. On mine I needed to drill out the hole a bit as it was too narrow to fit my dial gauge in. See picture.
6. I also needed to shorten it slightly as my dial gauge was not long enough. See picture.

edit: somewhere in this process you should consider adding a vent hole such that the compression when the piston is at TDC does not affect your reading. See Mark6299's post


















Clarification: Shortened it slightly as described above in step 6


How to test your timing

Note, the Yamaha service manual has a section on how to test and set your timing to zero degrees. I highly recommend you refer to this, it’s better than my guide below.

Steps: (pictures of each below)
1. Remove your fuel tank. Drain your radiator fluid and then remove the hose that attaches to your cylinder head.
2. Screw in your new tool!.
3. Remove your flywheel cover.
4. Rotate your flywheel counter-clockwise, and while doing this pay attention to your dial gauge.
5. At a certain point your piston will reach Top Dead Center (TDC). At this point your dial gauge will stop and start turning the other way. Set this point on your dial gauge to zero degrees by unscrewing the set screw and rotating the face.
6. On a 2000 YZ125 my timing needs to be set 0.02”/0.52mm below TDC. Refer to your service manual for your number (I think YZ250s are 0.007"?). To do this rotate the flywheel clockwise (ie the other way to the way you were turning it before) until it gets to 0.02”/0.52mm (depending on your dial gauge). Note my bike was very slightly advanced.
7. Look at the notch on your flywheel. Is it perfectly aligned with the mark on your stator? If not, loosen the stator screws and align them.
8. You have now set your timing to zero degrees!

Yes I know my bike is pretty dirty, but I’ve spent heaps of $$$$$ time and effort on it to make sure it runs great!
And yes the engine mount is broken lol














What timing is:
The Wikipedia article below explains it better than I can.

At its simplest – timing refers to at what point the spark plug fires. So by setting my timing to 0.02”/0.52mm Below TDC, that means that when the piston is 0.02”/0.52mm below the top most point of its cycle, the spark plug fires.

What a minute, wouldn’t it make more sense for the spark plug to fire when it is at absolute TDC? No – to quote Wikipedia: “The need for timing the spark is because fuel does not completely burn the instant the spark fires, the combustion gasses take a period of time to expand”

Changing your timing such that the spark plug fires further from TDC (ie advance the timing) or closer to TDC (ie retard the timing) has various implications. I won’t discuss those here, nor am I an expert on them all.

Note that aftermarket cranks are notorious for being set several degrees retarded from the factory and so you should always test your timing if you buy an aftermarket crank.


Credit:
Mostly, the TT community. I've learnt so so much on here and saved so many $$$ by learning how to do things myself.
Carver's original YZ250 timing thread
Wikipedia
Pete's bike blog
Mark6299's post regarding a vent hole

Edited by tim512, 19 December 2011 - 07:14 AM.

If anyone has any suggestions, corrections or otherwise please let me know and I can edit the OP


edit 1: added comment regarding a vent hole per MarkYZ250's post.

edit 2: added a section at the start "why should I test my timing"

edit 3: edited credits and minor formatting

Edited by tim512, 19 December 2011 - 07:13 AM.

Awesome!!! thread!!! i say this should be a sticky:thumbsup:

Great job man!!!!!!!!!

Hey ah, if what the purpose of the dial indicator is for is to detect TDC and then check FW and stator plate - couldn't you just do a visual with the head off? Also, what's up with your top motor mount?

shrubitup said:

No because its a very precise measurement, can you visually see a movement of 0.001 inches?

And yea its broken lol, I don't know how the previous owner managed that

Really good thread man, thanks.

I was about to get this done so its come at a perfect time.

Such an overlooked topic here. I don't even fully understand it. I've done it on my truck, but never to my 98 cr250r but I sure would love to at least see where I'm at. Looks I've got some reading to do. Thanks a ton for posting this thoroughly with pictures and everything. Seriously though, the pictures make a night/day difference on information I take in about mechanics.

BlackCR25098 said:

I think its quite overlooked too and something pretty much everyone needs to think about at some point. My timing was slightly advanced, I retarded it slightly (maybe 0.5 degrees roughly) and now it 'feels' like it runs a fair bit smoother

Now I just need to tackle my jetting. My bike isn't making this easy.




Thanks everyone else for the praise and reputation!!!

Good work Tim, a picture is worth a thousand words!

One thing I will note is for steel framed yz250.  The gap between the head and backbone of the frame is very small.  So before you glue or epoxy your dial gage into the threads, triple check that you don't have any clearance issues.

tim512 said:

no but can yoiu really see 0.001 inches of offcorse when you adjust the plate to the indentation of the FW?

hardhitwarrior said:

I agree you introduce some inaccuracy there, but what is a better alternative if you want to test your timing? Take your cylinder head off and stick a ruler down your cylinder to try and measure 0.02" ?

Using a dial gauge (which is securely in place) as described above provides a very accurate reading and IMO you likely to be able to set your timing to within 0.5 degrees of where you want it to be at. That's pretty good IMO

GMO397 said:

I agree, likewise with my steel frame 125. Luckily after shaving off some of the spark plug it fit in quite well for me, however others should be wary of that.

tim512 said:

In your pictures, you did not seam to screw the sparkplug adapter in all the way.  I know the dial indicator is very sensitive but I wonder how much that would affect the reading.  Also you have nowhere for the compression to escape except for around the gap between the gage and plug adapter and between the spark plug threads.  This could make the spark plug adapter act like a small piston and the entire setup would move up and down possibly giving false readings.  It your thread and I do appreciate the fact that you went through the trouble to do all this for fellow TT members.  I would only add a vent hole somewhere and I would screw it in all the way.  Except for that, GREAT JOB.

Mark6299 said:

I would agree.
With the build up in pressure, and the inaccuracy of the heads threads to the plugs threads, the indicator could easily be moved .001".

Is your dial indicator hollow if you remove both ends of the shaft.  For some reason I think the JandJ is, but I could be making stuff up.

hardhitwarrior said:

if you use a ruler you risk combining the error of both visually lining up the lines and of eyeballing with a ruler.

but it should be close enough would it?

Very good write up!
Would like to add that if a timing light is available,, double check the final timing.
I had a (bad) cdi that the advance was way off and the bike ran like crap even after doing a dial gauge setting. One used Flea-bay cdi latter,,runs perfect!

how does a timing light work?

scalejockey said:

Do you mind elaborating on your problem and how you used the timing light  a bit. Might be worth adding it to the OP. Also, my bike seems to be running quite similar to that too lol and I have a suspicion its electrical related, probably CDI too.

hardhitwarrior said:

Kinda 'old school' but,,It's a strobe light that flashes when the spark happens.As the bike is running you can see the exact spot where the spark is happening, You connect the units clamp to the spark plug wire and the light or "tool" is powered by 12vdc,so you'll need a spare 12v battery.
It's a very handy tool,it can show you all sorts of ignition problems.
Watch close what the timing does,jumping around,intermitant,not retarding off idle,(yes,retarding) These bikes are a little odd for "normal" advance times.
My dad showed me how to use one 40 years ago working on cars in his shop.
There could be something on youtube now days..