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A31 engine

Started by tom hoek, 01 Jul 2014 at 19:27

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tom hoek


I now have it all together and the motor (a31) is catching on

I have a question: How much oil is in the engine when it is empty?
  (if you start the first time)

regards Tom hoek



It must be exciting hearing it try to start for the first time!

The engine is a dry sump design. In the crankcase compartment will only be a very small amount of oil; that which has drained down and not yet been scavenged by the oil pump and returned to the oil tank. The timing chest should have a pool of oil it it; enough that the lower cam gear wheel will dip into it. The level is automatically maintained by a hole drilled through the back wall of the timing chest that serves as a weir. Any surplus oil above the level of the weir drains over into the crankcase chamber. It is a good idea before running the engine for the first time to pour some oil into the timing chest to have an initial supply. After that, leakages from various points will collect in and maintain the level in the timing chest. Oil mist blowing through from the crankcase chamber will also lubricate the timing chest.


tom hoek

Hello all en Doug
I drove 10 kilometers by bike is very nice  :D

Now there was much oil in the crankcase 1halve gallon!
Now I think the pump is too fast.
how much should the pump be open?
(rotary knob)

I have 20 w 50 motor oil in the engine?
Is  this  good?

Greetings from  Tom Hoek


Hello Tom,

A half-gallon of oil in the crankcase is too much. I would expect it to have been smoking a lot with the oil level that high. Remember there are two compartments. The crankcase should be nearly dry. The timing chest should have some oil in it (1/4 pint?)

With the recirculating system like the A31, Douglas recommended leaving the regulator (sight glass) valve well open. Only restricting it sufficient to prevent over-oiling or excessive consumption. This is a little different than total loss systems like on the EW or 2-3/4hp models, where you only want a just a drop or two of oil going into the engine every few miles. You want a goodly amount of oil constantly flowing into your A31.

It sound to me that either the pump is not scavenging the oil and returning it to the tank, or the oil is finding its way into the engine faster than it can be scavenged. If the pump is scavenging, you should see oil returning to the oil tank compartment from the top of the return stand pipe, just inside the filler cap opening. By design, the oil pump should not be able to pump a larger volume of oil into the engine than the scavenge can remove. So I wonder if oil is draining down into the engine when it is not running, filling up the crankcase chamber. There is a ball and light spring in the joint between the oil sight glass and the timing chest casting. This is a check valve, and it is there to prevent oil from draining down into the engine (and filling the sight glass and then engine) when the bike is not in use. Some models have a valve on the line from the oil tank instead that you close when the engine is not is use. Just do not forget to open it before you start the engine!

Douglas recommended Castrol X.L. My understanding is this is something like 50W. I run anything between 30W to 50W, depending on what is on sale. 20W is probably a little too thin, but otherwise I do not expect running a multi-grade oil in this type of engine is a problem.