Aermacchi ss350 timing question

Setting static timing on a Aermacchi 350

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6hds
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Aermacchi ss350 timing question

#1

Post by 6hds »

Picked up a project, a 72 SS350. After sorting out a lot of wiring issues I focused on getting it to run. Motor is supposed to be a Ron Lancaster rebuild. To set the timing I locked the mechanical advance with a homemade washer to full advance. With the flywheel on the "advance" mark and a test light on the points the points plate has to be rotated to the end of the slot to get close to light the light. I expected the points plate to somewhere in the middle of the slot. The middle of the points plate slot is actually about where the factory "master mark" for timing is. Any thoughts before I might uselessly remove the cam cover to look for something that isn't there? Am I missing something? Thanks, Gary
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Re: Aermacchi ss350 timing question

#2

Post by RUBONE »

Is your points gap right? The gap setting affects where the timing occurs.
6hds
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Re: Aermacchi ss350 timing question

#3

Post by 6hds »

Thanks for the response Robby. Points gap is .018 as rider handbook says. Found the exact "high spot on the points cam with a dial indicator. Also every time I check for the light/buzzer to go out I'm rotating the crank through its cycle to mostly eliminate any gear lash error. I think the points cam/ mechanical advance is directly on the end of the cam so a "one tooth off " situation is can't happen. I'll find this out soon as I'm waiting for a shop manual to arrive. With not being able to retard the spark close enough to the mark a nasty kick back is not what I'm looking forward to. I'm going out to the shop this morning to get a fresh look at it. Thanks, Gary
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Re: Aermacchi ss350 timing question

#4

Post by chuckthebeatertruck »

Oh, you're a lucky guy having a later model with the timing window. On my 69 the fastest way to set it is to either attach a degree wheel to the generator or just pop the head and measure.

Anyways, the first set of non-NOS points I put in the little orange beast neither the plate nor the condensor fit properly. The condensor, in particular, wasn't grounding well and that caused some running problems at speed.

Back to the plate . . . what I discovered is that I could EASILY reduce the points gap from .018 to .015 simply by laying my thumb on the point spring. In other words; the tension was "eh" and so that tiny bit of pressure seated the point block against the cam. In other words; I wasn't actually setting the points to .018 and was, in fact, setting them much wider. A wider gap setting advances the timing . . . so once I started setting my points to .015 to begin with the problem went away entirely.

I'm currently running 25 to 26 degrees at full advance -- which retards to 5-6 degrees for starting. This is only a couple of degrees retarded from stock; but it seems to work much better with the fuel in my area (Chicago) without overheating or pinging. Starting is a very reliable 1-2 kicks from cold affair.

The other thing that I did was to play with the plug gap. I found .020 to give the most reliable starting and overall running.

The final thing that helped was mileage. My fresh motor didn't really become fun until around the 1000 mile mark.
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Re: Aermacchi ss350 timing question

#5

Post by 6hds »

Thanks for the revealing the tips you've learned. I'll reset the points at .015 and see if the timing mark gets closer and to see if I get the same variation you experienced with the spring. I am curious about the amount of advance built in the mechanism. I'll go out tomorrow and put my degree wheel on the generator and see what I find. I went out today and confirmed what I found yesterday. I'm close to the advance mark but if I was to guess, lining up the master mark puts the advance at 40+ degrees, which can't be good. I still don't know why the points plate has to be rotated all the way in the slot to get the timing close to the advance mark. Thanks again, Gary
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Re: Aermacchi ss350 timing question

#6

Post by chuckthebeatertruck »

When they went to the 350 in 69, hd dropped the overall advance to 28 degrees, 7 retarded. In 73, they moved it up to the mid 30s (can't remember the exact number).

When you get your manual, you'll see they were constantly fudging with the advance. I went up to 10:1 with the latest rebuild and found I could decrease the timing without losing anything or overheating. However, my plug strap says I'm on the edge at 25 degrees, any less at full advance and the heat might build too fast.

The other thing that made a huge difference on mine was replacing the advance springs and carefully fitting everything. I did that the season BEFORE I discovered the point spring. It was a mother to boot and the kick back sheared a kicker ratchet gear right on the four splines. Lesley at moto Italia laughed at me on that one.

