£0.00
(0)

Main issues with the V8 Camshaft on Rolls-Royce & Bentley cars

Matt goes over the main issues with the V8 camshafts, push rods and hydraulic tappets / hydraulic lifters (UV11163PA) for Rolls-Royce & Bentley cars from 1960 onwards including the Silver Shadow, Spirits,  Bentley T, S Series and Arnage.

“Hi there, welcome back! So today we are going to talk about camshafts. I have two camshafts here and these are from V8 engines, so they are very similar camshafts and have been used pretty much on all the Bentley V8s from when they were introduced in 1960, or early 1960’s on the S2.

This one here in the front is a used camshaft, this has been returned to us as a core unit, potentially to be reconditioned. This one here is a new one. The difference between these two as you can see, this is unused so it has still got the blackening on it but after a bit of wear that will come off and it will come polished like this. The difference between these two camshafts, as you can see is that this one has an extra lobe: one at the front and one at the back. That is to run the brake pumps. So after the Rolls-Royce Silver Shadow was introduced they used the hydraulic pumps for the braking and suspension system all the way up to the Arnage series. So this camshaft hasn’t got those pumps because the Silver Cloud uses servo assisted brakes and not hydraulic, so that’s the difference between these two camshafts. I brought the used one up so we can show you some issues that you can get with camshafts.

They stay pretty much the same all the way throughout the V8s. It’s not an overhead cam so it drives a follower. This is driven through the centre of the engine and it drives a follower which pushes the push rod up into the cylinder head, which pushes on the rocker shaft and rocker arm which then pushes the valve open inside the combustion chamber.

Slight differences that happen obviously are the brake pump lobes on the S types, they are introduced for the Silver Shadow series. Then at the late Silver Shadow II on the B series engine they change the back flange, I believe it’s the back. The front of the camshaft here is where the timing gear is bolted on. What a camshaft does is to open and close the valves in time with the pistons coming up and down so that you have the right flow of gases coming in, so as the piston comes down the inlet valve opens. That draws in the air of fuel mixture, then the inlet valve closes, the piston comes up to the top and compresses the mixture, spark plug goes off, power stroke forces the piston down and as the piston gets to the bottom, then the exhaust valve starts to open, so as the piston comes back up to the top, it drives the exhaust gases out through the exhaust. That means that it has to be in perfect time because it’s all happening very quickly so there are a number of different ways that companies will use to time the camshaft to the crankshaft.

Sometimes you have a toothed belt, most modern small engines will have a toothed belt which is catastrophic if it fails because obviously the pistons carry on moving and the valves stay where they are and you end up having pistons smashing into valves. That can happen on any set up but a rubber belt is probably the easiest thing to break. The other common method is a chain which is stronger than a belt, so is less lightly for failure, but what Rolls-Royce use is a gear so because this is a four stroke engine the piston has to move up and down four times or stroke four times for one cycle. So the valves only open once for every two strokes of the pistons, so each valve opens once for each two stroke of the piston. You have to slow the camshaft down to half the speed of the crankshaft so the gear on the cam is twice the size of the gear on the crank. What you have is, you have these holes in the end of the camshaft where the gear bolts onto and they are actually offset, so you can only fit the cam gear on in one position.

You also have the same situation with the crankshaft gear. The crank gear can only go on in one position. I think it’s on a woodruff key and then you have a mark on the cam gear and a mark on the crank gear that you line up. Effectively what that means is that you can only put it on one way. That means that the valves will be opening up at the right time for the pistons so that is critical. If you ever have to do that, then when you do fit the gears, always turn the engine over by hand, just to make sure there is no interference between the valves and the pistons.

The next thing to talk about are the problems that you might get with camshafts. If you have a noisy top end, you might find that your tappets are noisy. A lot of the time if you have worn lobes on your camshaft it can cause problems. Having the lobe worn flat will cause the tappet to not turn as it’s pressed up, So, when these are made, or re-manufactured, there is actually a taper cut and the lobe is at an angle and what that does is as it lifts the tappet it actually turns it. The idea of that is that you have not got one constant place of wear so you are constantly turning the tappet.

What happens is when the lobes wear they can wear flat and that causes the tappets to not turn when it’s running and that can wear down the tappet and wear down the camshaft even more. The Arnage T, the twin turbo Arnages suffer with tappet failure. What happens is… no one really knows why.. but it’s often one of the back lobes. It will work fine and you won’t notice anything wrong with it until the tappet fails completely and you get a knock. You dismantle the engine, take the tappet cover off, and you will find that actually the tappet is worn down a quarter of an inch and the lobe is worn down and rough because it’s just eaten through the bottom of the tappet. Now it will still work just fine until it goes so far through the tappet that it hits the inside and the oil leaks out.

These tappets are hydraulic self-levelling tappets, so what happens is that this valve, this top inside here, the height of it is determined by the car so you put these in dry and when these are dry you can actually push this against it’s own spring pressure and it will be loose. So when you first fire the car up you will get a kind of rattle as the oil is forced into these tappets and it finds it’s height. If you prime these first before you install them in the engine, it will be too high and actually you could risk bending a push rod or something because It’s over primed and it is too high. So you always have to fit a tappet dry and let it self prime.

What can happen as well with the tappets is if you have done several head gaskets on the car, if the head gasket has failed a couple of times and the head has been skimmed and quite a lot material has been taken off the head then what that does is that it lowers the head and it lowers the position of the rocker shaft which means that effectively your tolerances on the tappet are going further down. The tappets have an area within which they can operate and if you over skim the head you can actually move it down so far that it becomes out of tolerance, then your tappets won’t prime properly and you may not be able to get it to run quietly. Effectively, you could run a shorter push rod but I don’t think they make a shorter push rod than standard.

On the S Types I think there are different lengths of push rod you can use to overcome this problem. But that is one of the issues if you over skim your heads. Because of the problem with the lobes wearing, we always suggest that if you change a set of tappets, you change the camshaft as well. If you get noisy tappets and you put in a set of tappets and then you find the tappets are not turning, then they are just going to wear out very quickly so it is always recommended to change the camshaft with the tappets.

Always, obviously make sure that you have good oil flow up to the camshaft. One of the problems with these is that you need quite a lot of access to get the camshaft out. So it comes out from the front and you haven’t got enough room in the engine bay for that, so it’s pretty much an engine out job to do the camshaft.

The back of the camshaft drives the distributor gear and again that has to be timed obviously because your ignition timing is just as important. That’s pretty much all I can think of to talk about on these camshafts. If anyone has any other questions, please feel free to ask! Thanks for watching.”

Click here for the interactive parts catalogue relating to the S2 Camshaft and Valves

PictureProduct CodeDescriptionPrice (excl. VAT)
UV11163PA-XHydraulic Self Levelling Tappet£47.83
UT14120PA-APush Rod£43.36
UE36782-XCamshaft£834.75
Tags: , , , ,
Posted in Technical
Pin It

Comments are closed.