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MG TD TF 1500 - TF Oil Pipe Head to Block to Gauge

The oil pipe from the block to the head on my TF is installed upside-down. The pickup for the oil gauge is at the head instead of the block. The oil pipe on the engine is pretty beat up, so I am going to install a better one and change the pickup location for the gauge.

I have two XPAG oil pipes. The diameter of the hole in the threaded outlet for the oil gauge on one is about .125". The diameter of the hole in the threaded outlet on other is about 0.055". The holes for the oil pipe (not for the banjo bolt) in the banjo fittings to the block and to head appear to be the same diameter on both oil pipes, but difficult to confirm. I don't know what engines from which the pipes were taken.

I haven't removed the oil pipe that is currently on the engine, so I don't know the diameter of the hole in it.

Here are my questions:
> What was the reason for the two sizes of holes for the gauge?
> Is there any reason that I should not use the oil pipe with the larger diameter hole for the gauge?
> Was the oil pipe with the smaller diameter hole for the gauge made for a different engine?

Here's why I asked:

The TF is an early model TF681, XPAG/TF/30452, built 14-Oct-1953 (fifth day of regular production). I am trying to keep it as "original" as practical.

Anders Ditlev Clausager and NEMGTR TSO June 2001 describe a change to the oil pipe: "Reduced internal dia. lower banjo fitting - block to cyl pipe." Dec. 1953, XPAG/TF/31943. However, it appears that my pipe has the same diameter holes for the oil pipe but smaller diameter hole in the threaded outlet to the gauge, not to the oil pipe.

The TF Service Parts List ADK804 shows the same oil pipe for TDs and for TF/TF1500. #X24285. It does not mention a change with engine #XPAG/TF/31943.

So, it looks like I should use the larger diameter .125" diameter pipe.

Thanks for your help and advice.

Lonnie
TF681
TF7211

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LM Cook

I don't know if there were production changes, or if they just used whatever was available, or maybe a previous owner changed out a part, but the bottom line is that it doesn't matter. Oil doesn't flow through that hole, it only measures pressure. There is no volume aspect to the equation. Both parts will give exactly the same pressure reading.
Steve Simmons

Very well explained! ID would only matter if active flow. George
George Butz III

they probably had needle flutter at low revs. The smaller hole would act as a damper.
Large commercial gauges have an adjustable orifice in the base. I worked on steam piston engines in the mid 50's and fluctuation would soon wreck the Bowden mechanism that moves the needle..
I have a low tickover and can see the movement of the needle on a my hot engine.
Ray TF 2884
Ray Lee

Good point, Ray. If the smaller hole is the later one then you may be onto something there.
Steve Simmons

Thanks for your responses.

I finally found the factory explanation for the reduced diameter in the TD/TF Workshop Manual, Section A.45:

MODIFIED OIL GAUGE PIPE BANJO
"Commencing at Engine No. 31943 the lower banjo coupling on the oil pipe (gallery to head) has the internal diameter reduced to .055 in. (1.39 mm). This is to prevent the possibility of a hydraulic knock in the oil pipe which was encountered on some earlier models."

> What is "hydraulic knock in the oil pipe" and what did it affect? Is that the fluctuations that Ray mentioned? Or is it a knock-sound sometimes experienced in home water pipes?

The description of the change by the WSM, Clausager, and the NEMGTR is misleading to me. The change was not to the diameter of the hole that connects the copper pipe to the head; instead, it was in the diameter of the hole that connects the flexible line to the oil pressure gauge, which matches the two oil pipes in my original post.

Maybe I was misled by numerous discussions about too much oil going to the valve train and suggestions to restrict the flow with a restriction in the banjo bolt. (I can't agree with that suggestion.)

Although Neil Cairns seems to agree when he noted that "small holes in the banjo bolts, on later engines made even smaller" in the section titled "The Oil Guage" of his MGCC Y-Type Register article "The XPAG Oil System",
https://www.mgccyregister.co.uk/technical-information/the-xpag-files/engine/the-xpag-oil-system/?doing_wp_cron=1707571581.6318039894104003%E2%80%A6

So, just to satisfy my "picky gene", I'll use the older model oil pipe with the .125" diam. hole in the threaded outlet to the oil pressure gauge in TF681, and the banjo bolts that are currently in the engine.

Lonnie
TF681
TF7211
LM Cook

Lonnie you are correct.
W A Chasser

This thread was discussed between 27/08/2025 and 20/09/2025

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