Latest News

Update on the Bristol Mercury

Story added 12th March 2009 by Fred

 

Reading last years initial write up on the Mercury 20 rebuild, I see I said we had a usable magnesium alloy casing for those corroded items which at the time had been removed.  That was true then, but is not so now.  The casings removed first from our rebuild engine were for the accessory drive units from the rear of the wheel case and the front cover of the timing case.  Though both the front timing case and the outer cross shaft casings had bad corrosion including holes we had in the package of spares from Strathallen usable replacements.  However, when we removed the sump and the wheel case itself, we not only found holes and corrosion in the items from the rebuild engine, but all the spares were as bad or in some cases worse.  Barney has spent much effort in the past couple of months carefully cleaning out the corrosion from the best sump and wheel casing plus the next best so when we have the casings welded we will also have spares.  This may sound a bit of a disaster, but the best casings are limited to one hole each and though some internal corrosion was present in other areas it was not too bad being in thick sections of wall which cleaned up with a good safety margin.  Barney is nearing the end of this work and we will shortly be having a chat with a friendly specialist welding firm.  Barney has also cleaned up the main engine casings which are aluminium alloy forgings and are fine.  Toby has painted all these casings and the serviceable magnesium alloy casings ready for assembly.

I suppose the best description of what we have found on this engine now it is almost completely stripped is that virtually all fits and clearances measured to date are within new tolerances, unlike the recently completed Merlin.  All engines have three levels of tolerances, the first being new manufacturing levels which any new engine from the factory would comply with.  The second is the maximum worn tolerance, which is the limit of wear that a component can be re-used for a further full engine life and the third of course is the beyond maximum worn tolerances which renders a component reject for use as is.  Needless to say depending on the component, repair schemes do exist for some reject components to re-life them, like for instance crankshaft re-grinding/lapping and the fitting of undersize bearings.  So far with this engine we can say that because of the as new tolerances in most areas, no repairs will be necessary to the engine core and it looks as if the engine has not done too many hours.  The only area where wear has been outside new tolerances is in the pistons and cylinder assemblies though most is in the maximum wear tolerances.  We do have reasonable spares for most items in this area.

This said we have had to look at repairs to some steel items as well as magnesium alloy because of the dreaded corrosion.  One of the large roller main bearings showed some corrosion pitting on the races and rollers.  For this a specialist bearing company SPC Bearings will lightly grind the races and supply us with new slightly oversize rollers.  In addition, some of the ball bearing races in the wheel case and accessory drives were lightly corroded and the same company luckily had new items in stock as they are still a current size and meet the Bristol specifications for clearances and end float.

Crack testing has been completed on the important core items without any crack indications.  Items tested include the two crankshaft halves plus their maneton bolt and nut, the master rod, the articulating rods and their wrist pins with retaining bolts, the supercharger impellor, the cam ring and all other internal shafts and gears.  The only item not striped and evaluated to date is the reduction gear which is one of the last items fitted to the engine after rebuild.  The master rod and articulating rods have been re-assembled, but cannot be assembled to the crankshaft until the repaired main bearing is fitted.  The big end bearing is fine being in new tolerances and will do another life.  The accessory drives have been re-assembled with their new bearings where required, well oiled and sealed ready for fitting to the engine.  An oil pump has been built up and Toby is part way through the fuel pump for which new bearings have also been obtained.  Toby has also tested a large number of valve springs to obtain a set within the required load/compression limits and has refaced a set of inlet valves, some from this engine and some from our spares stock.  We have new exhaust valves as we bought two sets when we top overhauled the Lysander engine some years ago.  Phil’s dad Jim has been busy measuring pistons and valve gear for us and is now truing the end caps removed from unserviceable exhaust valves which have now been fitted to the new exhaust valves.

The (SVAS) have bought us a stroke honer to deal with the cylinders and a company in Harlow (Pace Engineering) who I used to use extensively in my long gone professional life has made us, FOC, a honing cabinet.  This gives an enclosed rigid mounting for the cylinders during honing and also provides a recirculation system for cutting oil during the honing.  We will move on to the cylinders when time permits, although, Barney has evaluated all the late type cylinders we have on site not currently fitted to serviceable engines.  They have been divided into four main categories.  Firstly cylinders with no corrosion and within dimension limits which only need glaze breaking.  Secondly cylinders with no corrosion but worn close to or out of limits which need honing and then plating back to size.  Thirdly corroded in need of honing and if dimensionally reasonable after this, plating back to new size and finally badly corroded cylinders which are not recoverable.  We should have enough from one to three to build this engine, though the plating is in itself a specialist task as it must be done with the alloy heads in place.

We have also finally managed to more or less sort out what Mercury engines and parts we have at Old Warden and these are as follows:-

Mercury 8.       1.  Complete ex-Gladiator, very tired, but good casings, on display.

                        2.  Ex Strathallen, hulk in back store, complete except cylinders and pistons, unknown condition, but hopefully will provide spares or a new core for the ex-Gladiator engine.

Note.  The Mercury 8 is an early engine strictly only suitable for the Gladiator.

Mercury 20.     1.  In Lysander serviceable.

                        2.  Ex Strathallen currently on rebuild as universal spare for Gladiator or Lysander.

                        3.  Parts of at least two other engines, spares only, not enough parts to build a complete engine.

Mercury 30.     In Gladiator serviceable.

 

By Steve McManus.