Timing an inner rotor 2T with strobe

[alexbrown64]

Hi, i want to time a bike that has an inner rotor and outer stator with a timing light.  The manual just says align stator to centre of its curved slot.  I can statically time a PVL as it has timing marks on inner rotor and stator.  But what is the procedure to time the configuration below using a timing light.  Where do i put the marks, do i use a dial gauge to set tdc or an amount before tdc, can i use a basic car strobe, etc.. Can some one write up a set of instructions.  I have done a search but can't find a definitive guide.
Bike is Suzuki RM80N.  Suzuki manual does not give a mm btdc, but  the 77B manual states 1.04mm btdc and that model had a mark on stator and rotor.
Thanks in advance,
Alex

[sleepy]

Use the timing light on it with the motor around 6000rpm and add your own timing marks using the edge of the stator as a reference. Once you have a mark then time it with dial indicator down the plug hole to whatever timing you feel it should be. Only way to get it spot on is to use a dyno but if you get it around 1.0mm btdc it will be close.

[oldfart]

13 degrees +/- 1 degree at a whopping 12.000 rpm   (straight from the Suzuki Bulletin ) 

[alexbrown64]

Oldfart, do you have a link to that bulletin.  My N manual and this link bboth says 18.5 degrees at 11000. https://onedrive.live.com/?cid=407D7EF0965D3991&id=407d7ef0965d3991!5446  How is the timing set using degrees?  Do i need a degree wheel?

So i am still unclear, Sleepy, are you saying use a dial indicator to set the piston to around 1.0 btdc.  Then scribe a mark on the stator plate and a corresponding mark on the rotor.  Then rev it to 6000 an they should line up?

[oldfart]

http://www.ozebook.com/compendium/techbuls/index.htm

[sleepy]

Oldfart, do you have a link to that bulletin.  My N manual and this link bboth says 18.5 degrees at 11000. https://onedrive.live.com/?cid=407D7EF0965D3991&id=407d7ef0965d3991!5446  How is the timing set using degrees?  Do i need a degree wheel?

So i am still unclear, Sleepy, are you saying use a dial indicator to set the piston to around 1.0 btdc.  Then scribe a mark on the stator plate and a corresponding mark on the rotor.  Then rev it to 6000 an they should line up?

No you need to use the timing light first to work out a firing piont for that ignition set. Best way is with a marker pen put a mark on the rotor, then run the motor with the timing light at around 6K or higher(if Suzuki list the timing at 12000 go to that) and add a mark on the stator that lines up with the rotor mark. That then becomes your timing marks to use with either a degree wheel or a calculated distance before TDC. I did a quick drawing using 46.8 as the stroke and 90mm for a rod length and came up with about 1.5mm equal to 18deg.
I always thought it was funny that Suzuki used to tell you to use a timing light to check the timing when the marks are on a moveable stator. It didn't mater where the stator was the marks always lined up. 

[Lozza]

Add the website 'torquesoft' to your favourites. You will need the bore/stroke/ and rod length to input to convert mm BTDC to degrees. A degree wheel is mostly inaccurate.
With the reference mark on the backing plate, scribe a line on the rotor that lines up at TDC.

Start the engine and rev it with the timing light watch the mark move clockwise where it stops(usually about 7000 on an 80/85)moving hold the engine there and mark the backing plate in line with the mark on the rotor.

The hard one is next, if you rev the engine to peak revs when strobed the timing mark should come back toward the TDC mark, where it stops retarding mark that point on the backing plate.

Then with a dial gauge or verniers with the head off  convert those 2 marks from mm BTDC to degrees. You then have a max and min advance, then you can move the backing plate to match 13/14deg at 12,000. Which is about right


or

you can save yourself all the grief and buy one of these that will tell you the amount of advance

http://www.ebay.com.au/itm/Digital-Timing-Light-Innova-Professional-Mechanics-with-Advance-Dwell-Tacho-/131459667902?pt=LH_DefaultDomain_15&hash=item1e9b9b57be

 

[sleepy]

Don't waiste your money on a timing light like that unless you a fix TDC reference. With a TDC marked on a movable baking plate it is useless. You could add an fixed reference mark bolted to the crankcase to get your TDC that is indipendent from the stator but that is a lot of mucking around.

