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Cam bearing oil restriction
#1
I am considering reducing the feed to the cam bearings, i have read that it is possible to fit drilled 1/8bsp threaded plugs into the galleries, my question is, is it a necessary to add o rings to the bushes at the same time, or is that just a further improvement? The bush has a groove Running across the bearing face so I can’t believe it would be under much pressure, especially with a reduced flow. 

I don’t currently have access to a lathe so keen to avoid paying someone to do machining work for me if possible!
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#2
Some solder around the feed hole will reduce leakage there. The face slit feeds the timing gears, many of which are transmitting far more peak power than origianlly..
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#3
Tom I think the appropriate answer depends somewhat on your engine set-up.

A more usual way to restrict the flow is to thread a brass plug into the oil hole in the bush, Loctite it in then re-drill to a smaller size.
On a pressure fed engine running at say 30 - 50 psi 3/32" dia gives sufficient supply.

On my engine I have no seals on the front cam bush and it runs dependably. However mine is a 3-bearing engine with oil feed to the big ends from the centre main bearing. Those who pressure feed from the front sometimes have difficulty getting enough oil to number 4 big end and this may be a reason to seal your cam bushes against leakage. Certainly worth thinking about if using a standard pump and you have high rpm ambitions. Just don't forget your timing gears need some oil.
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#4
Hi Tom

I don’t think it does any harm to restrict flow to both front and rear cam bearings as long as your oil pump is in good condition and you have a 2 bearing splash fed engine.

As Chris says at the front it is a simple matter of running a 1/8”BSP tap down the oilway and screwing in a brass plug with a hole drilled through it.  With my first special build (when I did not have a lathe) I took an old brass oilway plug sawed off the flats and drilled with an 1/8” hole.  Loctite the plug in.

At the rear simply turn the cam bearing round and drill a smaller hole at 180 degrees. 

If you want to add o rings to the front cam bearing you are in lathe territory 

Cheers

Howard
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#5
Hi Tom,
Are running splash or pressure fed engine ?
My Engine is pressure fed.
I have soldered up the oil groove in my front cam bearing and fitted a restrictor in the oil gallery which is just a bit of brass with a 1/16 hole in it.
The bearing has also had the O ring mod done to it.
I would not mod then cam bearing oil feed on a splash fed engine though.
If you are running a splash fed engine an overbored oil pump will help make sure enough oil gets around
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#6
Hello Tom
I went through the same question about the oil feed to the timing gears a short while ago. I decided to leave the feed through the bush standard having decided that the back pressure created would not increase the oil going through the jets to the crank, and in fact could reduce it. My engine is a bog standard splash fed two bearing. If you're pressure fed it's a totally different situation.
While you have it all apart, and if you still have the Austin square headed pin locating your cam shaft front bush, it may well be worth reworking this to take a 5/16 thread into the bush itself. The original pin tends to wear, along with its thread in the crankcase, and allows axial movement of the bush and an oil leak up the pin. The new bolt can be sealed with a dowty seal onto the top face of the crankcase.
Colin
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#7
Thanks all. I have a splash fed car with a bored out oil pump. I am in the process of fitting an oil filter and thought the additional restriction might push too much oil to the rear cam bush, I will maybe just reduce the feed to that slightly and leave the front bush alone. The project I’d already suffering from mission creep as it is.

Incidentally, my dad pointed out how the oil flow escaping between the outer face of the front bush and the crankcase can erode little tracks like tree roots, and sure enough that is the case on my engine, have others seen this? It looks like something from a geography class!...
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#8
Hi Tom,
Its very artistic.
I have seen several like it as well as tracking on the outside of the bush.
I suspect its dirty oil causing the damage over a period of many years.
The rear bush is unlikely to lose too much oil
It is oil loss from here that lubricates the oil pump drive gear so do not restrict it on a splash fed engine.
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