8 replies to this topic

[VAR1016]

I am hoping that one of our subscribers can help with what is a very specialist question.

I have a Lucas PI unit Mark II dating from 1973.

It is 6mm bore and came from a Ford FVA engine; I have checked the fuel cam number with Cosworth who confirmed that the unit "belonged" to a FVA.

Since 1996 I have used the unit on my modified Lancia Fulvia, with great success and stunning reliability.

My question concerns the shims that are used to pre-set the overall fuel characteristic.

When I acquired the unit, there were far too many, fitted between the diaphragm retaining plate and the metering unit body. After many experiments to establish appropriate fueling I left the reduced number of shims in the same place, with a neat stack of spare shims to hand.

Recently I noticed a petrol leak issuing from between the shims themselves. I removed the endplate and it then occurred to me to think "why are the shims here? Surely it makes more sense that they be fitted between the outside of the diaphragm plate and the outer plate that carries the fuel cam?"

So after fitting a new diaphragm, I moved the shims to the outside of the plate and all was well; no leaks. Another advantage is that on dyno sessions, one can re-shim in five minutes or so without distrubing the critical diaphragm (fuel at 110psi remember!).

However just a couple of weks later, the new diapraghm appears to have failed - petrol is coming form the "tell-tale" pipe. So before I strip it again, I should be interested to hear any expert opinion.

I have searched the web and can find nothing concerning the race units - plenty about the road cars and their fuel pump problems though!

Thanks in advance

PdeRL

[Ray Bell]

Your best clue is probably in contacting someone who race prepared cars that used this kind of injection...

People who built up F5000 engines, especially, should know where you're going... and dyno operators who tested the engines too.

[VAR1016]

Originally posted by Ray Bell
Your best clue is probably in contacting someone who race prepared cars that used this kind of injection...

People who built up F5000 engines, especially, should know where you're going... and dyno operators who tested the engines too.

Thanks Ray.

I have found the man: Bob Blurton in Tamworth, who was Lucas Product Manager and attended Grands Prix for 20 years of his career; he looks after the historic racers.

Incidentally, for anyone who cares to know, my suspicions were correct: the shims should be on the outside of the diaphragm plate!

However, it would seem that the problem is that there is perhaps a small obstruction in the spill pipe back to the tank; this stresses the diaphragm and has probably caused the leak.

Best wishes

PdeRL

[desmo]

[VAR1016]

Well today has been a LUCAS PI DAY.

All is now resolved: first I measured the "spill" from the unit. This is critical as it is indicative of its condition.

For those who do not know, the Lucas metering unit effectively comprises two moving parts: a rotor and a shuttle. These are finished like jewelry and are made of hardened steel They are lubricated only by the petrol/gasoline that runs through the unit. Clearance is about a tenth of a thou.... (1/10000 of an inch). The "spill" is defined as the amount of petrol that clears the seal in one minute. Today, my unit passed 52mL of petrol in that time; this means that there has been no wear at all since it was last checked three and a half years ago - and 52mL is top limit. This is a road car driven in London traffic quite often (thanks to Livingstone and his marxist accomplices in the town halls, London is Hell).

I love Lucas injection!

The problem was caused by the spill pipe running to the tank; I have replaced it with some 4mm pipe and this has cured it. Many thanks to Ken Mills Injection of Fulham, London and to Bob Blurton of Tamworth Staffs, for all the help.

Car is going like a bomb!

PdeRL

[Ray Bell]

Good work... now you can come see if you can do anything with my Kugelfischer...

[desmo]

Scary being at the top limit still. Doesn't sound readily rebuildable, might want to start looking into 5mm pipe.

We had a poster here some time back who as a young engineer worked at Lucas developing mechanical FI systems. Pity he's no longer around often.

[VAR1016]

Originally posted by desmo
Scary being at the top limit still. Doesn't sound readily rebuildable, might want to start looking into 5mm pipe.

We had a poster here some time back who as a young engineer worked at Lucas developing mechanical FI systems. Pity he's no longer around often.

No I put that badly: I mean it is the minimum one expects from a perfect, new unit; forgive me, I have been tired lately! I believe that over 85mL/min is acceptable.

PdeRL

[RTH]

There is actually a way of eradicating the common cold....................Give it a Lucas part number then nobody could get it !