Yamato 202 timing question

[static-blur]

Hi

I'm hoping for a bit of clarification with setting the timing on my Yamato as this is my first time attempting this.
I'm using the Setting the point gap and the ignition timing on a Yamato 80 & 102 instructions from yamatoracing.com since my 202 has the 102 point ignitions.

My first question is what position do you have the spark advance lever in while setting the timing?

Started by following the instructions, I got to step 8 and assumed Rotate magneto was meaning the spark advance lever. Started to rotated the lever til the points just started to open and realised something wasn't right as the lever was nowhere near the magneto stop bolt area. The advance was in the retard position on the motor while I was following the steps. Was this a newbie move?

I thought I would ask for some advice on here before continuing on.

1) Remove starter pulley
2) Remove spark plugs
3) Rotate crank till point follower is on the tallest part of the point cam. On the 102 it is where the cam key is.
4) Set point gap on both points to 0.012”-0.016”, I prefergapping to 0.012”.

5) Install dial indicator in cylinder #1. Rotate engine to top deadcenter. Zero dial indicator. Rotate engine backwards (counter clockwise) till points close (recommend using a buzz box). Note how many thousands on the dial indicator.

6) Install dial indicator in cylinder #2. Rotate engine to TDC. Zero dial indicator. Rotate engine backwards till points close. Note how many thousands on the dial indicator.

7) Take cylinder with the highest reading and install the dial indicator in that cylinder. Rotate the engine to TDC. Zero the dial indicator. Rotate the engine backwards to desired setting. Factory recommended specs for the 102 is .200”-.250” BTDC.

8) Rotate magneto to the position where the points are just opening or closing (recommend using the buzz box). Rotating the engine a fewthousands above and below your desired timing setting should open and close the points.

9) Set magneto stop bolt and secure magneto.

10) Install dial indicator in the other cylinder. Rotate engine to TDC. Zero dial indicator. Rotate engine backwards to desired timing setting. Open points slightly till points are opening and closing a fewthousands before and after your desired timing setting.

11) Remove timing equipment. Reassemble engine. Check spark quality. Install spark plugs.

[DeanFHobart]

Along with the dial indicator, use either an ohm meter or an electronic device called a "Buzz Box" to exactly tell you when the points open or just close. Doing it by eye is not very accurate. The Buzz Box can be purchased from Ric Montoya in the USA or Mike Ward in the U.K. Who are the Yamato dealers. Good luck.

[static-blur]

Thanks for your reply I'm using a dial indicator and ohm meter for making the adjustments, was just wondering what position should the spark advance lever be set at while making the timing adjustments?

[dwhitford]

Max-advance position. The whole point of this timing exercise is to establish max possible spark advance. The instructions you're following are wildly convoluted in my opinion.

[ZUL8TR]

Assuming your ohm meter is accurate enough to detect point position

Here is what I do after cleaning points:

1) adjust 1 point set gap, I use 0.013" for more coil dwell compared to 0.016" max but not at min to allow for some rub block wear over time, I arbitrarily pick top cylinder.

2) place dial gage in top cylinder zero out at TDC, rotate engine CCW beyond desired depth about 0.020" then CW to desired timing setting, this takes up any small clearance in bearings and correctly favors the upstroke for the timing. Note carbon on piston will affect this gage reading, need to clean carbon if any.

3) rotate the mag lever toward advance (to right ) until your buzz device just detects points opening, lock the mag at that position with the mag locks, if you are not using mag locks you should be to keep settings true), otherwise adjust the mag stop bolt for that position at full mag advance.

4) now place dial gage in lower cylinder zero out at TDC, rotate CCW beyond desired as in 2) then CW to desired depth same as top cylinder

5) adjust that point such that buzz box indicates points just opening, a little trial and error here to get the feel so result is very close to the dial gage setting. Point gap will not be the same as cylinder #1 but will be close (and not less than min 0.012") and no worry just slightly different coil dwell.

You are done, but check regularly to see if still as set, things change, the idea is to get both points to fire at the same piston position BTDC which 1) thru 5) do and theoretically be at 180 degrees apart if the engine is perfect in clearances and even wear.

I use this buzz box model 12-16903 (available at several locations), very accurate with buzz and light and relies on coil inductance rather than resistance

http://www.aircraftspruce.com/catalo...nchronizer.php

I just connect the 2 alligator clips to the kill wire 2 prong connector already wired into the mag.

[Larry M]

Very good rundown on timing a motor. The only thing I question is the carbon on top of the piston. I don't think it makes a difference in setting the timing regardless how much it is built up. It could be 1/4 inch thick and you are still timing the motor to the top just the same as if it was a piston that had a high dome. We had this discussion in a small engine class and was told the carbon doesn't change anything in the way of timing if using a dial indicator. If you are using a degree wheel I can see it might make a minute change nothing I would worry about.
Larry Mac

[ZUL8TR]

Larry Mac
The carbon I was referring to was a small amount that would influence the shaft of the dial gage resting on the piston as it moved up to the desired setting. I had this happen where the dial gage shaft rested on some carbon and it affected the reading of the gage because carbon was being crushed slightly enough to make erratic readings. I agree on what you say about the carbon not affecting the timing provided it is a solid place for the gage shaft during the settings.

Pete

[Shane_B]

Yeap - easy enough to remove head and clean off carbon every year before race season (found by accident WD-40 does a great job loosening/removing carbon). I know this is off topic of timing, but I also remove and check mating surfaces of exhaust cover and powerhead/tuner pipe each year as poor seals there will rob power...

[ZUL8TR]

Good to know on the wd 40 I assume you use a scrubber pad, what type do you use?

[Shane_B]

the green 3m pads work for tough parts but even the blue ones on sponges for kitchens work well - less abrasive for delicate areas... The wd 40 just soaks into the carbon and softens it up.

[static-blur]

This is awesome advice! Thanks everyone for the information!

[rsdfour]

What is coil dwell ?

[ZUL8TR]

What is coil dwell ?

That is the crank rotation time or crank shaft degrees of rotation that the points are closed and the coil is being charged. When the points open the coil discharges and the plugs fire. Point gap affects coil dwell, closer gap more dwell, wider gap less dwell. The factory point gap range for the Y80 and 102 is 0.012" - 0.016". Based on their internal primary and secondary wire wraps design coils only need so much dwell to reach full charge and more dwell just adds extra heat to the coil, and the longer the points are closed they are subject to current flow longer and that can cause point burning, pitting, etc. The Yamato point gap range is the factory design spec and gaped in the range is OK. But with high rpm operation there can be point bounce where the movable point arm momentarily does not follow the cam profile and wear of the ignition parts that cause erratic operation and all that affects coil dwell and spark intensity. So some extra assurance is dialed in with the closer gap for more dwell to insure adequate spark is present, but not below 0.012"on the gap.

[rsdfour]

Got it thanks