Perkins 4.212 CAV injection pump - bleed screw locations?

[aesmith]

Hi,

This is a Massey Ferguson 50B digger, around 1976. According to the any reference there should be two bleed screws on the CAV injection pump, one on the intake side that bleeds when you work the lift pump, then another one further downstream but still on the low pressure side, that bleeds when you crank the engine. On this installation I have only been able to locate the first, it's the one with damaged screw head just above the CAV plate in this photo. Can anyone point me to the second screw? I don't want to undo the wrong thing. Bleeding just at the lower point, it takes a lot of cranking before she fires up, even though it shows fuel nicely at the injector unions when they're slacked off as the final bleed step. Thank in advance, Tony S
IMG_0614 by ANTONY SMITH, on Flickr

 

[Gordon Gould]

I have a similar CAV pump on my TD7. The bleed screw is in your photo. On the top cover to the right of the bracket. It is the broken off one in my photo. The lower one will work too but you won't get as much air out because it is lower.



gg

 

[thepumpguysc]

The MAIN bleed screw is right above the name plate.. double screw.. 5/16-7/16.. loosen the small screw5/16 & retighten after cranking.
THAT bleeds the air out from the lift pump, to & thru the inlet on the injection pump..
The upper bleed screw is the broken screw on the top cover.. the one w. the screw in it.. right side.
THAT screw SHOULD LOOK LIKE the one by the name plate.. its been replaced.
Loosen THAT ONE, AFTER the engine is running..
ACTUALLY, you don't have to mess w/ the upper one AT ALL.. the air will come out after its been running..
Have you checked the condition of THE LIFT PUMP?? maybe its not pumping at all.. hence the hard start.. just because the hand primer is working doesn't mean the pump is pumping while cranking the motor..

 

[aesmith]

Thanks. So it looks like the second bleed screw on mine is effectively where that hex head bolt is, top right corner of the pump in the picture. I'm not quite sure what you mean by loosening that one "after the engine is running", surely the engine won't start until the pump is properly bled? Actually since posting, I've looked again at the manual and I see that the second upper bleed screw is bled by working the lift pump, the same as for the lower. That's different from the other CAV pump I've worked with on a Volvo marine engine, on the Volvo the second bleed screw only bled when the engine turned over giving a little low pressure spurt of fuel at each turn, but nothing just from working the lift pump (conveniently the Volvo had both a decompresser and a starting handle). I'll try the upper screw next time I need to bleed. The Volvo had a DPA pump, not sure if the Massey is DPA or DPS.

Regarding the lift pump, I've just been assuming it's OK since the primer works. Something else to check, and I actually have a spare replacement lift pump somewhere as it happens.

When I say slow to start, I'd say after bleeding it takes something like 10 seconds of cranking before it fires. That seems a long time, especially round about 12 seconds when you realise it's not starting and need to go back over the bleeding stages again.

Thanks again.

 

[DLTTrekkers]

The bottom bleedscrew you use to let the air out....the pump will let the rest of te air out by the leakoff at the injectors

 

[aesmith]

Thanks again. Maybe a long shot, but can anyone tell me the size and thread type for the bleed screw and seat? As you can see I need to replace the lower bleed screw as it's damaged, and I'd like to have a proper bleed at the upper position. Items for sale seem to either call them "small type", or "large type" or give the thread size. Ideally I'd like to be able to identify the correct part before removing the existing bits.

 

[thepumpguysc]

Mr. Smith.. There are 2 fuel circuits inside the pump.. the lower bleed screw lets air out in the pumping circuit..
The upper is the low pressure circuit.. The engine will/should start & run by bleeding the hi pr. circuit..
THEN you open the low pressure circuit to get the remaining air out of the housing itself.. BUT.. its usually not necessary, as the pump will do it by itself..
The part #'s for the bleed screw assemblies are DELPHI-CAV part #'s>> UPPER-7240-20B [8.00].. Lower- 7240-20A [22.00]
You could remove BOTH & compare the sizes.. IF the upper is the same size as the lower.. order the lower P#..

 

[aesmith]

Thanks, this is all great information. Will bite the bullet and replace both bleed screw asap. Each time I've bled the system I've worried about that damaged screw, one day I might not get it undone.