RPM - Am I imagining things?

[jshwhite]

I've got a Kubota L3710. Last time I was out bush hogging I thought the tachometer was reading incorrect RPMs - seemed to be showing higher than it was really running at. I thought I must have been imagining it. Well, I was bush hogging this afternoon and noticed it again. A fair amount of seat time will teach one the "sound" of the relative RPM, and it just sounds like it is running a little lower than it is showing. Is that possible?

Is that possible? Is there a simple/cheap way I can test it? I'm assuming it is a mechanical tach right? If it is off, what could be causing it?

Thanks!

 

[JimRB]

If you come by my house we can try my mechanical tach to your PTO shaft.
Shop for a wide range of tachometers, from non-contact tachometers, panel mount tachometer, laser and strobe tachometers. From manufactureres like Monarch, Electromatic, Checkline, SKF, and more!
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I have one like this by Biddle
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[jshwhite]

If you come by my house we can try my mechanical tach to your PTO shaft.

Thanks for the offer, but I'm afraid it might be a bit far

Thanks for the links. I just ordered the one from Amazon. I have needed one for a long time, but I had no idea they were available so cheap. I'll have it in a couple days and I'll get some answers

So, if it is incorrect, what could be some causes?

 

[jshwhite]

I haven't received the tach yet (tracking shows I should get it tomorrow), but in the meantime this problem has become more frequent and more obvious.

One thing that has helped it become obvious is that it is intermittent. For example, today it was running great while bushhogging and stopped, disengaged the pto, and throttled down. A minute or two later I throttled back up and it's reading 2500 RPM (540pto) but sounds like about 2100rpm. I throttled all the way up to 2900rpm for it to sound like 2500 rpm. I headed to the shop and by the time I got there (several times throttling down and up to go through gates) it was normal

Does anyone have any idea what could be causing this. My first thoughts are something dirty and sticking, or maybe the tach drive slipping?

Thanks.

 

[SPYDERLK]

I haven't received the tach yet (tracking shows I should get it tomorrow), but in the meantime this problem has become more frequent and more obvious.

One thing that has helped it become obvious is that it is intermittent. For example, today it was running great while bushhogging and stopped, disengaged the pto, and throttled down. A minute or two later I throttled back up and it's reading 2500 RPM (540pto) but sounds like about 2100rpm. I throttled all the way up to 2900rpm for it to sound like 2500 rpm. I headed to the shop and by the time I got there (several times throttling down and up to go through gates) it was normal

Does anyone have any idea what could be causing this. My first thoughts are something dirty and sticking, or maybe the tach drive slipping?

Thanks.

Wide open should always be the same rpm. Is it?
larry

 

[BeezFun]

al
Does anyone have any idea what could be causing this. My first thoughts are something dirty and sticking, or maybe the tach drive slipping?

Could the slip clutch on your bush hog be slipping? If it is the hog will be turning at a lower speed and will not sound as loud to you, leading you to believe the engine is running slower. One easy way to tell is (carefully) touch the clutch after you've used it for a bit. It shouldn't be any warmer than the rest of the bush hog.

 

[jshwhite]

Wide open should always be the same rpm. Is it?
larry

I don't run it wide open very often, but as best I remember wide open is about 2800 rpm. Today it showed 2900-3000 rpm (and sounded like 2600).

Could the slip clutch on your bush hog be slipping? If it is the hog will be turning at a lower speed and will not sound as loud to you, leading you to believe the engine is running slower. One easy way to tell is (carefully) touch the clutch after you've used it for a bit. It shouldn't be any warmer than the rest of the bush hog.

That's funny you mention that. Yesterday, for the first time several years, I had a problem with the clutch slipping. I tightened it up though, so no problems there. However, it is definitely the engine I'm hearing, because it has done it a few times without a load, or even without any implement attached.

I did pull the dash enough to get my hand behind it and check where the cable attaches. It was a little loose, so I threaded it finger tight - didn't make any difference.

I can't wait to get my tach tomorrow and see how far it is off. I'll post what I find out.

 

[boomer1025]

I haven't received the tach yet (tracking shows I should get it tomorrow), but in the meantime this problem has become more frequent and more obvious.

One thing that has helped it become obvious is that it is intermittent. For example, today it was running great while bushhogging and stopped, disengaged the pto, and throttled down. A minute or two later I throttled back up and it's reading 2500 RPM (540pto) but sounds like about 2100rpm. I throttled all the way up to 2900rpm for it to sound like 2500 rpm. I headed to the shop and by the time I got there (several times throttling down and up to go through gates) it was normal

Does anyone have any idea what could be causing this. My first thoughts are something dirty and sticking, or maybe the tach drive slipping?

Thanks.

I would say the tach drive cable is dry and needs lubed. Pull the cable, clean it off with some WD 40, then grease it with a light weight grease

 

[jshwhite]

I would say the tach drive cable is dry and needs lubed. Pull the cable, clean it off with some WD 40, then grease it with a light weight grease

OK, thanks for the suggestion. I'll give it a try.

 

[art]

To get behind the dash WD-40 would go down the cable easily. Normally they might jump a bit when this is happening.