Oil by-pass mod 2.4E

[niels]

Dear All,

For 5 years I own a 911 2.4 E. After too much oil consumption rallying the car, I decided to take the engine apart myself. Appears to be first time for this engine. Many things are really worn, camshafts, rockers etc. Overal view is good, though.

Long block is completely original. I would like to execute the oil by-pass modification Dempsey describes to my block. Besides a youtube movie explaining what needs te be done, I cannot locate the proper values for the hole size, exact location etc. to use for the machining.

Can anybody provide these please?

I'm also of the understanding that the relieve valves need to be changed? Which ones I should purchase?

For introducing purpose, this is my car. It will be vipergreen when it is finished. I live in the Netherlands.

[ajwans]

Do you have a mill?

I don't remember off the top of my head the hole size but I can measure it if nobody chimes in.

The head of the mill was laid over 27-28 degrees off centre to intersect the lower passage.

It's a simple operation for someone familiar with the equipment, fortunately I had help.

andy

[niels]

Andy

Thanks already for the info.

We have a mill/machining equipment, I will get aid from an experienced machiner. The 27/28 degrees is only on one plane (Z-X)? Than it will not be that difficult to put in, I presume.

[sithot]

Best left to a competent machine shop.

[niels]

Thnx,

The guy who helps me, is more than competent I assure you. We only need the values.

[tom1394racing]

Remember to upgrade to at least the 4 rib oil pump when doing the bypass mod.

[niels]

I thought one could keep the pump (which properly functioned) and only do the mod?

I'm not going to race or rally the car anymore after restoration.

[tom1394racing]

You can use the original 3 rib pump, however.......

When Porsche introduced the oil bypass changes in the 1976 7R case, they also introduced the new 4 rib pump. The 4 rib pump has a reduced capacity on the scavenge side and an increased capacity on the pressure side. The oil bypass modification routes excess oil back to the pressure side of the pump rather than to the sump and is thus designed to work with with the 4 rib pump. As best I know, when the oil bypass mod is performed, one also upgrades the oil pump.

[304065]

Niels,

You don't have to upgrade the oil pump to do the bypass modification, but it sure helps.

As you probably know the whole point of the bypass mod was to allow the factory to make the pressure section of the pump longer, and reduce the size of the scavenge section. The reduced oil quantity in the bottom of the case due to bypassing excess pressure allows this.

I think this is what our friend Tom is saying-- while it's not necessary to change, you would certainly want to change. Edit: Looks like we are posting the same answer at the same time and that is why great minds think alike!

You don't have to change the springs, either, as a result of the bypass mod. The spring change was a service bulletin in 1978 intended to correct low oil pressure for the 3,0 SC motor.

You should consider, however, having piston squirters installed.

Warning: I had the oil bypass mod done and went to a four rib magnesium pump and now I have HIGH oil pressure.

Our friend Craig Garr has developed a nice jig to perform the oil bypass mod. You might reach out to him via PM, this is a lot easier than setting up a mill just to drill a single hole. Even with the mill, if you miss the oil supply passage when you drill, you've destroyed the case.

http://forums.pelicanparts.com/911-e...ification.html

http://forums.pelicanparts.com/911-e...ification.html

Good luck! Nice looking car.

[niels]

Many thanks for all your comments, very helpfull. The pelican links contain many interesting discussions and data. I will think it over.

The piston squirters are present (72case). We will remove them and give a thorough cleaning.

My idea was, based on zero experience so more a guess, to have little more oil pressure on the squirters by executing the mod and thereby allow the new nikasil pistonset enough cooling.

The old stuff functioned fine with 200000 km plus. Pistons worn etc but oil pressure as new.

Guess i'v to rethink this, no hole yet in the block so ....