Technical 650 engine swap

[gordinir8]

Although i didn't had plans of replacing my 500cc engine right now, it just happen to find a very good unit at a very fair price so i just had to buy it It is an overhauled 650 together with a gearbox and hasn't been fired since overhaul. The guy that rebuild it is a mechanic that build it for himself but in the end he abandoned the ''126'' project. So far looks pretty good and i am not going to do anything on it. Maybe later put a sporty cam and port the head but i just want to test the car before and after any modifications. Right now i am only checking things like carburetor, alternator etc.

I have opened the gearbox to see whats inside and looks like at list one gear ( i think is the 1st) is worn, i would like to know your opinion about it, should replace it?

Also if you have any digital documentation related to 650 engine to share please let me know.

Thomas

 

[phoenix1]

Hi.don*t forget to use the driveshafts from your old 500 gearbox as they are a different length. The only tricky bit is the heat transfer pipe fouling the starter.

 

[fiat500]

I am pretty certain that first gear will be noisy, but even new it's noisy. But the real problem is that I think it may be likely to jump out of first gear.

Here's a comparison of old and new:

https://www.fiatforum.com/500-classic/444396-126-syncromesh-gearbox-rebuild-2.html?p=4220643

 

[gordinir8]

I think i will replace at list this one, only the big 1st gear.

 

[gordinir8]

Hi.don*t forget to use the driveshafts from your old 500 gearbox as they are a different length. The only tricky bit is the heat transfer pipe fouling the starter.

I will order a pair of new shafts since mine are worn, as for the air duct i am thinking to discard the metal duct and replace it with a long silicon tube all the way to the tunnel. This one is heat resistant up to 150C i think it is enough.

 

[gordinir8]

Is there any chance to have a 126 gearbox that is not synchromesh ? Can you tell if mine is synchronized from the picture above? I am a little worry because mine has only one o-ring at the selector shaft and for what i know 126 has a seal also.
I have start to disassembly it and make my shopping list.
Thomas

 

[the hobbler]

All the 126 model gearboxes had synchro on 2nd. 3rd and top.

 

[gordinir8]

So i guess i have a early type without a seal at the selector shaft.

 

[Toshi 975]

So i guess i have a early type without a seal at the selector shaft.

Could be quite the opposite as there are three types. One o-ring groove, 2 grooves then no o-ring as there should be a small lip seal in the housing.

 

[gordinir8]

I think I'm gonna add a seccond groove to add one more o ring as in the picture above. Thanks

 

[gordinir8]

Is there any gearbox assembly instructions available? Unfortunately i don't have the haynes manual yet. Is it common with the 500 gearbox?

Thomas

 

[thepuddlejumper]

Hi, look on YouTube I saw a gearbox build it was very good as the guy showed everything to allow you to rebuild.

Ralph

 

[the hobbler]

Tom; I have a 'Haynes' for the 126---would you like me to copy out the pages regarding gearbox re-building for you?

 

[gordinir8]

Yes if this is not a problem is i'd like to have it.

 

[Paolo66]

https://drive.google.com/open?id=0B-ryUAMymms9UXlzdHFUVVJaLTQ

Here is a link to my 126 workshop manual in PDF

 

[gordinir8]

I am inspecting my new engine before installation and i have found that the flywheel cogs are a little worn, not that bad but still worn. Do i remember well that installing the 500 flywheel in the 650 is a kind of tuning because 500 Fly wheel is lighter?

 

[the hobbler]

The 500 flywheel is 2-1/2kg lighter than the 126 flywheel---which is about as light as you want to go for a 'road-tune' engine. if you make the flywheel too light, you run the risk of a 'lumpy' engine, particularly when it is idling. I have a '500' flywheel on my tuned 650 engine, but occasionally the starter 'misses' and just spins. I just let it all settle down and try again--normally then with no problem.

 

[gordinir8]

2.5kg is quiet a lot of weight and certainly don't want to go lighter than this. On the other hand if you consider it as a normal tune i will go for it.
Is your starter missing sometimes because the two fly wheels are not identical or something is worn there.

 

[the hobbler]

If I remember correctly (it is about 4 years since I did the tune-up on my engine) the 126 flywheel is a bit thinner than the 500 item. Compare them before you fit the 500 flywheel onto your 650 engine.

 

[gordinir8]

Yeap engine is out, pretty straightforward job to do. I think for one person job is easyer to remove engine and gearbox as separate units. I have to take care engine bay before put new engine.