How do timing

[HiGuy]

I want to check the timing on my bike but I don't know what to do. I have the manual but that just gives the specks. I would like to know how to adjust it and how the things works.

[dbeardslee]

Higuy - do you have a timing light?

[prometheus578]

Timing is permanently set on these bikes and is quite accurate.
No adjustment is possable... nor needed.
All the guts are behind the left side engine cover.
Remove the cover and you'll see the timing wheel and the pointer.
I suppose if you want to play with things, you could hook a timing light to #1 spark plug wire and watch the wheel spin round and round.
Anyway... behind that wheel is the pick-up coil assembly.Two pick-up coils.. one for #1 and #4, the other runs #2 and #3.
Here's how the game is played:
There's a bump on the crank shaft... we shall call it a reluctor.... because that's what it's called.
Anyway... as the crank turns... this reluctor passes by one of the pick-up coils. That coil produces a small current and send that to the ignitor unit... which we shall call the brain box. That signal tells the brain box to fire a set of plugs.
When the crank turns 180 degrees more, same thing happens, 'cept the other pick-up coil is now sending the message to the brain box.
To change the timing, on would have to adjust/spin the pick-up coil assembly plate.... sort of like on an older bike with points and such.
Thing is... This assembly plate is not made to spin... can't be adjusted, as there's no reason to.
Oh, don't get me wrong, (and I better point this out now before the "gear heads" chime in...) Yes, it's possable to modify the pick-up assembly plate so that one can rotate it, but it's really not needed, nor worth the effort.
The gear heads will tell you different, but if you try it and dick things up... I'll be sitting here laughing.

[egsols]

Prom,

He's got a 79

HiGuy

If you only have the spec's what manual do you have, just the owner's one? You may want to invest in a clymers or equivalent.

But like Prom said, why do you want to dick with it? The only reason I had to check mine was because the PO had some shop work on the bike and they f%^&ed up all the plumbing. They had the petcocks reversed with the vac line from the octy going to the vac advance and a line from the port on no. 2 carb going to the intake. The only reason it ran was cause the prime lines were run to the octy sooooo the "on" lines were actually running prime. The shop even noted on the work order for him to shut the petcocks to off when he parks the bike.

Short story long, they compensated for no vac advance by setting the timing 26 degrees advance at idle.

My other '79, i checked the timing but never had to adjust it.

[TADracer]

It is just a check but should be done from time to time though I have never had mine move (unless I did it).

Static timing on a 79 special is 5 degrees before TDC which is noted by the F mark on the timing wheel under the left side cover.

Attach a timing light to the #1 cylinder and warm the motor up to operating temp. The F mark should line up with the pointer at idle of 1100 +/-. If you are there you are OK. If not then set your static timing by loosening the two phillips screws and slightly rotating the timing mechanism until the F mark and pointer line up. Then you check your centrifugal advance by disconnecting the vacuum advance line and plugging the nipple on the #2 carb. Run it up to about 4500-5000 RPM and you should be on 31 degrees (though there is no real mark on the timing wheel for this). If it does not advance then you should service your centrifugal timing mechanism. Vacuum dashpot can be checked by just sucking on the vacuum line. If it retracts all the way and stays as long as you hold the 'suck' then it is OK. Thats about it.

[HiGuy]

Confused

I am fine with getting timing gun but I don't understand how I can figure out that it is at 36 degrees when my timing plate is spinning at a thousand rpm or more. the Repair manual that I have says the same thing as all you but I don't get how I can tell that it is at the right place or not when I can see it.

[egsols]

That's the whole idea behind a timing light. It works of the number 1 cyclinder and strobes with the firing of the plug.

When you point the light at the timing disk, with the bike running, the disk will appear to stand still, thus allowing you to see the timing mark and the current timing.

Remember the strobe lights at the dance halls, made everybody look like they were dancing in slow motion? Same principle.

