Maughan & Sons


Vincent motorcycle engineering



▲ Graham Maugham admires a reconditioned Vincent engine.


▲ Vincent advance and retard pinion.


▲▼ It's possible to build a brand new twin cylinder Vincent engine. If you're thinking of racing a Vincent, or putting together a custom job or a special, this might be the way to go, go go go go go go ...


"Genuine Sump" T-shirt

£14.99 plus P&P

So crucify us, but we couldn't help it. Just when our Sump "Goggles" T-shirt was getting started (and doing very well, thank you), we went ahead and created another. Why? Who knows? Bloody-mindedness? Sexual deviancy? Curiosity? Greed? Malice.? Or just for the hell of it?


Either way, here it is. Fifteen quid's worth of prime 100% pre-shrunk black cotton, conceived, designed and printed in England, and ... well, you don't want to know all that technical stuff. You just want to know if they're a decent bit of clobber and worth your hard earned money, and they are. And they look good too.


It's an original design unavailable anywhere else, and will age nicely. The postage, incidentally, is a flat rate regardless of how many T-shirts you buy.


You can click here to visit the appropriate page for more info, or click on the T-shirt image. Then you can buy or not buy. But make sure you read the small print on the shirt...


Great T-shirts are great things. You live with 'em, and suddenly you can't live without 'em. And these are highly addictive. So be warned.


▲ Vincent magneto (Lucas).


▲ Valve spring detail on a twin cylinder Vincent engine.

▲ A fresh pair of Vincent engine cases will set you back £1950 minimum (2009 prices).


▲ "HRD" stands for Howard Raymond Davies. Davies, a WW1 despatch rider and fighter pilot, was also a TT motorcycle racer and built his own bikes in the 1920s. In 1928, Phil Vincent bought the company and incorporated his name into the business, thereby capitalising on the "goodwill". Smart move.


▲ Vincent engine shock absorber components freshly machined.


▲ Vincent rear suspension shock absorber/dampers are easily and relatively cheaply refurbished. Expect to see a real improvement in handling. Maughan's can sort it out for you.

▲ Inside of Vincent twin engine crankcase. These cases are very strong and upgraded and machined to modern precision tolerances. You'd need dynamite to blow these up.


▲ 500cc Vincent Comet engine. Comets are derided by some as being "half a proper Vincent". But Comets owners recognise that these single cylinder bikes can more easily be pushed to the limit than the big twins. Comet's are every bit a true Vincent as the rest of the breed. We like 'em fine.


▲ Chromed Girdraulic fork on a customised Vincent Comet.

Maughan & Sons - Vincent precision engineers and spares manufacturer

Telephone: 01529 461717


Maughan & Sons have been manufacturing spares for Vincent singles and twins since 1971. Now operating out of Sleaford, Lincolnshire, the firm is owned and managed equally by Graham Maughan and Steve Hayward. Despite being busier than ever—Graham Maughan still manages to spare a little time to share some essential Vincent insight and wisdom …

"My father, Tony Maughan, started the company soon after he left the Royal Navy following 23 years of service. He was a founder member of the Portsmouth Section of the Vincent Owners Club and began in a small way making parts at a time when there wasn’t much around. My father passed away a few years ago, and I took over the business with partner Steve. The company has two other staff; Steve’s wife Sharon and son Lee.

"The strength of Vincents is that they’re well built and well engineered bikes. I’m as enthusiastic today as I was 20 years ago.
The Shadows were road tested at 125mph. Most Rapides are certainly capable of 110mph upward. But maintenance and repair is a little more complicated than it is for some other marques. Owners of Triumphs, Nortons and BSAs are often surprised to find just how many parts there are in a Vincent. It takes a while to get used to the different design. But it isn’t as daunting as some might think. Certainly most Vincent owners understand their machines pretty well.

"Rebuilds can be very expensive, however, when compared to most other bikes. You can expect to pay around £6000 for a totally reconditioned engine—and that price can climb significantly depending on how far you want to take it (prices as of 2009).

"Currently, a lot of Vincent Comet owners are taking their engine capacity up from 500cc to 600cc. Many Vincent twin riders, meanwhile, are opting for the 1200cc conversions. We can help with both.

"It is possible to build a brand new Vincent twin engine. In fact, a completely new bike can be made. One such machine sold at auction a few years ago and fetched £30,000. Brand new engine cases start at £1950. We used to supply engine cases to Matt Holder and machine them right here. But these days we’ve got so much work on that we use John Wyatt cases that come ready machined for Steve to rebuild an engine."


