TR4/4A Tachometer

shoopal · Jul 3, 2015

I have an RN1517/00 tach and it's making a rubbing noise between the magnet and the little cylinder attached to the needle. I guess that there is a bushing or whatever is in there that is worn. On ebay there is listed a 1319/02 for sale $30 including shipping but the chrome bezel is different.
Does anyone know if I can cannibalize the guts from the 1317 and repair mine?
Thanks
Al

HerronScott · Jul 4, 2015

Hi Al,

Are those typos on the part numbers? I've got the following listed as tachometers for TR4 and TR4A's

RN 1409/02 - Early TR4's with convex glass - TR4 RHD to CT15053, TR4 LHD to CT11307
RN 1417/00

They don't seem to match the TR2-3A part numbers either.

RC163
RN 1402/09
RN 1411/00

Scott

TRopic6 · Jul 4, 2015

Aloha Al,

I found the ad and 1319/02 is for a Spitfire. While there are probably some common parts, the ratio is 3.55-1, same as a TR6. The ratio for TR 3/4 tachs are 2-1 and I don't know how they attain that (weaker magnet?). Maybe the magnetic bar is running too close or at an angle to the alloy cup. Anyway, try to get a spare TR4 tach and take yours apart. Anthony Rhodes has a PDF on "Repairing Jaeger & Smiths Speedometers"; Google that and you'll see how it works. At least tachs are simpler!

Happy Fourth - Jeff

ed_h · Jul 4, 2015

If the tach is similar to a TR6 unit, there would have to be something broken or bent inside for the magnet to scrape the eddy wheel. I don't think a worn bush by itself would cause this. Here is some info and a lot of pics of the inside of a TR6 tach and speedo.

https://bullfire.net/TR6/TR6-40/TR6-40.html

Ed

shoopal · Jul 5, 2015

Hi and aloha to all and thanks for your replies.
My tach is 1417/00 from a 65 TR4a CT61301. Anyway, I took it apart and the grease seemed pretty dry. Not surprising for a 60 year old car.
I will try to reassemble with white lithium grease when the auto supply stores open after the 4th. The bullfire link was really interesting but seems to be an incredible amount of work given that Nisonger will rebuild it (I haven't checked the cost yet but I would guess around $200)
I'll post further info
Al

CJD · Jul 5, 2015

I am sure cleaning it is all you need. The aluminum drum is very fragile, so a slight bend is all it takes to keep it from rubbing the magnet spinner. The speedo is complicated, but there are only 2 moving parts in the tach...so $200 for just a quick clean and lube sounds pretty pricey to me!

At most it's an hour long job. The bearings dry out and make noise or cause a pulsing indication, but I have never seen bearings worn out. I'm sure it's possible, but usually the mechanism locks up and frays the cable long before the bearing goes.

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TR4/4A Tachometer

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