Technical 650 conversion

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Technical 650 conversion

Leo6

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Aug 4, 2015
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Hi guys dropped my 500F off for some body work and a starter motor rebuild about a month ago and thought while the engine is out for the engine bay to get painted I'd explore the option of building a 650 block I have into a Arbath spec.
My problem is I would need a 126 gearbox. So my question is does anyone know of one available in Adelaide? Are there any overseas companies that would post one to Adelaide? And lastly has anyone recently built an Arbath form the 650 and has advice and costings?
Thanks
 

the hobbler

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Jul 25, 2012
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Sounds like good idea to me! However, you don't have to go the whole 'complete gearbox' change route. The 126 bell housing will fit in place of the 500 bell housing on the gearbox, If you are very careful when you remove the 500 bell-housing, and keep all adjustments "as is" you will probably get away without having to re-set all the diff back-lash adjustment. Being that you have a 500L, your gearbox will probably have the 25mm drive-shafts already--you must use 500 drive-shafts, 126 shafts are too long. Inspect your shafts during the strip down, any suspect wear on the splines, change the shafts. I would suggest that you fit new couplings as a matter of course. You will also have to fit a 126 starter ('pull' type are still available, new) as it has a different bolt pattern and fits in a different place vis-a vie the 500 starter.
I have compiled a "suggested modifications" sheet for tuning the 652cc engine---if you would like a copy of it, contact me directly and I will patch it through to you-- [email protected] I am no expert, but my (tuned) 652 engine has proved reliable and, for a 500, quite rapid. Subject to which carb/cam/exhaust/tuning combination you carry out on the engine, you can expect about 30/34bhp at the flywheel. Whayever you do, all the best with the project. (y):)
 

the hobbler

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Thought I had lost this version of my answer--it sort of "just disappeared", the it "just re-appeared"!--very curious Alice
Sounds a good idea to me! However, you do not need to go the 'complete gearbox' route. The 126 bell-housing can be fitted to a 500 gear 'box'--you have to be careful when doing the change otherwise you have to re-do all the diff back-lash adjustment, but by being careful and keeping everything 'as was' (adjustment wise) you can get away with just changing them over. You will need a 126 starter--the 500 starter will not fit onto the 126 bell housing---different bolt arrangement, different position. One thing to remember--the 126 drive-shafts are too long to fit into a 500. You therefore HAVE to fit 500 drive-shafts, but if you have 500F, you will probably have the 25mm shafts already in the gear-box.
I have a "suggested specification" sheet for tuning up the 652cc engine--gives about 30/34bhp at the flywheel. If you would like a copy of it, e-mail me direct and I will patch it through to you-- [email protected] I am no expert, but my own engine has proved reliable, and surprisingly quick (for a 500 that is!). There are also a couple of pukka Abarth mods that are well worth carrying out when you tune the 500/126 engine--those mods are included in the 'bumph' sheet.
Another thing to remember is that if you make the beast go faster, you will have to look at uprating the brakes. To a degree the ordinary 500 brakes are fine, but if you start using the extra performance, they become marginal. Is it a complete 652cc engine that you have? or just a bare crankcase? Whatever you do, all the best, keep us informed.(y):)
 
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Leo6

Leo6

New member
Joined
Aug 4, 2015
Messages
94
Location
Adelaide
Thought I had lost this version of my answer--it sort of "just disappeared", the it "just re-appeared"!--very curious Alice
Sounds a good idea to me! However, you do not need to go the 'complete gearbox' route. The 126 bell-housing can be fitted to a 500 gear 'box'--you have to be careful when doing the change otherwise you have to re-do all the diff back-lash adjustment, but by being careful and keeping everything 'as was' (adjustment wise) you can get away with just changing them over. You will need a 126 starter--the 500 starter will not fit onto the 126 bell housing---different bolt arrangement, different position. One thing to remember--the 126 drive-shafts are too long to fit into a 500. You therefore HAVE to fit 500 drive-shafts, but if you have 500F, you will probably have the 25mm shafts already in the gear-box.
I have a "suggested specification" sheet for tuning up the 652cc engine--gives about 30/34bhp at the flywheel. If you would like a copy of it, e-mail me direct and I will patch it through to you-- [email protected] I am no expert, but my own engine has proved reliable, and surprisingly quick (for a 500 that is!). There are also a couple of pukka Abarth mods that are well worth carrying out when you tune the 500/126 engine--those mods are included in the 'bumph' sheet.
Another thing to remember is that if you make the beast go faster, you will have to look at uprating the brakes. To a degree the ordinary 500 brakes are fine, but if you start using the extra performance, they become marginal. Is it a complete 652cc engine that you have? or just a bare crankcase? Whatever you do, all the best, keep us informed.(y):)

Thanks Hobbler I've sent you an email requesting your 650 info. Yes I am starting with a complete 650 which has now been striped and had the head ported. I've canned the Arbath idea in lieu of rebuilding the 650 with a ported head and mild cam. I came to this conclusion after considering I live in Australia and the 695 would probably struggle in the heat and I'd prefer more reliability as well as the cost savings!. I've also sorted a 126 gearbox to go with the motor and am now looking for a decent bolt on front disc brake system that suits the standard 12 inch wheels. I'm also looking for a stainless steal exhaust system for the 650, would you have any suggestions? Greatly appreciated Daniel.
 

the hobbler

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Both "Van de Laan Fiat 500" and "Axel Gerstl" can supply stainless exhaust systems---both are about E250. I expect with a bit of sifting through other supplier's web-sites you will find other sources. I took my spare engine/head assembly down to my "custom exhaust" makers and they made an exhaust for me (there are pictures of it somewhere on the Forum)--if you want to know the measurements of mine, just let me know and I will take a tape-measure out to it. It was made for my (eventual) '695' engine, but I have run it on my current '650' engine and it sounds really good.(y):)
 

the hobbler

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Jul 25, 2012
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Found the pictures of my 'Stainless Steel' exhaust---look on "Your opinion about sports exhausts", dated 14/01/2018. If you read the notes you will find that I have also put the dimensions with the pictures. Hopes this helps.(y):)
 

Paolo66

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Feb 6, 2013
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There's a few nice one's on dangelomotori.it. He does a lot of nice racing stuff.
 
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