I have a Scag Cheetah with a Briggs and Stratton engine. When I've been cutting for a few hours and I stop the engine I often find that the battery does not have enough power to crank the engine to restart. I've taken to putting the battery on charge when I finish. I see the amp meter registering +2V while idling but when I engage the PTO it drops to -2V - I presume the amp meter should be registering positive volts at all time.
Does the amp meter reading point to any particular fault?
Thanks for that although, while it's obvioulsy very comprehensive, it looks like a daunting read! Given the amp meter reading any recomendation as to where I should start the diagnosis process?
Start by first identifying which charging system you have, look at the color of wires and connectors you have on your engine. Then test the voltage regulator and stator according to the appropriate procedure. This will tell you if the charging system is working properly. Disregard you Amp meter at this time and post what you find.
Crank it up check the charging see what you have. Then leave your meter on and then pull pto and check to see what you have. If it's not charging look under the key switch panel and look to see if you have a yellow wire that might be burnt. If it is charging and you pull the pto the discharges might be look at a bad clutch.
My wiring is 10 or 16 amp regulated (page 16) of the pdf.
However, it is not clear to me where I can find "test the voltage regulator and stator according to the appropriate procedure" in the pdf. Could you point me to page number?
Luftydog - in rereading my early post I may not have been clear: by "at rest" I simply mean engine off. by "running" I mean egine on.
Yes I thought so. So it charging. I would test the clutch ohms at this point and a draw test on the clutch but at this point we already know that it is drawing too many amps!!! Everything pointing to a bad clutch so far. But make sure to ohms and amp test it just that one extra step. Those test depending on what clutch you have. Like gt1,gt1a,gt2 ohms should 2.8-3.2 and some more gt2.5,gt3.5,gt5 2.0-2.4!!! To low is bad as well as to high in those numbers. Check those out and if things don't like right I'll give you the amp draw readings and specs. These numbers are based on the wiring in the us so you might have to covert If needed. Also check and make sure your ground is good. Just remembered the ohms test must be done when cool.
Hi Rivits,
Thanks for the document. It's a piece of gold! I will take a closer look tomorrow but it certainly points me in the right direction.
Hi Luftydog,
Thanks for the info. Funny you should mention the GTx.x numbers as it made me remember the PTO and Clutch are one of the same! I had the PTO replaced in July last year and remeber its part number was GT something - I've just done a web search on GT3.5 and there was the Ogura products line that I remember buying! Maybe something has come adrift in the PTO area.
Again, many thanks to you both - I'm well underway now with the diagnostic part. I will post when I determine the problem.
Well I determined that my mower provides 29.6 volts (page 7.10) and is therefore a 16 amp system. Unfortunately testing such a system requires a DC shunt tool which I don't have. Do I need that tool to take my testing further?
Hi Luftydog,
My ohms reading was 2.2 which is correct for GT3.5 clutch. I'm pretty sure this is what I bought and that's definately the clutch which Scag specifies. Unfortunately the amps test was a failure: there is a two wire lead from the clutch to a connector from the wiring harness - the connector has a black and two blue (connected) wires. With the engine running and clutch engaged / disengaged I failed to get any amp reading. I presume this isn't possible and somehow my meter probes aren't making a good contact. However, before I take this further, can you just confirm a zero reading isn't possible.
2.2 is on the low side have to make a jumper to the connector and use meter to complete the connection in between them have to move the meter to amps as well. All you have to do is make the connection and turn the key and pull pto don't have to run engine.
Thanks for the response although I'm not fully understanding this part "have to make a jumper to the connector and use meter to complete the connection in between them". Are you telling me to disconnect the clutch cable from the wiring harness connector then join the two cables using a home made cable long enough for me to meter the clutch more easily and knowing I have a solid connection when I attach the meter?
No I haven't checked the condition of the battery but will do so. I did notice in one of the screen shots you sent that possible causes included a faulty battery and I did plan on following that clue today. The screen shot also mentioned a coil and a switch. In my case I presume the coil is actually the armature so I presume I should be inspecting those and checking the air gap, correct? What is the "switch" that I should also be checking and how should I check it?
Am I right in thinking my amp reading can be regarded as "significantly below" the expected amps?
Not the armature they talking about the air gap in the clutch itself that coil windings. Right off thinking .004 or four thousandths. In us. But if you look at the 3.5 closely it says above or below those numbers. You tested yours and by the numbers it is below specs assuming your battery is good from a load test and that it is charging correctly your clutch is under those numbers. Make sure you have a good ground from battery to engine make sure is tight and good contact. Take your voltmeter from pos to the battery and black to the block and check more than one place to make sure the ground is good. In all cases in the scags always start by checking the ground first it's a lot of causes to their failures. For the switch they are talking about in the pic is the pto switch. If everything checks out good like the battery charging double check the numbers in both test for the clutch mainly the draw test. Far as testing the switch should be able to ohm it out for continuity should open and close for that power to flow to the clutch. Might have to pull the book to see just how to test just the switch. I have seen a lot of them being replaced because the clutch is burning them out. So if your replacing switches the clutch just might be your issues. Double check those numbers closely and look back at the chart just to make sure yours is within specs. Hope this helps you out. Your very welcome and appreciate your patience it's hard to explain and solve issues at times through words on the intertrap or intercrap. Lol
Great - will have a closer look at all of this over the weekend. My ground is ok - its the first I did when I started looking at this issue. I've been caught before with "odd things happening" only to find the ground was flaky.
I've checked out the battery by simply buying a new one - the one in the Scag is the original and over four years old so maybe time for a replacement anyway.
Will let you know how things progress.
For those which may read this thread in the future here are two interesting B&S documents I stumpled across:
That made me think about also the Briggs big block vanguard will take a different clutch and it will not come out and show you this in the ipls. For some reason they take a bigger clutch and I forget how to find it. Think it might show two with different numbers and for the two it will or may not show the clutch I heard a lot of times of them putting the wrong clutch on and it going out and then it comes back smoked. Have seen and heard of this also burning up the stator and regulator at times.
But wouldn't Scag have all this sorted, i.e. the clutch they specifiy in the Scag parts list is appropriate for the engine and the job it will be doing?
Best I can remember it has to do with the voltage and amp draw that makes them different and they show them but have to be looked up different best I can remember. But the big blocks do call for a different clutch than just some other Briggs or Kawasaki or Kohler's.
Fixed!! I think - at least the sympton has gone away - the battery no longer discharges while mowing. The fix was the new battery - it seems the original would take a charge using a trickle charge overnight but would not do so while mowing.
My readings haven't changed though: 2.3 Ohms and 4.85 amps.
I checked the air gap on the clutch and that was definately out - more like 0.0024 rather than 0.0015. So I will make sure I check and adjust that from now on.
Again, your patience and knowledge has been very much appreciated. If you are ever in Adelaide let me buy you a steak and a nice bottle of red!
Thanks for your patience as well. Also thank you for the updates and what the cause was in your case as it might be all cases as we know. If I ever get that way will def. let you know I don't fly or do boats either so that kinda says something but like to see other places. Stay In touch. Cheers ?
Might be little more detailed here and more how to directions. Sorry about the double posting give this a go