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8N gear or speed to run bush hog 540 PTO RPM's?

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Porter, Michiga

07-27-2003 08:04:37




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I've tried running it in first gear, throttle wide open, but the output of the PTO doesn't seem to be sufficient. I have 4' King Kutter bush hog mowing heavy weeds. If I try to run in second gear, will I be going too fast to do an efficient job of cutting the weeds down? Will running in second gear increase the PTO output? I'm new at this and would appreciate any info on this subject!! Thank you!

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Ron -TX

07-27-2003 22:20:15




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 Re: 8N gear or speed to run bush hog 540 PTO RPM's in reply to Porter, Michigan, 07-27-2003 08:04:37  
Porter,
Is your King Kutter new? I had a similar problem with my 8N using a Rhino 5' cutter. I checked the oil in the gear case of the cutter, and it was very low. Filled with 90wt gear oil, and haven't had a problem since. I bought both the 8N and Rhino together and both were used. Also if the weeds are high, you may not be able to cut a full 4' swath. At least I can't when the grass is about 2' high.

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Rob

07-27-2003 09:35:43




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 Re: 8N gear or speed to run bush hog 540 PTO RPM's in reply to Porter, Michigan, 07-27-2003 08:04:37  
Weeds are not a heavy load, a thick stand of healthy grass is a load. Weeds are easy. A 4' mower shouldn't be a problem at any RPM. You have power problems. You need to troubleshoot and fix that tractor.
See if this helps:
There is a quick test you can do from the seat. Warm the tractor to normal operating temp. If it won’t warm up or maintain a constant operating temp then the tstat may be wacked.
Put the tractor in high gear and get her just rolling forward a little bit and at idle and then quickly pull the throttle to 1/2 speed. Do this with your good brake partially on. You want a heavy load on the engine as you give it a lot of gas in high gear. You want to make it pull really hard. If the clutch slips then you’ll have to adjust or replace it.
1. If it backfires the fuel mix is too lean or you have a shorted ignition (pull the spark plug wires one at a time and watch for a regular spark without a miss) or sticky valves (you can hear a sticky valve).
2. Your timing is ok if you hear a constant slight pinging (spark knock). 3. If it doesn't ping set the timing and make sure the mechanical advance is free to operate. I hear that if the wrong screw is used on the points it can interfere with the mechanical advance weights. 4. If it pings excessively then set the timing. If that doesn’t correct the pinging then pull all the plugs, clean em up, and set the gap. While you have them out take a compression test on each cylinder with the carb throttle full open. You are looking for 90psi minimum at starter cranking speed. If you get normal compression then you need to check and set that timing! If you have 140+psi pull the head and clean the carbon off it. Make sure the valve stems are not gummy. Low compression says ‘fix my guts’ or it’s a new rebuild that isn’t broken in yet.
5. If the engine pulls evenly and there is no indication of late spark or excessive carbon, check the system for a lean mixture.
6. If the engine pulls unevenly then check the spark at the spark plug boots.

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david - OR

07-27-2003 09:33:32




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 Re: 8N gear or speed to run bush hog 540 PTO RPM's in reply to Porter, Michigan, 07-27-2003 08:04:37  
PTO RPM is independent of the travel gear selected by the tractor transmission.

An 8N engine should be able to power a 4' bush hog through almost anything (in first gear) short of 3 inch diameter trees. 1800 RPM or thereabouts is appropriate to get 540 RPM PTO speed.

Full throttle (2200 RPM) is overspeeding the bush hog unless you have a step-down Sherman.

Selecting a higher gear increases the horsepower required because you are cutting more weeds per unit time. The engine will bog down more, not less.

If the grass/weeds are relatively light, second gear makes the job go a little faster.

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max

07-27-2003 09:24:25




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 Re: 8N gear or speed to run bush hog 540 PTO RPM's in reply to Porter, Michigan, 07-27-2003 08:04:37  
Porter
You don't want to brushhog in second gear with the 8n. Could lose the gear.



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Rlach

07-27-2003 09:11:31




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 Re: 8N gear or speed to run bush hog 540 PTO RPM's in reply to Porter, Michigan, 07-27-2003 08:04:37  
If my memory is good, the 8N engine must be operated at 1580 rpm to obtain 540(or is it 536 ?) pto rpm. Pto rpm is directly related to engine rpm, not to ground speed. These numbers could be different if a Sherman step-up/step-down or similar auxilliary tranny are installed in the tractor. Also from the original proof meter book that came with the 8N 1952, the maximum engine torque occurs between 1500 and 1700 engine rpm(again if my memory is good because I do not have the booklet here now). This means that if you operate the tractor at full throttle you are well over 540 pto rpm and less torque is produced there. Anyway, if the load is a bit too much for the engine torque at maximum engine rpm, automatically the engine rpm will decrease to guess it : maximum engine torque rpm. Similarly, this is why a IH 784, 246 CID engine, max. 67 pto HP @ 2200 rpm, 540 pto rpm @2150 engine rpm has a different performance on a given snowblower if you compare it with a MF 275, 248 CID engine, 67 max. pto HP, but gets 540 pto rpm at around 1700 engine rpm. IMHO, the 8N maximum performance should be reached in first gear with throttle 3/4 open. If it doesn't work, i would investigate the 8N engine or the bush hog conditions.
Rlach

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jdchet

07-27-2003 08:31:27




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 Re: 8N gear or speed to run bush hog 540 PTO RPM's in reply to Porter, Michigan, 07-27-2003 08:04:37  
I've found when mowing heavy weeds that my 8N with 5 foot Howse rotary cutter does pretty good at 1/2 to 2/3 throttle in 2nd or 3rd gear, depending on terrain. You may have other issues going on like improper setting of the front height versus rear of deck, maybe engine is tired?



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