KAD32 Rev Counter When Compressor is Running

dragoon

dragoon

Well-Known Member
Joined
13 Oct 2003
Messages
1,744
Location
Gosport
Visit site
Hi,

I was helping a friend today with his boat. He has twin KAD32's, but one of them has a strange fault.

When the engine reaches the speed where the compressor clutch kicks in, the rev counter suddenly drops to 1500 RPM (but the engine itself doesn't).

The RPM stays at that (on the guage), until the engine revs are high enough for the clutch to kick out again, and then the RPM suddenly goes back to that of the engine.

I've checked the obvious - connections on the sender of the engine etc. There seems to be some gubbins on top of the motor in a black box related to the function of the compressor (a relay, a fuse and a dedicated box with a speed control potentiomenter) - this all looks okay in that it's clean and no water has got in.

Any ideas as to what the problem could be?

Cheers,
Paul
 
Bear in mind that on a KAD32, the small lower flat belt between the crank and the circulation pump drives pretty much all the ancillaries via pulleys and other belts (except the power steering pump).

And, maximum load on that belt will be when the supercharger kicks in.

Also, the rev counter measures speed from the alternator.

SO, if that little flat belt is slipping either cos it isn't tensioned correctly or cos the ribs are worn, I'd expect to see what you are seeing: it means that the circulation pump, alternator, supercharger etc. are all slowing down as the belt slips when the supercharger kicks in.

dv.
 
evening s28. as a 32 owner i ALLWAYS want to know all, and more, about it. so here goes. i take fully what you say about the belts, but would,nt the super running at halfish revs cause the engine to show black smoke as it gasps for more air? sorry in advance if its a stupid question.
 
Maybe, maybe not.

With twin engines and one working at 100% you might not notice a big difference as the turbo kicks in around 2000rpm anyway. The acceleration would be slower, though.

The 150hp version of the AD31 doesn't even have a supercharger, and two of them power an S28 nicely too.

With a single I think you would definitely notice.

Of course, I could be wrong, and it could be something completely different!!!

dv.
 
just a general point when mine started to slip once, off durrdle door, if memory working, the squeal could be heard in jersey! it turned out the idler pulley lock nut worked loose.
 
I haven't read the other posts so forgive me if it's already been said:

It's belt slip, simple as. As I saw above, it's most likely the circulation belt as it drive everything, huge load on it when the charger is running. Run your engine for a few minutes to warm up the belts, and tighten them up a bit (not too tight though) and the problem will disappear. Was happening me for a few weeks there, but I knew why it was happening and belt slip wasn't excessive, but since I tightened up the belt (Only the circulation needed tightening) the problem went away

So what the heck does this have to do with RPM? Well, as S28 states, the RPM gauges sources it's info from the alternator, so if the circulation belt is slipping, everything else (servo, charger, alternator) aren't running as fast as the engine is

Hope this helps
 
The RPM sensor comes off the compressor. It's a tooth counter device. The symptom you describe could be the electro magnetic clutch on the compressor slipping before it finally grips. I had the same problem and replaced the clutch mechanism (which unfortunatly comes as a complete unit with the electro magnetic bit) for about £300. The job was quite easy (with the right circlip pliers) and very sucessful.

in addition the RPM sensor is for the compressor engine speed relay only, not to be confused with the RPM signal for the rev counter which comes from the W on the alternator as explained above.
 
>The RPM sensor comes off the compressor.
Huh? Wrong! At least on a KAD32.

There is no rpm sensor on the compressor.

There is an rpm sensor on the timing case which acts off the gear teeth, but it is used to figure out whether to engage the compressor or not. This sensor does not drive the rev counter. The rev counter is driven by the alternator.

dv.
 
Thanks to all who replied.

S28, thanks for explaining how it works - now I understand it more, as I had incorrectly assumed the sensor for the compressor and the RPM gauge were all from the sender on top of the timing case.

Thinking about it, there was a brief squeal as the compressor engaged which I thought could be normal and/or the sound of the clutch itself.

I'll bet it's the belt. If it's not, we can try Wiggo's suggestion of swapping the speed control relays.

It will be a couple of weeks before we know now as he's not down at the boat for a while.


Cheers,
Paul
 
morning. in my case, the clutch makes a positive clonk when switching on or off. ANY type of squeal how ever long or loud etc SHOUTS..........check the belts first!!!!!!........... if it turns im wrong im quite happy to have my head sawn off in public.
 
As soon as I started reading the first post I was thinking 'check the belts' Moving down the other posts it was getting louder in my mind and your post finally said it 'ITS THE BELTS'
Just for peace of mind I check the tension on mine about every 6 months knowing what problems can arise from them, it also gives you a chance to inspect them.
 
[ QUOTE ]
As soon as I started reading the first post I was thinking 'check the belts' Moving down the other posts it was getting louder in my mind and your post finally said it 'ITS THE BELTS'
Just for peace of mind I check the tension on mine about every 6 months knowing what problems can arise from them, it also gives you a chance to inspect them.

[/ QUOTE ]

A tip I got from a KAD owner when I first got one was to regularly check the belts, it was good advise! It's only fair to assume that the circulation belt doesn't last too long in these engines (esp if loose) as it's driving a LOT when the charger is engaged
 
Im afraid I have to add this as its down to my experience.

The drop in revs on the counter is down to voltage drop in the system, basically ive had this problem, its a short in the clutch compressor and sooner than later the fuse will blow or the black box fail due to overload, it simply burns out the relay inside.

The problem is in the coil, fit a new clutch and it will be fine.
 
I did say it could be something else /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif

The way to find out for sure would be to swap the clutch to the other engine, and see if the problem moves with the clutch.

...having checked the belts!

dv.
 
[ QUOTE ]
The drop in revs on the counter is down to voltage drop in the system, basically ive had this problem, its a short in the clutch compressor and sooner than later the fuse will blow or the black box fail due to overload, it simply burns out the relay inside.
The problem is in the coil, fit a new clutch and it will be fine.

[/ QUOTE ]
Paul, I had this problem on a KAD43 a couple of years back (which you helped me with on this forum) The black box had previously failed which was replaced on guarantee. I had, shortly after this, the telltail RPM drop and replaced the coil and clutch assembly which solved that problem. The interesting thing was that the coil was in perfect condition and there was no shorting out or earthing but the problem was solved. Is there anything else that can cause the problem because a couple of years on and it's starting to show again.
 
That's some interesting reading - good thing I tightened my belts before reading this or you'd have made me rightly paranoid!
 
You must log in or register to reply here.

Share this page

Top