Intake Manifold Insulator Option
Posted: Sun Jun 17, 2012 9:24 am
Obviously has seen better days.
Someone (name withheld to protect the guilty) said that he had used Norton intake manifold insulators on his 750. At a couple bucks each they are significantly cheaper than the Ducati ones. Norton didn't use rubber based insulators like Triumph or Ducati, instead its a phenolic insulator (phenolic materials can be engineered to have extremely low thermal transfers, ideal when protecting the carb from the head heat). While the rubber blocks do they same thing as you know they tend to shrink and leak.
The challenge with the Ducati manifold is the spigot and I believe pins holding the blocks in place. I think there are pins, I don't know for sure as there aren't any on my bike.
While the intakes are the same on the 750 Norton Combats and the big Ducatis (32mm) it's the spigot that throws the next roadblock in place. The options are to mill off the spigot or opened up the insulator.
By opening up the insulator with a Dremel I was able to get them to fit over the spigot. Because the phenolic insulators are so efficient typically you only need one thin one, but because of the spigot I just used two insulators. I had not anticipated having to use two for each carb and had just bought three (incase I messed up one carving it up) so for now I just did the front carb as it was the worse (and easiest to get to).
Lastly the bolt spacing in slightly different, so I elongated the holes in the insulators a smidge. Maybe a millimeter.
Then assembled with Yamabond (actually I think it's Threebond but you know what I mean) and since that was about midnight last night I didn't fire up the bike as I'm quite sure all of the neighbors would have called the cops on me.
So the test will be in a little bit and I'll let you know what happens. I definitely had a bad leak so it should be apparent.
If you're wondering you can get the insulators from any Norton dealer. I use Old Britts and they are wonderful to deal with. Well, except their website uses frames which is a pain to link to.
http://www.oldbritts.com/alt_067842.html (what you are looking for is a Gasket, Heat Insulator, 32mm for a 1972 model (they also used them on the later 850s).
The Norton part number is 18-063458 and the cost for one insulator is about 1/10th the cost of a single Ducati rubber one. So, like I said, I can afford to experiment.
: I don't know whether the Ducati rubber insulators/isolators also had some kind of anti-vibration function - which I guess you'd lose with the phenolic ones - ?
that I am, I tried to remember the last time I put gas in the tank. Unfortunately you can't just look in the tank to see how much there is. 
So I drained some gas out of the other bike, put that in and that sure made the Ducati happier. 