Stripping and rebuilding Vincent engines


Vincent engines are wonderful things. Over the years they’ve had a lot of  post-production development. But they are complicated and there are still many older machines around that benefit from a fair amount of remedial work.

Here at Maughans we strip and rebuild a lot of engines for both the twins and the singles, and one of the first things we get to grips with is the main bearing housings—which are nearly always in need of repair, especially the Series B and C models.

In the early days, Vincent gave the bearing housings a two thou interference fit, which means, in simple terms, that the main bearings are two thou “too tight”. This was correct when the castings were new. But when worn through age, this clearance allows the outer track of the timing side bearing to slip from its housing and “walk” up the crankshaft and scuff the securing nut, wearing a groove. It’s not really dangerous. It’s just not ideal and risks introducing metal particles into the engine.

Our solution is to re-bore the bearing races and machine a new, tighter sleeve to holds the bearing. The interference fit is now 3 thou—which might not sound like much. But these small tolerances make a practical difference.

On the drive side, the main bearing tends to simply spin rather than walk. The complete process of remachining is a little more complicated and requires some careful clocking up with a mic and accurate line boring. But the improvement is well worth it.


Vincent oil pumps problems and wet sumping


"Wet sumping, as with most old British bikes, is another issue. The first problem is the oil pump itself which wears—and which is easily replaced.

"But there is also the problem of clearance between the oil pump body and its crankcase housing. The oil pump fits into a one inch diameter hole. When this hole wears, it allows oil to travel past the pump into the crankcases.

"Our solution is to grind and fit an oversized bronze pump sleeve bored to the correct oil pump diameter. That effectively cures the wet sumping."


Cranks and crankshafts repairs


"Crankshafts come next. The usual problem with Vincent cranks is that the mainshaft turns in the flywheels. The crank assembly is a press fit and relies upon friction and pressure to hold it in place.

"We strip the cranks and machine the flywheel/mainshaft hole oversize, usually to 1-1/16th or 1-1/8th inch. Then we machine a new mainshaft to suit.

"As part of the process, we true the flywheels by machining the faces and rim. Just the smallest amount of material is removed (usually 5 to 10 thou). The important thing is to ensure that the hole for the crank pin is square to the flywheel faces.

"Once the remachined flywheels and shaft is fitted and trued, the assembly is sent off—along with the con-rods—for dynamic balancing. We don’t send the pistons because these are always of a known and matched weight.

"The standard balance factor for a Vincent Crank (twin or single) is 46 percent—unless, that is, the engine is destined for an Egli frame, who have their own balance preference.


Con-rods replacements and repairs


Vincent con-rods are generally excellent. But they do suffer damage, often due to bending or twisting. They’re not always of a matched weight, which will cause an imbalance and vibrations in the twins. In fact, sometimes there’s a significant weight difference.

Unfortunately, we’re running out of original rods. Carillo are the best aftermarket suppliers. They’ve been supplying Vincent conrods for years.

We can repair damaged rods by remachining both the small and big ends to ensure they’re true and inline. The big end bushes, where applicable, are machined to accept a new sleeve (made of EN31 steel). The small end bush is lead-bronze. The repair is a lasting one.


Vincent engine barrels reboring and relining


A common thing with Vincent barrels, is that they often lose the fit between the cylinder liner and cylinder muff. There’s supposed to a 5-6 thou interference fit to ensure that the liner is snug and secure; in other words, the cylinder liner needs to have a cylinder bore 5-6 thou undersize. If the bore is too large, the liner will become loose and the clearance will be taken up by burnt engine coke.

This layer of coke, between the cylinder liner and the muff (cylinder) holds in the heat, which can result in a seized engine.

Incoming cylinders needing work are generally heated in an oven until the liner drops out. Nine times out of ten a lot of black coke comes out with it. We clean up and machine the cylinder bore, then fit an oversize liner with the correct bore size for a standard piston. Liners are made of spun cast iron, incidentally.

The final job is to hone the cylinders to finished size. This is handled by Steve who always hones the bore to near exact tolerance, and then leaves the cylinder overnight to complete in the morning. The reason for this is that things settle, not least steel. The liner protrudes a few inches from the bottom of the barrel, and this is unsupported. So it can “relax” after honing. If it does, you could end up with a piston nipping up during running-in (or even later). So the final honing is a two stage process.

 This would be less of an issue in an age of less exacting tolerances. But modern machining and materials allows us to be more exacting, which has its own demands. And with pistons now running a 2-3 thou clearance, instead of 4-5 thou, you can’t afford to be sloppy.


