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Spigot Bearing? Not the usual question
Xtreme Kermit - 11/11/13 at 09:53 PM

So it struck me...

Standard practice is to take an FWD engine, turn it round and add a spigot bearing.

Makes perfect sense to me - however: why do FWD engines NOT need a spigot bearing??

David Jenkins - 11/11/13 at 10:06 PM

Automatics don't need them?

Only guessing, as my x-flow came from an auto Escort, and I had to clear out a slightly dusty hole and fit a new bearing. I know that's RWD, but I was wondering if it was the same for FWD.

[Edited on 11/11/13 by David Jenkins]

Xtreme Kermit - 11/11/13 at 10:14 PM

Good point. I remember swapping engines on a manual Granada. The engine we got was from an auto and didn't have a spigot.

Maybe something to do with the way the torque converter bolts on.

David Jenkins - 11/11/13 at 10:23 PM

But don't rely on anything I say about FWD cars - I know three-fifths of very little about how their engines and gearboxes fit together!

[Edited on 11/11/13 by David Jenkins]

britishtrident - 11/11/13 at 10:23 PM

All down to the arrangement of the gearbox shafts, in a rwd gearbox the first motion shaft and tail shaft have to be able to turn at different speeds therefore a one piece shaft is not possible.

scimjim - 11/11/13 at 10:27 PM

To prevent a rwd manual gearbox long input shaft "whipping" it's supported in the end of the crank. There' is no long input shaft on an auto box and the torque converter is bolted to the "flywheel" (starter ring gear flex plate).

Bare - 12/11/13 at 02:52 AM

quote:
Originally posted by Xtreme Kermit
So it struck me...

Standard practice is to take an FWD engine, turn it round and add a spigot bearing.

Makes perfect sense to me - however: why do FWD engines NOT need a spigot bearing??


For fit and available space reasons FWD trans have a Much shorter input shaft length, requiring the additional support.
RWD typically have long gangly input shafts. Presumably cuz the designers' could give a rats' ass re compact design and likely were fixated on placing the Gearshift in a desirable position.
Although more than a few 'older' designs FWD's still fitted a pilot bearing in the flywheel hub.
Later more Moderne design ones do not.
Autobox / torque converter situation is of an entirely differing design they don't even have Flywheels per se.

mcerd1 - 12/11/13 at 10:28 AM

quote:
Originally posted by Bare
....likely were fixated on placing the Gearshift in a desirable position...


but that also moves some of the weight into the middle of the car for better weight distribution


its always much better to support a shaft close to its ends rather than have a cantilever hangin out the end, that way it puts less load on the bearings so they can be made to last longer with cheaper bearing


a lot of modern boxes are made so compact that they can get away without a spigot bearing, but that doesn't make them any better....

MikeRJ - 12/11/13 at 02:07 PM

The short answer is that the input shaft of a RWD box is supported only by a single bearing within the box (the one behind the "nose" on which the clutch release bearing mounts), and therefore requires a second bearing outside of the box to provide sufficient radial support. Grab the input shaft of e.g. a Type 9 with your hand and you can waggle the end around a surprising amount.

The input shaft on most FWD boxes is longer and supported by two bearings, spaced some distance apart so has sufficient radial support without a spigot bearing. Some FWD boxes do need a spigot bearing however.

Xtreme Kermit - 13/11/13 at 08:43 PM

Cheers for th imparted wisdom guys!

Velly intalesting

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