Yesterday I had a new noise in my 140, DHC. Awful loud, jatting, incisive noise which sort of came and went away during a 15 min drive. But noisy 80% of the time, Hardly heard with bonnet open, standing on the side. Not a loose rev counter cable connection at the camshaft end. I suspect it might be a loose connection behind the instrument, but thought Íd ask here before removing the under dash cover boards.(It ´ s not the heater fan which I first suspected.
It could be wear inside the mechanism of the rev counter, or maybe simply a lack of lubrication. I had the same thing on my Iso Grifo at one time - almost a squealing sound which came and went intermittantly. A rebuild of the instrument cured it.
You could disconnect the tach cable at the engine end and see what happens.
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Thanks. Robś suggestion is far easier, but I fear that Chris is bang on when he thinks that cleaning and lubricating will sort it. And this might cure the somewhat erratic movement of the needle, which doesn´t move in a smooth, linear way along with the engine revs.
I need to drive it about 350 miles to my summer house, for several reasons. Disconnecting the cable at the engine end might be good, to spare me the noise and potential damage of the instr internals.
A few drops of thin oil poured into the engine end of the cable, held upward at the fire wall hole grommet, could perhaps be a short term remedy…?
I wouldn’t. Oil applied indiscriminately through the cable drive hole of an instrument can do a lot of harm. The correct grade of watch or clock oil should be used, and only applied to specific points in very small quantities.
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Tach and speedo cables are usually lubricated with a graphite solution. It used to come in a little squeeze tube, but since they are all electric now, I don’t know if your local auto parts store will carry it anymore.
Agreed, you don’t want to get a whole lot of oil inside your tach or speedo. One or two drops in the shaft, but that job would be better done on the workbench.
Update: today was the first drive since I posted the problem. Unplugging the C-tek charger, I then grabbed the rev counter cable half way between the firewall and camshaft, and pulled it to the side. Of course it didnt move much, but the noise did not show up during the half hour drive😊
Perhaps the pulling moved the instrument end of the cable by a fraction, or changed the angle of attachment…
We’ll see what happens during the next couple of drives…
I luv it when wiggling something, banging on it, or ignoring it…is the solution.
Nick
If that movement of the cable is all you did and the noise stopped, then I suspect the nut on the tach end of the cable is not fully screwed onto the tach, so yes, it would be at the wrong angle of attachment.
Sadly the noise is back. Losening either alu lick nut did not help. Neither did retightening. Today I did the 350 miles to my summer house, but removed the cable at both ends and withdrew the cable. Might be as suggested above, that the rev counter needs to be removed and sent to a specialist…But before I do that: is the cable suppoaed to have this 8mm play? I can easily pull the wire back and forth inside the outercable.
Any assistance on this is much appreciated. The cable looks quite new
Peder,
Was there maybe a small washer missing at the end of the shaft to hold the nylon end in when the nut was tightened up. It seems that is spinning and should be held tight.
Matt
If the rev counter has been working all along and not intermittently with the movement of the inner cable, then I’d be inclined to suspect the instrument itself. I’ve experienced horrible sqealing from a rev counter in the past, which sounded like a dry bearing or something. A rebuild cured it. As long as the cable engages reliably at each end I wouldn’t worry too much about the cable itself.
I would suspect the cable. Mine has about 1 mm of axial or end play and it is the original.
Forgot to mention: the alu locking nut where cable enters rev counter gets very hot. Thats why I removed the cable the other day, prior to my 350 mile drive.
Today I put thecable back, and within munutes of idling, that nut isbeginning to get hot…
Very strange. With cable out, it turns very nicely inside the iuter tube!
Hot shaft bearing. Did you try squirting a shot of WD40 oil into the drive socket?
No. You mean at the instrument end of the cable?
I mean the bearing in the tach.
It’s a round shaft with a square hole, rotating inside the round protrusion with the threads on the outside.
If it was dry it would certainly make a squeeky noise.
Peder,
If that nylon bush is spinning in the housing then the friction will heat up the nut at exactly the spot you are saying. Rob, from memory is the bush in your cable free to spin?
Matt