Inlet manifold - what are these screws for?

[StevedTR4A]

Hi all

Some help please.

On the inlet manifold of my TR3A are two screws each in line with its carb. Also approximately halfway along the manifold, between the carbs is a small upstanding tube with a screw positioned to seal it off.

What would a PO have done this for? - as some means of balancing/tuning?

Would appreciate any comments

thanks

Steve

[Don Elliott]

He may have been using these new holes he drilled to connect some sort of vacuum gauge or manometer to help with the tuning. Or maybe someone was using these holes to inject water spray into the manifold with the combustion mixture for improved performance.

 

If you (or the concours judges) don't like to see them there, you could take off the manifold (and all the bits too) and have someone with a TIG welder, weld the holes closed using an aluminium wire rod. Then you can file and sand over the finished welds and no-one will be able to see where the holes were.

 

For now, I'd remove them and put some sort of seam sealer or silicone into the screw threads and then screw them back in, to make sure the threads don't allow any air it get in.

[StevedTR4A]

Thanks Don

As you suggest, for now, I will remove, seal and replace.

 

Must admit I have never heard of injecting water spray! - interesting.

 

cheers

Steve

[Ian Vincent]

Hi Steve,

 

Almost certainly the one in the middle is for a vacuum guage. I fitted something that looked identical back in the past when I had a car that I suspected had a burnt valve.

 

If you aren't planning to do concours, I would leave it where it is - a vacuum gauge is a useful piece of diagnostic equipment.

 

Rgds Ian

[angelfj]

Thanks Don

As you suggest, for now, I will remove, seal and replace.

 

Must admit I have never heard of injecting water spray! - interesting.

 

cheers

Steve

 

perhaps this was used in the past as a source of vacuum for some accesory. For example, it is not uncommon to see moto-vac units added to TR's to assist with braking. Another thought is that this was used to monitor vacuum. Some mechanics tune engines by using a precise vacuum gauge. regardless, you don't have to make a permanent closure at this time. just find a plug that fits and I suggest you wrap it with teflon tape

 

here's an old photo showing a TR3A with a vacuum servo booster added. note the vacuum line connecting to the inlet manifold.

Edited April 24, 2009 by angelfj

[StevedTR4A]

Thanks guys

All interesting stuff. As I do not plan to do any concours events I will leave "as is".

I am suprised that the small tube is offset from centre of the manifold. I guess its position is not critical for taking vacuum readings.

The engine runs fine with the normal "hiss" balancing so do not plan to go the vacuum tuning route.

Cheers

Steve