Vincent cylinder heads repairs and replacements


Cylinder heads and lead free seats are a regular job. If a Vincent is running well as it is, we advise that owners leave it alone until it needs work.

In that case, we strip and inspect and check the exhaust port threads first. These get damaged easily and can be reclaimed by welding and remachining, or—our preferred method—by boring, re-threading and fitting a bronze ring machined to the correct size.

Cracks to the heads are rare, but can be repaired. Or new heads can be purchased easily. For valve guides, we use an aluminium bronze. For the valve seats, we use an appropriate hardened steel. The materials are better than original and last longer. Naturally, we always stick with stock imperial sizes where appropriate.

Spark plug holes do wear loose, so we helicoil. Damaged cylinder head fins—and cylinder barrel fins, for that matter—are repaired. Steve handles that too, but he doesn’t weld the broken fins on. He’s become so good that he can generally build up the cooling fin with weld. By the time it’s finished and bead blasted, it looks perfect and it lasts.

Vincents have a rocker tunnel cast into the cylinder head. We sometimes get heads in which the tunnel is quite badly worn. The repair is to machine the tunnel oversize and make oversize rocker bearings.

You can machine the tunnel and sleeve it back to correct tolerance. But it’s easier to bore and fit a large diameter rocker bearing. The original size rocker gear can be used.


Servicing and re-machining Vincent clutches


A lot of people have fitted multiplate clutches to Vincents—which they were never designed for. But many owners are purists and like to use the original Vincent clutch which is comprised of a primary plate and a pair of shoes that works similar to a brake drum.

This arrangement works well, but can be a little slow in use and doesn’t like fast changes. Some call it a centrifugal clutch. It has a self-servo action.

One of the wear-problems is the pivot points on the shoes. One of them usually wears worse than the other. But we re-bush them both and re-machine to size. The shoes have to be carefully set up on a fixture, but it’s not a difficult job once you understand how a Vincent clutch operates.


Vincent gearbox repairs and conversion


Gearboxes are usually strong and reliable. But Vincents fitted with sidecars, in particular, exact a large load on the mainshaft that travels  right through the box. This shaft has the clutch on one end and the gear change mechanism on the other. Sliding on top of this is a G4 hollow shaft with two bushes. One is an Oilite bush that can, in rare instances, break up. We make a phosphor bronze bush with an oil scroll in it. We also make a needle roller conversion which is better still.

Oilite bushes are generally excellent. But in this application, the engineering can be improved. To finish it off, we fit an seal to prevent oil travelling along the shaft and dropping into the gear change cover and then out onto the road.

Another oil seal conversion is for the drive side main bearing. Vincent used to fit a seal carrier and seal on the single-cylinder Comet, but it doesn’t fit the twin. The inner spigot on the twin’s drive sprocket sticks out and fouls the seal. We’ve made a modified sprocket specifically for the twins. We’ve achieved this by “moving” the web. Our sprocket is the same overall thickness. But the inner face allows for the fitment of a seal carrier between the engine sprocket and crankcases. This sprocket, incidentally, fits twins with or without the seal carrier.


Valve timing gears


New valve timing gears are a good upgrade. The original gears, although generally sound enough, are a bit rough and ready. Modern Vincent timing gears are made from nitride steel. It’s a straight tooth form and runs closer tolerances which translates into smoother running with less engine noise.


Suspension repairs and upgrades on Vincents


Another good upgrade are the front and rear fork dampers. Once again, it’s a question of better materials and more improved machining. Old dampers coming into the workshop are stripped and inspected and refurbished with new internals that include modern seals. The price is from £80 each. A completely new damper is £160 (2009 prices).

We’re renowned for repairing the front fork lower link. The link has two eyes, each with a bush. They get worn and twisted. We reclaim the link by first straightening, and then undersize bushes are fitted and line bored on the lathe. It’s an important thing to do because it’s the “centre point” of the fork and can dramatically improve handling that’s slowly deteriorated. We use a special hard-wearing phosphor bronze that’s very expensive. They’re lubricated by two grease nipples. The whole job costs around £130.

Some owners fit plastic bushes. But we don’t recommend that.


Typical prices are as follows: New barrels cost £80 standard. A reconditioned flywheel is around £500. A multiplate clutch conversion costs around £300. Exhaust port reclamation cost £60-£70 (per head). Main bearing reclamation costs: £200-250 (2009 prices).



Maughan & Sons

Vincent precision engineers and spares manufacturer

Telephone: 01529 461717



More Vincent contacts


Vin Parts International


The VOC Spares Company


The Vincent HRD Owners Club



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