We were given 3 or 4 options when it came to valve spring compression rates with each spring group being clearly marked with different colour strips. Again taking the Eng’s advice we opted for one of the spring compression rates from the middle of the range but also took along 6 engine sets each of the other spring options as spares. All of our engines were fitted with titanium valve collet retainers which required all valve spring end faces to be very carefully ground and polished to prevent spring to collet retainer chaffing.
We had already decided back in the UK to reduce the inlet valve head diam from 36 mm to 35 mm and the exhaust valve from 33 mm to 32.5 mm for the 250 and 256 cc engines and we proceeded in having 6 or more sets of valves modified to these dimensions in the machine shop – we recognized that with thinner valve seat contact areas we may be required to dress the valves and seats more frequently but as it was already our intention to check valve to rocker clearances after every race and practice session and to lift the heads if there was any sign of deterioration, we felt having smaller and lighter valve heads would be an advantage.
Ron Kenward had already demonstrated to me how he ‘hand dressed’ rocker arms back in the days he was campaigning a four valve Rudge and his Excelsior Manxman and I brought the set of 175 Moto Parilla rockers Ron had dressed back in the UK to Milan – You can therefore imagine my surprise and delight when one of our assistants walked into the race shop and showed us a set of rockers he had dressed at the factory which looked virtually identical to the ones Ron had prepared.
Dressing the rocker arms entailed removing any excess material, particularly from the ends and sides of the arms, using in the main a bench grinder fitted with a fine grade wheel, taking great care not to remove too much material at one time causing ‘ bluing’ (tempering) of the metal – each pair of arms took well over an hour to complete
A week later one of our assistants arrived in the race shop with a set of alloy rocker arms which appeared to have been machined from billets and with 2 sets of alloy push rods with steel capped ends – The alloy rocker arms were manufactured by an outside supplier and there was apparently only the one set now sitting on my work bench available. The alloy push rods were manufactured, it was claimed, by Moto Parilla some time in the past and these 2 engine sets were the last they had in stock.
After consulting with the Eng we decided to fit the alloy push rods into the 125 only, keeping the other set in reserve. Later when we assembled the 250/256 heads we tried fitting the alloy rocker arms to the 250 engine but found that even after extensive fettling of the heads there was very limited clearance in several areas. We therefore decided to stay with our dressed steel rocker arms with the intention of testing the alloy arms later when a suitable opportunity arose.
Many years later a 175 Moto Parilla owner and enthusiast showed me a set of alloy push rods with steel capped ends that looked identical to the ones we used in the 125 engine – he claimed these push rods were used by Moto Parilla in an earlier standard production model but he did not know when or in which model?(Webmasters note: I have just such a set in my 1953 175 TS)
Working on the 250 and 256 engine cylinder heads, we fettled the inlet ports in accordance with Phil Irving’s recommendations – all as illustrated in ‘Tuning for Speed’ We also had to open up and blend the entry of the inlet port to match up with the bore of the 30 mm Dell’Orto racing carbs – this operation on a Moto Parilla head requires considerable care to avoid breaking through into the valve spring recess oil drain hole located in the head casting passing down very close to the port in some head castings!
Apart from removing any irregular machining or casting marks, we did not modify the exhaust ports or the combustion chambers of the heads in any way.
We removed weight from the engine and cycle parts when ever we found an opportunity but the primary reason we waisted the barrel and head studs was to gain more constant cylinder head gasket pressure. We again saved weight when cutting away the front of the RH outer crank case cover but this was primarily to allow air flow through the cover assisting engine cooling
We initially set the compression ratio of the 250 and 256 engines at 8.5 to 1 and the 125 at 8.8 to 1 using composite head gaskets on all the engines. However we were given a number of solid copper gaskets of varying thickness to enable us to reduce the compression ratios when racing behind ‘The Iron Curtain’
The Eng strongly advised us use a semi synthetic Shell S.A.E 40/50 racing oil and NOT to add any Bardahl which many riders were using in their bikes at the time. During the previous three years I had been contracted to Castrol Oil and was proposing to use Castrol ‘R’ in my Moto Parilla engines but we took the Eng’s advice and only used the recommended Shell oil through out our 1964 campaign.
