Seized engine strip

[ColinMarr]

Time to clarify a few things! I think:

•   The early Aprilia had aluminium alloy rods that fitted directly onto the crank pins. Sounds nice, but apparently it didn’t prove too durable.
•   Later and modified engines had hard demountable metal (bronze/ steel?) shells with thick white metal bearing material cast in, which was between 1 and 3 mm thick. About the same as the mains, I think.
•   Thin wall bearings with bronze/ steel caps and a thin layer of bearing material, say 0.3 mm (0.012 inch) thick, came later and may have been retro fitted to Aprilia engines.

‘Stoning down’, as I have suggested would only be appropriate for thick white metal and the reduction in cap thickness would be negligible in terms of any reduction in overall strength.

Purists and rich men eat your hearts out!

Colin

[davidwheeler]

I suggested to Serdi that we make new bronze backing shells to fit between the later series rods and shell bearings but they said the the rods themselves were not good enough so I went the route of new steel rods and Vibration Free.  This is an expensive route!  The rods were £200 each and Vibration Free at half price were still £411.   I suspect that, if they have to do it again, it would be cheaper as they now know what to do.  I wonder though if the best thing to do would not be new bronze backing shells and thin wall shells mounted in them.  It works very well in the Lambda and I doubt if it would cost a lot more than new white metal.  I have a set of spare rods if you need them!!

[DavidLaver]

YIPPEEEE!!!!

Got a couple of half hours at it this weekend and the crank and pistons are now out. 

Took but moments to clean the bore tops with a PROPER wire brush in a cordless drill.  After all the soaking and tapping back and forth over the weeks (months?) prior the pistons could be pushed up to the bore ridge by hand.  I then used a 3in wide strip of ply as a drift against the bottom of the rods and a small rubber mallet (I've got more than a draw full of different hammers) to pop the rings then eased them the rest of the way out by hand. 

So went three of the four.

The problem was that on some of them the bolts have been pushed up, and on one of them a bolt head caught on a liner.   What to do?   With the rings out the top I couldn't push it down.  Remove the rings?  Compress and re-insert?  The bolt couldn't be pushed down by hand, and putting a nut on the end and pulling didn't work.  After a soak (for the bolt) and a ponder I put a stack of washers on the bolt and tightened the nut down a bit, off again and add another few washers, tighten a bit more and so on and the bolt moved almost all the way back (the head had turned so fouled on the rod rather than seating) but far enough to be able to wiggle it past the liner and out.

With the pistons and rods out and the crank was free to turn without obstruction and feed the timing chain out.

I could also spin the crank and the oil pump drive until the drive gear taper pin was accessible and drive that out.  Easy enough with the right size drift - the first was just the right size to jam in the hole rather than drive it all the way through but with THAT free I found a blunt burr from removing the cotter pins was the right size and the prize pin popped out, gear slipped off, and the shaft came out the top with finger pressure.

The fuel pump drive pin is the next target.  It moves down in response to the small rubber mallet but it needs to be teased up.  Its soaking for now.  The "mystery screw" inside the fuel pump mounting flange (previous posting) just pokes out the other end into the crankcase - maybe to plug a hole or crack?   Should there be a hole to let a bit of oil mist into the fuel pump drive?

Crank lifted out as easily long as it was held level so as the thrusts didn't pinch it.  The main bearings look well worth a try and no obvious damage on the crank.  Once its all clean I'll measure.

Piston little ends are tight.  I soak and wiggled one until it was loose but again just how loose is a "race tollerance" and how loose is a "rattle from the little end"?  With this engine am happy to "suck it and see".   

Pistons are Hepolite +30.  No broken rings and only a few remain stuck.

Maybe its the timing chain tensioner next.

David

[davidwheeler]

Well done!  Nice that you are making such good progress.   I did fit a 2CV petrol pump at one time (it bolts straight on) but have now just covered the hole and fitted an electric pump which is much better and saves much engine churning in the mornings.

[DavidLaver]

Tipped the photos out of the camera into the back of the PC last night. 

The question is if that's a repair to the front of the block or if they're all like that...?

The pic of the crank and again of the rods and pistons merely by way of celebration.

David

[davidwheeler]

No, they are all like that it allows access to the gears at the front of the crank.  If you withdraw the crank gear and oil flinger you can then remove the crank without extracting the distributor drive shaft.  The back is similar as I recall but my spare engines are buried in a steel cupboard so I cannot be sure.
When you finally reassemble, make sure you put in place something to prevent oil tracking along between the crankshaft pulley and the crankshaft (see "mysterious oil leak"!).

[Parisien]

Loved this thread guys....simply wonderful, I can only assume it all worked out as it should have in the end?


P

[DavidLaver]

Its all a bit Marie Celest at this point.  Every time I pass I spray a bit of WD40 its way.  Hardo to see me getting even 10mins on it before Christmas.  Who knows over the Christmas season...everyone else glued to the TV and sneak away...

David

[davidwheeler]

There is a return scroll thread on the crankshaft at each end and this depends on a close interference fit with the aluminium.  Yours looks unworn so should be OK within the limits of 1938 technology.   My oil leak is getting better as crankcase pressure drops as the rings bed in.  That is the trouble with using modern oils, there is so much less wear that running in takes a loooong time.

[davidwheeler]

I have a set of new genuine SSS pistons (72.7mm) that I bought from Harry 40 years ago and are now surplus to requirements.  No rings but Alan at Clupet Piston rings just down the road from here will be able to make some.  The crowns are very slightly domed so standard compression.