How do timing

[psycoreefer]

tripple post bonus!!!!!

Originally posted by oseaghdha

Timing runs straight off the crankshaft. It wouldn't even care if your camchain fell out on the road. It would happily go on sparking as long as the motor was turning over.

You could prove this by cranking a motor that has the head removed, the Ignition timing marks should still line up perfectly.

[psycoreefer]

Originally posted by dbeardslee
Point is you don't want it sparking when the valves are open.

True. But the only way ignition timing can ever change is by moving the pickup coils in relation to the reluctor on the crank.

The stretch of a cam chain will never change you ignition timing, so a timing light can't be used to judge valve timing. the only way to figure out how stretched it is would be to pull the covers off and look at the timing marks on the Cam's themselves.

The exception to this is modern cars where a cam position sensor in combination with a crank sensor is used to determine when to fire plugs and injectors. I suppose then your Cam timing might effect when the plugs fire.

[oseaghdha]

Originally posted by dbeardslee
Then explain to me why timing changes when the cam chain is replaced. ...........

I don't believe it can, unless something was disturbed during the chain swap. Like if you accidently whacked the timing disc or pointer.

My understanding of proper timing is that it's a function of three things - position of the crank, position of ignition, and position of the valves at ignition. I see what you're saying about timing not changing, i.e. when the crank is at 10 degrees btdc the piston will always be in the same position, but the valves will not be if the length of the chain has changed.

All true. But other than installing a degree wheel on the crank and an indicator on a cam follower, I don't know of any way to check valve timing. I have to rely on the camchain tensioner to keep my valves behaving properly. There is no communication between the two systems, and so they must be independently adjusted.

[dbeardslee]

I don't believe it can, unless something was disturbed during the chain swap. Like if you accidently whacked the timing disc or pointer.

Didn't whack anything, and it did change. The manual says "The ignition timing should be checked at 4000 miles intervals, although it is unlikely to require adjustment unless the ignition pickup assembly has been removed in the course of the overhaul." I check mine pretty regular, and every now and then it needs adjusted.

[psycoreefer]

run away thread warning....

I don't want anyone to think I'm saying it shouldn't be checked, check it as recommended or as often as you want, checking never hurt anyone. As part of my new bike routine I checked my timing, you never know what a PO did to the bike, mine was spot on. Maybe the plate could drift a little over time if the screws aren't tight enough, or maybe the pickups age and start picking up the signal a bit later. I don't know enough about how that works to say it can't change.
The only thing I can say is Yamaha must have felt it couldn't change enough to be a problem because they replace the adjustable timing plate with a non-adjustable one on later models. But then again maybe that change eliminated the chance for "drift" and the need to periodically check the timing.

dbeardslee -
out of curiosity, how much do you think it changed when you replaced your chain? 1 degree? half that? 10 degrees?
I'm just guessing but I think there is going to be some bit of error when you check the timing with a light, just like any other measurement. What the margin of error is I don't know but maybe the differences your seeing are due to that "error". For me personally I don't think I'd bother to adjust it if it was off just by less then 2 degrees. Have you ever noticed a difference after makeing and adjustment? Maybe I should check mine with again with a more critical eye.

[dbeardslee]

psyco - as I recall it advanced the timing by 5 or 10 degrees. Don't remember exactly (been 5 or 6 months ago), but I remember thinking it was pretty significant. I notice a difference in the way it runs - backfiring, power, etc. when it's set correctly and when it's advanced too far. It'll still run regardless of where it's set, it's just a question of how well.

[psycoreefer]

Thats a lot, I was expecting you to say it only moved a tiny bit, something that would reasonably be within the margin of error. I can't think of any reasonable explanation for a change like that, guess I'm in over my head.

[HiGuy]

Maybe not timing

Well I pulled the plugs to see what they looked like and it turns out that they are wet and black and one was very sooty. I think that something may still be up with the timing or advancement but I think I should work on my carbs first.

[HiGuy]

timing off, bad springs maybe?

