I had been thinking about how I could improve the Coupe's performance beyond that of a standard Marina TC, if you have read the article on the cylinder head improvements, I refer to a book by Peter Burgess called " MGB 4-Cylinder Engines for Road & Track", and published by Veloce (ISBN 1-903706-77-7 or UPC 36847-00277-0); following their lead I went and bought a Piper BBP 270 fast road camshaft. I chose the 270 as I believed that it wouldn't require too much other engine modification to get the best out of it. Piper claim 12 bhp more than standard MGB (or Marina TC) and seeing as the existing cam is the softer Super De Luxe one, the improvement should be even greater. This isn't the wildest cam in the world, but it is a significant improvement.
Whilst the engine was out for the 5 speed gearbox changeover, I took the opportunity to remove the old cam and fit the Piper one. The Piper is the one at the bottom in this picture.
If you have not changed a cam before, the best thing to do is to follow the car manual (Haynes) for the steps to take and the Cam manufacturers fitting manual for the specific settings.
I shan't go into all the detail here, but will highlight some of the practical issues, the equipment needed to install and set up the cam and the problems that I found. Most of what I cover would apply equally to a camshaft change on an A series engine.
Following the Haynes manual proved to be quite straightforward except on one item. I suspect that the section was lifted from the MGB manual, as it did not say anything about removing the mechanical fuel pump. On a standard Marina the mechanical fuel pump runs off the camshaft with a lever arrangement moving backwards and forwards against a special cam, on the picture above it is the round one third from the left. What I did was to follow the manual and when it said draw out the camshaft, mine moved about an inch and then stuck! What I worked out was that as you draw the camshaft out, the fuel pump camshaft lever slides off the pump cam and because it is spring loaded it jams against the next cam lobe, stopping the cam coming out any further! The solution was straight forward enough though, remove the mechanical fuel pump from the side of the block until the new cam has been installed.
Installing and Timing
Installing the new cam is straight forward, just slide it in keeping it level and use lots of assembly lubricant. The lubricant isn't just used to ease installation, it's main purpose is to lubricate the camshaft on start up until the oil pressure is up, more of which later.
The timing of a performance cam is the key step in setting it up. To achieve the required power output, the inlet and exhaust valves must open at the exact point in the engine cycle that the manufacturer has specified. As little as one degree out will change the performance of the engine.
The first job is to establish Top Dead Centre (TDC) for cylinder number one. Fortunately I had the cylinder head off so I could easily check where TDC was. To do this I used a dial indicator which if you haven't used one before, rides on whatever surface you put it on and registers movement of that surface relative to the dial by movement of the needle on the dial. I set mine against Number 1 piston top. Interestingly, even with the dial gauge, you can swing the crank pulley through 3-4 degrees at TDC without the dial registering any movement. You have to take the range and select the centre of it and call that TDC. The picture below shows the dial gauge measuring movement of the camshaft which I'll come to next.
Having established crankshaft TDC, what I did was to insert the number 1 inlet push rod and set my dial gauge on that (as the pic above), then roll the camshaft round until it registered its highest point, which corresponds to the inlet valve being fully open, this establishes where abouts the came is, you then roll the cam back until the timing marks on the chain sprockets match as per the Haynes manual. Then fit the timing chain and crank and cam sprockets, if you are exceptionally lucky it will all slot straight on. What is more likely is that you will have to move the camshaft a few degrees one way or the other to get it to slot together. The next step is to identify how much you moved the camshaft as this needs adjusting out.
For the Piper 270 cam, when number 1 inlet valve is fully open, the crank should be 107 degrees before TDC. To measure this you attach a graduated timing wheel to the crankshaft, reset the crank to TDC with the dial gauge and then mark TDC on the timing wheel against a pointer (bent welding rod). You then transfer the dial gauge back to the inlet push rod and rotate the crank / cam round until number 1 inlet is at it's highest, then read of the crank degrees. As you can see mine was at 102 degrees at one side and 106 degrees the other side of the maximum lift (not shown). The average of the two readings was 104 degrees, so I was 3 degrees away from ideal (107 - 104 = 3).
You then have three choices;
Being a cheapskate, I opted for the camshaft dowel route. Moss-Europe offer dowels with offsets of 1 to 9 degrees.
As the higher lift cam will put more strain on the rocker assembly, together with the already fitted double valve springs, I checked the rocker assembly and found that the rocker bearings and the shaft were well worn after 71 thousand miles, so I have replaced the rocker shaft with a tuftrided one from Moss-Europe and had my local engineering shop put new bushes in the rockers, machined to match the new rocker shaft. The wear you see occurs on the underside rather than the top. If you imagine the pushrods and the valve springs both push upwards from opposite sides, pushing the rockers up hard against the underside of the rocker shaft, squeezing out the oil lubrication. The worst wear on the rocker shaft was at the number 1 inlet valve, the surface is stepped and there is a hump where the oil gallery runs in the bush. Needless to say, the bushes inside the rockers were just as bad, so they got re-bushed into the bargain - don't do one without the other it's a false economy. I found out the hard way the Moss Europe can sell standard new rockers cheaper than I could buy the bushes and have them fitted and reamed to fit the rocker shaft. The new tuftrided shaft is shown below.
The next step is to fire up the engine, the new cam means that you have to run it for 20 minutes or so continuously at above 2000rpm for it to bed in, that's why you plaster everything in cam lube on assembly. If not the cam followers will grind through all the surface hardening, meaning another camshaft in short order.
As part of strip down and rebuild, you need to remove and later replace the jack spur that drives the distributor. I managed not to position it it in the same place that I left it, which meant that all my white timing mark on the distributor and its clamp were out of the window. I had to roll the distributor through 90 degrees in order to get the car started, once running I could use my strobe to set it up.
Well you can certainly feel the difference in performance. The tickover is a little lumpier but not too bad and she sounds lovely. My main problem is that the ideal ignition timing for the new cam is way different from the old one, she pulls like a train up to 3500 rpm on the SDL distributor and then nothing more, as the SDL distributor is way too retarded at higher revs; so I can't exploit all the extra performance. What I now need is a matching performance distributor or mapped ignition. These can be bought from various sellers for between £80 & £150. I fancied going one step better than keeping the points and clockwork and have opted for a fully mapped ignition ECU called a Megajolt system, which is do-it-yourself engine mapping.
As it happens Brian Viney had been there before me and no longer needed his MegaJolt / Kimmins mapped ignition now he has gone all injected Zetec -y with full engine management, so I have bought it off him to fit. I'll start another string to cover its' installation and any problems.