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Author Topic: Crank Pulley Nut  (Read 809 times)
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megaera
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« on: October 03, 2017, 07:57:46 PM »

I know this has been covered previously - but I am getting thoroughly confused.......

I have just replaced all the belts etc on my 1985 Coupe VX. The crank pulley has a 38mm nut - right hand thread. I have a second 1985 Coupe VX - which also has a 38mm “normal” thread nut.

I recall a while ago, someone posted on this forum about crank pulley nuts and whether they were left or right hand thread. Apparently, the is some debate over this.

Below is a quote from Guy Croft’s site, which I have copied/pasted:

: Difference between crank with nut & crank with screw
Quote
Post  by Guy Croft » Tue Jan 06, 2009 9:36 am

Yes, Lancia Volumex block engine code is 828B7000, I am building one here and I just checked it. The crank in this one has a reverse thread bolt as have all the Vx units I've seen (pretty sure anyhow) and the rods have nuts and bolts


Now, I have no doubt that Guy Croft has seen considerably more VXs than I have, but neither of my current cars have left hand threaded bolts. My original HPE VX I had back in the late ‘80s had a 38mm nut.

So - can someone knowledgeable please enlighten me as to which cars had 38mm right hand thread nuts and which had left hand thread bolts?

As an aside - is it still possible to obtain a date of manufacture from a VIN number? i would very much like to know when mine were built!

Thank you!
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rossocorsa
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« Reply #1 on: October 03, 2017, 08:29:51 PM »

Send me the vin number, as regards the nut they are all normal thread AFAIK at least the two I've had off. I can check the parts fiche though to see if there are any variations
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megaera
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« Reply #2 on: October 03, 2017, 09:20:13 PM »

Thanks Alan - sent you an email!
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squiglyzigly
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« Reply #3 on: October 03, 2017, 11:00:27 PM »

Never seen left hand thread on a vx. Every one I've worked on and owned have been right hand thread. Probably amounts to 15+ cars.
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megaera
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« Reply #4 on: October 04, 2017, 09:20:49 AM »

Never seen left hand thread on a vx. Every one I've worked on and owned have been right hand thread. Probably amounts to 15+ cars.

Thanks! I’m glad it’s not just me......

So exactly where are all these cars with left hand threads Wink ?

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squiglyzigly
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« Reply #5 on: October 04, 2017, 02:00:59 PM »

I'm really not sure. Maybe they've had replacement cranks from later cars. Fiat Croma, 8v Thema, 8v Delta, 130tc etc etc? They might be compatible with minor changes to flywheel spigots.
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Beta coupé VX (completed April 2017)
Beta Saloon 2000 s2 1979 (in progress)
Aprilia RSVR 2002
Aprilia Tuono R (130 rear wheel BHP) mad as a box of frogs
Alfa 159 sportwagon
peteracs
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« Reply #6 on: October 04, 2017, 02:16:21 PM »

Hi All

I may be being a bit dim here, but wouldn't the direction of the thread be such as to have a tightening action when the crank is rotating? So I would expect them all to be the same direction?

Peter
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rossocorsa
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« Reply #7 on: October 04, 2017, 04:40:13 PM »

Peter I think one is a nut the other a bolt which maybe explains why the threads are different
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megaera
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« Reply #8 on: October 04, 2017, 07:37:34 PM »

Yes, Alan is quite right.

Sorry Peter - I wasn’t very clear. Apparently, there is either a left hand threaded bolt or a right hand threaded nut. I was curious as to how many forum members have come across the elusive bolt.....
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peteracs
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« Reply #9 on: October 04, 2017, 07:43:48 PM »

Peter I think one is a nut the other a bolt which maybe explains why the threads are different

Hi Alan

Hmm... to my simplistic view the thread direction for the nut and a bolt should be the same assuming the crank rotates the same way to have a tightening effect?

Peter
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rossocorsa
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« Reply #10 on: October 04, 2017, 07:45:34 PM »

Tbh I'm not sure, twists my brain a bit thinking about it
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HFStuart
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« Reply #11 on: October 04, 2017, 08:02:12 PM »

The engine rotates clockwise. The natural action of the load on the crank pulley would tend to loosen a normal right hand thread. Early twin cams had a left hand bolt to counteract this. I suspect Fiat twigged that with everything held by the key on the shaft and done up FT there was no chance of it coming undone anyway. The switch from bolt to nut was most likely to avoid confusion between left and right threads.

All speculation on my part but it seems plausible.
« Last Edit: October 04, 2017, 09:04:03 PM by HFStuart » Logged
rossocorsa
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« Reply #12 on: October 04, 2017, 08:21:59 PM »

In do think the nut has much more surface area against the pulley surface which must help
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WestonE
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« Reply #13 on: October 05, 2017, 06:27:59 PM »

Ok Chaps

Some 8V Integrale Cranks are Left Hand thread bolted and I have seen a VX engine with a LH thread bolt crank, but it was a very late engine.

Cheers

Eric
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rossocorsa
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« Reply #14 on: October 08, 2017, 06:14:36 PM »

Modification 7938 refers

https://photos.app.goo.gl/ikSL9yoyIByhxHID2
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megaera
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« Reply #15 on: October 08, 2017, 11:22:18 PM »


Thanks Alan! The wonders of Google translate:

new trimmed engine shafts and new continuous shaft speed shaft changeover  Grin
« Last Edit: October 08, 2017, 11:24:07 PM by megaera » Logged
Deltona
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« Reply #16 on: November 20, 2017, 09:05:15 PM »

Ok Chaps

Some 8V Integrale Cranks are Left Hand thread bolted and I have seen a VX engine with a LH thread bolt crank, but it was a very late engine.

Cheers

Eric

All engines with external oil pumps (integrales etc) have a L/H threaded bolt.
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