[DavesXS]

Even simpler, just pull the cover off the left side. Start the motor. Warm it up. Rev the motor. If the disk moves when you rev it up your vac advance is probly fine.
If the carbs are tuned, and it fires right up, your timing is probly fine. If carbs are tuned, and takes a long time to crank, then get a timing light and start checking.


And to the guys that think there is no bennifit to changing timing. Why is that the thing to do when adding performance mods to crotch rockets. You old schoolers should have heard of "bump the timing" right?
With filters, 4-1, and jets, the next thing would be to bump timing to 6 btdc if we were talking gsxrs, or kz's, or ninjas. Right? Or am I wrong about this?

[egsols]

I used to run my old datsun 1200 26 degrees advanced. Sure I burnt plugs out fast, but it had lots of go compared to the stock setting.

Don't get me wrong, I'm not against playing with it, but when I played with mine I didn't really notice an improvement, I mean these things already have enough pull. I found that the stock setting works good for power, plug life and ease of starting.

[dbeardslee]

hyguy - I always put a little chalk mark on the timing wheel where the idle timing is supposed to be set. In your case that would be 10 degrees btdc. Makes it a lot easier to see where the mark is when the timing light hits it. I set mine so the 10 degree mark is right on the pointer when the engine is running at 1000 rpms. If it's off, there are two phylips screws in elongated holes around the outside edge of the pickup coil assembly. Loosen those screws and you can rotate the whole assembly to adjust the timing. I move it with the engine running, and no loose clothing close to the timing wheel. Once I've got it set at idle, I rev it to 5k and make sure it's advancing to 36 degrees.

Timing lights generally come with two battery clips that supply the power. On Betsy I always use an external power source (12v battery charger) rather than connecting to the battery. That way I don't have to take the seat off, and I seem to get a more positive connection to the light that way. I've also seen battery operated lights, but haven't tried one. Like Egsols said, connect the inductive lead to the #1 spark plug, and the light will flash every time #1 fires when the button on the light is depressed.

Gotta have a timing light. I recommend the lights with the xenon bulbs. Plenty bright enough and cheap. Harbor Freight has one for $13.

I think it's a good idea to check it every once in a while. As the cam chain stetches, timing will change a little. I know when I put the new cam chain in, the timing changed quit a bit.

[oseaghdha]

Originally posted by dbeardslee
...........................

I think it's a good idea to check it every once in a while. As the cam chain stetches, timing will change a little. I know when I put the new cam chain in, the timing changed quit a bit.

Hmmmmmmmmmmmm........

Not.
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.

[dbeardslee]

Timing runs straight off the crankshaft. It wouldn't even care if your camchain fell out on the road.

Then explain to me why timing changes when the cam chain is replaced. 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.

[psycoreefer]

As for where 36 degrees is on the wheel for "total advance check" I think the following might get you a "close enough" mark. That means as long as its some where close to that mark I'd call it good.

36 = 1/10 of 360. 360 degrees in a circle.
Look at the wheel and imagine it divided into 10 segments. place a mark where the "next" segment would start after the "T" mark. That should be close to 36 degrees advance. I think. Depending on how accurately you imagine things. Or you could meassure the distance between the 'C' and 'T' marks then multiply that by 7 and make a mark that distance from the 'C' mark. I think C is supposed to be TDC and T should be 5degrees, 7x5=35.


Please don't judge my intelligence by the above described procedures, I'm trying really really hard to avoid doing any work today.

[psycoreefer]

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

Depends on what timing your talking about... "valve timing" or "ignition timing".
Valve Timing is the relationship between piston position and valve opening. Valve timing would change with a new/old timing chain.

Ignition timing is the relationship between spark and piston position. Ignition timing (what you check with a timing light) shouldn't change.

They are independent of each other, because they are both based only on the position of the crank shaft, although you need both to be right for an engine to run properly. The valves don't care when the spark plug sparks and the spark plugs will happily spark with the valves either open or closed.

[dbeardslee]

Point is you don't want it sparking when the valves are open.