Mac 85-SX 21cc
 

I have a mac 85-Sx Ibeleive it is a 21cc but not sure.
Iam not getting any spark and I think it is the coil.
Does anyone have one or have any use for this motor?

It is the same motor as displayed in this thread http://www.rcuniverse.com/forum/m_85...tm.htm#8582806

Thanks,
Jeff

RE: Mac 85-SX 21cc
 

I might possibly have a coil if I didn't throw it away. Can you post a good pic or two of the coil?

AV8TOR

RE: Mac 85-SX 21cc
 

Here are the pics of the coil.

Iguess it is also possible that the gap was wronge. I havne't meesed with it and would assume it was in the right location.
Seems like it was set dead center when Ijust took it off to take the pictures.
What should I set the gap to and how can I measure what gap I am putting it at? use a spak glug gauge?

Or possibly it was just very greasy and dirty never thought of that as a possibilty until I took the pics.

RE: Mac 85-SX 21cc
 

The gap of the coil to the magnet of the flywheel should be about 0.020 inch or about the thickness of a matchbook cover. Do not use steel or magnetic metal to set the gap. Brass or plastic or paper is fine.

Regards,

Richard

RE: Mac 85-SX 21cc
 

Sorry, don't have that particular coil. Clean it up good, and the flywheel too. Make sure the grounding lug isn't grounded out somehow. They don't go bad very often, but it is possible. Try a fresh spark plug as well.

AV8TOR

RE: Mac 85-SX 21cc
 

Thanks for looking.
I cleaned both and re gaped it with a business card but it was touching the flywheel when I tried to start it so I gapped it again with a thicker business card and it didn't touch but it still didn't have any spark. http://www.rcuniverse.com/forum/js/f.../sad_smile.gif

What are you refering to when you say grounding lug?

WhenI first tried to get this thing running I noticed the little coil that was connects to the plug was rusted so I sanded it and cleaned it but it had also worked it's way loose of the plug wire which was a little rusted so Icut about a half inch off so get to clean wire.

I am wondering if possibly maybe the wire is bad and maybe not the coil?
Is it possible to check the coil any other way?

RE: Mac 85-SX 21cc
 

I was speaking of the ground terminal that the kill wire hooks to. You ground that wire/terminal to kill the engine. I have seen where that terminal gets bent over against something grounded and then the mag won't have spark.

AV8TOR

RE: Mac 85-SX 21cc
 

Ok that makes more sense, it semed to be ok, I disconnected the kill switch so there shouldn't be anything causing it to ground out.

RE: Mac 85-SX 21cc
 

Ihave a coil being mailed to me keeping my fingers crossed it will get me going!

RE: Mac 85-SX 21cc
 

replaced the coil and the motor now has spark. Have to make some new gaskets and try to fire the engine up this weekend.

I am thinking about using this motor for an airboat but not sure how to connect a prop since there isn't any room unless Iremove the clutch?

RE: Mac 85-SX 21cc
 

does the engine turn counterclockwise from the direction shown above? and does that clutch nut have right hand or left hand threads? if it turns counterclockwise and the threads on the crank are right hand, it's as simple as a standard prop adapter like I've made many of... if left hand threads it's doable but requires pulling the crankshaft and drilling and tapping for a stud. If it turns clockwise from the picture shown you would use the other side and do the same thing.

about spark, you've tried a couple different plugs? set the coil gap with a business card? just checking, it being a stand alone magneto should get spark above a certain rpm...

RE: Mac 85-SX 21cc
 

Sorry it should have said NOWhas SPARK. http://www.rcuniverse.com/forum/js/f...ular_smile.gif

Well I haven't really looked at the rotation of the engine I will have to get back to you on that.
As far as the clutch goes I haven't looked at those threads either should I try to remove it or just look at the threads?

RE: Mac 85-SX 21cc
 

it'll need to be removed if you make it an airboat engine but that nut needs to be there if you try to start it, it looks like there's enough threads visible to see if it's right or left hand threads.

RE: Mac 85-SX 21cc
 

Ok motor spins countrer clockwise and cank threads look to be colockwise.

RE: Mac 85-SX 21cc
 

that makes it easy to make a prop adapter...

RE: Mac 85-SX 21cc
 

Nice thats good to hear! http://www.rcuniverse.com/forum/js/f...ular_smile.gif

RE: Mac 85-SX 21cc
 

What size pusher prop you think I would need?
Someone else recommended a 3 blade prop either 13x8 which might be a little to big or a 10x7 which might be a little to small?
Isaw that tower had a few in the middle of these sizes that might work?

RE: Mac 85-SX 21cc
 

With the engine turning countereclockwise why are you thinking of pusher prop? Pushers do not cool effectively since only the vehicle movement is passing over the engine. A regular tractor prop with the engine facing forward is the best approach, I think.

Good luck.

Sincerely,

Richard

RE: Mac 85-SX 21cc
 

Ilike the way the pushers look rather then a pull setup.
I know a puller cools the engine better but I also have a water cooled head so I could water cool the boat if I wanted.
So with that said which would be best for PULL &PUSH?

RE: Mac 85-SX 21cc
 

With a WC head, water needs to be going through it or the engine wil get hot.

The problem that comes into play is getting the needles set on the carb. After that it is smooth sailing

RE: Mac 85-SX 21cc
 

How is setting the needles a problem? What you mean by that?

RE: Mac 85-SX 21cc
 

Maybe my feeler guages are old, but the three that I have include one blade that is brass, and this was always the one we used to set the air gap on fly wheel maganetos. Guess I am dating myself, but it has worked well for me, most recently I used it to set a Maytag twin off of a gas powered Matag Washing Machine. I also have a variety of weedies and chainsaws, but have converted most of mine to electronic set-ups. I will check my stash (my wife says I never throw anything away) and see if I have a coil that matches your picture.
FLATHEAD::::

RE: Mac 85-SX 21cc
 

It will be stationary as you go through the needle adjusting phase. Most likely start-run-stop-tweek the needle -start again-run-stop-tweek the needles again, etc

If you wait between runs for it to cool down it may be OK?

RE: Mac 85-SX 21cc
 

Thanks but I already have a coil that soeone else gave me and it is now working! http://www.rcuniverse.com/forum/js/f...ular_smile.gif

RE: Mac 85-SX 21cc
 

Oh I see what your saying now. http://www.rcuniverse.com/forum/js/f...ular_smile.gif
In order to tune in the field or while running You can make a water bottle with water outlet in order to help tune while the engine is warm.

If I do not go water cooled and stay air cooled you think it will be ok as a pusher?
Or you think it would get to hot and need the pull prop?