POST 27 - APRIL 2012 - ENGINE REBUILD PART 3 - SHORT MOTOR

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Please keep in mind when reading this particular post that I am but an enthusiastic amateur albeit taking a good deal of care.  My goal is to build a very reliable smooth running engine, but if I make a mistake, it will probably be a big one!

Although only last October, it seems to be an awfully long time ago (especially in memory recall terms) that I dismantled the engine. I was encouraged to do the re-build myself after several offers of technical assistance from friends and acquaintances.  My initial requirement was to find a first rate machine shop, ideally with some XK engine knowledge.   After some research I decided on a company quite local to home,  AMAC in Northallerton.  Always very busy and with an excellent reputation, I was forewarned that it may be gone a while, and so it was.  As I have the luxury of time, this was not really a problem. Four months later and right on cue, I got the call at the end of February advising that the Block, crank and other associated bottom half components were ready for collection.  The cylinder head repairs and machining were still to do, but this would give me plenty of stuff to be going on with.

Courtesy of friend Dan at Classic Jaguar in Texas I received in December, a set of beautifully engineered Ross forged alloy pistons and Total Seal rings with individual piston weights differing no more than half a gram. AMAC do a similar balancing job on the con-rods, after which they dynamically balance the crank with flywheel, clutch pressure plate and front damper.   Dan also supplied a nicely engineered modern rear oil seal conversion, which just required the scroll to be machined off the crank and the appropriate seal area to be turned down to 2.632 inches.   With the front oil seal also upgraded to a modern type my past 'persona non grata' status at some posh driveways may be reviewed.

Wonder what Sigmund would make of this?

Checking the block, I'm greatly encouraged by the spotlessly clean condition of all the internal oil ways. AMAC pickled the block and cleaned masses of compressed gunge from the crank. Running  spiral brushes through the various oil passage ways shows not a vestige of anything unpleasant. Great start.

And this !  Surely a Turner prize photograph.

Mechanic mate Mel produces a tube of Graphogen assembly grease from the back of his garage, last used in the mid 80's he tells me and no longer needed.  Apparently modern car engines are very rarely re-built. When they fail (which is unusual) a replacement is normally acquired from a breaker.

The main bearing shells are installed dry into the block and caps and Graphogen grease is coated onto the bearing surfaces.  The top half of the new rear oil seal is fitted using Locktite on the machine screws.  The crank is gingerly lowered into place and the caps (centre with new thrust bearings) are fitted.  End-float is checked and measures an ideal 0.08mm, just over 3 thou. 
Lightly lubed bolts and hardened parallel washers (in place of the original tab washers) are gradually torqued down to 72 LB FT. The bottom half of the rear seal conversion is installed, again using Locktite.  Afternoon visitors take turns to spin the crank and marvel at the smoothness of reciprocation.  I should think in all, around an hours work for a professional.  Allowing for thinking, socialising and tea drinking, a good days work for me.

End float measurement.  Also clearly shows bottom half of oil
seal conversion and Graphogen assembly lube on main bearing.

Completely confident with the crank installation, I move on to to the pistons, con rods and big ends. AMAC have precisely set the gaps on each piston ring in its bore with a very neat miniature grinding machine.  Including the 3 part oil ring set this equates to 5 rings per bore, 30 in total. Not something I would even attempt by hand.  With new con rod fasteners, the question of torque wrenches versus new fangled stretch gauges arises. All highly technical, but I think that a well lubricated factory spec of 37 LB / FT of torque will provide the necessary clamp forces for my application which is unlikely to exceed 5000 RPM ( I believe applying around an amazing half a ton load on each con-rod bolt at maximum G)

Total Seal rings come with very specific fitting instructions.
Two Spirolox wrist pin retainers each side replace usual circlips.
Note new type of nut for con-rod bolts.  No washers or lock tabs
of any sort.  Seems odd but I am assured it is totally correct.

Ross forged piston with Total Seal rings

Con rod little end bushes were virtually unworn and in excellent condition. Big ends were sized and found to be near perfect. Con rods, gudgeon (wrist) pins and pistons were assembled. Spirolox wrist pin retainers were supplied instead of the usual circlip. My initial attempts to install these fiddly little coils of sprung steel were hugely frustrating.   By early afternoon and at the point of giving up, (8.00am Austin Texas time) I make a call for help to Dan, and after a little explanation from his engine builder I'm popping them in like a pro. Just looking at the design gives me great confidence in the inherent security of these things. Two on each side of the pin seems a little OTT but why skimp when its known to be an occasional cause of disastrous failure.

Spirolox gudgeon pin retainer opened up ready to be pushed
in to the groove bit by bit.  Easy when you know how.

Machine work on the engine block was pretty much as predicted with number 3 bore re-sleeved and all taken out to +30 thou.  The deck sloped 15 thou out of parallel to the line of the crankshaft (apparently not unusual for this vintage) and this has been corrected with a not inconsiderable skim.  The pistons with 25cc of dome now sit between 26 and 31 thou above the deck.  Temporarily swapping Pistons and rods between the cylinders gives another slightly different set of numbers, showing that both con rod length and crank throw are jointly responsible.  These variations I understand are accounted for by original machining tolerances.

Very accurate but Heath Robinson device to measure piston to
deck height.  Steel block holding gauge was a tow ball spacer
in an earlier life.

Assuming the head is also skimmed  a maximum of 25 thou this will effectively increase the compression ratio from 8:1 to around 8.75:1  Changing from the standard 15 thou gasket to a 40 thou composite item will bring this down I calculate to 8.4:1 (comfortable 95 octane country) which is more or less where I would ideally like to be.

One part of the re-assembly I have been a tad apprehensive about is the installation of the distributor drive mechanism as there seem to be a number of opportunities to get this wrong.  I usually only require one!
In fact, it turns out to be quite straightforward.  With Pistons 1 and 6 at TDC the distributor drive shaft should look like the picture below with the drive line at approximately the 5 minutes to 5 position.   Its only when you come to set the valve timing that you need to ensure that the larger segment is to the right.  If it's a little out, your distributor will point in not quite the right direction.  Not ideal, but not really a problem.  However, if you installed it entirely the wrong way round, your distributor would need to be 180 degrees about face, and that wouldn't be good.

With 1 & 6 at TDC, position of distributor drive shaft - 5 minutes to 5
Larger segment to the right when you get round to valve timing.

Assembling the distributor drive turned out to be a two man job.  My helper held the drive shaft in place with a bar and socket pushed up the orifice, whilst I carefully aligned the cog with its woodruff key and tapped it on to the interference fit shaft with an old socket.     

Distributor drive - awaiting lock washer and nut.
Note the increased O/D collar on the crank to accommodate a modern oil seal.

Final task on the underside is to fit a new oil pump and the oil pick up assembly.  A metal gauze filter appears to cover the inlet to a round metal chamber, which I reason must be full of all manor of nasty gunge but I can't see any way to get into it.  I drop it into large bowl of thinners in the hope that this might dissolve its unknown contents .  Very strange, it seems that its made of a metal so light that it floats.  This is very exciting.  The penny finally drops.  I can't get into it because it's completely sealed.  Its actually full of air.  Yes - its a float, with the oil pick up pipe passing through it.

New oil pump and incredible floating err - float

With the oil pump, float assembly and associated metal work back in place and one final check on torque setting and all other fasteners, this completes the main part of the engine bottom half assembly. 

Next scary task is try and make some sense of all of those complicated looking sprockets, chains and things driven from the crank shaft.