Tuning Differences in 126 blocks

[Bounding Bambino]

I was wondering, which of the 126 blocks are the most saught after when planning to build monster 700-800cc engines.

Im slowly on the hunt for a lower case, and there seems to be 4 versions of the 126 blocks. Obviously im looking for one that has the increased base thickness strength for cylinder over boring and such.

Seems like the general choices are:
126A5 000 - from 594 fiat 500R's

126A 000 - from 594 fiat 126's

126A1 000 - from 652 fiat 126's

126A2 000 - from 698 fiat 126 BIS engines.


Basically the rough plan right now is to do a 80mmx80mm engine ~804cc. with all the bits and goodies. But for now, just keeping an eye out for the block as that will likely be the only stock piece on the engine.

Looking to see what feedback folks suggest for which block to choose who have gone down this path.

 

[the hobbler]

For a start, forget the BIS crankcase; the BIS was water-cooled and a flat twin (like the Giardy). Look for a 126A1 crankcase, the 652cc '126' engine. The very last of the Polish '126'models, the ELX, had no fitment for a distributor as it used the Fiat 'Nannolex' electronic ignition. Unless you can get hold of a COMPLETE Nannoplex system, give these crankcases a miss as well. I say this because variouse odd little parts of the Nannolex system are almost impossible to find. The '652' are available new from various Continental sources, but if you can get a complete engine, so much the better---Poland a is good hunting ground for a 2nd hand 126A1 engine. Depending on the barrels you can obtain, you might need a spacer plate between the barrels and the crankcase.

 

[Bounding Bambino]

Fantastic..
Yes, i was leaning towards the 126A 000 or the 126A1 000 as best choices.

Now obviously the 126A1 being the one you recommend. Is the non 1 version, also a possible alternative?, even though it was used in 594'cc.. or are the 126A1 (650's), blocks the best choice as they have the thicker cylinder base bracing. Just wondering as i have a lead on a 126A 000 block.. Haven't found a 126A1 yet.


In-case your wondering for cylinders.. again, many many options way down the road to choose. Im just dreaming right now lol, but there is a aluminum finned nikasil/alusil coated cylinder kit ive come across in 79.5 and 82mm bores.. a 80mm stroke x 82mm bore would be a nice 844cc.

 

[Toshi 975]

To my surprise the 795cc engine that I rebuilt recently was based on a 594cc crankcase. Machining out the crankcase to take the larger cylinders very much diminishes the sealing face on the crankcase so the engine builders made the cylinders a light press fit into the crankcase to restore the seal.
There seemed no problems with crankcase strength, depending upon power I think that you are more likely to bend or break the crankshaft than the crankcase.

 

[the hobbler]

In the light of David's (Toshi) comment, yes you could use a '594' crankcase---a 126A. It just that using a 652 crankcase ,126A1, will mean less machining. I still stand by my suggestion of trying to get a complete engine(of either type)---you will end up with all the 'little' bits that you need--timing-chain cover, crankshaft seal-ring and oil-thrower, oil-pump etc. Being that they will be 'ex factory' the chances are that they will be a lot better quality than the 'pattern' parts---and fit correctly! No matter how 'customised' your engine will be, there are a number of 'factory' parts that you will HAVE to have. I will be putting a letter with the photos i promised you within the next couple of days.

 

[Bounding Bambino]

Awesome, thanks for any tidbits of info you can throw my way. I am definitely on the hunt for a complete engine also, no doubt about that. Right now i have sourced down a case, which would help with basic mock up and such. Nothing will go to waste