MFI drive belt replacement

[ctv283k]

I realise this subject query ought to be in the Technical Area but since that cupboard is norally bare I think most Early 911 folk refer to this section. The car is a 2.4T ex-USA, which I have owned for 7+years.

I'm currently overhauling the MFI system to resolve a fueling issue which is causing the engine to under perform throughout the gear ranges. Once at cruising speeds the car drives well; it's just getting there where the problem lies.

Following a performance check at Lambs Garage, Clowne, Debys, which found an additional 15bhp, up from 121(!), it was suggested to have the injectors checked for leakage, operating pressure and spray pattern - since found ok. The throttle bodies too have been removed for cleaning to ensure all air passages are clear. With the engine bay almost bare I decided to get the MFI pump functionally checked and this will be done next week in conjunction with checking for correct injector flow rates - the drive belt sprocket needs relacing anyway due to drive teeth wear. The drive belt has to be the original 1972 one judging from its condition and has to be replaced.

The bottom line question is, has anyone devised a short cut method/tool to facilitate a new drive belt to be fitted without the need for heat exchanger removal etc?

 

[38F3E1]

Hi Cliff & Julie.

You have to remove the tinware from the front of the engine (gearbox end, on the side where the MFI pump sits) to be able to get the belt off the lower pully as it won't clear otherwise. Tinware can be removed from underneath with the heat exchangers in place but it is an pig to do. Rear of car jacked up and on axle stands as wheel on that side needs to be removed to give you working room. Car must be secure as you have to crawl underneath to do it.

Heat exchangers off makes it easier but you still need to do the above. I have done it myself with the heat exchangers off and my specialist has just confirmed it can be done with heat exchangers on as he did one that way three weeks ago.

From memory with the heat exchangers off I could do it with the wheels on and the car not jacked up by half crawling underneath and reaching forward but it was all done by feel not by sight. Having the car on stands or ramps would have made it much easier.

Ian.

 

[Robin]

Further to what Ian has said, if the drive pulleys need to be replaced it is easier to just drop the engine down to remove the pulleys and replace them with new ones. You should replace both at the same time as fitting a new toothed belt. They are light alloy and extremely lightweight and I am amazed to know how long they last. Be sure to tension it properly by moving the MFI pump on its mountings.
One final thing have you replaced the large fuel filter recently? there should be around 1.5 litres of fuel flow through the filter per minute, this is much reduced if the filter is blocked and therefore the engine will be down in power and usually a bit lumpy.

 

[ctv283k]

Thanks to both of you for your quick responses on this subject. I think the fuel filter was replaced not that long ago (have to refer to my mainetnance log), but a new one would be a good idea. I will atempt the removal of the lh engine cover, less heat exchanger, whilst the pump is away at Notts Diesels.

I've checked the clearance between the end of the cam shaft sprocket and the cover and there is room for the belt to pass through the gap sideways. For sheer beligerance I may fashion a fork-like tool from two 20swg pieces of steel sheet riveted together and use the old belt to see if I can develop a short cut. If it works, I'll report back. A long period of silence will infer that I'm removing the aforesaid cover!

 

[38F3E1]

Yes let us know how you get on with your idea. And good luck :- )

Also let us know how you find Notts Diesels as their name has become become more prominent this year for servicing MFI pumps.

Ian.

 

[ctv283k]

I did develop a fork-like tool to fit the MFI belt and a trial fit using the old belt proved it could be achieved, but there was so much filthy oil soaked dust etc. in the cover that I didn't risk inserting the new belt and getting it plastered in the aforesaid muck before it had even turned the pump. If the cover had been clean, and I suspect most won't be, it might be worth it.

The Cover, as you rightly stated, was a fiddle to remove, but once I had cleaned it up, the re-fitting was quite easy.

Nottingham Diesels may not have a tidy workshop, but they do have one of the partners there called Steve who really knows his stuff. He has been working on MFI pumps for some years now, previously with a company called Coldwells in Basford - also in Nottingham until they went bust a few years back. He has a test rig which, if you take your injectrors with the pump, will provide flow rate checks. All the standard adjustments for rich/lean set-up can be done. No doubt he is also able to perform leak and pressure tests on injectors as well as spray pattern test though I had those checks performed elsewhere.

Steve carries a number of spares and has drive pinion seals (a common source of oil leaks) specially manufactured for him. The seals are like hens teeth since neither Porsche or Bosch seem to supply them.

When I took my pump to be inspected and functionally checked on the 8th Dec, he had 2 other pumps being worked on, one of which was being upgraded to the 2.7 engine standard. Some of his MFI work is done for 911s used in historic motorsport. My pump is ready for collection so the turn-round time is quite quick. For costs please send me a private mail to cliff.doe343@btinternet.com

Notts Diesels can be contacted at 01159475894 - ask for Steve.