Moss Engineering

33 Kings Lane
South Croxton
Leics. LE7 3RE

 Moss Engineering | About us | Whats New ! | Scott Motorcycles | Other Interests | Links |
 november 2015 | february 2014 | april 2012 | september 2011 | june 2010 | january 2010 |
 september 2008 | sept 2008 | may 2007 | october 2007 | february 2007 | december 2006 | october 2006 | september 2006 | august 2006 | archive |

Paul Dobbs RIP 05/10/70 10/06/2010

We are very saddened to announce the death of Paul Dobbs whilst competing in the Isle of Man TT Supersport race on 10th June 2010


The passing of Paul Dobbs has left a big hole in the lives of those who were fortunate to know him.

He was one of those rare people whose love of life was so infectious, that it lifted the mood of all around.

I was introduced to Paul by long time friend Tony Harris the maker of BT-H magnetos.  I had asked if Tony knew anyone who would like to race my Scott whilst I recovered from some crash injuries.

Tony told me of a young New Zealander with previous racing experience “down under” who was so keen to race that he had recently competed in a seven hour endurance race for mopeds with his partner Bridget.  I was impressed with his will to race and a Mallory VMCC meeting was arranged.

I had just accepted the handling faults of my particular Scott but Paul having experienced its bad manners, was determined to improve things and advocated moving the rider weight forward.

This improved handling and Paul had some inspiring rides on the bike with about 35bhp available.

Paul’s spirited style was well captured by Nigel Clark of Mortons with that fully airborne shot going over Cadwell “mountain”.  The publicity attracted other better funded classic and modern race teams and led to Paul being supplied with top class race bikes for the Isle of Man TT races and North West 200 events, plus other mainland races.  Paul still tried to find time for at least one race meeting where he could ride the Scott. 

I have expended much time, money and effort racing my Scott and decided that I should be fair and give Marina a holiday this year without bikes.

Marina wanted to see a bit more of Europe, so we made plans.  I had just finished the rebuild of a Scott engine for Gulio Caimi of Milan.  Gulio had asked for some guidance over several aspects of his Scott, so I decided we could call in briefly during our travels. I should also give credit to Eddie Shermer who rebuilt the transmission to top spec, Sean Hawker who found a new magdyno body and rebuilt it as new and Martyn Bratby who reconditioned the carb in great style.

On 9th June we were travelling in France when I received a text message from Paul Dobbs to say that the TT races were going well but he would not like to return to New Zealand without racing the Scott if at all possible.  I replied that he could take my rides at Lydden.  Paul responded to say that he would change his tickets for his return flights and ride at Lydden.

The next day, June 10th, I had a text message to break the news that Paul had crashed in the Supersport race and died instantly.

Paul had an unusually sunny and positive outlook on life and was well liked and respected by all who knew him.  He was almost a member of our family, so the loss was profoundly felt.

Paul had the natural ability to sort out handling problems on motorcycles and had been employed by Triumph to do just that for a period.

I do not possess this ability to such a degree and with his help on chassis setup and Alan Middleton on exhaust development, we were able to make significant progress. I owe Paul a lot.

Paul had expressed a wish, that when his time came, he would like to be buried on the Isle of Man.  The funeral hearse was to carry his body on one final brisk lap of the mountain circuit, with as many friends as could attend to follow the hearse on bikes if possible.

As I was unable to attend, then to represent the Scott part of his racing life, My son Richard attended and followed the hearse round the mountain course.  He said that he thought that a new lap record for hearses up to four litres capacity had been set and he was sure that Paul's spirit would enjoy the joke.

A thoroughly good man and a dear friend who enriched the lives of everybody he met.  Rest in peace Paul.

September 2008

It has been a good while since this was updated, as Richard, who always did the website work, has been engaged in other business. I am finally trying to get to grips with this and hope that you will forgive the “Rough Edges”

First let me review the progress with the Scott racer over the last three years.

The feedback from Paul Dobbs had been that there was not enough weight over the front wheel.

