Technical 126 650cc engine transplant..

[The Whitakers]

#Update ...…


Bit of a manic tear down last night!....surprisingly enough though the amount of wear is minimal throughout. You can still see the honing in the cylinders and no lips whatsoever at the top and bottom of the piston stroke. The cam is like new and the big ends and mains are cool although I have a set of big ends so i'll change them just because why not...…


Ordered all the bits for the rebuild so the rest of the week will entail clean down and re-assemble ready for the swap at the weekend...…..


I'll take pics as an over view but wont have time to go to much into detail...…

 

[Hobo1960]

I'll be watching this thread with interest as a 126 transplant is something I'd like to do when time permits. I've noticed that some of the prices being asked for used 126 engines have got a bit silly. I've seen a seized one on eBay for £450, just the engine, no gearbox!

Can anyone confirm that a 500 gearbox with 126 bellhousing will fit a 126 engine? I read somewhere that the 500 gearbox is a stronger unit than the 126, is this correct?
I'm not too fussed about synchro as I enjoy double declutching, but fitting a 126 engine and transmission is probably the best solution and will allow me to mothball the entire 500 engine and transmission.

 

[The Whitakers]

I'll be watching this thread with interest as a 126 transplant is something I'd like to do when time permits. I've noticed that some of the prices being asked for used 126 engines have got a bit silly. I've seen a seized one on eBay for £450, just the engine, no gearbox!

Can anyone confirm that a 500 gearbox with 126 bellhousing will fit a 126 engine? I read somewhere that the 500 gearbox is a stronger unit than the 126, is this correct?
I'm not too fussed about synchro as I enjoy double declutching, but fitting a 126 engine and transmission is probably the best solution and will allow me to mothball the entire 500 engine and transmission.

I believe you are correct in saying the 500 box is stronger but to be fair the amount of power you can get out of these lumps isn't going to blow a mesh box apart...….get a mesh box in there mate......and yes you have to swap the bell housings over (or so I have been told)….

 

[Toshi 975]

It sounds like you have got yourself a good engine there. If it has minimal wear I would definitely not replace the big end bearings as the ones you have a most likely the factory originals, best quality and already run in

 

[Hutbed]

I've noticed that some of the prices being asked for used 126 engines have got a bit silly. I've seen a seized one on eBay for £450, just the engine, no gearbox!

It may be an unfair comparison as I am currently in Sicily, but I just bought my 650 engine complete with trans and 28IMB carb for €400.

 

[Hutbed]

Specifically a 126A1 engine in supposedly running condition (I doubt it) from a salvage yard.

 

[the hobbler]

It is quite an easy job to fit a '126' bell-housing to a '500' gearbox. Support the gearbox so that it is standing vertically, with the bell housing at the top. Remove the boot holders on the side of the box and then the big bolts that hold the bell-housing to the gear-box body. Carefully remove the bell-housing , making a note where the bearing play adjuster rings are (in order that you dob't upset the diff adjustment). If you are in any doubt as to the condition of the drive-shaft splines, this is the time to fit new shafts and couplings. Remove the '500' bell-housing---fit the '126' bell housing and bolt in place. Naturally, clean all mating surfaces and put a light smear of 'goo' on the mating surfaces. Refit the drive-shaft boot rings and clutch operating parts as required.
Despite the fact that I have a '126' 'box in my 500, I still tend to double-d-c on most down-shifts--much more fun! Remember, unless you are VERY good with your down-shifts, only select 1st gear when the vehicle is stationary--I tend to slip into 2nd very briefly (to align the gears) prior to selecting 1st
All the best with the conversion---let us know if there is anything that you need help on---it is what this Forum is for.

 

[The Whitakers]

Specifically a 126A1 engine in supposedly running condition (I doubt it) from a salvage yard.

Well that’s what I have just got, why is it special? I note it has double valve springs so it must be fast lol...

 

[The Whitakers]

It is quite an easy job to fit a '126' bell-housing to a '500' gearbox. Support the gearbox so that it is standing vertically, with the bell housing at the top. Remove the boot holders on the side of the box and then the big bolts that hold the bell-housing to the gear-box body. Carefully remove the bell-housing , making a note where the bearing play adjuster rings are (in order that you dob't upset the diff adjustment). If you are in any doubt as to the condition of the drive-shaft splines, this is the time to fit new shafts and couplings. Remove the '500' bell-housing---fit the '126' bell housing and bolt in place. Naturally, clean all mating surfaces and put a light smear of 'goo' on the mating surfaces. Refit the drive-shaft boot rings and clutch operating parts as required.
Despite the fact that I have a '126' 'box in my 500, I still tend to double-d-c on most down-shifts--much more fun! Remember, unless you are VERY good with your down-shifts, only select 1st gear when the vehicle is stationary--I tend to slip into 2nd very briefly (to align the gears) prior to selecting 1st
All the best with the conversion---let us know if there is anything that you need help on---it is what this Forum is for.

Am I right in saying I need to use the 500 shafts on the 126 box?

 

[fiat500]

Am I right in saying I need to use the 500 shafts on the 126 box?

