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JLO / Cuyuna twin cylinder timing hints. (Read 2938 times)
restomajic
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Show the link to this post JLO / Cuyuna twin cylinder timing hints.
10/11/04 at 7:25am
 
On another forum I answered a few JLO / Cuyuna timing questions and I thought it might help someone here.


Cuyunas [and JLOs ] are quite particular about the way the timing is set. You did all the things that would get another brand of engine running, but a Cuyuna is going to test your skills. I will give you a list of pointers I have found neccesary. (1) It is impossible to clean the points properly while they are in the magneto plate. Take them out and hold them up to the light. If the two surfaces of the contact area are not perfectly flat and mated correctly, they are junk. It is impossilbe to file them back to proper shape. Others may tell you it is, but trust me, you can't. (2) Cuyuna timing can NOT be properly done while working through the flywheel unless you have many hours of practice. The factory timing marks on the outer fan housing will only help if the sled is getting brite blue spark on both sides.(3) Most brands of replacement points do not fit properly. Bosch is the only way to go. The other brands of points often use a larger pivot plate that interferes with the end of the magnet or won't sit flat against the magneto plate. Yes, I know Bosch doesn't make the points anymore. Beg borrow or steal some at the next swap meet. (4) You will need to follow the factory procedure using a dial indicator, continuity light and some sort of tool to hold the advance arm back while the timing is adjusted. The correct procedure requires setting the initial gap, checking the number one side for opening at the proper distance BTDC by turning the magneto plate. Then you must repeat the whole deal again for the number two side except for turning the mag plate. (5) Early books tell you to remove the heads, but I have never had trouble using the dial indicator through the plug hole. Canted plug heads will require removal [Cuyuna didn't use them , if I remember corretly.](6) The advance cam inside the flywheel is often rusty. It must be cleaned off, or replaced if it is heavily pitted. (7) Get an old pillow case or other lint-free cloth and wipe out the flywheel to remove any small particles the have been attracted to the magnets. This will be a PAIN IN THE A$$. It must be cleaned completely, including picking out every last piece of dust dirt and lint. Inspect for broken or chipped magnets. Small chips on the edges [less than 3/16ths"] are probably OK but cracked magnets mean the flywheel is junk. [8] Number one cylinder IS the PTO [ Clutch ] side. (9) I usually change the condensors while I am in there, but it is probably not neccesary. (10) Clean everything with a good electronic cleaner. (11) Even though wires look good, they must be checked for continuity with a testlight or multimeter. (12) Give up and sell me the sled at an outrageously cheap price! LOL. [ Sorry, I was just trying to see if you were still paying attention.]

These hints will also work with most other brands that used the Bosch magneto assemblies.

I have a scan of the JLO service manual that I can e-mail you if you need it. Contact me at: Skiwhizrescue1@yahoo.com
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Show the link to this post Re: JLO / Cuyuna twin cylinder timing hints.
Reply #1 - 10/11/04 at 12:46pm
 
Gary,

In regards to #2, is it possible to time a JLO (old flywheel fan type) without the flywheel on? My other sleds need to have the flywheel on for the cam to work.
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restomajic
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Reply #2 - 10/11/04 at 5:21pm
 
Jim,

To be truthful, I have never had a flywheel fan twin apart. I just removed one today for safekeeping and haven't torn into it. A quick look in the parts book makes it look very much like the later axial fan versions. The trick with the later engines is to have an extra cam. [ Even a rusty one will work. ] I take off the flywheel and slide the spare cam on the shaft. The cams are a very close fit and allow you to set the initial point gap fairly accurately. Just set the follower on the top of the lobe and set the points with a feeler gauge. In a pinch, the cam can be removed from the flywheel, just make sure you use Loc-tite when you reinstall the retaining screws. Using a spare cam also eliminates the need for the advance arm tool.

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Show the link to this post Re: JLO / Cuyuna twin cylinder timing hints.
Reply #3 - 01/09/06 at 12:55pm
 
Mine is a 74 400 Rockwell. I put new points in it along with crank seals. It has spark and runs but has no power. It will idle for 30-60 seconds and then quits. It seems to spit and sputter quite a bit, but it doesn't seem to be back firing. Any ideas? Thanks
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Reply #4 - 01/10/06 at 4:06am
 
As much as I hate to say this, it sounds like leaking seals or gaskets to me. Look at these two pages for the factory recommended procedure for testing the crankcase for leaks. The Cuyuna has a bolt on exhaust manifold, while the JLO has tube style exhaust ports. This will require a couple of rubber plugs. I use some expandable type freeze plugs designed for automotive use.

http://www.ultralightnews.com/cuyuna/page28.htm

http://www.ultralightnews.com/cuyuna/page29.htm
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Show the link to this post Re: JLO / Cuyuna twin cylinder timing hints.
Reply #5 - 01/17/06 at 9:59am
 
I ordered a complete gasket and seal kit. Are there any things to look for while rebuilding. Are these engines known for warped crank cases or anything unusual. The motor only has 650 miles on it. Thanks for the tips.
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Show the link to this post Re: JLO / Cuyuna twin cylinder timing hints.
Reply #6 - 01/17/06 at 8:04pm
 
When the seals arrive make sure they are flexable. Quite often seals will harden on the shelf. You should be able to easily distort the inner lip and it should return to original shape quickly. Lube them with grease when you install them.

The cases should be checked for flatness but I rarely find major problems. I smooth out any dents or dings I find by rubbing it on a piece of 400 wet dry sandpaper glued to a piece of plate glass.

Buy a new tube of sealer. Don't try to use a partial tube.

Follow the factory procedure for cylinder height and pressure test before starting the rebult engine.

Premium fuel, Premium fuel, Premium fuel, Premium fuel, Premium fuel. Don't forget.... Premium fuel.
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Reply #7 - 01/24/06 at 9:38pm
 
I put all the gaskets and seals in. It runs the same. I have to feather the thottle to keep it running. The pto side does not seem to get hot like the mag side. When we pulled the pto side plug wire, it ran about the same. When we pulled the mag side wire, it ran, but even worse. I have NGK B8ES spark plugs in it, but I think it takes B7ES, which cross references to Champion N3C. Would that make much of a difference? Also, what is the exact fuel/oil ratio. I do not have premium gas in it, but should tomorrow. Any last ideas, I'm about ready to give up on this motor. Thanks (motor No. 2F-400-7)
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Show the link to this post Re: JLO / Cuyuna twin cylinder timing hints.
Reply #8 - 01/25/06 at 4:33am
 
Yes, get some premium fuel and the correct heat range plugs and try that. Have you tested the crankcase as discribed above? If you have, that eliminates the seals and gaskets as the problem. Check the plug caps and wires. Start the engine and touch the wires and caps with your bare hands to confirm they are good. I would mix the fuel at 40 to1 and avoid oil that you find on the shelf at the gas station. I prefer Amsoil or Arctic Cat oil, but use Castrol in a pinch. I do not like Mobil or Valvoline oils, not because they don't work, because they leave so much more residue behind in the engine and in the fuel tank in left over the summer.

NGK plugs get colder as the number goes up. This is opposite of the other brands.
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Show the link to this post Re: JLO / Cuyuna twin cylinder timing hints.
Reply #9 - 02/01/06 at 8:39pm
 
Could you give me some info. on the timing specs. I'm pretty sure the timing is off. Also, do you know what the point gap should be. Thanks
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