It was necessary to lift the seat higher than the long tank and move it forwards over the tank to try the revised weight distribution. Paul had pronounced the handling transformed and had considerable racing success with this layout.

It was, however, untidy and so I had the tank shortened, so I could have the seat in the same position but lower behind the tank. The seat mountings were modified to suit the new seat position. Unfortunately, the exhaust system would not now pass the revised seat mountings and so it had to be modified with a big hammer! It was not beautiful, as I am no expert with sheet metal. The result was that the power was down from 35 to about 33 bhp and the handling had deteriorated again.

The original cylinder head was not of my original manufacture and was not from high strength aluminium. It had been welded and machined several times, so the decision was made to replace it with one of my high compression heads. To go with this, a new pipe was made by “Spec” a local specialist. He looked at my previous efforts without comment, but I could see his lip curl.   


The path of the developer is strewn with difficulties and when more metal was eroded from my aluminium barrel in removing the existing chrome plating, the bore was left oversize. Silk pistons were now not big enough, so I made some 660cc pistons from old castings I had from 1977 in LM14 “Y” Alloy. All initially seemed OK, but then I was troubled by a water leak into the LH crankcase.

The barrel was an early casting and the four holding down bolts had gone through to water. I had fitted stainless blind inserts, but the recent plating erosion had exposed the threads of the insert in the side wall of the exhaust port. Water was leaking in by this route. What to do? I had put a lot of work into this barrel and do not have time to make another one as I must attend to the engines of my customers. I decided to try and seal the leak by pouring some slow set epoxy into the water space of the barrel near the exhaust port. In this state I took the bike to be tested on the Heenan and Froude dyno of Dave Holmes. To my great surprise, it recorded 41.9 bhp which was a big increase in power.

The bike was entered in the VMCC races on June 22nd at Mallory Park with Paul Dobbs as rider. Paul reported that the handling had not improved and that the engine had tightened, but had become free again.

Soon after this meeting, and without time to strip and check the motor, We journeyed to make our attempt at the speed run for the fastest Scott record down at Woodbridge airfield in Suffolk. We had the big dustbin fairing fitted for the occasion, and moved the seat position to enable Richard to really get down behind it. Preparations for this event were assisted by Daiji, A meticulous and spirited Japanese man who had been working with us for the previous couple of weeks as part of a British tour of vintage and classic motorcycle engineering workshops.  It was obvious from the beginning that it was difficult to start, but we put this mostly down to the tall gearing and maybe attributed a little to the possibility that the new exhaust was causing a pulse in the inlet tract which was affecting the charge flow at starting revs. A possibility brought to our attention by another Vintage racer who had himself suffered it.  Though these both might have been factors, the lions share of the problem was likely caused partly because, as later we realised, by at least one partially stuck in ring.


Richard made a sighting run, but sensed that it might have partially tightened even during this. Events were taken beyond our control however when extreme cross winds got up and we were advised against any further high speed runs. Richard did some quarter mile runs on his Scott, so we still had a good weekend.

The next day, the engine was stripped and it was found that in the areas near to where the epoxy had been cast into the barrel water space, this had hindered cooling and had likely contributed to seizures on both pistons. Both rings were stuck in their grooves.

No wonder it was hard to start!

The pistons were reground on the outside diameter and the piston crowns remachined to drop the compression a little. As regards the handling, I wondered if the height of the seat was significant, so I raised it about 15mm. It was in this condition and without much confidence, that Richard and I went to the Beezumph track event at Cadwell Park. I suppose that if you keep fighting against adversity, you might be allowed a little success and indeed we had it, as the bike went better than it had ever gone, both as regards power and handling!  



Top speed is estimated at approx 115mph naked with a definite boost from the exhaust. The handling was much improved with the higher seat position and I found myself going into corners at speeds that I could not safely do before.

