Engine Rebuild
Since the original re-commissioning in 2008, work around the engine had primarily centred around stemming fuel problems and numerous oil and water leaks until the time came for a rebuild. We had always known that this was on the cards, the only question was how long would she last in acquired condition. Other than excessive oil smoke from the breather and a tendency to overheat, she had always run quite smoothly, no nasty knocks or bangs etc, but by the end of the 2014 season it was evident that she was starting to struggle. So, decision taken that she would come off the road and await her slot with Paul Morris for what we initially thought would be a top end overhaul.
What followed was over a year of set-backs as problem after problem became apparent, amidst frantic searches for parts that in some cases were unobtainable.
The list of work is exhaustive – pretty much every moving component in the engine has been replaced. The only parts that were left in situ were the cylinder liners as there was little sign of wear – although that decision may turn round to bite us, see later comment.
First off the heads, which were excessively worn. New valves, seats and guides later, and they looked like new. The piston heads were cracked due I believe to impact from the valves at some point, so again new pistons, rings and pins were sourced. The injectors were sent away for refurb. Then attention turned to the crankshaft, which superficially did not show any wear……….until removal of the bearing caps revealed deep scoring to the bearing faces. The interior of the engine was very clean with little debris to indicate any fouling of the metals, and I can only surmise that the block had been re-assembled with the already damaged crank at an earlier rebuild. Note, we know the engine has its origins as a vertical unit that at some point has been converted to horizontal form – but who or where this work had been carried out is lost in time. It was thought possible to grind the crank, but in the end we could not source sufficiently oversized bearings and hence a new crank and matching bearing set as the only option. It was then discovered that the oil pump was worn, and we then had the dilemma of whether to put her back together knowing that the pump was weak, or bite the bullet and replace the gears. We took the route of caution, but could not obtain new or replacement gear wheels, which had to be made from scratch. When they arrived and trial fitted into the casing, one set was fractionally too tight and didn’t turn freely – more delays and time lost.
Finally by early 2016 she was starting to come back together. We decided to add an oil filter as further protection for all the rebuild work, but once again trying to find a unit off a Reliance or suchlike proved fruitless and we ended up converting a vertical housing from a 590 to suit the 691, with the filter unit separated and mounted remotely as would once have been the case. Why did LT have a policy for removing and blanking off oil filter assemblies?
Even this was not the end of the story. Trial running showed that she would build temperature at an alarming rate on any prolonged incline. In fairness she had probably always done this…..only we were oblivious from not having any gauges, or even a working overheat buzzer! Back to the drawing board……
The conclusion was that all we could do was improvise and attempt to overcome the inherent design failings of the class – few people will be aware that the Merlin radiator is actually smaller than seen in many traditional front engine vehicles – to then have this slung at the rear offside out of the main airstream, and no wonder they had a tendency to overheat! First step was to extend the capacity of the standard radiator by c50%. Next the electric fan assembly (itself a replacement for the original mechanical drive which had sheared off and disintegrated a few years back) was modified to include a third fan unit, ensuring that air was drawn across the full face of the extended radiator. Lastly, we had managed to salvage an original louvred external radiator panel from MBS 464, which had latterly been in use as a storage shed at a boatyard up until 2011. The panel was badly wasted but was expertly welded by Dick Turpin (owner of SMS 678), and now helps to direct air flow in towards the radiator. These panels tended to be replaced by a flat mesh grill during service life – possibly to aid cooling when a vehicle was stationary or sitting in traffic. See External Restoration page for pictures of the louvered radiator panel.
Trial runs during Nov and Dec 2016 have been encouraging – the temperature gauge barely reaching 75 degrees even on an incline or a fast motorway run. The real test will come during the warmer summer months, but for now it is a case of keeping fingers crossed………
Although the 691 now makes all the right AEC sounds and fires up freely without managing to fill the barn with noxious fumes, one issue that persists is that she is still quite smoky, particularly on initial pullaway. With the engine performing well in every other respect, the thinking is that the new piston rings need time to bed in to the cylinder liners, which were left unchanged during the rebuild. The plan is that we will get some mileage under her belt during 2017 and see how the condition settles down. It’s been a long, fraught and expensive journey, but hopefully attention can now start to turn away from the constant challenge posed by the mechanical units.