And, I'm running both a later aluminum sleeved cylinder (69 used cast iron) and a 72 head, so my results should be closer to what you are staring at.
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Re: Aermacchi ss350 timing question

#7

Post by 6hds »

Wow, Thank you Chuck. Sounds like you've got a lot of experience with these singles. My hours compared to your years. When I bought this it was not run for a long time so before trying to start it I looked at the carb, ignition, valve clearance, etc. Wiring needed the most attention to get everything to work the way it should. When I got to points and timing I removed the advance mechanism, which looked like it was squirted with chain lube and the seal behind it had no signs of leaking. So a complete disassemble and a little wd-40 got it ready. I did notice that there is no "flat" or pin to locate the advance, so it can be installed correct and 180 out on these. Thought that was odd. The previous owner gave me a Moto Italia catalog with the bike so I placed an order of odds and ends I needed with Wesley a couple weeks ago. I found him to be very open and helpful with all my novice questions. When I had the left cover off to look inside I could see a "new" starter ratchet gear that must have come from Wes. I'm writing down all your info and pinning it on the board out in my shop for reference. If other questions come up, and they will, would you mind me sending you a PM here? Thanks again, Gary
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Re: Aermacchi ss350 timing question

#8

Post by chuckthebeatertruck »

Be careful on the ratchet gears. There are minor, but real differences based on the year and the left outer cover. When the support was added to the left cover (72, but don't quote me) the depth of the ratchet gears changed to account for the support. Again, it's really minor, but real -- and something I learned the hard way when I swapped to the braced cover. Similarly, the early 250s had an extra "ring" on the them that made the whole stack stand higher -- again, they had a different left cover. Outwardly, all the gears look very similar -- but the minor differences add up.

The result of mix and match is imperfect meshing of the already weak teeth on the kicker quadrant. If you continue to kick it out of alignment, you'll find the first two or three teeth on the quadrant get worn to nothing and will eventually start to bind the mechanism. As this happens, the whole kicker action starts to unwind the ratchet gear and way more force than is necessary is applied to the tiny little spring ring that holds the ratchet gears in place. when that pops loose . . .the gears shift and bind up the kicker.

Really, the sprints only have two weak points -- the kicker and the generator. The generator is a "you have it or you don't" problem and is more about wobble than anything else. The kicker is an odd thing. Guys who straddle and kick with their left seem to have trouble starting the bike, but rarely seem to have kicker issues. Guys who are used to kicking big twins or sporties tend to stand on the left side and boot them so hard stuff breaks -- but the bikes fire up easily.

The solution is really simple: either roll the bike backwards onto compression THEN kick or put her in 3rd and bump start. I admit that I am often too lazy and just break things. I haven't yet learned that I don't have to kill the bike when I start it :-) But, I've gotten really adept at swapping kicker parts. So far, the latest NOS set is holding up well. Keep in mind that the 10:1 piston is why I'm destroying stuff -- you'd think a single point increase wouldn't make that much difference -- but for some reason it really does on the sprint.

I have much more experience with brit singles and I missed having a thumper around after nearly 20 years of only twins. So, I bought the sprint on a lark at a swap meet years ago, intending to refurbish it, ride it for a summer and sell it in the autumn. I was shocked at the availability of NOS parts and how "cheap" it was to fully restore. I then went through the same timing and starting problems you described. By the time I sorted them and had a dead nuts reliable bike -- I discovered I really, really enjoyed riding it. So much so, I find excuses to take it for a run and then fix whatever vibrates off or cracks or just plain goes sideways. At this stage, I've tidied up so many little things I feel pretty confident taking the sprint just about anywhere (and I do). I find that after 50 miles my butt and hands say I'm good -- but it's an amazingly competent small bore bike for putzing on country roads at 45-60mph. Mine doesn't get horribly buzzy until 60 . . . so it's great for a fun run as the acceleration through 3rd gear is just fun with a capital F.

The only sucky part is that the fuel mileage is through the roof -- and so I have to make sure I'm topping her off regularly to keep the fuel fresh during the summer. Otherwise, she might sit for a few weeks and run a bit ragged.