I am 67 now and want to have some racing while I am able. Over my 38 years of racing, I have fallen off many times, but in past times, without significant damage to myself. The last two occasions , however, I broke several bones and I am wondering if the bones are getting softer or I have just forgotten how to crash safely. I am loaded to go to Lydden tomorrow and am resolved to be restrained until I feel truly confident. Life is a short and precious gift and to go through it without any risks must be very boring. Racing, especially Scotts, has brought many moments of pure ecstasy to my life. If I had my time again, I would change nothing!

On the work front

More evidence of poorly assembled crank assemblies.

A Scott owner from Australia, Kelvin Mears, is rebuilding a Scott and sent me his cranks and rods to refurbish. In looking over the cranks, I saw a strange pattern on the LH main bearing ring. It has to be accepted, that although the main bearing design may look light, they very rarely give trouble.

In this case there was a bright line down the middle with a darker band each side. Closer examination showed that the crank had been loose in the flywheel and had been rocking about in use for so long, that it had worn the main bearing ring into an arched profile. Next we looked at the tapers of the cranks, and here was clear evidence of fretting and even some metal transfer from the flywheel. I sent a message to Kelvin to check out the flywheel and back came the reply “It is ruined, what can you do”? I replied that I could supply a new centre section that could be fitted into his flywheel after the old centre was bored out. I think I had better make a small batch as it is much cheaper to make others once you have a setup. I should explain that Kelvin had not sent his complete engine due to the high cost of freight from Australia, although I much prefer to have the whole engine. From the UK, this week, came another enquiry. Can I have a look at an engine as it vibrates. I suggested that the owner checked the security of the engine and undertray in the frame. He responded that this was all secure, so what else could he check? Check the truth of the flywheel, I replied. It should run within 0.003” on the periphery and about 0.005” on the side of the rim.

A little later came the reply that the periphery was running out 0.010” and the side of the rim had a massive 0.040” wobble. Sounds like another tapered flywheel insert is needed. It seems such a shame that so often tapers are destroyed just through lack of correct assembly. Remember, after you tighten the centre bolt, the cranks MUST be knocked up (See assembly section on website)

The cranks will travel a further 0.010” in this process. If you just tighten the centre bolt only, the cranks will be loose within 10 miles.

It is my contention, that there is a fault in the design of the Scott crank that has gone back to the earliest times. I maintain that the keyway should be at right angles to the crankpin, not in line with it.

In the “in line” position, at the point of maximum load when the piston is near TDC, the loading is taken by that area of taper that has at least 50% of it’s load bearing surface missing, by virtue of the taper.

If I make another crank run in the future, as the remaining stock is dwindling, it might be better to make the cranks with the keyways rotated 90 degrees. Talking to Richard, he suggested we could also make a 360 degree motor to have a fashionable “Big Bang” engine, or we could do a 270 degree crank so it sounded like a vee twin Ducati. I told him that I was hardly tolerated now by some purists and that such talk could have me thrown from the club. What else? Well I finally sent John Hughes consignment in nice boxes to San Diego. I wrote about this for Graham Parker to consider for inclusion in our Newsletter, so you can read it there and if you are not receiving the newsletter, then Why Not? It is free and we do it for you not profit! If you are not on the distribution list, just drop me a request at

Finally, I had an enquiry for a complete new engine, but I explained that a bespoke Moss replica engine from new high strength castings would be expensive. I asked how the bike would be used and was told, as a brisk road bike. I suggested an engine using a new, old stock, Holder crankcase with reground main bearing cups, an iron barrel bored for Silk pistons, a High Comp head and new high strength cranks, new flywheel etc. With some gas flowing, this would make a good engine at about 50% of the cost of a “One Off” all alloy competition type motor. An order was placed and we are starting to get components gathered together. In order to proceed with several earlier jobs, I am involved in reconditioning about 30 con rods as a batch. It is completely uneconomic to do them individually, due to the considerable time spent setting up the machines for the different operations.

We will leave this here and when I return from Lydden, I will add a few lines and pics about that.

Until then,

Best wishes,

Roger © 2003

email or