Measuring Piston Position

[Rob Neal]

Trying to get the rebuilt A65 to run properly I'm checking the ignition timing yet again. Setting the firing point I'm using a timing disc (34 degrees BTDC) and cross checking this by measuring the position of the piston.  For this I have a DTI and adaptor fitted via the threaded spark plug hole.The equivalent piston position should be 7,7343mm BTDC (seems a bit precise but anyways..). However the plug is angled relative to the cylinder axis centre line.  So that I can adjust the DTI reading to place the piston in the correct position does anyone know what the angle of the plug relative the cylinder bore is?  I can then use simple trigonometry to work out the numbers.  Thanks.  Rob

[limeyrob]

Had the same problem on an A10 recently. I ended up measuring the angle with a gauge off the top fin.  I can't find where I wrote it down as there's a chance its the same. I spent some time comparing the piston measurement with the timing disc and was surprised to find i could get a more accurate reading off the DTI/plug gauge than the disc.

[DAVE BRADY]

Hi,

To overcome the angle issue I use a hex key that cannot got through the plug hole but can be held upright and by rotating the wheel I find TCD with the final position being at the end of an up stroke to eliminate any backlash.
Using a thick feeler gauge laid flat on the top fin I mark the TDC position on the hex key (made easier if coated with felt tip).  Now measure the BTDC position above the TDC mark and away from the plug hole scribe or mark with a junior hacksaw blade.
Put the hex key back in the plug hole and turn the engine backwards until the BTDC mark is below the feeler gauge.  Then carefully bring the piston up until until the feeler gauge and the mark on the hex key line up.

Another thing to remember is that if you have the head off or before you fit it, measure the BTDC position and set the static timing.

Dave.

[Rob Neal]

Thanks for the input. Timing now set to 7,734mm BTD using the 'dipstick' method and checked at 34 degrees BTD with a timing disc.  Still won't run so just to check with those who know. A good spark on both sides from the new electronic ignition set up and new spark plugs. Good compression L&R both at 137psi.  Valve timing checked (several times) to timing marks on gears.  Problem noted, plenty of suction found when blanking right carb inlet with my hand but hardly anything on the LH side.  Strange with such good compression. Cover off shows valves operating with no obvious problems noted. But it must be the valve timing mustn't it noting lack of suction on LH carb?  I set valve timing with pistons at TDC. Timing set with LH piston at the correct position BTDC (rather than the right). No rags or debris in the carb or cylinder head inlets. So why doesn't it run?  New Wassell carbs thoroughly cleaned out with carb files, carb cleaner, U/S bath (many times).  Good fuel flow from tank (Cleaned and new filters), carbs flood ok when tickled, floats set to correct height (2mm below face) using modern black floats with the bendable tang. Got spark, air, fuel, compression....won't go.  Aaagh!  I've had it apart and back together again so many times it's driving me nuts.  Any thoughts?? (apart from a lighted match into the tank which has crossed my mind!!). BTW rebuilt head (no cracks), new valves, seats, guides, springs (T&L Engineering), Valve clearances ok (8 thou inlet, 10 exhaust) new pistons, rings with new sleeves matching pistons (Again T&L).  In desperation.  Rob

[LightningAndStarfire]

If you have electronic ignition I assume the mechanical advance/retard unit has been removed.So proper ignition advance is provided from the electronic ignition.

The timing has been set with some indicator light?

[chaz]

I got my A50 back in 2019, with covid and other problems, the restoration has taken a while. It is fitted with the Micro system. I marked the ignition plate on removal but with time and cleaning the marking has been lost.
I down loaded the instruction sheet from the web site and re set.
was it clockwise or anti? pos earth changed to neg will that change,? a custom loom? all factors to consider.
finally , this weekend I found a small window of time to have a go at starting it. As the fuel has been sat for a few months, the battery is still holding charge.
a squirt of easy start, kick and a single bang.    then nothing
left a while ,same routine  and then a single bang.
then a longer squirt and its running until it runs out of easy start.
fuel coming through and it keeps running, revs  a bit high but happy days.

all I can add, is re check fitting details, make sure its running and set up the right way CW or ACW as specified. I set TDC with a depth gauge, valve clearances set. No disc and no setting plug.
make sure its on the correct cylinder.

[DAVE BRADY]

Hi,

Good point about direction of rotation.  The rotor for the timing goes anti-clockwise so it is the left hand hole to line up on.
As the EI fires both plugs at the same time it, doesn't matter what cylinder is used.
I always use the right side as I can set the rotor and adjust the stator all on one side.

Dave.

[Rob Neal]

I have double checked that I have the angle of rotation correct and have set it to the 'A' or anticlockwise mark as per the instructions. All of the original ignition set up, including the mechanical advance/retard has been removed and replaced by the electronic kit.  Fairly confident the ignition is OK now so will move on to the valve timing.  Will remove the timing side case (yet again!) and check the alignment of the timing gears.  A thought though, does anyone know if there's any info about that shows when the inlet/exhaust valves begin to move relative to crank rotation?  I'm thinking that this would act as a check against the timing gear markings to see if they are indeed correct.

[DAVE BRADY]

Hi,

Can you post an image of the timing gears as they are?
I think page B29 of the workshop manual has an illustration.

Dave.

[Gup holland]

Could this be some help

[Gup holland]

Why i am seeing different no about the 34 degree crank angle btdc,
7.7343mm or 7.216mm

Am i missing something or what????workshop manual 00-4177

[Jim S]

Gup

The dimension 0.3045 inches is consistent between the two documents however with the metric conversion, there is an error. 25.4 mm/in x 0.3045in=7.7343mm which is the value given in the complete table. The document showing only the 34 degrees value has the metric conversion error.

Jim

[Gup holland]

Thanks Jim that makes all clear,

I had a bad grade in school about calculations   

Greets gup.

[Rob Neal]

Thanks for the replies.  Gup, the valve timing info sheets look really useful, thanks.  Rob

[Rob Neal]

I'll send a picture of the valve timing gears set up as soon as I get the timing cover off.  Currently have a house to-do list I need to get cleared before I can get back in the garage.  Only fair as I did promise to do these jobs in exchange for being allowed to buy another bike last week!  (1976 Suzuki GT750 since you ask!  I know, it ain't British, sorry).  Rob