Narrywoolan*

Engine Rebuild: Part one - February 2018.

An annoying habit of many Aprilias is drive train vibration, something that over the years I've worked on eliminating. However, 1070 always has had some engine vibration issues, as well as a constant engine "ticking" noise. At last years Castlemaine Rally I had the chance to compare my Aprilia to another with a Don Wright rebuilt engine, mine definitely had more vibration and assorted noises, simply put it wasn't as smooth as it should be. Therefore I decided it was time to investigate and do a possible rebuild.


1070 last had a complete engine rebuild back in February 1991, click for details.  I believe later work also included hardened valve seats for unleaded petrol, valve stem seals and I did the rocker gear in 2016, click for details. I can only estimate the kilometres done since 1991 to be around ±50,000.

Remove engine, disassemble, inspect and measure.

Using my engine hoist I've found it's easiest to remove the engine gearbox and radiator as one lump. I bought the hoist ten years ago and it has had a lot of use! Not only removing Lancia engines but lifting rear ends, moving lathes, milling machines and many other heavy objects.

Once on the bench it was a simple task to remove the radiator, gearbox, starter motor, distributor, fuel pump and the rocker cover before tackling the head. Removing the head requires all the rocker gear to be dismantled to gain access to the central head stud.

This was the first time I'd removed the head it so it was done with some trepidation as Aprilia engine blocks can get very corroded. Initially the bottom of the head looked fine and the head gasket didn't reveal anything nasty.

The top of the block had a lot of muck around the cylinder liners. I've been using Red Line Water Wetter with demineralised water in the cooling system so perhaps all this stuff formed in there in the past? After cleaning it all out the top of the block looked very good with no sign of corrosion.

Speaking of corrosion, the photo of a 2nd series block, below left, shows the extent it can reach. You can see the corrosion around the centre head stud, the alloy around the cylinder liners can get much worse than this which can lead to water leaks and/or the liner coming loose. The damage to the areas around the outside is from the water passages in the head gasket where they overlap the edge.


Compare the two head gaskets on the right, the copper version is an aftermarket Excelsior that was on my engine and the other is a modern composite to the same pattern as a Lancia original. Look at the highlighted holes, in the copper gasket they clear the inside edge of the block, on the other they don't. It would appear the original gasket design could cause some corrosion.

At this point I got my automotive genius Morgan Mike to come around for an inspection. He suggested before I go any further we should check the compression ratio and measure the bores. Standard compression ratio for a 1st series engine is 5.75:1, the observant will notice the pistons are non standard, the bores all measured 73.95mm, standard is 72mm, the stroke was the original 83mm, this added up to a 1426cc capacity, slightly more than the original 1352cc. With that in mind we measured the compression ratio to be 6.23:1.


Next was the exciting bit of removing the pistons and crankshaft! So off with the sump, the crankshaft oil feed and start to remove some big end bolts and con rods.

A note of caution here, be very careful not to lose any of the oil pressure safety valve components under the tab where the oil feed screws into the block, as there is a spring and ball valve in there, 38-4572 & 48024, that can easily pop out and get lost!

Removing the conrods and pistons revealed some nasty truths! 1st the engine had always made a ticking noise that adjusting valve clearances and rebuilding the rocker gear didn't resolve, see here for the rocker rebuild. Pulling out no.1 piston revealed a broken piston ring, the source of the ticking noise, luckily there was no damage to the bore.

Next taking off the big end and mains bearings revealed all was not well at all with some of the white metal bearings starting to break up. Luckily none of the loose pieces of metal had made their way out into the sump or oil ways.

A note on engines. Up to engine number 7700 the conrods ran directly on the crankshaft, after that they were fitted with steel backed white metal liners. Therefore 1st series engines have two different types of conrods and crankshafts. The crankshaft mains journals are the same size, standard is 55mm, the rod journals are 45mm on the earlier version and 43.5mm on the later. In the photo below on the left the top rod is the later type fitted to my engine and the bottom the earlier type that ran directly on the crank. The crankshaft photo on the right shows the later type at the top and the earlier version below. Note different oil feeds to the rod bearings.

Even though 1070 is a 1937 model the engine is not the original, that vanished back in the mists of time, this engine is a composite from a number of sources. The block is 1938/1937, it has two date stamps, the sump is off engine 3652. The crankshaft, dated 1951, is the later type, the conrods are also the later type, interestingly dated 1947 & 1948. In the photo above the top piston is an AE, as fitted to my engine, the bottom is an original Lancia.


After a lot of thought, consultations and examining the bank balance, the decision was made to buy new bearings from Cavalitto, getting the old ones re white metalled was thought to be fraught with problems.


When the engine was rebuilt back it the UK the did do a very nice job of fitting modern mains oil seals, a lip seal at the front and a large O ring and lip seal at the rear. The photos show the modifications to the crankcase, sump and the seal on the crankshaft, all very neat and leak free.

The block was then pressure washed clean. Morgan Mike came back with a truck full of measuring equipment. First the bores were checked to be round, they all came within 0.02mm top and bottom, so no issues there. Next we checked the pistons, all had wear marks from uneven contact in the bores and the top ring lands were worn to 0.010", not good. Finally we checked the crankshaft. The mains journals measured 53.60mm, 1.4mm under standard. The rod journals measured 42.42mm, 1.10mm under standard.


Checking against notes from Lancia England they have the maximum grind limit of minus 0.813mm for mains and minus 0.41mm for big-ends. So the crank has been ground substantially under size! However, Mike feels that because of the design it should not be a problem. The new Cavalitto bearings are all capable of being bored to those sizes.

New Cavalitto mains bearings
New Cavalitto big-end bearings

My final task before taking the engine to the re-builder was to paint around the top and bottom of the block with Glyptal 1201 Red Enamel to help prevent future corrosion.

Conclusion at the end of part one!


The engine has gone off to Rob Miller to be inspected and then re-built. At this point we have new mains and big-end bearings to fit, but first the crankshaft will be crack tested. The pistons and rods will be inspected with the minimum of new rings. The bores will be deglazed. Then the crank will be balanced along with the rods and pistons weighed to be exact, so stay tuned.