Static ignition timing inquiry

[Muckroot]

Hello,

I just rebuilt my engine and replaced a fair number of parts, and I am now having an odd problem statically timing the spark.

Known variables:
I do not know when the last time the engine ran before I rebuilt it.
I had Hugh's Handbuilt rebuild the crank, it is not rephased.
I replaced the original cam chain with an endless chain from mikes.
I replaced the advance unit assembly with one from eBay, mine was severely worn.
I replaced the points with new ones from mikes, and almost all of the screws for the points and their plate.
I replaced the points lobe with a new one from mikes.
I gapped the points at .035mm, and set the valve lash at the recommended gap.
I did my best to follow the cam chain timing procedure when reassembling the top end, specifically I recall ensuring the engine was at TDC, making sure the score line on the cam sprocket was level with the heads, and making sure the pin for the advance plate on the cam was at 12 o'clock.
I statically tensioned the cam chain as recommended, it still moves in and out slightly (1 or 2mm), and is flush with the housing for most of the cycle.


Here is the engine at TDC, found with the stator marks and verified by observing the pistons in the cylinder. Also, the pins that secure both the cam lobe and the advance disk are seen to be at 12 O'clock. I assume this means my cam chain adjustment is correct, and that I did not incorrectly set the cam chain off one tooth when reassembling the top end.



The Problem:
When trying to set the spark timing with a static indicator light I am unable to get the timing mark on the rotor to fall in the F zone on the stator housing. I have the points plate all the way clock wise (fully advanced). This has brought the timing mark a little closer to where it should be, however it is still too far counterclockwise of the F zone.

Hypothesis:
Based on my understanding of the mechanical parts at play I believe I either installed the cam chain one tooth clockwise of where it should be or the new endless chain from mikes requires a break in period to stretch to the correct length (although I would think that would only move the timing mark farther counter clockwise, not clockwise.)

Anyone have any ideas?
Anything I can do that will move the timing mark into the F zone? Any way I can verify definitively that I correctly installed the cam chain and timed the cam properly? Will it hurt the engine to attempt to dynamically time it by running it in it's current state?


Best, Muckroot.

 

[5twins]

Those pins and pin holes you're looking at where the points cam and little disc for the advance unit mount are not what you should be looking at to verify proper cam timing and installation. You should be looking at the pin hole in the cam on the advance side, the one that properly locates the advance unit on the cam .....

You may have to remove the advance unit to see it but maybe not if you get lucky. On the backside of the advance unit, there is a pin pressed into it above the slot for the locating pin. This is to stop the locating pin from falling out .....

That pin is visible on the front side of the plate as well, and if you're lucky and the notched retaining ring isn't covering it, you'll be able to see it .....

 

[Muckroot]

the pin hole in the cam on the advance side, the one that properly locates the advance unit on the cam .....

I took a look at the advance plate and decided to remove it so I could get the best possible look at what I'm working with. for these pictures the engine is at TDC as found by the timing marks on the stator. It looks like I timed the cam perfectly, it's dead on where it should be. Slight problem however, the hole in the cam where the locating pin for the advance unit should go is blown out. I'm guessing the pin was improperly installed at some point. Some genius drilled a new hole opposite the original, moving the spark timing 180 degrees around. I'm kicking myself for not catching this when I installed the cam.


It also looks to me like the new pin has been filed down, and I remember it riding below the outer diameter of the skirt on the back of the advance plate, which caused undue wear on the original advance plate, prematurely wearing it's slot out of correct timing. I figure I've got two options here. Re-install the advance mechanism, being careful to install the advance disk on the advance rod 180 backwards to compensate for the locating pin. OR tear the head down and buy a new cam. I'm really leaning towards the second option because
A: there are so many new parts in this engine It'd be foolish to buggar them in the next 10,000 miles by skimping on the 8 hours of work and X amount of dollars it'll take to replace the cam and
B: I really want to do this build right. I am very motivated to have a reliable, trustworthy engine that I can road trip with and not worry about breaking down because of a stupid locating pin failure.

Input and thoughts on my predicament are most welcome.

Best, Muckroute.

 

[5twins]

For the time being, can't you just install a new, proper length locating pin?

 

[Muckroot]

For the time being, can't you just install a new, proper length locating pin?

I don't think so, I tried pulling it out with needle nose pliers when taking the pictures so I could inspect it and it would not budge. I really gave it the business as best I could without damaging it.

As far as replacing the cam goes, it's a set back for sure but I only just got the wiring mocked up so it'd spark, and the bike doesn't even have brakes or a complete rear axle yet. I just have to suck it up and pull the engine back out and swap the cam.