Yamaha TRX850 Enthusiasts Forum

I've lost the crank position while checking and adjusting the valve clearances. How do I know if when the TDC mark is lined up I'm on the firing stroke. Does it matter? Does the TRX waste a spark?

Can anybody help?

Peter

embo850 wrote:I've lost the crank position while checking and adjusting the valve clearances. How do I know if when the TDC mark is lined up I'm on the firing stroke. Does it matter? Does the TRX waste a spark?

Can anybody help?

Peter

Loose sparkplug on first cyl and check it´s in TDC!

Yes, but how do I know it's on the firing stroke TDC as far as the crank and therefore ignition timing is concerned? Could be exhaust stroke TDC and therefore no spark.

embo850 wrote:Yes, but how do I know it's on the firing stroke TDC as far as the crank and therefore ignition timing is concerned? Could be exhaust stroke TDC and therefore no spark.

If you have valve cover off you kan look at the lobes on the cams (away from eachother), but do it as per manual and check mark on crank & mark on cams vs. those thingies holding cams & marks on camsprockets.
Servicemanual can be downloaded on here.

Wasted spark at end of the exhaust stroke

So it does waste a spark.
Thanks very much for that. I can put it back together now.

It has 2 coils and they turn at crank speed to a spark is "wasted" although, not really wasted, it helps to clean up the exhaust if there's any unburnt fuel at the end of the cycle

just drop a pencil or long dowel in the plug hole it cyl1. Turn it over to the T mark (lobes on 1 should be pointing away from eachother).

Check the height the pencil is sticking out.

Now turn it over one revolution. Check how far the pencil it sticking out.

Whichever revolution the pencil it stikiing out farthest on, when the T mark is lined up and the lobes are pointing away from each other is TDC on the compression stroke

I know I'm old and forgetful but can you expain how the pencil grows on different revolutions?

the pencil goes through the plug hole so the bottom of it is on the top of the piston. As the piston rises and falls on revolutions so does the pencil

Yes I understand that bit, but not the bit about the pencil sticking out further on differant strokes, as the piston travels the same distance up and down the bore it will only show when the piston is at th top of it's stroke.

yep but the intake lobes wont be in opposite directions with the T on the magneto lined up when you are on the exhaust stroke

We used to make the TDC markers out of an old plug! bit of a stard to get it hollow, but then a rod down the centre, can be marked as well. Line up with marks, rod (or pencil) out as far as it will go and timed to perfection lol.

Cobba, put your rod away! And no jokes about lead in the pencil either

Dave E

Then you can throw the remains of the plug ceramic at an unfriendly neighbour's windscreen - makes a perfect mess!