Re: My New CF

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Post by Phil Bradshaw » Club admin » Fri Sep 14, 2018 12:51 am
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3669
The ideal for split propellor shafts with centre bearing is for the vertical angle of the front shaft being the same as the angle of the axle pinion shaft. (Took a while: long time since I thought much about Hooke joint theory and suchlike.)

Fudge factors apply with having the CV plunge joint on the rear shaft and range of alignment of the centre bearing cushion. Confounder is vertical arc of movement of the pinion nose as the rear springs flex on acceleration.

There's no spacers or anything else different about overdrive mountings according to GM parts listings, just a flange yoke instead of a sleeve yoke at the front.

Try it as it is first, keep the original centre bearing position then worry about what to adjust if something looks obviously wrong or the shaft vibrates.

One thing to watch for is judder or thudding on starting off which, with the engine mountings and torque reaction bar sorted, may be the centre bearing cushion being bashed to death because the front shaft angle is incorrect.
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  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: My New CF

Post by MattA24 » Subscribing Member » Fri Sep 14, 2018 9:51 am
Joined: Wed Jan 15, 2014 9:06 pm
Posts: 195
Thanks Phil, I'm going to sit and digest that and see if it goes in.

I had a feeling that whatever I did might end up being a bit hard on the centre bearing (and the last one has a hard life, it looks like), which is why I bought a £13 Transit bearing not a £69 OEM one ;)

Re: My New CF

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Post by Phil Bradshaw » Club admin » Fri Sep 14, 2018 11:54 am
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3669
There you go -

Image

Support bracket for centre bearing changes with model and variant. Bearing lateral alignment is in line with transmission tailshaft regardless of front shaft inclination to horizontal.
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  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: My New CF

Post by MattA24 » Subscribing Member » Fri Sep 14, 2018 11:45 pm
Joined: Wed Jan 15, 2014 9:06 pm
Posts: 195
One big question that keeps bubbling up to the top of my mind is the cylinder head.

The plan is to stick my LPG kit on this van, which would of course require hard valve seats. I'm guessing there's no good way to know whether the van has already had some fitted?

On the one hand, it's obviously had plenty of money spent on it over the years, so I'd not be surprised to find it had been converted. It runs very nicely for something that's lived in a hedge.

On the other hand, there was an empty fuel additive bottle in the wardrobe.

I guess the only way to be sure is to pull the cylinder head? Even then, is it that easy to spot the new seats? :?:

Or I could set the valves nicely, then drive around a bit on LPG and see what happens to them? :?:

PS: thanks for the prop shaft diagram Phil, its finally starting to make sense... :thumb:

Re: My New CF

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Post by Phil Bradshaw » Club admin » Sat Sep 15, 2018 1:18 am
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3669
Check the valve clearances.

If the exhaust valves already are tight then chances are it's a bog standard head.

If the clearances are not too far out then adjust as normal and note (a) mileage, (b) which valves need adjusting and (c) by how much (number of clicks or full turns of adjusting screws) so that you have a reference point.

After about 1000 mile check exhaust valve clearances, note mileage etc. and compare with previous results.

If any exhaust valve clearances are closing up then standard head is more likely; if none are closing up then hardened seats may be fitted.

Seat recession depends a lot on how hard the engine is driven so check clearances again at 3000 mile and then every 3000 mile until it is apparent that the head needs hard seats, or the head is fine and longer intervals are adequate.

If running on petrol then use lead replacement additive until hard valve seats confirmed: seat recession in cast iron cannot be prevented, only slowed down a bit (as was the case then leaded petrol was all the rage).

If running on LPG then use Flashlube or similar intake lubrication system: even if hardened seats are fitted the valves still need protection.

Propellor shaft

Whatever transmission is fitted to a Vauxhall OHC engine the alignment of the transmission tailshaft and axle pinion shaft to horizontal remain parallel (with engine mountings fixed, that is!).

Bearing carrier should be attached to the support bracket without flexing the cushion, i.e. carrier and bearing both perpendicular to the front shaft axis.

So the answer is to change the angle of the dangle of your centre bearing support bracket to keep the front shaft in line with the transmission shaft.
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  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: My New CF

Post by MattA24 » Subscribing Member » Sat Sep 15, 2018 8:42 pm
Joined: Wed Jan 15, 2014 9:06 pm
Posts: 195
Phil you talk good sense I guess! The temptation is to try and settle the cylinder head question now because I'm about to change the radiator and timing belt and whatno, so while I had all the ancillaries off it seemed like a great time to dig in a bit further but provided the valves aren't already well out of cock I'll just fettle them and keep records.

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