P/N 641531 Tach adapter

[spduffee]

When one of those little parts break in half upon removal you think, "oh dangit. another thing to put on the list". The little part that broke was the tach cable adapter on the back of the accessory case. Little did I know, to replace it will cost upward to $400. One of the great benefits of belonging to this group is that great people offer their help. Aryana came to te rescue right away - was going to ship a spare to me right away; unfortunately, he discovered his too was broken, almost in the same place as mine.... Does anyone out there have one of these little pieces, with which they would like to part? The engine is out for a quick repair and it can't be made airworthy without it. Your assistance in avoiding paying gold prices for aluminum is much appreciated!

[hilltop170]

Wish I could help with the adapter, I have one that I will never use but its 3000 miles away. I haven't checked prices lately but you can probably get a digital tach for about the same price and totally do away with the adapter, cable, firewall penetration, and possibly inaccurate tach itself. The digital tach takes its signal off the mag switch. They come in 2-1/4" and 3-1/8" sizes.

[170C]

Unless you are going for 100% originality, I definitely recommend going the digital tach route. Eliminates oil leaks, tach cable issues and unreliable tachometers.

[bagarre]

Going the digital tach route will probably be the fastest and about the same money ($400.00)

Another idea is to have one made by a local machine shop.
It's a cast part but they should be able to replicate it with billet aluminum on a CNC. Not sure what that would cost tho.

But the digital tach will get you in the air the fastest.

[GAHorn]

How does the digital tach dispense with the tach drive adaptor? If the engine is run without the adaptor you'll have a heck of an oil leak.
Contact EnParts, Lancaster, TX. They sell salvaged engine parts.

[spduffee]

Thanks all for the tips! I had considered the digital route for the reasons mentioned by others. There is also a service called e-machine shop. They have their own software for 3-d modeling which estimates the production cost for you, then you hit "order", et voila. If it were somewhere else other than where oil might leak out, I'd go that route. Late today I finally found a part at Wentworth for $65. I'll try EnParts, too. These little parts kill me! Has anyone ever seen how much one of those flimsy instrument panel bezels cost? Insane! Anyhoo, thanks again!

[c170b53]

I might have one, what's it look like?

[GAHorn]

How does the digital tach dispense with the tach drive adaptor? If the engine is run without the adaptor you'll have a heck of an oil leak.
Contact EnParts, Lancaster, TX. They sell salvaged engine parts.

I've seen a simple screw cap in place of the tach cable to seal it up. But you still need the adapter to make that work.

Yes, that's my point...you cannot simply not have the adaptor....(or something to replace it.)

In ANY CASE, SPDUFFEE, .... be absolutely CERTAIN you also install a NEW seal inside that replacement adaptor or you'll likely still have a heck of a leak. The old seal mated with the old spindle, and unless you install a new seal it'll leak, almost certainly.
Also, remember to orient the seal correctly. The open side of the rubber faces the engine.... Some seals have dual metal covers, but close examine the rubber gland opening to assure it still faces to keep oil inside the engine.

[bagarre]

Could you machine a flat cover plate or does something protrude? (if using a digital tach)

I still think one could make this with a CNC machine pretty quickly. The needed dimensions could be reversed from the broken piece and the design spec of the seal.

It would be a function of patience-vs-cost tho. (wait to find one, pay top dollar for one or pay a shop to make you one)

[GAHorn]

bagarre, the tach drive slips over a slotted spindle which protrudes from the accessory case.

[c170b53]

I think we have a winner

IMG_0114.gif

Not perfect, no seal but might do the job. Pls PM

[spduffee]

You're right Aryana. I'm going to join first thing tomorrow morning. Thanks again!

[GAHorn]

The mounting ears on these things are usually broken by un-evenly, overtightening the nuts which hold it onto the accy case.
This is usually the result of someone attempting to stop an oil leak in the area by excessively tightening against a damaged or previously-used generator gasket. (Sometimes a homemade gasket is too thick/soft and allows too much compression, resulting in the same error.)

Remember, there's no real oil-pressure involved at this location...merely a seepage of gear-case oil slung onto the tack drive spindle. Whenever replacing a generator, DO NOT CUT the new generator gasket at the tach drive adaptor "triangle". Install the gasket intact, including the tach adapator area. Also make certain to REPLACE THE (old) TACH DRIVE OIL SEAL any time the adaptor is removed. Old oil seals take a "set" against the spindle and will not reliably seal when re-positioned after removal of the adaptor.

Flat washer, then (new) lock washer, plain nut---evenly torqued....only snug sufficiently to engage the lock washer (not specified, but about 50 in lbs) ...and alternately similarly to automotive wheel lug-nuts or head bolts. (A "dab" of Permatex No. 2 on the flat surface of the adaptor will seal it to the gasket. Early assy's used fiber or nylon lock nuts with no washers, but these are difficult to torque evenly at such light settings. It's better to use the washers and plain nuts, IMO. If you worry about vibration loosening the nuts (not a problem really), place some sealant on the exposed threads on top of the nut.)

Good luck.