912 engine running a Mech Tachometer.

[Colin Thorpe]

Hi All,

I have a friend who would like some advise.

I would like to convert my 912 engine to run a mechanical tachometer in my 356. I would like to know which 356, 3rd piece to use.( with the least amount of modification) I have the choice of 3 here. one from a 1956.The other 1959. The other one from an industrial engine this seems to have larger oil pump gears and not done much work. Is it OK to swap 3rd pieces to different engines? obviously feeling for any resistance when assembling.I have heard about enlarging the dowel holes and letting the bearing centralize. Is this a Do or a Dont. Any other tips would be much appreciated.

[Greg Bryan]

I believe you can use mechanical tach gears in a 912 3rd piece - no need to change it . You will have to use the corresponding oil pump cover, of course. The 'big' pump started in the 61-62 timeframe and the oil pump bore and depth is the same through the end of the 912.
The pump gears and cover are expensive - it might be cheaper in the long run to have your tach converted to an electronic version.
I don't know if you can even put the small pump cover on the later case, but I wouldn't recommend it. The large gear industrial cover will go on the 912 case, but if you've got a good cover on your existing engine, no need to do it.
Case and 3rd pieces were matched and numbered up until the 912 when they dropped the number on the 3rd piece.

[Ron LaDow]

Hi All,
I have a friend who would like some advise.
I would like to convert my 912 engine to run a mechanical tachometer in my 356. I would like to know which 356, 3rd piece to use.( with the least amount of modification) I have the choice of 3 here. one from a 1956.The other 1959. The other one from an industrial engine this seems to have larger oil pump gears and not done much work. Is it OK to swap 3rd pieces to different engines? obviously feeling for any resistance when assembling.I have heard about enlarging the dowel holes and letting the bearing centralize. Is this a Do or a Dont. Any other tips would be much appreciated.

The tach drive is independent of the timing cover; mechanical tach drives were fitted to 'big pump' engines from 1960 until sometime in the early C production.
You need a mechanical tach drive lower gear and a mechanical tach drive oil pump cover so you can thereby contribute to wear on the oil pump drive gear tang and avoid the chance to fit a full-flow oil filter so you can keep dirty oil in the sump!

[Ashley James]

There's a company in the U.K. That fits modern electronic guts to mechanical Rev counters, so there's bound to be many more over there. Assuming it's not a simple job to adapt the existing one, which seems the simplest option.

[Dick Weiss]

The difficult problem of re-building the oil pump during a conversion is making sure the gears are matched in length and if the pitch-line (on the teeth) isn't worn. If so, they could be turned around end-for-end (use a press to R & R), check the spacer diameter to the pump cover's bore-clearance, and finally the drive shaft endplay--this would be difficult if the 3rd piece isn't removed from the case to feel the rotation not being 'pinched' when installing the pump cover.
When I rebuild oil pumps, I also modify the drive-tang edges w/a 15 degree angle to minimize wear in the camshaft slot.

I'd suggest an electric tach coversion would be simpler as the cost would be similar to the labor & parts involved listed above.

Dick

[M Penta]

I installed the oil pump gears and cover from 64C engine into 912 engine that is currently installed in my car, so that I could retain the mechanical tach.

It works fine, but if I did not have the gears already I probably would have gone with an electric tach instead (and a full flow oil filter!).

[Steve Proctor]

You can have your cake and eat it too (mechanical tach and full flow) in either a 356 or 912 engine. See above for details in a 912 - big oil gears with tach drive helix, oil pump cover. Send the oil pump cover and third piece to Competition Engineering or perhaps Ollie's as well, who will plug the pump output port in the third piece, drill the oil pump cover, install a brass insert and thread in a fittings for oil lines to and from a remote filter housing. I have been running this configuration for over 30 years in various cars / engines and prefer the funkiness / originality of the mechanical tach. To be really trick, find one of the load-reducing industrial engine oil pump interface units that increases the bearing surface from the 12mm or so of the oil pump drive tang approximately 3X. I'm surprised no one is reproducing this interface unit.

[Albert Tiedemann]

You can have your cake and eat it too (mechanical tach and full flow) in either a 356 or 912 engine. See above for details in a 912 - big oil gears with tach drive helix, oil pump cover. Send the oil pump cover and third piece to Competition Engineering or perhaps Ollie's as well, who will plug the pump output port in the third piece, drill the oil pump cover, install a brass insert and thread in a fittings for oil lines to and from a remote filter housing. I have been running this configuration for over 30 years in various cars / engines and prefer the funkiness / originality of the mechanical tach. To be really trick, find one of the load-reducing industrial engine oil pump interface units that increases the bearing surface from the 12mm or so of the oil pump drive tang approximately 3X. I'm surprised no one is reproducing this interface unit.

Mike Smith in the UK [PR Services] offers this conversion. Interface unit [center section of faux Oldham coupling] and shortening of interfacing gear. Check website for cost.

[Mike Smith]

AB says -

To be really trick, find one of the load-reducing industrial engine oil pump interface units that increases the bearing surface from the 12mm or so of the oil pump drive tang approximately 3X. I'm surprised no one is reproducing this interface unit

.


Many thanks for the `Plug` Ab - you will have gathered by now that we are the Worlds worst Sales Men

[John Hearn]

Click here for link on Oldham coupling

https://prs356.co.uk/porsche-parts/all/ ... m-coupling

KTF
John

[Steve Proctor]

Bingo...

[Mark Sabbann]

Ab, please contact me.