750GT Rolling Basket Challange

Post pictures of your twin cylinder Bevel Drive Ducati (pre-1985) along with a description here.
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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Tue Sep 02, 2014 8:32 pm

OK ..... my 750 GT is running great, but it has a few irritating oil leaks. I recon that the one I'm chasing in the counter-shaft sprocket area is from a porous casting and waiting for oil dye to track that one down.

The other ones are coming from the top of the bevel shaft tubes. I tried rotating them to seat a miss-aligned o-ring and thought that might have done the trick, but they're back. So, looks like pulling the heads off this winter and replacing the seals. Background: the engine was just overhauled with all new gaskets, seals and o-rings. It has aluminum bevel shaft tubes that replaced the chrome plated ones.

I'm thinking about replacing the original o-rings with square-section rings:

Image

or maybe "quad" rings

Image

Anybody grappled with persistent bevel tube leaks using these types of seals as an alternative to the o-rings? Maybe some other approach that worked?

George
Canada

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abmartin
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Re: 750GT Rolling Basket Challange

Post by abmartin » Wed Sep 03, 2014 1:07 pm

Perhaps the problem is with the aluminum tubes. From my experience the standard steel tubes work well.

Bruce
1979 900SS
Fredericton, NB
Canada

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Wed Sep 03, 2014 1:39 pm

abmartin wrote:Perhaps the problem is with the aluminum tubes. From my experience the standard steel tubes work well.

Bruce
Others with chrome or stainless ones seem to have had this problem too. And can't imagine why, if the aluminum tubes are the same dimension as the chrome ones, there would be more of a leaking tendency. Anyway, looks like if I try different seals, I'll be blazing a trail. Hope it doesn't lead to be getting REALLY good at pulling the engine out and the heads off.

GD

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BevHevSteve
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Re: 750GT Rolling Basket Challange

Post by BevHevSteve » Thu Sep 04, 2014 6:14 pm

These are 1 of those things that you really must pay attention to, newly rebuilt doesn't mean all the crap got out of the grooves.... Every little bit must go. Also, the orings used could have just been too old and hardened to work.
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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Thu Sep 04, 2014 6:39 pm

BevHevSteve wrote:These are 1 of those things that you really must pay attention to, newly rebuilt doesn't mean all the crap got out of the grooves.... Every little bit must go. Also, the orings used could have just been too old and hardened to work.
Well I guess I'll find out when it comes apart this winter. Got to have projects, right?

wdietz186
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Re: 750GT Rolling Basket Challange

Post by wdietz186 » Fri Sep 05, 2014 5:24 pm

The turn usually does the trick but as Steve said the grooves need to be clean and the o rings resilient. Not being the trusting sort I use a thin coat of the non hardening Permatex Aviation sealer- the brown brush on liquid - on the end of the tube before I install and carefully wipe off the tube after. Admittedly old school but it seems to work where silicone stuff doesn't.

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Fri Sep 05, 2014 8:38 pm

wdietz186 wrote:The turn usually does the trick but as Steve said the grooves need to be clean and the o rings resilient. Not being the trusting sort I use a thin coat of the non hardening Permatex Aviation sealer- the brown brush on liquid - on the end of the tube before I install and carefully wipe off the tube after. Admittedly old school but it seems to work where silicone stuff doesn't.
Kind of like belt AND suspenders.

wdietz186
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Re: 750GT Rolling Basket Challange

Post by wdietz186 » Sat Sep 06, 2014 5:14 pm

And a fat gut to keep it all under constant tension!

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Sat Sep 06, 2014 7:20 pm

wdietz186 wrote:And a fat gut to keep it all under constant tension!
"Kind of like belt AND suspenders"

The sign of a cautious man (from some noir film I can't remember the name of - with Richard Whidmark perhaps?)

ducadini
750 Sport [BEVEL]
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Re: 750GT Rolling Basket Challange

Post by ducadini » Sun Sep 07, 2014 1:39 am

Installing aluminium tubes should've solved the problem .
They expand more when warm, sealing better.
However it was (is ?) difficult to find tubes with a 31 mm OD, so most turned down a 32-3 mm tube, maybe the OD isn't the same as standard.
I found some standard 30-2 mm tubes and turned the INSIDE down (to loose some grams) except for the last 20 mm to save the strength for the o-rings.
Went to the o-ring shop and bought a few pieces each of rings that had a diameter a bit bigger, and the OD bigger and smaller(could be both metric and other).
Then a few minutes of fitting them in the head and fitting the tubes 'till you find the right combo. COULD be different for other engines so experiment.
Never used any sticky stuff on those and they were very visible oil-free and checked at tech-spec.

ciao
ducadini
Nego i ricordi peggiori
Richiamo i migliori pensieri

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Sun Sep 07, 2014 6:07 am

ducadini wrote:Installing aluminium tubes should've solved the problem .
They expand more when warm, sealing better.
However it was (is ?) difficult to find tubes with a 31 mm OD, so most turned down a 32-3 mm tube, maybe the OD isn't the same as standard.
I found some standard 30-2 mm tubes and turned the INSIDE down (to loose some grams) except for the last 20 mm to save the strength for the o-rings.
Went to the o-ring shop and bought a few pieces each of rings that had a diameter a bit bigger, and the OD bigger and smaller(could be both metric and other).
Then a few minutes of fitting them in the head and fitting the tubes 'till you find the right combo. COULD be different for other engines so experiment.
Never used any sticky stuff on those and they were very visible oil-free and checked at tech-spec.

ciao
ducadini
Thanks Ducadini

I see that the aluminum tubes on this one have been turned down by maybe a mm at the ends where the o-ring mating surface is.

