Throwback Thursday: Servicing Cosworth DFV Formula 1 engines, 1975

“Basically it achieves that by persuading enough fuel-air mixture into cylinders and burning it efficiently enough at the highest possible crankshaft speed. At that moment, from what John told us, with the latest cylinder heads and larger exhaust pipes and recently introduced taper intake trumpets (plain cylindrical for most of their length), it still doesn’t reach peak power at 10,750rpm, proving that it isn’t breathing that restricts but the mechanical limits of the unit.”

“The normal working range is between 8500 and 10,500rpm. An electronic ignition cut-out is fitted which nominally stops the engine being revved beyond about 10,600rpm. Firstly because even these relatively sophisticated rev-limiters gradually lower the limit during their life, and secondly a rev-limiter cut-out switch is provided because a few hundred more rpm can be allowed to the driver desperate for that little bit extra. Drivers do go to 11,000rpm, but it isn’t recommended.

“At that speed, at the bottom of one of the eight pistons’ stroke, it is stationary. It has to be accelerated from that brief rest to near-enough 75mph in 1¼in, then slowed down again in the same distance. And it has to do that each way every three-thousandth of a second. The acceleration involved is around 230g.”

So, how long between rebuilds?

Back in the days where truly tiny independent teams were still common in Formula 1, this varied a lot. McLaren tended to rebuild engines after 600 miles – or one weekend, practice and race.

Showing the remarkable evolution of the DFV, Nicholson said: “When it first came out in 1967, we were probably getting 1000 miles out of them. OK, we were running to 10,000rpm then, but they were producing say 420 to 440hp. Now they’re running to 11,000rpm, really, and that extra is not good for them.”

What wears?

As providers and maintainers of race-worthy engines, Nicholson Ltd’s job primarily was not to measure the wear of each part, but to avoid the results of a crucial breakage.

“Pistons get replaced every 1000 miles,” Nicholson said. “They won’t do two race weekends. If you had a failure because of a piston, which in turn broke the engine – even a secondhand one that cost £4000 – that would have bought you a set of pistons for every race in the season, so it isn’t worth economising here.”

Valves and valve springs, meanwhile, would last two race weekends.

“Crankshafts, with a bit of luck, will run a long time, depending on how they wear,” Nicholson said. “I’ve only seen one or two cranks break in the four to five years I’ve been doing DFVs. They wear on the thrust faces of the webs – the end of the journal where the side of the rod rubs. There are different thoughts on why this happens. The end float on a pair of rods in place is set between six and 12thou, but it’ll increase to 15 or 20thou very quickly – in one run. I think it’s something to do with the nitridising of the crank – it’s too hard, it splinters, and the splinters dig into the con rod, which isn’t particularly hard compared with the crank. Then the con rod works like a little grinding wheel.”

Con rods themselves, Nicholson said, he could never get hold of – although fortunately they didn’t fatigue too quickly. Camshafts, while prone to wear a bit at the lobes, would last an entire season. He'd never seen cam followers break.

“Cylinder blocks have a fair old life. If a main bearing tunnel or cylinder liner register gets out of shape – which they do – we rebore to suit a 15 or 20thou oversize bearing or liner. This lets you use the block, if all goes well, for a couple of years.” The cylinder heads lasted longer still, although Nicholson did have to replace the valve guides once a year.

Bore wear wasn’t an issue, due to the teams’ eventual acceptance that an air-cleaning device didn’t have to siphon horsepower.

Originally, DFVs’ throttle controls would cause a lot of trouble, especially their metering unit rods, but, said Nicholson: “now we have our own little rod-end jointed linkages instead of the ball ones, and we haven’t had one break since”. Metering units were changed regularly.

A standard rebuild and its cost

A full Nicholson rebuild of a DFV cost £800, (around £6200 today), with the engine itself costing £10,000 new (£77,000). Today’s Formula 1 V6 hybrid engine costs into the millions.

A standard rebuild in 1975 involved two of Nicholson’s fitter-mechanics, “who start by stripping the engine down and cleaning it for inspection. The user should have supplied mileage and maximum revs used.

“Nicholson has a Magnaflux crack-testing rig, on which crankshaft and connecting rods are tested. Pistons (at £25 each) and possibly valves (£7 each, and there are 32 of them), and valve springs (£4 each) are replaced.”

Nicholson explained: “We have a kit of gaskets, oil seals, bearings for oil pumps, water pumps and all those sort of things – we automatically put them in. Maybe I overdo things a bit, but it’s the way McLaren works and it’s the way I’ve been taught. I probably spend £50 more on seals and gaskets and bearings than I have to – but I think that’s right. A team has half a dozen mechanics, thousands of pounds of transporter and equipment, and out goes the car and brm-brm-brm that’s it, all for the sake of a £2.50 bearing.”