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Clamshell timing advance

motorhead99999

motorhead99999

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does a timing advance make a noticeable difference with the ms 290 ,310, or 390s. Just wondering if it’s worth my time doing it to my 290 or 390. Both are muffler modded. The 390 has a pop up piston in it.
 
Huskybill

Huskybill

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When working with tapered shafts its actually the mating tapers that holds the shaft in place. The key is insurance the the two mating parts won’t miss aline. I would lap the shafts together first. Then clean and assemble with the offset key.

On the Swedish dirtbikes there is no keyway on the tapered primary output shaft. The correct torque on this taper holds it.
 
Old2stroke

Old2stroke

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Depending on the diameter of the crank, removing 0.010" off the key should give about 5 degrees change in timing. When modifying timing, it is a good idea to make marks on the cylinder and the clutch body (not the flywheel) where TDC is and use a timing light to know where you are starting from, then you will know for sure what your changes have done. Just remove the spark plug and ground the side electrode with a test lead and run the saw with a variable speed drill turning in the NORMAL direction of rotation of the engine. Many people have said that the key doesn't have to be there to hold the flywheel in place and this is generally true but if you are experimenting and haven't seated the FW as well as it should be and then try to start an engine with to much advance, it can kick back against the starter hard enough to move the FW. If you have removed the key and your timing changes haven't done what you expected, recheck with a timing light.
 
dmb2613

dmb2613

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When working with tapered shafts its actually the mating tapers that holds the shaft in place. The key is insurance the the two mating parts won’t miss aline. I would lap the shafts together first. Then clean and assemble with the offset key.

On the Swedish dirtbikes there is no keyway on the tapered primary output shaft. The correct torque on this taper holds it.
The key is made to the flywheel on the 1127 series saws no such thing as an offset key for one of these you are correct however in that the taper holds the flywheel stationary on the shaft.
 
dmb2613

dmb2613

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OP, don't take every thing you read as the gospel , there are a lot of armchair quarterbacks posting on the internet
I have only done 35 or 40 of these 390 popup builds , so I could be wrong too. But I have only been wrong once in my life and I was mistaken then lol
 
huskihl

huskihl

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Help me understand there are different ways to advance the timing. Are you talking about filing the key way slot in the flywheel?
Have you looked at the fly wheel in your 350? It’s very similar to what this gentleman has. The key is cast along with the fly wheel at the same time. It’s part of the fly wheel. File part of it away, assemble it, and tighten the nut
 
Huskybill

Huskybill

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Ok the key is part of the flywheel I forgot about that. So they file off 25% of the key to advance it. Old age and brain fade strikes again.
 
dmb2613

dmb2613

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Bill, if you are not sure of something please don't post it, that will only confuse the OP , that will help no one
 
motorhead99999

motorhead99999

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Iv done some work on a couple different 1127 saws And know the key is casted in the flywheel. THAts why I was curious as to wether or not it’s worth doing and risk messing up the flywheel. Like mentioned above I can make some marks for original timing if it doesn’t go good. I did the timing bump on my ms660 because it was a key and I had more so I wasn’t worried about it. Thank you for the input.
 
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