Alloy Rocker cover and breather

[moggiegeek]

Some will shudder but I have an alloy rocker cover and it has no breather. I would like to fit it and so have sourced a 5/8inch UNF breather take off for a 1/2 inch hose.
Is it a relatively easy job to tap a hole drilled in the correct point of the cover where the casting has a circular, thicker area.
I have a simple pillar drill.
What drill would I need for the first hole which would then be tapped - will a hand held tap then be OK?
How would I ascertain threads per inch on the take off fitting?
Hope you can help

[grumpydad]

Hi
drill size 17/32
hand tap fine
why do you need thread per inch ?

[les]

Hand held tap will be ok, start with 1st tap( which has a decent taper to it) check the fit of the take off before you completely pass the tap through all the way, (you may find the thread too loose if you use the complete tap length). The tapping hole size will probably be around 9/16 inch but check the tapping size drill for a 5/8 unf thread on Google.

[Declan_Burns]

According to my charts the drill size should be 14.75mm. I think the 17/32" would be slightly too small.
Some of the American charts recommend 37/64" which is 14.68mm.
Regards
Declan

[mike.perry]

What engine is it for? If it is for a 1275 then you do not need a breather

[philthehill]

You can never too many breathers.
If it is a 1275cc, 1098cc or 948cc engine the pipes can join up and feed into the air filter, the PCV or carb.
The breathers can be fitted to the rocker cover, the timing cover, the disused fuel pump aperture.
As regards your original question regarding the TPI the 5/8" UNF has 18 thread (tips) per inch (TPI) but some take offs are 5/8" UNS which has 16 TPI.

[mike.perry]

I found that on my 1275 with alloy rocker box there were smaller pools of oil on the drive if I just had one breather from the timing chain cover to the PCV[frame][/frame] The take off on the rocker box has been blanked off

[bmcecosse]

Oh but yoy DO need a breather - especially on a 1275 engine !!!!!!!

[mike.perry]

OH NO I DON'T!!!

[Boomlander]

Great - Summer pantomime!
All together now........OH YES YOU DO!!

[bmcecosse]

I can only lead the horse to the trough.....I can't make it drink.....

[mike.perry]

Strange then that BMC managed without a rocker box breather on their 1275s

[bmcecosse]

Fine on new/excellent condition lowly stressed engines...... There's no doubt the PCV is a great improvement, but not everyone has that. I know what works for me.... We'll be getting comments about leaky oil caps next.... The subject can go on for ever..

[moggiegeek]

For those who asked it's a breathed on 1098. I've now drilled and tapped the alloy rocker cover. The take off has about 1" of thread, I know its probably just a question of trial fitting and turning engine over by hand to see that it has clearance re rocker arms - has anyone done this mod and found out roughly how much clearance there may be?

[philthehill]

If you have a standard cam and standard rockers there will be adequate clearance between the valve gear and the alloy rocker cover.
I have a full race cam and 1.5 ratio roller rockers and there is adequate clearance between the alloy rocker cover and valve gear.
If you are concerned put the rocker cover on and with the plugs removed turn the engine over. You should be able to feel or hear any contact between valve gear and rocker cover. If nothing felt or heard remove the rocker cover and check the inside of the rocker cover for any contact marks.
If nothing refit the rocker cover and enjoy.[frame][/frame]

[bmcecosse]

The interference risk is only with the non-standard breather that has been fitted....