m55 H fuel pumps

[speeder]

Q.

the engine block has two mounts for fuel pumps
i have noticed that in the mounting areas ,only the top
fuel pump has a direct hole,passage through block and into
crank area,
where the botton fuel pump does not
have a passage into crank area, is this right?

On my 30H also uses two pumps
with a top pump and botton pump
they are connected with a small hose
is one pump feeding the other?

thank you

[sam]

Yes, it was originally thought the small displacement of the 30 would not adequately pump fuel so the first group was made with 2 pumps set up to increase pressure.

[trident]

Mk 55, Mk 30 fuel pumps

Let's expand on what Sam said... the Mk 55 and the 44's have better crankcase pumping action than the Mk 30, due to larger displacement, with essentially the same crankcase volume... so they run fine with a single pump.

A Mk 30 pumps fine on one pump at high speed.

Some 30H's had two fuel pumps, some had one, with the second boss machined but blocked off with a blank backing plate.

However, ALL service Mk30's had two pumps, hooked up in series, not parallel, as the service motor could run out of fuel idling. By series, I mean the output of one pump fed the input of the other. On one pump they were fine at high speed, but they barely pumped at very slow idle. Two pumps, in series, fixed that.

Hope this helps.

Jerry Wienandt
Trident Racing