Spigot bearing (bush) and input shaft length

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Prophead
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Spigot bearing (bush) and input shaft length

Post by Prophead » Mon Aug 14, 2017 6:58 pm

I have a Porsche 924 that has had an RV8 3.5 (SD vitesse I think) conversion done. As a result of a clutch issue I have the entire drive line out of the car. I have decided to replace the torque tube (drive shaft) and gearbox with those from a Porsche 944 because the shafts in the 924 are a) only rated to 200ft-lbs b) can only use a 924 friction plate which is too small (not enough friction surface).

By upgrading to the 944 torque tube shaft, which is 1" with 23 splines, I can use an RV8 9 1/2" friction plate (the flywheel and coverplate are both RV8), and the shaft has a much higher torque rating than the 924's.

I was doing some further checks today to ensure fittment will be ok and realised that at the clutch end of the torque tube shaft (lets call it the input shaft) on the 944 shaft is ~10mm shorter than the 924's. The part of the shaft that is actually shorter is the reduced diameter section that slides into the Spigot bearing. Having made further checks and measurements I believe that the 944 input shaft will be long enough to slide into the spigot bearing but by only 10-11mm, were as the 924 went fully in to about 22mm (approx the length of the spigot bearing).

Do you think that the reduce length of shaft entering the spigot bearing will cause any issues? It should still locate the end of the shaft correctly.


Porsche 924 GTv8 Track-day car project
Porsche 944 2.5 Lux gone but not forgotten

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ChrisJC
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Post by ChrisJC » Thu Aug 17, 2017 7:59 pm

I wouldn't have thought so - it's not like it can go anywhere.

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Prophead
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Post by Prophead » Thu Aug 17, 2017 8:32 pm

ChrisJC wrote:I wouldn't have thought so - it's not like it can go anywhere.

Chris.
That's what I was thinking but want to check. This is the first time I've done anything like this and its on a custom setup. It's a total ball ache getting the transmission out and into these cars with the engine and clutch up front and the gearbox at the rear, everything has to come out. So before committing to reassembly just wanted some input from some more experienced folk.

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Porsche 924 GTv8 Track-day car project
Porsche 944 2.5 Lux gone but not forgotten

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DEVONMAN
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Post by DEVONMAN » Fri Aug 18, 2017 7:59 am

You may be able to fit the bush slightly less deep into the end of the crank and get a little extra support for the shaft .
1950 A40 Devon Hotrod with 5.0 twin turbo RV8. (10 things to make you smile)
EDIS8 wasted spark, Holley Injection.
Been as far as the Moon and back in 54 year of driving. Same Car, 5 engine upgrades !!!


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Prophead
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Post by Prophead » Fri Aug 18, 2017 9:11 am

DEVONMAN wrote:You may be able to fit the bush slightly less deep into the end of the crank and get a little extra support for the shaft .
Interesting idea. Will need to check the clearance to the friction plate, maybe just a couple of mm will be enough. At the end of the day the 944 shaft was designed to fit into a roller bearing that is only 10mm deep, so should be sufficient support for the shaft end. My concern would be increased wear rate of the phosphor bronze bearing used in the rv8. Always a compromise somewhere, guess I will just have to suck it and see.
Porsche 924 GTv8 Track-day car project
Porsche 944 2.5 Lux gone but not forgotten

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