Need Help identifying this old tach

It looks like there is a part number starting with a 4H under where it says Caterpillar Tractor Co. on the face, but the rest of the number is obscured by the needle, if you can post that number we may be able to help.

Hi Josh,
cannot help with what it was fitted to but most common was wheel tractor scrapers in early days, and On and Off Hi-way trucks later on--maybe other applications I have missed.
With the RED Tell-Tale Needle, the Dirt Boss could keep an eye on scraper drivers etc. by re-setting the tach with a key thru the swinging cover on the side of the body.
The Tell-Tale needle cannot go past the Stop Pin at 12 o'clock so if an operator really oversped the engine that is the highest read reading!!!!
The T-T needle is at about or just above the reset speed as shown in your pictures. Cannot re-call if they go back to zero or not.

Also these Tach's were available to retro-fit or as an Attachment for Track Tractors etc.
Could also be used in Industrial applications.
They would normally be used where there was danger of operator abuse from overspeeding--ie, travelling downhill in too high a gear etc. and not controlling the engine speed.
Cheers,
Eddie B.

We operated several Caterpillar 619 Motor Scrapers fitted with Jones tachometer in the sixties,

Lou McMaster
Hickory, Pa.

It looks like it came off of a scraper from the 60's. The tattle tale usually was pinned at apx. 2,200 RPM and would only go higher if the engine was over-revved. Does it have a place to insert a key in the chrome round cover on the side of the tach? That was to reset the tattle tale back to the apx. 2,200RPM mark.

In the '70's an operator I worked with was dispatched to a jobsite to find a brand new 631 scraper to run. He immediately reached up in behind the tach and the tach key was still there. He helped himself to it and made copies. I was the recipient of a copy which saved my ass a couple of times for over revving. Coming down steep grades and if you bounce it will over rev quickly if your aren't careful.