'75 Oil Overflow in Amals

After completing a head gasket replacement on the '75 MK III, I checked the oil level in the tank and found it to be well below the end of the dipstick. Knowing that the MK III had a factory anti-wet sump valve installed, I assumed that I had drained the oil in the tank and crankcase prior to starting the head removal last season. I should have verified that was the case as it turned out to be an incorrect assumption. So, after topping off the oil tank with 2 quarts of oil, I finally got the bike running. After a few minutes of operation I noticed a large pool of oil accumulating under the transmission and immediately killed the engine. It turns out the excess oil had vented through the oil tank overflow outlet and had drained into the upper part of the air box. Sufficient oil had accumulated in the air box that it started flowing into both Amal carburetors prior to draining through the lower air box access panel area and then onto the garage floor.

The question that I have is: what is the recommended remedy for this situation? I'm mostly resigned to removing the carburetors and cleaning them up, but is that the only alternative? Will the normal aspiration of the carburetor tend to clean up any surplus oil or is it necessary to remove, teardown, and clean the carburetors?

ColoCommando said:

Knowing that the MK III had a factory anti-wet sump valve installed, I assumed that I had drained the oil in the tank and crankcase prior to starting the head removal last season.

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The MkIII anti-drain valve only helps to slow the process down, but the oil will still drain to the sump if it is left for long enough.

ColoCommando said:

The question that I have is: what is the recommended remedy for this situation? I'm mostly resigned to removing the carburetors and cleaning them up, but is that the only alternative? Will the normal aspiration of the carburetor tend to clean up any surplus oil or is it necessary to remove, teardown, and clean the carburetors?

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You simply over-filled the system with two quarts :shock: of oil,-that's all.

Always drain the sump and return the oil to the tank if the level in the tank is low, and only check the oil level and top it up to a maximum of half way between the high and low marks on the dipstick after the engine has been run for a few minutes so any oil that has drained down to the sump will have been returned back to the oil tank.

[Edit]Remove as much of the oil as you can from the airbox and drain the carbs, if it still starts OK then any oil should disperse. Personally I prefer to vent the oil tank breather into a small catch bottle.

L.A.B. wrote:
The MkIII anti-drain valve only helps to slow the process down, but the oil will still drain to the sump if it is left for long enough.

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That was certainly the case here. The bike has sat for the best part of 8 months.

L.A.B. wrote:You simply over-filled the system with oil,-that's all.

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I understand that, but my question is mainly concerning any cleanup that may be necessary to get the Amals functioning properly again. Any advice for that? Thanks!

Yes, sorry, I posted before I'd fully answered your questions.

I have now edited my previous message to include that.

L.A.B. wrote:
Remove as much of the oil as you can from the airbox and drain the carbs, if it still starts OK then any oil should disperse. Personally I prefer to vent the oil tank breather into a small catch bottle.

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That is easier that what I had anticipated so I'll be glad to give it a try. I really do not like the way the oil tank breather vents into the air box so when you say that you prefer to vent into "a small catch bottle", I'd like to ask how you would implemented that idea. Specifically, where can a small catch bottle be reasonably and safely mounted?

All advice is appreciated!

As for an problems you might see from the oil in the Amals... might subdue the mosquito population when you start it up (smoke a bit). When it stops smoking you know the oil is gone.

ColoCommando said:

That is easier that what I had anticipated so I'll be glad to give it a try. I really do not like the way the oil tank breather vents into the air box so when you say that you prefer to vent into "a small catch bottle", I'd like to ask how you would implemented that idea. Specifically, where can a small catch bottle be reasonably and safely mounted?

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There has been some previous discussion about how air from the breather system can potentially bypass the carbs and be drawn into the engine, thus upsetting the fuel mixture.

The two short lengths of carb intake balance tubes and tee piece can be removed and replaced with a single piece of tubing, the separator can be disconnected or blanked off from the airbox and pipework and a longer tank breather pipe fed into a catch bottle positioned in a convenient place somewhere.
My MkIII doesn't have its original airbox, so the breather pipe is routed down between the engine and gearbox to a catch bottle at the lower end (I made the catch bottle one from a builders chalk line refill container) where it is out of sight, as it sits between the plates of the lower part of the engine cradle. Normally the bottle stays dry, so it's not actually doing much at all.