Well I went and did the timing and finally understood how it worked but as it turns out I thin that the timing unit may not be good becuase at idle it was just perfect on the mark but when I rev it up to 5400 it shoudl be at 36 but is at more like 45 degrees, the buddy mechanic (bless his shop) helped me tinker with it a bit and it was always advancing much higher than it should be I think. Since my plugs all kinda look bad and I smell gas coming out of the pipes some times I am wondering if I am getting pre ignition and while some of it is burning it is doing it too late and I get pops and stuff. I also realized that the plugs I was running were a bit colder than the the facotry ones. I had a bp7es instead of a bp6es. I couldn't find any NGK ones so I got some denso and I'm going to see if that works any better. How would I go about figuring out why my advance is going too high? If there are springs and it is the springs that have a problem what would I do? I do have a parts bike that I think is a 80 or something. The Headlight relay off of it says 3H5 on it.

[dbeardslee]

HiGuy - First make sure your vacuum lines are going where they are supposed to. The vacuum line from the advance should be connected to the port on the #2 carb. It connects to the carb itself, not to the carb boot. There are two springs on the advance unit and I suppose if they were weak it could result in the ignition advancing too far. I took mine off and cleaned it up but I wasn't having trouble with it.

The first thing I would do is check to insure your pointer is set correctly. I've heard some members use a pencil (clean pencil, eraser end down) in the #1 spark plug hole to see when the #1 cylinder is at tdc. With the bike in neutral and the timing cover removed, you can rotate the crank with a 6mm allen socket on the bolt in the center of the timing plate. When the maximum amount of pencil is sticking out of the hole, your at tdc. Make sure the pointer is at the corresponding place on the timing wheel.

If you want to check the governor assembly, the first thing you have to do is remove the 6mm bolt in the center of the timing plate. Put it in gear, and block the back wheel with a 2X4 so it can't turn. Remove the bolt and the timing plate. Take a careful look at the back of the timing plate - it only goes on one way. When you reassemble, if it looks like it isn't spinning flat it's on 180 degrees wrong. Remove the two bolts in the elongated holes along the outside of the assembly and remove the pickup coil assembly, and you'll see the governor assembly under it - that's the thing with the springs on it. It should pull straight off. Not sure how you would check the springs to see if they are in spec, or where you would get replacements. I'd try cleaning it up first, and see if that makes a difference.

For an exploded diagram and parts list check the yamaha fiche . The governor assembly is still available through bike bandit for the nominal fee of $140! I wouldn't start buying parts 'till I was sure it was the problem. The governor assembly for the 79's and 80's are different part numbers, so I don't know if you could use the other one you have to check.

The other part of this system is the vacuum pot, but I don't know if that could cause it to advance too far, or if the pickup coil assembly itself could be the problem. Anyway, this post should bump this thread back up to the top so maybe an ignition expert will weigh in.

[TADracer]

Jaron,
This is a long thread and I am sure I have missed something in all the reading. But if you have a 79 special and your pointer is set to TDC then I am pretty sure your timing specs should be as follows.

Initial static timing (checked at idle with vacuum dashpot connected to the #2 carb) - 5 degrees before TDC. (Standards are 10 degrees). This is the easy part to check.

Next you check your centrifugal advance mechanism. Your centrifugal advance mechanism will not advance any farther than the stops will allow. The springs only control how fast the advance comes on with crankshaft speed. Your centrifugal advance is cehcked with the vacuum dashpot disconnected and the port on the #2 carb plugged. Raise your RPM to around 4500 to 5000 and you should be at 31 degrees (36 degrees for a standard)

If you do this check with the vacuum dashpot connected to the #2 carb you will get a reading around 50-53 degrees when at your high checking RPM, which is right, because the vacuum is high and the dashpot is adding its own advance to the mix on top of the static advance and the centrifugal.

The centrifugal mechanism works at crankshaft speed and is slower to react to throttle position whereas the vacuum mechanism works off of the vacuum signal in the #2 carb at the butterfly which is quick to react to throttle position. The two work independently from each other and from different inputs.

Once all this is set up correctly then the chances of it moving out of time is slim but it is worth checking every year or so just for peace of mind.