M20 oil pump priming after engine rebuild?

Post Tue Mar 20, 2012 5:07 pm

I've just carried out a partial rebuild, pre facelift pistons with new rings/big ends into a facelift block, and fitted my old head. I've turned it over for half minute or so and no sign of the oil light going out. I pulled out the oil pressure switch and turned the engine over again a couple of times, dry as a bone.

It's a 325. I disconnected the filter housing/oil cooler pipe set up from the old engine and left them on the car when removing the old engine so they should still have oil in, didn't change the filter as it was new about 500 miles ago. I didn't take the pick up off the new block when fitting the new pistons so nothing disturbed there. The block I used for the rebuild has been in the garage a year or so, but had a sump on and pistons/crank in place not stripped to a bare block.

Any ideas anybody? I don't want to just keep cranking/start it up with no oil pressure and shag the bearings if there is some way of forcing/priming the oil pressure. Thanks.

Post Tue Mar 20, 2012 7:05 pm

pull the fan and front timing cover off.

remove the cambelt and spin the oil pump drive with a cordless drill, look for oil coming out of the spraybar to confirm oil is moving

I'ts almost defo OK, they can take 3 mins+ to make some pressure from a dry rebuild , especially if the block was chemically cleaned.

Let us know how it went

Post Tue Mar 20, 2012 8:49 pm

Top tip thanks, will give it a try in the morning.

Post Wed Mar 21, 2012 12:58 pm

No luck after a couple of minutes with the drill, battery charging again now. Is there any access for the oil from the top of the housing? ie if I overfill the sump with oil (excess to be drained again afterwards) would the oil be able to get in and lube the pump? I reckon the pump may have gone dry from standing.

Really don't want to start taking the engine out again to drop the sump, supposed to be at Brands on Saturday, I'm away tomorrow and have stuff to do on my own car Friday so time is running short. Thanks

Post Sun Mar 25, 2012 9:54 am

Did you manage to sort this Brian, and if so how?

Post Sun Mar 25, 2012 10:32 am

Yes and no. Ended up dropping the crossmember to get the sump off and swapping the pick up pipe assembly with another one. If you are leaving an engine sitting for a while always leave the oil in the sump

I was thinking back and the engine hadn't actually been left that long, I picked it up in the Autumn from a chap on the zone doing an M50/M52 conversion.

If rebuilding I think just inverting the assembly pouring in a bit of oil and letting gravity get the oil to the pump before bolting it on should be fine. Spinning the oil pump sprocket over without the cam belt on is something I'll be doing from now on in any case to get the oil circulating to the top end (16mm socket on a battery gun)

Post Sun Mar 25, 2012 9:09 pm

It's not the first time I've heard of this, gearpumps should self prime quite readily, so my thoughgts are that the pump can't clear the air in it through the oil filter.

In fact, that rings another bell about how this was cured, loosen the oil filter off so it's not sealed to prime the oil pump.

Similar problems can be found after oil changes as well.

edit - after oil changes using non bmw filter.

Ps) oil only flows through the cooler when it reaches over 100c in temperature, the rest of the time it's effectively sealed off.

Post Sun Apr 01, 2012 7:27 am

As a by the by, I've had a look at an old block I stripped down. Any problems again, it looks like an easy cure is to unbolt the filter/cooler pipe housing. There is a vertical oil hole behind this housing that is the feed from the oil pump. So some oil fed down there with a gear oil bottle or similar would drop directly down into the oil pump and "reverse prime" it.