[sleepy]

Just because Oldfart ask me I thought I'd give him the formular for calculating the BTDC piont. It can aslo be done with a scale drawing as well.

A bit of maths to work out the grey matter.

R= rod length
S= half stroke length
TA= timing angle

R+S- sq root(R sq-(sin TA x S)sq) - cos TA x S = BTDC

Sorry I don't know how to get the square or square root symbol while typing.
Try it out with a stroke of 48mm and a rod of 90mm with a timing of 14deg and you should get .903mm. You will have to find your own sin & cos values.

[oldfart]

Tried it out after our conversation and it worked out spot on.   Rm 250 T timing was way out using factory  plate guide ( .2mm)
Thanks Sleepy 

[Lozza]

Don't waiste your money on a timing light like that unless you a fix TDC reference. With a TDC marked on a movable baking plate it is useless. You could add an fixed reference mark bolted to the crankcase to get your TDC that is indipendent from the stator but that is a lot of mucking around.

Yes the timing lights work off a tdc reference(not btdc reference) the marks don't line up until the correct amount of advance is entered. There is no moving the backing plate. Move the backing plate and the timing changes, then a new advance  figure needs to be entered for the tdc reference mark to line up. A tdc mark on the rotor will not change no matter how far the stator is moved. Far easier than scribed marks at 1° intervals

[alexbrown64]

Thanks for all the reply's guys.  I will work it all out.  I have been working away, with no real internet so been a while since i could jump on forum.
Cheers,
Alex

[OverTheHill]

Unless you suspect a problem [think what i'd do is] just bolt it on with the slots about half way around but should be an original mark on one slot to line up [maybe not exactly half way], then fit the rotor on the keyway tightly then forget about it!!--rarely play up. If you're worried for some reason & want to strobe it just to see what it's up to--then mark the rotor to the stator with say twink correction fluid at TDC which you can guess [feel] pretty good with something down plug hole--just feel it rocking back & forth then just go 'THERE'. Twink stator & rotor as i said then if you want to strobe then do it by looking at a degree wheel or say the kids circle thingy out of their maths set as is smaller like an internal rotor and mark the rotor at say 5 degree intervals up to 20 & see how it reacts on the strobe. Not sure on these but probably will advance right up above idle & slowly come back till near tdc on full song. In saying that, the slots are there to allow you to advance it up a bit if it's flattening off too much at full revs. After all that  [my misquided theories]--& after you've strobed it--- if you have to move the stator plate then twink mark on said stator will become irrelevant so will need a good pointer screwed to the case to point at the rotor twink mark in relation to the tdc starting point. Damn it, just bolt it on & go racing but if you want to experiment then advance it say half of the remaining slot or alternatively retard it the same amount just to feel the difference, Cheers. ps hope that's legible as keep going back adding & altering things.

[chrisdespo]

DEGREE WHEEL = PROTRACTOR weren't you guys paying attention at Skool. lol

[OverTheHill]

Maths wasn't my strong point at school lol but now i have a [mini degree wheel] hanging on the nail with my big degree wheel [protractor--sounds like a bloody fast tractor to me], now the kids are probably wondering where theirs went. Protractor--reminds me of back in the "60's when dad used to go to the RSA for a beer & i'd get the diesel fergy & wind the throttle stop back on the injector pump [not 'realy' knowing what i was doing] & head of down the paddock & do some pedal brake power slides in the green grass, no helmet, no roll cage [no brains]. Fk i'f freak out big time if my kids had ever tried that trick--but dad never knew lol.