MCCULLOCH The official McCulloch thread

fossil · Apr 17, 2018

Weren't there any provisions on the flywheel hub to lock it into the flywheel?

I guess it's better to have the hub break out (maybe from a crack?) than have the flywheel explode. I have a cracked one from a 3700 that looks a little suspect.

heimannm · Apr 18, 2018

It is a little hard to see in this photo, but the insert has some deep knurling in it to help lock it in place. Die casting is an injection molding process where the molten metal is forced into the mold under pressure and would create a very intimate fit with insert. I have never seen another failure like this on any of the other flywheels. I don't remember which but in at least one of the other flywheels I looked at the insert was more of a hex shape, at least the portion you could see. That would certainly solve any rotational issues but they must have done something to lock it in axially as well.

Mark

Heavy · Apr 19, 2018

Points and capacitor get the same rpm as an electronic module? Or they do not work beyond 9,000 rpm because there is a point in the engine that turns faster and the points can not keep up? Regards

heimannm · Apr 19, 2018

I have measured some of the large frame saws over 11,000 RPM with points and condenser. The BP-1 is also a points and condenser saw and will easily make 12,500 RPM. The points are not such a limitation on a single cylinder engine since they only have to open and close once a revolution. On older V8 automotive engines with points ignition they had to open and close 4 time per revolution so at higher RPM there was a point where they started to bounce or "float" causing the engine to cut out.

This was a 640, the top tank gear drive model with the 87 cc engine.

Idle was nice and slow.

Mark

Heavy · Apr 19, 2018

The sp 125 at a maximum rpm is rated I have not found anything in acres? Does something have to do with different blocks? For example, what would a kart block be? regards

Steve · Apr 19, 2018

What exactly are you looking to do? Are you trying to modify the saw to spin high rpms? Or are you just courious the limits of breaker points till they float? I'm confused.

Heavy · Apr 19, 2018

I would like to know if it is true that with an electronic module you get more rpm or what is the limit of the points in rpm? I heard once 16,000 rpm with points but I never believed it because they did not teach a digital tachometer? I hope someone clarifies it.

Steve · Apr 19, 2018

It really depends on the points. With enough spring pressure and light enough points. Extreme high rpms are possible. If you where building a high rpms race machine I would chip it. As far as the mechanical limits of a specific saw I don't know. I've never tached any of my Macs.

Steve · Apr 19, 2018

I don't know if you would instantly gain 3000rpms if you converted to a chip. There are so many factors that contribute to that as well.

Bigmac · Apr 20, 2018

I am no mac expert but have done a lot f reading, and it makes sense, lol, maverick spark, if I have read correctly, is the point when fly wheel timing takes over for the points once the points float. If you think about it a 5 degree mac flywheel cant advance the timing five degrees, unless the points float, points are set by the crankshaft not the flywheel, dose this make sense.. or am I thinking wrong?

Bigmac · Apr 20, 2018

I have read(no practical experience) that kart guys would advance the flywheel even more for alcohol or other reasons by shaving the key, but it would set the points standard and once the points would float, the full advance would come on at high rpms...it is interesting to think about, and old school start retart or high rpm advance, either way kind of cool!

Heavy · Apr 20, 2018

The mac sp 125 without modifying it in how many maximum rpm tested with tachometer because before it was made with the ear outside the cut is classified?Regards

Bigmac · Apr 21, 2018

Hi everybody, new to the forum, I am looking for a source for a 797 tank gasket, I can’t seem to find one!

Bigmac · Apr 21, 2018

Bigmac · Apr 21, 2018

sawfun · Apr 22, 2018

Bigmac said:
View attachment 121670 View attachment 121671 View attachment 121672 View attachment 121673

That's a properly setup Mac doing what it does best, very nice to aee. Looks like a 50" ole 3 rivit bar, nice. I've set a few 125's up like that myself. They handle surprisingly well like that and are easier to your ears and body than an 880. Oh yea, way, way more torque too.

Al Smith · Apr 22, 2018

Regarding points and RPM's ,I have a 6-10 Mac,70 cc's with advanced timing that will crank 15,600 RPM and never miss a beat

Bigmac · Apr 22, 2018

Thanks sawfun, you nailed the 50” bar, here is the video of it running, I posted it in the saw video thread too. Probably should have put it here as well!

Bigmac · Apr 22, 2018

sawfun said:
That's a properly setup Mac doing what it does best, very nice to aee. Looks like a 50" ole 3 rivit bar, nice. I've set a few 125's up like that myself. They handle surprisingly well like that and are easier to your ears and body than an 880. Oh yea, way, way more torque too.

I have never ran an 088, would be cool to compare! I want to run my 797 with the 50” to see how it dose, it feels strong!! I also just finish up a kart Mac 101, but I haven’t cut a thing with it yet, just been hear cycling it and getting little bugs worked out! But I am getting excited to try it!!

Lee H · Apr 23, 2018

You have some very nice saws there Bigmac. The 797 will pull a 50 no problem
and you will love the 101 saw. They are a blast to run.

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