timing case drillings

Can anyone help me identify the two holes marked in green in the attached pic? Are they drain or breather holes? Just curious as I'm modifying the cases for my build as per suggestions from Jim etc.. I've already plugged the one obvious breather hole, relocated oil drain hole, and plugged OPRV drain hole (with proper mod to timing cover). The primary side case has been milled for Jim's crank breather... hence the enquiry

This looks like an in between version of some cases that I have.
The earliest 20M3 cases, like 127254 only had the upper green drain back hole, which was carried over from atlas.
Norton discovered the drain back level was to high for the tilted commando engine and by 128271 the casting had metal added and the lower drain back hole was added.
I would only guess yours is an early 20M3S because first there is no rear points...second the timing chain adjuster had moved forward closer to the cam...ie broad later pad. Also there is residue from the rear points lower inner pad bolt mound which is undrilled.

The most interesting part is that the failed starter machining was not done like it was at 162569, and was carried on part way into the combat 200000+ series. The later failed starter engines had an internal timing chest bosses that are not yet present on your 20M3S.

Thanks Dave, I was confused in identifying these cases even after consulting your website. I guess this is a weird transition example after all.

Anyway, based on your response I'm assuming both green holes are drain back holes, so I will plug them since I've relocated the drain nearer to the oil pump.

Cheers

Perhaps just an academic question but what if the green original drain holes are not plugged?
Would not the new drilled hole to the left of the oil pump mount drain the timing case efficiently so that the oil level would not get to the original hole?

I did my 230615 cases with the new drain hole and found the case is very thick at that area.

Bob Z. said:

Perhaps just an academic question but what if the green original drain holes are not plugged?
Would not the new drilled hole to the left of the oil pump mount drain the timing case efficiently so that the oil level would not get to the original hole?

I did my 230615 cases with the new drain hole and found the case is very thick at that area.

Click to expand...

Probably depends what the OP is planning in terms of a breather system!

SteveA said:

Probably depends what the OP is planning in terms of a breather system!

Click to expand...

I'm using Jim Comstock's rear (not sump) mounted breather

Both of the drain holes in question terminate at one point in the TS case joint, so I just plugged it there rather than fuss with 2 in the timing chest

acadian said:

I'm using Jim Comstock's rear (not sump) mounted breather

Both of the drain holes in question terminate at one point in the TS case joint, so I just plugged it there rather than fuss with 2 in the timing chest

Click to expand...

Yes, they were originally oil drainback holes. With the new drainback hole drilled you can plug them -at either end. This helps keep the crankcase pressure pulses in the crankcase where they help the reed valve work better. Jim

can these early commando cases u mention be modded? or earlier atlas cases for use in the forward tilted position?

or not a huge deal as is?

dynodave said:

This looks like an in between version of some cases that I have.
The earliest 20M3 cases, like 127254 only had the upper green drain back hole, which was carried over from atlas.
Norton discovered the drain back level was to high for the tilted commando engine and by 128271 the casting had metal added and the lower drain back hole was added.

Click to expand...

aah, just read this part.. & the rest

acadian said:

Anyway, based on your response I'm assuming both green holes are drain back holes, so I will plug them since I've relocated the drain nearer to the oil pump.

Click to expand...

acadian said:

Can anyone help me identify the two holes marked in green in the attached pic? Are they drain or breather holes? Just curious as I'm modifying the cases for my build as per suggestions from Jim etc.. I've already plugged the one obvious breather hole, relocated oil drain hole, and plugged OPRV drain hole (with proper mod to timing cover). The primary side case has been milled for Jim's crank breather... hence the enquiry

Click to expand...

To clarify a matter please..
My 72 engine no. 200918 has only the lower of the green oil drain way back to crankcase, so has a relatively high oil level within the chain case.
I'll probably be installing the JS Motorsport crankcase reed breather
So what modifications do I need to do (if Any) to
1. Lower oil level in the primary chain case?
2. Drilling additional breather holes between the two case
3. Closing any holes to change the way it breathes

As always very many thanks for your invaluable knowledge






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