Yes..and if your existing has the narrower, 19mm shafts you would be wise to replace them with new ones with an approximate 24mm diameter.

 

[the hobbler]

I think that you will find that the 126A1 engine/gearbox assembly (652cc) had the 24/25mm drive shafts. (some sites list them as 24mmm, others as 25mm). The 126 drive shafts are too long, so no matter which gearbox you fit,you MUST use the 500 drive-shafts.
I also think that all the 126A1 engines had 'double' valve springs as standard.

 

[The Whitakers]

I think that you will find that the 126A1 engine/gearbox assembly (652cc) had the 24/25mm drive shafts. (some sites list them as 24mmm, others as 25mm). The 126 drive shafts are too long, so no matter which gearbox you fit,you MUST use the 500 drive-shafts.
I also think that all the 126A1 engines had 'double' valve springs as standard.

Assuming it's just a straight swap on the drive shafts regardless of diameter?


Not sure what diameter my 500 ones are but they will be getting used in the short term, I'm not planning on doing any rolling smokies from the lights.....


Yes my A1 lump has double valve springs, I was quite surprised actually that it needs them. Assuming this is the best engine to tune then?


Rob

 

[fiat500]

Assuming it's just a straight swap on the drive shafts regardless of diameter?

Yes my A1 lump has double valve springs, I was quite surprised actually that it needs them. Assuming this is the best engine to tune then?

Yes, you can use the ones that are on your original gearbox...thicker ones is just the council of perfection. But although it's a relatively straightforward job to do it would be a pain in the a*** to have to tackle it again in the near future if you start to have doubts about them or if they show signs of wear or weakness.

As far as I am aware, all the engines of 499cc and above have double valve-springs. Even at a restrained road speed, the engine has to revolve at a relatively high rate because there are only two cylinders to supply the power. I suspect that valve bounce would be highly likely if the sophisticated design didn't have this feature.

The 652 seems to be the engine that is most frequntly subjected to tuning. Unless the pleasure of tuning appeals to you for its own sake, (now't wrong with that!), I'm sure that you will find the engine "as-is" will be be sufficient improvement over the original performance for most purposes.

 

[the hobbler]

The only thing to remember if you fit thicker driveshafts is to fit gear-box side-boots to match. The output bush and seal in the boot match the thickness of the driveshaft.
I personally always fit 'Viton' oil seals into the boots. For the 25mm drive shafts the seals to get are from 'Lancashire seals'---"Viton oil seals double lip R23/tc--with stainless steel spring" The actual part number is:--25x35x7 HMSA10V.

 

[Toshi 975]

The 652 seems to be the engine that is most frequntly subjected to tuning. Unless the pleasure of tuning appeals to you for its own sake, (now't wrong with that!), I'm sure that you will find the engine "as-is" will be be sufficient improvement over the original performance for most purposes.

When I rebuilt the 795cc Alquati modified engine last year I was surprised to discover that the original/doner engine was a 594cc. It was an expensive conversion carried out by Italtune & later Lanciana in 1984/5 when 652cc engines would have been available.

 

[fiat500]

When I rebuilt the 795cc Alquati modified engine last year I was surprised to discover that the original/doner engine was a 594cc. It was an expensive conversion carried out by Italtune & later Lanciana in 1984/5 when 652cc engines would have been available.

Good to know....I've got one of those (a 594cc not a modified Aquatica )
If I ever get bored it could be the one to modify.

 

[fiat500]

The only thing to remember if you fit thicker driveshafts is to fit gear-box side-boots to match. The output bush and seal in the boot match the thickness of the driveshaft.
I personally always fit 'Viton' oil seals into the boots. For the 25mm drive shafts the seals to get are from 'Lancashire seals'---"Viton oil seals double lip R23/tc--with stainless steel spring" The actual part number is:--25x35x7 HMSA10V.

https://www.ebay.co.uk/itm/163489943810

Truth is, if you go into the detail, there's a load of things you would be well-advised to check, replace and upgrade. But I guess that time is against you on this project.

 

[The Whitakers]

https://www.ebay.co.uk/itm/163489943810

Truth is, if you go into the detail, there's a load of things you would be well-advised to check, replace and upgrade. But I guess that time is against you on this project.

Yes this is true, it needs to be rolling by the end of the weekend. Pretty much everything is sat waiting a delivery of parts for reassembly. Once I get that everything can have its Pre assemble clean and start to be put back together. I’ve not bored people with rusty bit pics so will just post a pic of the rushed finished lump. I do have to say that the exhaust valves were an arse to re lap in, nearly recut them at one point but we got there...

Great input by all by the way, much appreciated

Rob

 

[Bigvtwin996]

......
I personally always fit 'Viton' oil seals into the boots. For the 25mm drive shafts the seals to get are from 'Lancashire seals'---"Viton oil seals double lip R23/tc--with stainless steel spring" The actual part number is:--25x35x7 HMSA10V.

This is the sort of info that we really need to have stored in one place in a sort of Wiki....(I hope he's got everything written down somewhere)
Once Tom's dementure sets in such info will be lost forever.....

 

[fiat500]

Once Tom's dementure sets in such info will be lost forever.....

What...Tom's lost his dentures?