Early 2 piece intake manifold issues

[tobydmv]

Well I figured out why I couldnt synch my carbs. The front cylinder instake manifold has a vacuum leak right near where the 2 piece intake manifold threads into the head. I tried tightening the lock ring but it still leaks. Upon loosening it I noticed the intake is very wobbly and wont thread fully into a secure workable position. When its threaded all the way in and secure the carb wont fit in between the jugs. Im forced to loosen it about 3/4 turn where its wobbly and leaking again. Both male and female threads appear to be clean. Of course the rear cylinder is vacuum tight and acting accordingly with the same intakes. So not sure what is going on but at this point i'm wondering if the later model rubber intakes are a better choice. The bike is a 80's model and came with the rubber intakes but one of the metal threaded stubs was rusted away from sitting and I swapped the heads out from an older bike. Has anyone had this problem before with the early 2 piece intakes or have any idea of fixing the leak?

[EVguru]

I suspect the manifold threads are worn due to them having come loose before.. I replaced one on an early Sport for that reason. The good used replacement was fitted with thread locking compound. The head threads wear far less.

NLM have the stubs available to convert heads.

[72degrees]

I suspect the manifold threads are worn due to them having come loose before.. I replaced one on an early Sport for that reason. The good used replacement was fitted with thread locking compound. The head threads wear far less.

NLM have the stubs available to convert heads.

Those stubs can be a whotsit to get out if you want to swap one from a late head to an early one.

Perhaps the stubs for rubber intakes would also screw in far enough to reach a bit of unused thread. The rubber bit can be swung through an appropriate angle so long as there is enough stub sticking out. How vital are the plastic shrouds that go over the rubber under the head end clips?

I discovered on close examination the other day that the rubber intakes for the 250 are the same as 350. Moulded in MM40 and measure up at the same internal diameter. I suppose being larger than required wouldn't be an issue. Could have saved myself a few bob.

[norbert]

I made myself a tool to get theses stubs out and in, using a nut that just enters in the tube. To get it out one should try it with a warm motor (if posible) or a bit of heat anyhow. With this tool you can do that best when the motor is mounted in the frame to be able to aply maximum force, and it has de advantage that the opsition of the sluts in the tube doesn´t matter, what sometimes can be a problem if you try it with a simple pieco of steel.

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[tobydmv]

Thanks for the info Paul. Spot on as usual. I found a NOS steel stub and might go back to that setup w the rubber boots. If one were to make some intake stubs, whats a better material? Bronze alloy or stainless maybe? As noted, removing the rusted and seized intake stub required an oxy-acet torch and a lot of work.

[EVguru]

I'd stick to plain old steel. Cheap and easy to machine and probably good for another 40 years. I may well have given up riding by then.

[tobydmv]

I called Kathy at Herdan and they had some steel intake stubs in stock. I also ordered new rubber intake elbows from Start Gomma and the bike no longer has an intake leak. Thanks guys!

[AntietamClassicCycle]

I called Kathy at Herdan and they had some steel intake stubs in stock. I also ordered new rubber intake elbows from Start Gomma and the bike no longer has an intake leak. Thanks guys!

Do you happen to have the part number for the steel intake stubs?

[72degrees]

13.04.39 according to a list I have, or also 13.05.56 on the NLMs parts.pdf (stainless steel).

[AntietamClassicCycle]

Thanks.

[tobydmv]

I made myself a tool to get theses stubs out and in, using a nut that just enters in the tube. To get it out one should try it with a warm motor (if posible) or a bit of heat anyhow. With this tool you can do that best when the motor is mounted in the frame to be able to aply maximum force, and it has de advantage that the opsition of the sluts in the tube doesn´t matter, what sometimes can be a problem if you try it with a simple pieco of steel.

Thanks for the tip. I used a 1" piece of steel pipe and key stock. I cant remember the key stock size though, maybe 3/16's JIC anyone needs the same tool.