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Old 10-09-18, 01:42 PM   #71
nickh
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What is wrong with the wet belt Nick?


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TBH I had never heard of such a thing until a friend's little Transit Connect van went bang and when he told me what had failed, my first thought was what a dumb idea!


NHH
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Old 10-09-18, 07:35 PM   #72
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Are not most engines not fitted with Oil seals?

Its not "rubber" per se, and although counter intuitive, works quite well. It just doesn't work well on an engine where the belt wasn't intended to run in oil in the first place

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How I meant was something that should be gripping shouldn’t be lubricated such as a belt.



Ollie
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Old 10-09-18, 09:43 PM   #73
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TBH I had never heard of such a thing until a friend's little Transit Connect van went bang and when he told me what had failed, my first thought was what a dumb idea!


NHH

As was mine too Nick, my immediate reaction was that it surely was flawed, and whilst it is still counter intuitive to me, the NVH side of the belt is reduced, parasitic loading reduced (therefore slightly better engine performance) and the belts life is increased due to reduced frictional wear at the point where the teeth enter and exit the mesh.


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How I meant was something that should be gripping shouldn’t be lubricated such as a belt.



Ollie

Key thing to remember Ollie is how that particular belt works, its a mechanical interface belt, i.e. toothed, it doesn't rely on a significant amount of pressure to attain traction as a V or poly V would. The teeth do all the work, but their meshing and unmeshing create a friction interaction, as well as a bit of belt vibration, all of which is not a benefit to the engine.



Clever system really, but one which needs serious care in respect of belt condition lifecycle, especially with diesels and high soot loading in the oil, that can quickly wear a belt out for sure!



Paul.
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Old 10-09-18, 10:35 PM   #74
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Sorry, I still think it's a dumb idea - what exactly is wrong with a chain?

NHH
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Old 10-09-18, 11:23 PM   #75
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Sorry, I still think it's a dumb idea - what exactly is wrong with a chain?

NHH
Chains' waste of space Nick, 50K and rattling like a good un, ask Dan he'll tell you.
I knew it was done for, so did everybody in ear shot, all except the Peugeot deal, who said it fine, it s supposed to rattle until the oil pressure adjusts it.
Having finally seen sense I had it replaced, and not by the dealer.
Now they tell me I should have brought it back, it would have been covered under warranty as of early this year.
I think for reliability Id still put my money on a basic Ford crossflow, even the little 950 3 bearing crank versions were good for at least a 150K of thrashing.

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Old 11-09-18, 09:06 AM   #76
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Sorry, I still think it's a dumb idea - what exactly is wrong with a chain?

NHH
Primarily Nick, cost.

Otherwise, NVH (noise, vibration, harshness), higher power consumption than a belt, lots of potential failure paths etc. The manufacturers probably have even more reasons, as despite all that, a chain is more compact, and easier to package (usually around 1/2" wide) than a belt (upwards of 1" wide). The major driver behind what few engines are still chain driven cams, being moved to the rear of the engine was an attempt to quell the NVH challenge by dumping the noise into the bellhousing rather than echoing out through the front casing.

If I had my way we'd all still have gear driven cams and pushrod engines which funnily enough I'm fairly sure the last engine I had any great involvement with designing did...............

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Old 11-09-18, 09:29 AM   #77
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I believe the reason for driving the valve mechanism from the flywheel end of the crankshaft, is to stop the torsional vibration of the crankshaft being felt in the valve drive mechanism.

Regarding the Ford cross flow; I thought the previous 1500cc engine as used in the early Corsairs was better.
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Old 11-09-18, 11:50 AM   #78
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A little off piste - but my woodworking lathe has a Variomatic style 'transmission' which I regularly lubricate with dry PTFE spray.Works a treat with very smooth speed control.
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Old 11-09-18, 04:00 PM   #79
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I believe the reason for driving the valve mechanism from the flywheel end of the crankshaft, is to stop the torsional vibration of the crankshaft being felt in the valve drive mechanism.

Regarding the Ford cross flow; I thought the previous 1500cc engine as used in the early Corsairs was better.
Yes, towards the end of their engine manufacturing life Gardner used that method and Dennis diesels, Rootes (for the TS3) Leyland and others had the 'timing' gears driven from the flywheel end from the 1940's. I believe the correct term is the 'Nodial Point'.

Pete.
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Old 11-09-18, 06:02 PM   #80
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I believe the reason for driving the valve mechanism from the flywheel end of the crankshaft, is to stop the torsional vibration of the crankshaft being felt in the valve drive mechanism.
This is absolutely correct, but it's more than just torsional vibration. A multi-cylinder engine "winds up" both the crank and the cam shaft.

Consider a Merlin V12. Let's say 1800hp at 2250rpm, i.e. 4200ftlbs of torque, so each pair of cylinders makes 300hp and 700ftlbs. The load (prop) is at the front, which means the rear-most pair are transferring 700ftlbs through the rear main bearing, coming forward the next pair are adding a further 700ftlbs to the second main bearing, and so on...

The cam drive is at the rear of the engine, where a drive shaft via some bevels, transfers drive to the cam shaft. Each set of valves puts a load on the cam shaft, and as you come forward each cylinder adds to the load.

The net result of this is that both the crank shaft and the cam shaft wind up, and in the case of the Merlin the outcome is actually measurable at the front cylinders - the valve timing is out!

In addition, the load is constant but the power delivery isn't, creating the torsional vibration mentioned.

As the war progressed, demanding more and more powerful versions of the Merlin, Rolls reached the point where the engine could deliver no more without serious implications to the front cylinders. The answer was to resort to an earlier design, which was developed into the Griffon. The Griffon is not just a "big Merlin", it is fundamentally different, and the main difference is that the cam drives are at the front, the same end as the load. This means that as the crank winds up, so do the cams, and the rear cylinder valves remain in time.

Hope this helps!

MP
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