Stuck barometric compensator - any tips?

[JP3480]

Hi people.

I own a 280 SL from 1971. It has had a lean running condition for some years that I have compensated by lengthening the injection linkage going to the injection pump. It means that the pump is never fully resting on its stop, and to fix this, I want to richen up the mixture throughout the entire range.

The injection pump was rebuilt 10 years ago and the BC has a yellow dot. I imagine that's a torque dot from when it was rebuilt, stating that it was torqued OK. However, it appears to be quite stuck. How much force can I exert on this part? At the moment, all I have done is sprayed WD40 penetrant on the part of the BC that connects to the pump, and I have used a "home made" 19mm. wrench that is both shortened to fit in the engine bay and chiseled down on the tangs to get it to fit. However, the BC does not budge.

The wrench is probably 20 cm / 8 inches long or so, so it's quite short.

I thought of using a small breaker bar and then levering it down to the chassis of the car with the 19 mm. wrench attached to the BC, essentially "pushing" the wrench towards the engine by levering a long breaker bar pointing downwards to the chassis.

Do you people have any tips? Is the housing attaching the BC made of aluminium? If so, I need to be extra careful before I do the above.

thanks.

[LindesayOne]

I, too, would be interested in a response to this question.
Since recently acquiring my 69 280SL I have, in the course of refurbishment, removed most nuts and bolts in the engine compartment. However, the barometric compensator resists all my efforts.

John

[Benz Dr.]

We made a wrench just to remove the BC. This thing can be on the IP very securely so we designed a wrench that works every time.

Since there's so little room to work around the left side of the pump we made our wrench so that it works above and beside the valve cover. Having enough room to swing your wrench is the main factor here.

We used a regular end wrench then we heated and bent it  90 degrees so that it works like a crow foot socket.  We welded a piece of solid rod to the side of the wench and then we bent the rod so that it points over top of the valve cover. We left close to two feet pointing over the valve cover and it works like ten men.

[LindesayOne]

Tanks Dan. Looks doable.

Good to know that the problem is not just a symptom of my incompetence!

John

[ja17]

Seems like some of the early ones were 19mm and the later ones were 22mm. A good quality skinny wrench is a must. JP3480 iI have used the pry bar trick you mentioned, and it has work for me. I like Dan's design on the special home made wrench.

[wwheeler]

Is the engine running lean at all ranges or just idle? Changing shims on the BC will effect the entire range.

There is also a screw on the back of the pump that can also be used to change mixture for the entire range. Actually is more effective than the BC.

If you are a full member, you have access to the info to easily make this change - https://www.sl113.org/wiki/Fuel/Injection#Pump

[JP3480]

Thanks for the replies. I would absolutely love to see the home-made wrench, @Benz Dr. I thought of doing just that with bending a wrench 90 degrees, but to get inspiration for a good design, I would love to see yours - if possible.

To respond to @wwheeler, the entire range is lean. It happened probably 2-3 years ago from day to day, so I suspect the BC went kaputt and leaned the entire range. I lengthened the injection linkage a few turns "temporarily" (been 3 years) to compensate and it has worked OK. It causes some weird running issues every now and then so I would like to do a full range adjustment on the BC to get the car back to going well again.

I think I'll try to soak it in a little more penetrant, and then I'll try with the pry-bar on the chassis against the wrench mounted on the BC (against a rag!). If that doesn't work, we're back to making new tools once again.

Thank you all for the help.

[wwheeler]

Ok. There is a info here on the proper length of the rod that comes out of the BC. They don't move much when working, so it only takes .003" shims to make a noticeable difference. I just took a 22mm wrench and cut it short on the beam. Then you can use a hammer to tap. All I needed but mine wasn't stuck like yours. The body of the BC is steel but of course it goes into the aluminum pump housing.

If it is shot, there is also a device someone made here to substitute for the BC. It doesn't automatically adjust for altitude though. For many, that is really isn't needed anymore.   

Even adjusting the BC for full range isn't prefect as is adjusting the fuel rod. Messes up the geometry a bit over the full range. The best is the full range screw in the back.

Joining the full membership here will unlock an unbelievable treasure trove of info.

[JP3480]

It's quite interesting that mine has a 19mm. BC on it as it's a '71. Was probably replaced with an earlier BC during the rebuilt.

I shiver knowing that it's a steel BC down an aluminium shaft. However, it does seem quite sturdy and everything is pretty largely sized. Do I have to be extra careful trying to get the BC off, or can I give it a little push? I'm super careful with things like spark plugs for this exact aluminium reason.

Thanks.

[Pawel66]

My 2 cents: soaking the place where it is fitted into FIP with 50/50 acetone/ATF mixture would not harm...

[JP3480]

I've sprayed it with WD40 "penetrant" for the night, I'll see if that dose anything. I tried prying it off with a long metal rod to the ground and it didn't budge.

I'll try making a tool for it during the weekend - I feel like that's a safer approach. The prybar seems to add a lot of push to the engine, whereas I hope a tool that rotates the BC above the valve cover will get more of the force to be rotational instead of pushing / prying.