Inlet stubs on early triples

Gravelroad

Gravelroad

Hero member
Location
Central Europe
G'day altogether,
by keeping the original cylinder head of my early 3C when restoring the bike, I ended also with those rubber sock type of inlet stubs. New rubbers came in 3yrs/8000k's ago when finishing the resto (fortunately Andy Wagner is stocking those rubbers).

During a close inspection couple of days ago, I spotted the rubbers creeping through the flange on two of the inlet stubs:
Creeper.jpg


Took the carbies off next, found some strange worms protruding into the inlet ports :o:
Inletworms.jpg


After taking the stubs out, I found the following mess >:D:

Stubs1.jpg

Stubs2.jpg

Rubbers.jpg


On the left in the last picture sits a new rubber for comparison. Old rubbers still soft and not embrittled, but totally out of shape.
Before I installed the rubbers 3 yrs ago, I had their insides dusted by talkum powder and put a slight smear of silicon grease inside the stub bores of the cylinder head, too. Greatest care was taken when bolting everything up.

Any thoughts how to improve the lifetime of this rubbers? Have there been some tricks in the past to deal with this shit?
I'm already thinking about putting a 0.5mm washer on the studs before putting the flanges on, just to sligthly release the pressure on the rubbers, but this might get things even worse?

Or do I need to live with it and replace the rubbers every 2 yrs?

Any suggestions appreciated.

Regards,
Stefan
 
Stefan,

Not normal wear! I was in the same situation 8 years ago when I put the cylinder head from engine #1579 (no I didn't brake the bike!) on my 3CL. Rubbers for the inlet stubs came from Richard Slater as nobody else had them in stock at the time and are still O.K to the present day. Contact Richard and see if he still has some in stock.

HTH
Gerald
 
Gerald, thanks for the tip, will give Richard a call, hope he has them still in stock. Bought already a set of replacement rubbers from the same source as the first set, but will try to return them in case Richard has them still available. Would have expected to get decent quality at 28 ? a piece, though.

Bike has seen only ethanol free fuel most of the time by the way...
 
Make sure you ask Richard where the rubbers came from if he has them. He sources some stock from Andy Wagner so you might end up with the same item.
 
Oh and in regard to the rubbers there are some aftermarket ones circulating that do not have the lip formed that sits in the groove, but let me say they are a very poor sealing manifold connection don't be surprised if you have some challenges.
My advice would be to remove and trim to fit then paint them with 3 bond to gain a complete seal.
 
Stefan,

I think I'd do away with the rubbers altogether.  Make new stubs with a  tightish sliding fit in the head and incorporate a sealing o-ring at the leading edge and a thick o-ring under the fixing flange so as not to distort it, should do the trick and will look 100% original.

IIrc, the bores for the rubbers are machined, so should be in line enough to allow the carbs to slide on and off "easily".

piet
 
Put an upgrade like suggested by phil/Piet to the backburner, and reassembled everything with a new set of rubbers, added a bit of sealant goo to the leading edge of the rubbers.

Will use the odd cold winter evening to think about an improved solution in detail, all the dimensions have been noticed so far. The bores of the rubbers are in fact machined, but the inlet chanel of R/H cylinder is not concentric to the rubber bore (around 1.5mm off). PO or even factory(?) adressed this by grinding the inlet stub to fit. I had overseen this on first assembly and placed the reworked stub on the L/H cylinder, Murphy's law, I'd guess. With that sorted and probably one ore two horses added to the stable, I'm not too sad anymore about the early failure of the rubbers.  :LOL:

 
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