crank shaft specs.

Moto Rumi technical problems or solutions
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jmensch
Posts: 22
Joined: Sat Feb 03, 2018 3:48 pm

crank shaft specs.

Post by jmensch » Wed Jul 15, 2020 7:45 pm

Hello from Miami, Fl. Regarding my Sport Formichino with poor performance, I had removed the engine, pressurized the crankcase and found significant leaks in all of the seals. Upon removing the crankshaft and using a lathe and dial indicator, I also found the alignment of the crankshaft was out of true by .006". I think it can be only .0015 ? I am thinking of sending it out to HVC cycle in Lincoln Ne. for rebuilding. They have had some experience with Jap 2 cycle engines. Before they undertake this they would like the following crank shaft specs:
Rod side play
Web spacing
a. width of the 2 webs when together
b.Center distance between both inner webs when assembled
c. Run out
Is this information available? Thanks, J Mensch

Lars
Posts: 306
Joined: Fri Nov 02, 2012 3:09 pm
Location: Sweden

Re: crank shaft specs.

Post by Lars » Thu Jul 16, 2020 9:03 am

I can not help you about the crankshaft specs, but perhaps someone else will pitch in with that information.

But have you considered just getting a new crankshaft assembly from Parmakit? They are expensive, at around 478 Euros (without VAT, plus shipping), but they come complete with new inner seals and seal carrriers installed. You only need to re-use the two outside carriers. And I imagine that specialist rebuilding of the old crank will cost something, too.

I ended up buying a new Parmakit crank for my Junior. Installing it right now. Here is where I ordered it from:

https://www.rrd-preparation.com/en/vile ... er-2t.html

Anyhow, just something to consider.

hugomez
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Re: crank shaft specs.

Post by hugomez » Thu Jul 16, 2020 9:57 am

Hi,

Same as Lars, I can't help with the specifications, however "maybe" Edoardo Marsiletti can help you with a brand new one, and definitely less expensive than the once from Parmakit. If not, Parmakit option is also very good.

You can find below Edoardo's forum profile. From there you can send him an email or private message.

LINK: memberlist.php?mode=viewprofile&u=24657

Moto-Rumi-Crankshaft.jpg
Moto-Rumi-Crankshaft.jpg (25.99 KiB) Viewed 1178 times
My little Formichino here: http://www.formichino.com/pictures1.html

jmensch
Posts: 22
Joined: Sat Feb 03, 2018 3:48 pm

Re: crank shaft specs.

Post by jmensch » Fri Jul 17, 2020 8:16 pm

Dear Lars and Hugo, thanks for your reply. In looking at the photo of the crankshaft, it appears that the end threads are not identical to the crankshaft that I have. In addition, mine uses round castellated nuts to fit into the recesses. Where can you get the finer threaded castellated nuts to fit these new threaded ends?

arthur lewthwaite
Posts: 692
Joined: Fri Dec 28, 2012 7:03 pm

Re: crank shaft specs.

Post by arthur lewthwaite » Fri Jul 17, 2020 8:46 pm

there is another member who lives in boca rotan in florida . i sent him a set of new bolts.

jmensch
Posts: 22
Joined: Sat Feb 03, 2018 3:48 pm

Re: crank shaft specs.

Post by jmensch » Fri Jul 17, 2020 8:50 pm

Thanks, if I purchase, can you send me 2?

Lars
Posts: 306
Joined: Fri Nov 02, 2012 3:09 pm
Location: Sweden

Re: crank shaft specs.

Post by Lars » Fri Jul 17, 2020 8:53 pm

The Parmakit crank I bought was a direct drop-in with threads identical to the old one in both ends. They also supplied a nut for the clutch side, for some reason, but I did not use it. The old one fit perfectly well.

The only adaptation I had to do was to shave off 1 mm in height of the woodruff keyes. The grooves in the new crankshaft was shallower than in the old one. But that was quick and easy to do on the bench grinder.

Here is a picture of the old and new Parmakit crankshafts:
Attachments
Rumi Junior crankshafts, old and new.JPG
Rumi Junior crankshafts, old and new.JPG (95.99 KiB) Viewed 1146 times

Ian Skinner
Posts: 554
Joined: Mon Aug 24, 2009 12:36 pm
Location: South Wales UK

Re: crank shaft specs.

Post by Ian Skinner » Sat Jul 18, 2020 10:42 am

Hi Lars

Thanks for the thread information, Parmakit used to use 12.125mm while Rumi was 12.50mm. So they have finally brought them to the Rumi standard!

Ian

Ian Skinner
Posts: 554
Joined: Mon Aug 24, 2009 12:36 pm
Location: South Wales UK

Re: crank shaft specs.

Post by Ian Skinner » Sat Jul 18, 2020 11:27 am

Hi jmensch

a) Width of the 2 webs when drawn together?

Controlled by the length of the wristpin when assembled with absolutely no protrusion beyond the recessed flywheel sides.

b) Centre distance between both inner wheels when assembled?

Controlled automatically when the inner wheels are pushed firmly together. The wheels must end up absolutely parallel to each other.

c) Runout?

0.000 - 0.002

Hope this helps

Ian

Ian Skinner
Posts: 554
Joined: Mon Aug 24, 2009 12:36 pm
Location: South Wales UK

Re: crank shaft specs.

Post by Ian Skinner » Sat Jul 18, 2020 11:33 am

Sorry, not Wristpin, meant Crank Pin.

Getting old, Ian

Lars
Posts: 306
Joined: Fri Nov 02, 2012 3:09 pm
Location: Sweden

Re: crank shaft specs.

Post by Lars » Sun Jul 19, 2020 8:27 am

Ian Skinner wrote:
Sat Jul 18, 2020 10:42 am
Hi Lars

Thanks for the thread information, Parmakit used to use 12.125mm while Rumi was 12.50mm. So they have finally brought them to the Rumi standard!

Ian
Hi Ian

No they did not!
Forgive my complete ignorance about this, I had no idea that the Parmakit threads were different from the orignal Rumi type. And it just occurred to me that the old crankshaft I replaced, was also a Parmakit!

I just measured the thread on the new crankshaft. It is still 12.125 mm. I tried the new nut supplied by Parmakit on an old Rumi crankshaft. I does not fit. Thanks for pointing this out.

jmensch, if you plan to buy a Parmakit crankshaft, make sure to get the nut for the flywheel side, too. As I mentioned, the clutch side nut is supplied, although not castellated (and I can´t see that it really needs to be). The flywheel nut definitely does not need to be castellated, in my opinion. On my Junior, I have a conventional hex nut and serrated lock washer at the flywheel. I like it better, since I don´t have the special castle nut tool required. Besides, there is no hole drilled for a split pin the Parmakit crank.

Lars

Ian Skinner
Posts: 554
Joined: Mon Aug 24, 2009 12:36 pm
Location: South Wales UK

Re: crank shaft specs.

Post by Ian Skinner » Sun Jul 19, 2020 5:12 pm

Hi Lars

I agree, I have been fitting Tach Drives to my machines for years, so tempting providence, I have never had one of my home-made non-castellated nuts ever come loose!!

Ian
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000_1000e.jpg (35.14 KiB) Viewed 1111 times

jmensch
Posts: 22
Joined: Sat Feb 03, 2018 3:48 pm

Re: crank shaft specs.

Post by jmensch » Mon Jul 20, 2020 9:02 pm

Thanks much for the information. I noted corrosion on the crankshaft when I removed the end seals. As this may have been a cause of end the seal leaks along with the .006" alignment error, I DECIDED TO PURCHASE A NEW CRANKSHAFT. I am now going to attempt to separate the center.

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