8 replies to this topic

[Zami]

Pulled my 20yr. Old build to freshen it up. (1380. Cooper S crank.)

Discovered a groove in the #1 rod bearing that initially looked stock. Then noticed what looked like a small brass restrictor plug poking out of the oil hole on the crank journal?
It looks like each rod journal has two oil holes. One of each of these holes has this brass restrictor plug pressed inside?

Where would I get a replacement?
How come the other rod journal oil hole doesn’t have this restrictor plug?
What is it purpose?

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[nicklouse]

sounds like it has been plugged and cross drilled. and something looks like it has moved.

[Zami]

Yes the plug has come out slightly and grooves the rod bearing. Trying to understand if this is a stock modification or some aftermarket idea.

[Spider]

What's the forging number on the crank?

[Zami]

Won’t have access to the crank until next week for the forging number, But it is an Original EN40B cross drilled crank.

[carbon]

The factory cross-drilled 1275 cranks used these brass restrictor plugs in the 'outermost' oilway for each big-end, with the other two drillings not restricted. The purpose of the restrictor is to limit the amount of oil flow, preventing loss of oil pressure at high rpm which might affect the main bearings.

 

There have been other reports of these brass restrictors moving and causing damage to the big-end bearing. I don't think these restrictors are available, so you have a few other options:

- remove them all, so no chance of them moving (should be fine for road use)

- get new set made up slightly oversize o/d

- remove the existing restrictors and refit with loctite 'bearing fit' or similar

[Zami]

Thanks for the responses. One of the top racing parts Co. inThe UK indicated that whenever they get one of the older cranks with the “bungs” Installed they remove them.

[Spider]

Some of these restrictors were not pressed but screwed in to prevent this from happening.

[Zami]

Just a quick follow up. I elected to remove the restrictors and not replace them. Finished building the engine. Now with 500 miles my oil pressure is 65psi at startup (cold), 55 psi running down the highway and 35 psi at idle. This is slightly below what it ran at before the tear down and rebuild.