One of the most interesting things we did find in ‘Aladdin’s’ cave was a 175 or 250 high cam crank case with a prototype oil pressure driven chain tensioner mounted in place of the normal spring tensioner – this prototype unit which consisted of an alloy block ‘piston housing’ a little smaller than a standard Swan match box, mounted on its side in the same position as the standard Moto Parilla spring action unit. There was a very small bore oil pipe pinned to the inside of the crankcase tower connecting the piston housing to the main crankshaft oil delivery union. In place of the normal springs there were two small pistons located in the ‘housing’ which pressed against the back of the chain sliders, once oil pressure was obtained.
This system for chain tensioning seemed to me to be well worth developing and I was seriously considering fitting the unit into our 250 engine; however, we were eventually discouraged from doing so by the Eng for reasons which I have now forgotten! – Perhaps he thought we were just running out of time?
We reduced the weight of the standard frames by removing all non essential lugs, the seat extension arms and excess material from the swinging-arm pivot spindle plate brackets. We declined the option offered to have the frames strengthened by welding additional tubing from the top of the swing –arm spindle brackets to the top tube of the frame as this would have added weight and I did not see any need for this modification as we did not have the top spec Ceriani forks or Oldani brakes as originally planned – If we had fitted these higher spec components I have no doubt the added frame stiffening would have been required and would have been beneficial.
The standard Moto Parilla/Marzocchi fork stanchions were shortened by removing 6 mm from the top of the stanchions. The pistons and damping diaphragm washers were replaced with higher quality and lighter alloy parts. We had three sets of 4, 6, and 8 mm thick alloy spacer washers machined to fit between the top of the fork springs and the underside of the bottom yokes to enable us to adjust spring preload
The bottom yokes were lightened by machining 5 mm off from the underside of the yokes and by drilling out material from inside the yokes arms. The top yoke steel pressings were lightened by drilling. At all times we filled the forks with the highest grade fork oil we could find of S.A.E 25.
Our rear suspension units were standard Moto Parilla parts but each pair were matched by testing 20 or more units on a compression and damping function rig Moto Parilla had installed on the main assembly line at the rear suspension fitting station.
Wheels and brakes were again standard Moto Parilla units with the exception that we fitted Ferodo green racing brake linings and modified the wheels by drilling the hubs and spoke flanges to reduce weight and improve cooling – this also made them look more appropriate for a racer! All our wheels were fitted with the very latest Dunlop triangular section racing tyres.
The 125 was fitted with 250 x 18 front and 275 x 18 rear tyres
The 250 and 256 were fitted with 275 x 18 front and 300 x 18 rear tyres
The standard MSDS seat bases manufactured from steel sheeting are very heavy so having brought some aluminium sheeting over from the UK to make three sets of rear racing number plates we had just enough sheeting left over to manufacture two seat bases in aluminium which were much lighter. I also found the standard seats to be very narrow so we made the new aluminium bases 30 mm wider than standard whilst still using the standard cover packed out with wider foam.
We hunted high and low in Milan for a pair of suitable alloy mudguards to fit the Moto Parillas but had no success. Being anxious to complete all our work before setting off for the Ring we just had the standard steel mudguards stripped and brush nickel plated – at least they now looked the part!
The exhaust down pipes were standard parts but in the case of the 125 we found a down pipe in Aladdin’s Cave with a bore 2 mm smaller than the standard 175 MSDS pipe and this we fitted to the 125.
The down pipe and megaphone fitted to the 250 were standard Moto Parilla racing parts and in the case of the 256 we also found a ‘special’ megaphone in the Cave which we fitted.