Engine numbers

[Tony Stephens]

Not a new topic, but I have studied previous contributions and am wiser, but still without the answer I was hoping to find......
Thinking ahead towards an engine for my Aprilia, I was looking at cylinder blocks. The engine I bought with the car, something of a bitsa I think, has a rather early block MOT97 1727, but there are a number of rather ugly plated external repairs to the water jacket where it curves in to the crankcase, suggesting that the whole thing may be depressingly corroded and expensive to repair. I have a spare, bare block complete with what looks like its own main bearing caps, which is almost uncorroded and clean in the water jacket: nearly in unused condition. But it has a number which I do not understand at all: an etched A, followed by stamped or engraved 120426.
This number does not contain either MOT97 or the less welcome (to me) MOT99 for a second series motor.
 Also 120426 seems an unfeasibly high number.
Anyone shed any light on this? Or do we think it has for some reason been renumbered. If so, I had better measure bore size and angle, or try and find other numbers elsewhere (bearing caps, perhaps?) to see what I have actually got, and if I can make use of it.

[neil-yaj396]

Isn't the 'MOT' number the casting number? i.e. it would always be the same for that series of engine. The stamped/etched numbers would be the actual in series engine number. That's the case on later cars.

[simonandjuliet]

Are you sure that the A is an A or could it be an F ?

Ardennes engines start with F and don't , as far as I remember, have MOT 97 (1350 cc) or 99 (1500 cc)

V early and Ardennes engines have different castings, they don't have "webs" under the head. Tony, do you have a photo of yours ?

I am away so can't take photos to explain what I mean !

[Tony Stephens]

 When I am at my spares location next (ministering to the Trojan) I will have a better look, inspired by your superior Aprilia knowledge, Simon

[Tony Stephens]

On checking again, I find my spare block with an odd number (12426,not as previously stated) has 4271 stamped on the crankcase bottom flange, and also on the main bearing caps, suggesting an  S1 engine. Why it has been renumbered in anybody's guess, although the mains caps are also marked 5007, perhaps an engine rebuilder. FWM Ltd have stamped their name on the water jacket gasket face at the rear.
It does have strengthening ribs  below the head face, as you see if myefforts at posting a picture are successful. PS: Sorry about the car boot contents confusing the picture!

[Andrew Cox]

I have just checked engine nos 3605 and 6720. The engine numbers are repeated from the exterior of the block to the inside of the block next to the no 2 main bearing journal although the later stamping isn’t preceded by the letters MOT . The casting for the water outlet on Tony’s would indicate that the block is first series and I would be fairly sure he has engine no 4721

[Andrew Cox]

I’m having a bit of trouble posting multiple photos. This should be of the internal number for 6720

[Parisien]

Yes Andrew, there's a size limit per photo file, try an image resizer, allows to put up 3/4/5 on a post

P