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Discussion Starter · #1 ·
As you know the predator 670 has a very limited charging system maybe 2 amps. Now if all you need to do is start the engine you're Ok. With my conversion (Re-power with a twist) I added an electric clutch and recently a winch that needed more amps. The Predator is a Honda GX clone so many parts of the Honda GX series will fit the Predator. This is my experience with changing the Predator flywheel with a Honda GX620 part.

The Predator stock flywheel is the problem! It only as three magnets so minimal amps are produced! The Honda engines have several charging amp options so its important to know the difference in how each option works. You need a flywheel that has 6 magnets to achieve high amps. I think these are the Honda part numbers for the two types available.

  • Flywheel (3 Magnets) 31110-ZJ1-850
  • Flywheel (6 Magnets) 31110-ZJ1-840

I found a used Honda GX620 flywheel with 6 magnets on ebay for $70. It looks to be a direct fit but the ignition magnet is not in the same location as the Predator!

20171025_154024.jpg
Honda on the left, Predator on the right. Note the Predator casting fills in where the extra magnets would go. My initial hope was it would be an empty space between magnets and you could just add three more. I envisioned selling a kit with magnets and epoxy to every Predator owner!

A sideline question: Do you think the extra casting between magnets harms the production of current in the coils? I personaly think so.

20171025_160618.jpg
Honda on the bottom. In this pic the key-ways are lined up and the obvious difference in the ignition magnet position. Not sure of the actual degrees, but if someone needs to know I can look into calculating it.

20171025_164500.jpg
In this pic the ignition magnets are lined up and you can see the difference in the key-way location. Its off by the width of the key-way.

This is where I could use some help! Seems to me the only way to correct or modify timing is to mount the flywheel in a location other than the keyed slot. I see on other sites competition type users (any small engine) will do this to gain a few HP's. This seems almost impossible! What do you do mount and remount the flywheel multiple times till you think you have it right?

Anyway I just eyeballed the difference as seen in the pictures to be one width of the key-way. Although I don't think is necessary I notched a key-way in the end of the crank so a modified key can be inserted.

20171025_170148.jpg

All worked good the engine started as normal!

The results!
Initially (old flywheel) the battery has around 12.25 volt on start and with the engine at 3000 rpm I would see a very slow increase of voltage to 13v (max).
With the new 6 magnet flywheel the voltage immediately jumped to 13.5v at high idle and increased with more RPM's
Sorry I don't have actual amp readings. It was late and didn't have time. Just a simple voltage check is enough for me that its working.

Other notes:
I also purchased the charge coil assembly for a Honda 620 and did not see any difference in that assembly visually. I don't think there is any reason to change this! I'm still running the factory Predator coils.

The voltage regulator is something I modified, but don't know how it affected the outcome since it did it before the flywheel change. I would say this should be done as you are adding more AMPS to the system. The regulator is only using only three wires and had 5 (two are cut off). One cut wire is the DC output and I spliced in another wire to handle the new amps.

I tried uploading pics of the regulator but its not working, I'll try later
 

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Discussion Starter · #2 ·
Regulator mods

reg3.jpg
The Predator regulator is only using three of the five wires on the unit (2 AC inputs and +B out). Although I don't know 100% whats behind the two unused leads, the one unused red wire ohms out to the +B red wire. It also was producing the same voltage as the +B so one assumes its +B too. This is good as the new flywheel setup is producing more current so the additional wire will help.

Its cut really short, but I was able to exact-o it out and solder a 14 gauge wire in. That runs parallel to the other red +B wire back to the termination point and fuse. I'm thinking one could add more wire past the fuse and to the battery terminal too.

reg1.jpg
A glob of silicone sealed the deal. One note and not pictured is a metallic gasket that was between the engine and the regulator. It is conductive and can cause a short to the new wire. I trimmed it back so this can't happen. I also added star washers to the mounting screws so the ground to the regulator body was solid.
 

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Discussion Starter · #3 ·
Had a chance to hook up my amp meter this morning and it has a limit of 10 amps. Just after start up it was maxed out, and soon after returned to 5 amps. Turned on the deck electric clutch and back up to 7 amps. Tuned on the winch and it maxed out. From all I know on the 6 magnet flywheel it was form a Honda with a 20 amp system. Sure looks like that's what I have now. Next question will be if the regulator will handle it over time.
 

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Really good thinking out of the box. I would suggest that the real fix for this is to TIG weld the old key way shut in the flywheel, and re-broach the new key way in the correct spot
 

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Discussion Starter · #5 ·
I'm not sure you need to notch the the crank at all. With the tapered shaft the flywheel should be set without the key. I think the only reason to have the key is for timing purposes only. Now I could be wrong that shaft is powering (in most models) your deck and snow blower. If you hit a solid object at full throttle maybe it could rotate the flywheel on the shaft.

I'm more concerned about any imbalance on the crank shaft in my case. (pun intended)
 

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Dan,

I have repaired a number of engines with sheared flywheel keys, from a sudden stop like you mentioned. And they were not driving anything from the fly wheel. And a few that sheared for no apparent reason.

Gordy
 

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Discussion Starter · #7 ·
Charging System Note:

After using the winch / dump bucket yesterday I had a circuit breaker failure on the Predator. The Predator engine comes with a 10 amp breaker that was obviously at its limit popping several times. As noted earlier the new flywheel is producing more than 10 amps so time to change out the stock breaker. For now I simply plugged in a standard 20 amp car type fuse assuming that's the new output limit.

Worked it for at least three hours today with no issues keeping a charge.
 

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This is what I have been considering, this makes sense to me. Now to look for machinist that could do this, might check with local Tech. College. Maybe project for a student?
 

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Discussion Starter · #9 ·
Using a die grinder to notch a new key way worked just fine for me. I have about 150 hours on the engine with zero issues
 

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I bought a gx620 flywheel, I also am borrowing a broach set from a friend. The plan is to weld key way shut and cut new key way. I will try to take some photos and post the results, wish me luck
 

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Just curious in all of this the indexing of the magnet for ignition timing seems to be always handled by new keyway or something, why not just relocate the pickup sending unit to adjust for magnet position?
 
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