GD

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Wed Sep 17, 2014 3:05 pm

I'd heard that there were self-locking, nylock output shaft nuts available, but had a hell of a time finding them. They are available from Maryland Metrics for about $9.25 each, P/N GUK7.

http://mdmetric.com/

I got a couple and tried one on the stock sprocket nut socket only to discovered that the stock nut has a 52mm O.D. and the nylock is 50mm so that socket was not going to work. A low-buck Craftsman socket got machined up to fit:

Image

Image

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Fri Sep 19, 2014 3:23 pm

Another leak from a casting flaw. A judicious application of JB Weld and it should be sealed up.

Found it with oil dye and black light flashlight. That stuff is fantastic - 1st time I've used it.

Image

(road test) Took it out for about 120 km. hither & thither and the sprocket area is "dry as a pommie's bath mat" as our Auz friends would say.

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Mon Sep 22, 2014 8:18 pm

Well here's a coincidence.

A friend (and author) that I go sport-motoring with from Vancouver, just sent me an email recommending a boook:

The Flamethrowers by Rachel Kushner:

http://www.goodreads.com/book/show/1580 ... methrowers

The year is 1975 and Reno—so-called because of the place of her birth—has come to New York intent on turning her fascination with motorcycles and speed into art. Her arrival coincides with an explosion of activity in the art world—artists have colonized a deserted and industrial SoHo, are staging actions in the East Village, and are blurring the line between life and art. Reno meets a group of dreamers and raconteurs who submit her to a sentimental education of sorts. Ardent, vulnerable, and bold, she begins an affair with an artist named Sandro Valera, the semi-estranged scion of an Italian tire and motorcycle empire. When they visit Sandro’s family home in Italy, Reno falls in with members of the radical movement that overtook Italy in the seventies. Betrayal sends her reeling into a clandestine undertow.

I ordered it and then looked to see if there were some reviews & ran across her web site that included a shout of her in the "about" page:

http://www.rachelkushner.com/about.html

Apparently she really is into Italian bikes and not just any Italian bikes!

http://cartoslibrary.wordpress.com/2013 ... otorcycle/

Image

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Mon Oct 27, 2014 12:52 pm

The weather here in Vancouver is starting to get more like what we all block out of our minds as soon as Spring gets here - like winter never happened. It's the season for the record for most consecutive days of rain (33) and getting close to that is not unusual at some point(s) during the next six months. Don't have to shovel rain though! Still, there are a couple rain-free days in there, though the leaves have mostly fallen off the trees creating mulch covered streets. Shop time.

I got a selection of carb needles to play with the mid-range jetting, which has seemed a bit fat running the K5, even with it down to the leanest notch. I think that I may have hit the sweat spot with K16's at the richest (bottom) notch. The exhaust tone is more even and it feels more cleanly responsive.

So the current set-up is:

MJ 125
NJ: 265AB
PJ: 62
Needle: K16 (bottom / richest notch)
Slide: 70/2

I decided to get ghetto with my bevel tube leaks before yanking the heads and replacing the seals. Made a little sealant packing tool out of a tongue depressor with a smile cut in it the same radius as the tube. Applied 3-Bond #4 to the tube / housing joint and rotated the tubes while packing the sealant into the tiny gap. Let set up and went for a road test ........................... absolutely dry. All the excess was removed with toluol so you can't tell I'm ghetto / shade tree.

Also took off the tach drive and installed a slightly fatter o-ring and now there is no more drooling from there either. It's damn near oil tight (for the moment).

I've got the front wheel off to fiddle with a bit too much run-out at the brake disc (.025"). I replaced the disc before since it was measurably warped, but didn't check to see if there was run-out at the disc carrier. Pulled that off and will be making a mandrel to locate on the wheel bearing bore and skim the surface to see if I can get the run-out down to a better number.

Other than that, probably won't be riding or posting too much for a while. Down to working on other people's stuff. A Sunbeam Alpine engine coming in tomorrow for overhaul. After that a Hercules iron straight-6 flathead from a 1936 Diamond T pickup, then a 1928 Rolls Royce Phantom I engine. Somewhere in there is a custom framed Ducati with a 99 900SS engine and all manner of trick stuff on it that needs a wiring system fabricated for it. That should all be done by spring then it's back to screwing off and riding old motorcycles with my crummy, dead-beat friends.

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