What followed was over a year of set-backs as problem after problem became apparent, amidst frantic searches for parts that in some cases were unobtainable.
The list of work is exhaustive – pretty much every moving component in the engine has been replaced. The only parts that were left in situ were the cylinder liners as there was little sign of wear – although that decision may turn round to bite us, see later comment.
First off the heads, which were excessively worn. New valves, seats and guides later, and they looked like new. The piston heads were cracked due I believe to impact from the valves at some point, so again new pistons, rings and pins were sourced. The injectors were sent away for refurb. Then attention turned to the crankshaft, which superficially did not show any wear……….until removal of the bearing caps revealed deep scoring to the bearing faces. The interior of the engine was very clean with little debris to indicate any fouling of the metals, and I can only surmise that the block had been re-assembled with the already damaged crank at an earlier rebuild. Note, we know the engine has its origins as a vertical unit that at some point has been converted to horizontal form – but who or where this work had been carried out is lost in time. It was thought possible to grind the crank, but in the end we could not source sufficiently oversized bearings and hence a new crank and matching bearing set as the only option. It was then discovered that the oil pump was worn, and we then had the dilemma of whether to put her back together knowing that the pump was weak, or bite the bullet and replace the gears. We took the route of caution, but could not obtain new or replacement gear wheels, which had to be made from scratch. When they arrived and trial fitted into the casing, one set was fractionally too tight and didn’t turn freely – more delays and time lost.
Finally by early 2016 she was starting to come back together. We decided to add an oil filter as further protection for all the rebuild work, but once again trying to find a unit off a Reliance or suchlike proved fruitless and we ended up converting a vertical housing from a 590 to suit the 691, with the filter unit separated and mounted remotely as would once have been the case. Why did LT have a policy for removing and blanking off oil filter assemblies?
Even this was not the end of the story. Trial running showed that she would build temperature at an alarming rate on any prolonged incline. In fairness she had probably always done this…..only we were oblivious from not having any gauges, or even a working overheat buzzer! Back to the drawing board……
The conclusion was that all we could do was improvise and attempt to overcome the inherent design failings of the class – few people will be aware that the Merlin radiator is actually smaller than seen in many traditional front engine vehicles – to then have this slung at the rear offside out of the main airstream, and no wonder they had a tendency to overheat! First step was to extend the capacity of the standard radiator by c50%. Next the electric fan assembly (itself a replacement for the original mechanical drive which had sheared off and disintegrated a few years back) was modified to include a third fan unit, ensuring that air was drawn across the full face of the extended radiator. Lastly, we had managed to salvage an original louvred external radiator panel from MBS 464, which had latterly been in use as a storage shed at a boatyard up until 2011. The panel was badly wasted but was expertly welded by Dick Turpin (owner of SMS 678), and now helps to direct air flow in towards the radiator. These panels tended to be replaced by a flat mesh grill during service life – possibly to aid cooling when a vehicle was stationary or sitting in traffic. See External Restoration page for pictures of the louvered radiator panel.
Trial runs during Nov and Dec 2016 have been encouraging – the temperature gauge barely reaching 75 degrees even on an incline or a fast motorway run. The real test will come during the warmer summer months, but for now it is a case of keeping fingers crossed………
Although the 691 now makes all the right AEC sounds and fires up freely without managing to fill the barn with noxious fumes, one issue that persists is that she is still quite smoky, particularly on initial pullaway. With the engine performing well in every other respect, the thinking is that the new piston rings need time to bed in to the cylinder liners, which were left unchanged during the rebuild. The plan is that we will get some mileage under her belt during 2017 and see how the condition settles down. It’s been a long, fraught and expensive journey, but hopefully attention can now start to turn away from the constant challenge posed by the mechanical units.