What's in inside a 4FL oil pump...

[Martin77]

So, after thinking about what Arrow said about uprating oil pumps for big bores, and being an inquisitive person, I decided to have a poke about inside my old 4FL pump. (I had removed it as the one way valve leaked allowing the engine to fill with oil when sat).

The stroke is checked with a dial gauge poking through the end cap, while the internal gear is turned with a spare finger, 0.25mm for minimum and 2.9mm for maximum.




So wondering if I can increase flow a bit I modded the small cam which controls the stroke..thus..



here's where it sits underneath the blanking plug. The small brass adjustment screw goes inside the middle of the cam and is eccentric, so when the screw is turned the cam moves in/out to fine tune the minimum stroke. It is a bit awkward to remove it.


Along with a bit of grinding on the top cam, I managed to get max stroke up to 3.4mm, or about 17-18% more flow.

What was alarming though, was when I stripped my current pump (4FL cast on the body and pulley) it had a different small cam inside giving max stroke of less than 2mm! so for the past couple of years the oil flow past 1/3 throttle would be much less than even the 125 ought to have! says a lot about fully synth oil I guess... and why the tail can is always dry inside. I wonder if they used the same pump body for 50cc versions?

Anyway, will fit the modded pump (which only pumps more past 3/4 throttle or so) and see how it goes next spring..

[ybk]

That's pretty neat, Arrow will be proud These pumps are quite bulky compared to the 3xv ones - the design has probably been improved upon significantly over the years..

[Martin77]

True, but it's also quite a bit better designed than the older ones, where you have to muck about with shims.. like you say, things move on!

[41juergen]

Hi Martin, have you finally tried the new setup of that pump? I'm struggeling with setting the stroke on my pump, how did you removed the blind cap and where did you sourced a new one?
cheers
Juergen

[Martin77]

sorry for the delay in responding Juergen!

I ran the oil pump just fine since I wrote the thread. It's been so long that I've forgotten the details, I can't remember how I removed the end cap, but I know I didn't replace it afterwards. I must have been able to get a sharp point in at the edge and lever it out carefully.

I will dig out my spare pump and refresh my memory!

[41juergen]

Perfect, thank's a lot! I'm still struggling to understand how that pump works and how to get adjusted correctly... 
Juergen

[jools]

Hi Martin

I was going to open up my spare 3XV oil pump as one of the check valves was also leaking and Gary (Arrow) says he can't service these.

did you manage to fix the leaking valve you mentioned in the first post ?

cheers

Jools

[Martin77]

No, I never investigated the valve and just bought a whole replacement pump..(yay for cheaper used parts for the 125's) On older pumps they merely pull out, but no idea on these. I can have a look later seeing as I probably won't be using this one again (sure I stashed it somewhere)

[Martin77]

How to set the 4FL minimum stroke-

Rig up the oil pump in a vice as per pic, I held it on one of the mounting ears (better use use aluminium jaws) allowing room to poke a finger inside and turn the gear cog inside.

Remove the central screw from the black plastic end cover and poke a dial gauge in. I don't have any extension pieces for mine so just screwed in a tube from an aerosol

turn the inner cog and you should see the dial gauge move up, then down once a cycle. Read the measurement, this is the minimum stroke.

If you wind open the pulley as if the throttle was opened, and do it again you will see the stroke increase illustrating the extra oil injected.

[Martin77]

To adjust the minimum stroke, release the lock screw (green arrow), the large brass screw behind is turned, and adjusts the minimum stroke. It has an eccentric pin on the inside, and will rotate fully, so it's just a matter of finding the spot where it gives the required minimum stroke. Give it a small turn, check again with the dial gauge, and fine tune.

Once happy, lock up the screw again and it's done. I can't remember what the minimum stroke should be, if you have the manual settings for it please post it up! (I used to know it when I set mine but since forgotten)


There is no need to remove the blanking plug to do this... I only did that to investigate how to increase oil flow. If you do want to remove the blanking plug I found a sharp pointed tool at the edge is enough to lever it out without damage because it isn't very tightly pressed in.

[SeaR1ck]

Same oil pump used on my tzm 150. You took yours further apart than mine. I had to replace mine. I ended up getting a new one from a dt125re like 06 I think.

I found that the stroke was the same between the one from the 150 and the dt125re. The difference was the plastic gear you turn with your finger.

The 150's had less teeth had bigger ones and the 125's had more smaller ones.

Didn't know about the adjustable cam piece inside it.

This pic is of the two gears black one from the dt125re pump. Yellow one from the tzm 150 pump. When I put the dt125re pump back together I used the 150's gear.

[jools]

Hi Rick,

Do the worm drives need changing also?

I know this is similar to LC250 and LC350 oil pumps, and you have to match both worm drive and oil pump gear otherwise they potentially chew the plastic gears up

[SeaR1ck]

I don't think so I just took it apart enough to measure the pump stroke. And when I put it back together I used the tzm's gear instead. Just to try and keep it close to stock.

Must be working fine think I put like 600 miles on the bike since swapping it. No problems since.

[41juergen]

To adjust the minimum stroke, release the lock screw (green arrow), the large brass screw behind is turned, and adjusts the minimum stroke. It has an eccentric pin on the inside, and will rotate fully, so it's just a matter of finding the spot where it gives the required minimum stroke. Give it a small turn, check again with the dial gauge, and fine tune.

Once happy, lock up the screw again and it's done. I can't remember what the minimum stroke should be, if you have the manual settings for it please post it up! (I used to know it when I set mine but since forgotten)


There is no need to remove the blanking plug to do this... I only did that to investigate how to increase oil flow. If you do want to remove the blanking plug I found a sharp pointed tool at the edge is enough to lever it out without damage because it isn't very tightly pressed in.

Hi Martin, can you explain a bit more in detail how you modified the excenter please, may be a pic? 
cheers
Juergen

[Martin77]

ok, so the inner cam controls how far the middle plunger moves. With the tall point of the cam prevents the plunger moving far, this is the closed setting, and is fine tuned with the brass adjusting screw.

The low part of the cam moves out of the way, allowing the plunger to move further in/out. To allow more movement of the plunger, this is the part that I ground down. See the lines on the pic.. orange showing where it can be cut down.

I also ground the lower sections on the gear to allow a greater difference between high and low positions, see blue areas in the pic.

If you remove the end sealing cap and operate the gear, you should be able to work out how it operates and go from there...