My next planned improvement is adding one of Ron's Center Stands. The right side "jiffy" is a total POS and I'd really like a more secure stand for the parking lots. Hopefully, I'll get that done before the spring riding season starts.
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Re: Aermacchi ss350 timing question

#9

Post by chuckthebeatertruck »

I popped open ye old service manual - the later bikes were timed at 34 degrees full advance.

69-72 was 28 degrees . . .

So, you might want to make sure you don't have mix and match parts before you drive yourself nuts -- or just set it by a degree wheel and not worry about whether the flywheel marks are correct.
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Re: Aermacchi ss350 timing question

#10

Post by 6hds »

Chuck, thanks for the info on the kicker issues. I'll have to take a close look at it. Got the manual in the mail today and the points and timing chapter has me confused a little. The pictures show two other case types, but not what i got. My vin says 72, but the motor pictures say its a 73. The frame section says I got a 72 frame. Anyway, I reset the points at .015 (rider manual says .018) and viola! I don't believe it but I see it. At .018 the points plate has to be totally CW to get the timing marks in the ballpark. At .015 the points plate is almost in the middle, close to the master mark. Just like the picture shows. Never though .003 would move that plate so much. I'm getting so much info from you I have to figure out how to print this. By the way. What are the shocks, eye to eye suppose to be? This one has 12.5" and they don't look right. I took them off and measured the mounts with the swing arm angle that looked right and came up with 11" or 12". I can't find any info anywhere. Thanks again. Gary
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Re: Aermacchi ss350 timing question

#11

Post by chuckthebeatertruck »

Things are now starting to make sense. I was wondering if you have a mix and match bike -- and it appears you do. No biggie -- it seems many sprints were repaired with what was on hand. It can be the curse of cheap "starter" bikes.

To your question on shocks; the ones I am running now are 12 inches eye to eye. I also run a 50/50 mix of hydraulic jack oil and ATF in the front forks to help control them a little better. The end result is a bike that just goes where you want it to . . .
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Re: Aermacchi ss350 timing question

#12

Post by chuckthebeatertruck »

You're not the first person to get caught out by thinking .003 or some such number is too small to make a difference.

When you think about it; it doesn't seem possible -- but that's because we're not used to thinking of these things as inter-related systems. We tend to treat them as separated and if we set this to the book and that to the book it should work -- right? But, the reality is that the book is a guide not the law and the real world kinda doesn't care about theory.

In this case, the points cam is essentially a half time cam and the Sprints open points every time we reach TDC.

If your spark advance for a 69-72 is 15/64 or .234 -- just how much movement on the points would it take to make a big swing on the point where they actually open?

Let's just play with this a moment. .234 = 28 degrees and .015 = 7 degrees (the fully retarded setting). Our total swing is .219 inches before TDC (.234 minus .015).

.219 therefore = 21 degrees of movement. .219 divided by 21 = .01 inches for every degree. Toss in the complications of where the piston actually is and where the actual advance mechanism weights might be . . .and suddenly you realize that a very tiny movement can yield a big result.

Wait till you get to playing with valve lash :-)
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Re: Aermacchi ss350 timing question

#13

Post by 6hds »

Chuck, In my quest for knowledge about these Italian wonders I talked to "the man" today. Ron lancaster, the Aermacchi flat track and road racing legend in Illinois. I wanted to find out for sure if the motor was done by him, as the previous owner claimed. Unfortunately, He said he goes by names and doesn't keep records past a couple years and doesn't record vin numbers either. Looking in every hole of this motor looks like new, so someone did a complete job here. My efforts to contact the the pre-previous owner are next. The shop manual pics that confused me about the year was straightened out by him. He said all 73's are 12v, electric start and 5 speed. So its a 72 for sure, including the frame. The numbers confirm this. Also the shop manual has a lot of errors that were fixed by "bulletins" to dealers. And Aermacchi wasn't afraid to make engineering changes in the middle of the year. Think about it, this was in the middle of the AMF years too. I don't fault the product, as I have 2 other AMF bikes, and their great. It was the bowing alley management that is to blame. Since I have to replace the shocks, so I think I'll go with something between 11 and 12" as I'd rather have it lower than higher, and i know theirs fender clearance down to about 9 1/4". I asked him about points and valve settings. Without reservation he said .016 and about .003 works for him. I'm looking to start it this weekend. Yippee! Thanks for all your info. Gary
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