Fuel pump

[cfm65@me.com]

Hi Gents,
My 250SL fuel pump is seeping a little fuel from the lower cover plate. The cover has a slight red tinge around the joint and the 6 bolt heads are wet. It is not dripping and no stain on the floor. Yet.
My question; could the lower cover be removed and the O ring replaced in situ?
Regards
Chris

[Benz Dr.]

Try tighten the screws before you do anything. I've found that once you remove the cover plate the O-ring can't be used again because it tends to swell up.

[cfm65@me.com]

TKS Doc,
Yep, I have nipped them up but the cover is still sweating a bit.

[rgafitanu@gmail.com]

Make sure the leak is not coming from the overflow spout. In any case removing the pump is easy, clamp the hoses and unscrew the pump bracket from the body. You wouldn't want to lose the impeller key, you also want to have a new o-ring seated properly, I wouldn't do it from under the car.

[cfm65@me.com]

Thanks Radu,
My pump is dry except for a little seepage, as mentioned.  I don't suppose the O ring will be found at the local hardware store?
Anyone got the excact size of the bottom O ring?
Regards
Chris Cape Town

[wwheeler]

The O-ring will need to be metric for sure and Nitrile (Buna-N). Not sure if your stores in Cape Town are metric or imperial? I bought a new fuel pump sometime back that was NOS, installed it and over time it weeped just as you describe. Turns out there was a bit of pitting on the plate from the part being in storage. I used the next size up O-ring in cross section and have had no problem since. If there is no corrosion pitting, then a simple O-ring replacement should do it.

Unfortunately, I do not have any documentation on that O-ring size. Once off, just measure the groove diameter of the pump and the width of the O-ring. Then match up with an O-ring chart. I can try to help given the above dimensions if no one else has the size.

[cfm65@me.com]

TKS Wallace,
Yes, we went metric in the early sixties and have been fully metric well before the seventies. I am one of the lucky few that started school in imperial measurements and pound/shillings and pence.
My tank is quite full at the moment and I will drop the pump at a later stage. In the mean, time I'll keep an eye on it.
Thanks for you help, much appreciated.
Regards
Chris

[rgafitanu@gmail.com]

The big o-ring is metric, 70mm with 2 mm thickness( I'm not sure, they are at home). Unlikely to find them at the local hardware store. The closest imperial o-ring would be a dash 039 1/16" wide. There are o-ring distributors on the web or try a local hydraulic service business. Or if you don't mind waiting I can ship you a set.
Are you sure all of the 6 bottom screws come out? Usually they break.

[cfm65@me.com]

Thanks Radu,
Is that 70mm inner or outer, or are O rings not measured inner and outer? Yep, the screws are free, I have tightened them all and they are not frozen.
Let me have a look at our local engineering and hydraulic shops. I'll let you know what I find.
Thanks for the offer to ship them. Much appreciated.
Regards
Chris

[Jowe]

If you take the pump out, why not refurbish it with a kit such as this: http://vintageeuroparts.com/a0010915201.html Then you get the correct o-ring and other parts.

[wwheeler]

Chris,
O-rings are normally measured by the ID and then the cross section or width. If the O-ring really is 70mm x 2mm for this pump, then that is 70mm ID x 2mm cross section. A 2mm O-ring would measure (.079") while the 1/16" imperial ring would measure (.070"), so actually smaller and you don't want that. The next Imperial size is up 3/32" and actually measures .103" and much too fat. 

No, what you are after is either a 2.4mm or 2.5mm section O-ring and they do exist. http://www.theoringstore.com/index.php?main_page=product_info&cPath=368_12_44&products_id=17874 This should be close enough. 2.4mm will give you (.094") or .016" fatter than a 2mm. (Sorry I go into inch sizing because I know what to look for). And yes, an Imperial 1/16" O-ring does NOT measure .062". It measures .070" and that is the way Imperial O-ring sizes are. Metric measures as it is called out. Confusing yes, but I deal with it all day.

Good luck.

[cfm65@me.com]

TKS Wallace,
Your description is much appreciated and Jowe is propably correct in suggesting I bite the bullet and do it properly, especially since mine is not leaking yet.
TKS Johan,
I think I will follow your advice and pick up a complete repair kit on my next EU visit.
Regards
Chris
Cape Town

[rgafitanu@gmail.com]

Chris,
Which type of pump do you have? The tall (early) or the short (late) one? Johan's link is for a short pump. I think Wallace made the o-ring dimensioning very clear. One thing from my experience, I rebuilt 3-4 tall pumps. When I tried to use o-rings thicker than 2 mm I had poor pressure on the output. Probably there was too much of a gap between the impeller and the cover.
The technical manual here is very detailed about these pumps.

[Rick]

There are suppliers that can provide o-ring and seal kits, assuming you have the short pump.   Check it carefully, they can start dripping from where the wires enter the pump.  All this is repairable but you do have to use care.  The bottom plate is easy and can be done right on the car if you choose.  Don't let the impellor fall off if you take off the bottom plate and don't reverse it.

[Jowe]

Johan's link is for a short pump.

I assumed it was the short style since Chris has a 250SL. Vintageeuroparts also has a kit for the long pump (which I have successfully refurbished my pump with). BTW, Vintageeuroparts are located in the US but ships WW. It's well known supplier on this forum.

[BaronYoungman]

Vintage Euro Parts is run by Babak... good guy, big Pagoda enthusiast and a member of this group.

[Tyler S]

The long pumps were used until 1968 280sl. My late 250sl originally had a long style pump. My Dad replaced it with a short style pump back in the late 80's. I still have the original in a box. He never threw anything away!

[cfm65@me.com]

Thanks Gents,
Yes, I have a short pump.
Thank you for all the suggestions. I have just(as in today) replaced an intermittent pump in my E Type, so Mr Pagoda is next in line.
Thanks again, much appreciated.
Regards
Chris
Cape Town