camshaft turning

[SilverSaloon]

Hi

this may sound like a silly question, but knowing little about this area i'll ask anyway

is there any way the camshaft or one of them may turn intermittently? its the one that drives the fuel lift pump i am most concerned about. the lift pump works fine "on the bench" but doesnt seem to function all of the time when fitted to the car.... i had the lift pump have a pipe going direct from a bottle of fuel into it, and the lift pump outlet to an empty bottle.... when i turned the car over, no fuel was pumped.....

however the other day i drove about 3 miles without problem.

any ideas?

cheers

derek

 

[BlackC55]

It is chain driven so I can't see how it would work intermittently unless it is partialy snapped.

 

[Druk]

Is the lobe on the shaft not part (an parcel) of the main pump camshaft? If the fuel pump cam is not turning then how are the rest of the lobes driving the pump elements?

I'll give you a tenner for it....no questions.

 

[chris846]

BMW R series motorbikes have the lobes pressed onto the camshaft. It's theoretically possible to shift them on a camshaft manufactured in this way, but it tales a mighty force, then again, you never know who's been in there before you. That said, it still wouldn't be on my list of top 100 reasons for your problem.

 

[Dieselman]

In short, I think the answer is no, it's a cast shaft. Time for a new lift pump I think.

 

[SilverSaloon]

In short, I think the answer is no, it's a cast shaft. Time for a new lift pump I think.

i've replaced everything in the lift pump, apart from the spring, which seems to be fine but i've ordered a new one anyway.... the only original part left is the casing and the pushrod, all of which are fine.

 

[johnsco]

It is chain driven so I can't see how it would work intermittently unless it is partialy snapped.

If the cam-shaft was "partially-snapped", I think you'd know about it big-time.
The only time I ever had a cam-shaft snap, there was a loud bang and the end of the cam-shaft came crashing out through the side of the crank-case.

 

[Number_Cruncher]

How are you determining that the lift pump isn't working? In my experience, these lift pumps are among the most reliable parts of an already reliable car.

 

[Druk]

Found this on Peachparts. Hope it isn't you.

'87 903.960 Injection Pump, not pumping - PeachParts Mercedes ShopForum

 

[bolide]

In short, I think the answer is no, it's a cast shaft. Time for a new lift pump I think.

I think it's also a hollow cast shaft. Now how do they do that? Rotating moulds, I imagine

Have you tried feeding the lift pump from a small container in the engine compartment? I wouldn't discount this being caused by the traditional 606 air leak

Nick Froome

 

[SilverSaloon]

I have tried several things so far. I have connected the main rubber fuel in and return pipes into a bottle of diesel. from this, i managed to start the car (in the end) and move it up the drive, turned around outside and back into the drive (as car was parked other way round).... all from a bottle. then, once car was a bit warm, i connected it back to the main fuel tank and cranked for ages and eventually it fired and i drove about 3 miles to put £10 worth of diesel in the tank. i then left it overnight and then it didnt start again and when i released the fuel tank cap i huge vacuum was there.

since then i have tried to run again from the can (as there is no fuel in the lines now as its been sucked back to the fuel tank) but it didnt appear to be pumping. I had the lift pump rubber "in" pipe in the bottle of diesel and i pulled the pipe going into the main filter and put it in an empty bottle. This meant the only (maybe) complication part of the system is the little black heat exchanger which the main "in" pipe connects to and the pre-filter, which has been cleaned. Last time i checked it didnt pump any fuel when cranking with this test.

i hope i dont have the same problem as the guy on peachparts, but i'm hoping as i did that 3 mile drive the problem isnt that bad....

unfortunately the stupid threads on the lift pump studs have come out of the side of the IP so i need to re-tap one or both sides before i can continue.

i've ordered up all new clear pipes and a new spring for the lift pump.

testing the lift pump "on the bench" with the 2 pots of fuel direct to the pipes in and out of the lift pump and me pushing and releasing the rod by hand pumps the fuel no problems, hence my worry about the cam.

 

[Druk]

I've got a dial gauge you can borrow to check the lift of the cam with the IP still in place. Was it you that phoned swmbo yesterday?