Strange new issue w/regards to timing.

[Saintly]

Ok, I'm a bit puzzled. perhaps someone can open my eyes as to what I'm overlooking here.

When I assembled my pan engine, I aligned the timer drive gear dot with the cam gear dot(even though I dont believe it makes any difference if you do or don't) . I then installed the timer, and static timed it with a testlight. (I set the breaker points to open @ tdc) This static timing method may not be everyones idea of correct, but thats how I did it and it got me close enough to start the engine.

Once started, I tweaked the timing and got it running at 30deg BTDC at full advance(3000 rpm). I did this with a sears/craftsman timing gun(strobe light). I run an open belt primary so timing with a strobe light is very simple: make a pointer (I use a piece of coathanger pinched between the top rear jiffy stand mount bolt) and make a bright white paint mark on the engines front belt pulley when the advance mark is aligned in the timing hole/window. Re-install timing hole plug, fire engine, pull triger on timing light, and adjust timer body until white paint line lines up perfectly with coathanger/pointer.

Now the problem is, after timing with the gun, the engine runs real nice & smooth for about 50 - 100 miles. Then it all of a sudden runs like crap. It gets hard to start and loses power. When I re-check the timing with the strobe/gun it has jumped 15 or 20 degrees to the retarded side.

First time it happened, I thought that I had'nt tightened the timer hold down clamp enough, and it had slipped. This is not the case, as it has happened 4 times now, and I made a reference mark with a sharpie pen indexing the timer body to the engine cases - it hasn't moved!

Something internally is "slipping" or jumping and causing the timing to go out. I've pulled the timer and double checked the drive gear roll pin -it's in and its fully intact(not broken into 3 peices and spinning) I also put a small tack of weld onto the bottom of the gear to ENSURE that it is not slipping on the shaft. But alas, it happened again!

I've now removed the cam cover and inspected all the gears. The timer drive dot is still indexed to the cam so it hasn't moved. The cam gear is a super tight press fit on the cam, but even if that had slipped, it wouldn't affect ignition timing with respect to crank position. If the pinion gear had slipped on the crank I don't think it would run right at all since the valve timing would be off and it might even bend a valve - which it hasn't( runs great when timing is re-corrected)

The only possible thing I see is the timer drive gear:

-continued

[Saintly]

- continued ( sorry had to piss bad)

Anyway, the timer drive gear looks like it is made from 2 gears.
There is the big portion with the straight-cut teeth, and there is the smaller part with the "worm gear" type teeth on it.

It looks to be a pressed together piece, with a solid roll pin indexing them together.
Although I suppose its possible for this to slip, I don't think it has since it's tight as hell with respect to itself and the rollpin is still there and intact.

I forgot to mention, when I assembled the engine, I reduced the end play of both the timer drive and the generator idler gears by shimming them with .015" shovelhead rocker arm shims. I got the endplay down to about 5-thou when checked through the tapped block hole with the cam cover on and torqued.

So there is very minimal endplay or "slop" in the timer drive.

Any idea what is "jumping" on me?

Thanks

[indianut]

Points are wearing or loose.

[Saintly]

No, wish it were that easy, but no.

Off by 20 degrees when it happens.

[steve_wood]

Bad condensor? Maybe try a known good one?

[Saintly]

Let me re-clarify.

The timing jumps 20 degrees retarded. I can verify this with a timing light.

If I then rotate the timer body counter-clockwise 20 deg(in the advance direction) to restore it back to the correct timing spec, she runs mint again.

There is nothing wrong with the point or condenser, it is "jumping time" on its own approx every 75 miles of riding.

[Bosheff]

Is it possible the point plate (Timer base plate) is rotating from vibration? Your method of strobe timing is nothing new, and is a considerably easier method than pulling the timing plug and getting a face full of oil. I am going to assume you are using mechanical advance timer (pre 65). You might want swap this timer with another and see what happens. When the fiber on the points wears, this will affect dwell, which in turn will alter yer timing....bosheff

[katto]

I had this one time and it was my timmer top, it was wore on the inside where it sits on the timer base. It has a small machined land. One look at mine and could see it was bad. Good luck. Katto

[hogboy52]

Well I'm confused because 20 deg. is the normal rotation. It will slide backwards on its own from engine vibration. I have a spring to hold it in the advanced position.

[Saintly]

Well I'm confused because 20 deg. is the normal rotation. It will slide backwards on its own from engine vibration. I have a spring to hold it in the advanced position.

Sorry I should have specified, I have the 66 & up type base with auto advance and single points.

The base does not have the fixed two-hole flange on it, but rather a round lip and uses a hold-down clamp. The body can be rotated indefinitely with respect to the cases.

[NightShift]

Dear Saintly,
Maybe you shredded a shim.

Respectfully,

[Kuda]

Sorry I should have specified, I have the 66 & up type base with auto advance and single points.

Any chance the advance weights are worn or hanging up in the base?

-Kuda (seen stranger things happen...)
'49 panchop

[awander]

I had an auto-advance timer on my '64, and I could never figure out why it would run great one day and poorly the next.

It turned out that the shaft and the cam were worn, and the cam was rocking aroiund on the shaft, and this altered the timing enough so that it caused the problems I had.

20 degrees different though-that is a lot of wear!

[duoglide58]

My bike would not hold time when I first got it. I would time it and it would run fine. Then it would act up and backfire and get hard to start. Checked the points and the gap had changed. In my case, it turned out to be worn bushing on the timer's shaft that were not holding a consistent gap and timing.
Is it possible the bushings are worn? I don't know how worn they would have to be to affect the timing by 20 deg.
Doug

[Sir_Rat]

Saintly...sounds like you are getting really familar with your timer and its drive gears. You have mic'ed n measured everything you can think of and taken steps to eliminate any possible causes. I would take a less technical approach at this point and just replace the timer. I call this the shade tree mechanic approach. It works well for me cause then I don't have to overburden my few remaining good brain cells with alot of technical info other than installing and setting the timing. Since you're only using one for troubleshooting, you dont have to go out and find a rare Genuine HD (I hope you are using Genuine HD) Auto advance timer, try the common single point mechanical advance one instead (Simpler is better right?)

Just a thought...hope it helps..good luck
Aloha....Mike