Post Number: 20
|Posted on Tuesday, 11 March, 2008 - 21:15: |
On starting the 6 cyl engine after rebuild, following all the directions in the manual re priming the system, the low pressure circuit has minimal flow to the rockers. The main oil gallery has approx 28 psi at idle but no significant flow from the valve end of the rockers. I removed the rocker shaft to re-tension the cyl head and cranked the engine with the starter, oil flows only slowly from the rocker mount hole in the cyl head. The relief valves were in good shape when reinstalled, are they likely to be the problem?
Any help would be very much appreciated.
David Hughes SED 347}}
Post Number: 1354
|Posted on Tuesday, 11 March, 2008 - 23:44: |
My experience is with my R-Type and a few others, but it is almost the same in this area.
I don't expect that you have any problem here whatsoever. Let me explain.
As the high pressure gallery has absolute priority on oil delivery, the low pressure feed to the timing gear and rockers gets next to none until you are driving with spare pump capacity. On idle there is no capacity to feed the low pressure line whatsoever. This is quite normal. If the high pressure is set high, then the low pressure system receives even less.
The acid test will be a drive intil warm, then have a look through the filler cap. I'll bet it's doused with oil by then.
So much so that I always fit modern valve stem seals as all that oil sloshing around the rockers and valve stems leads to totally excessive oil consumption after a few thousand miles on the old obsolete original type. Introcar offers a kit to update the seals without removing the head or valves. The seals cut oil consumption to a negligible level whilst extending valve life.
Post Number: 33
|Posted on Wednesday, 12 March, 2008 - 01:22: |
I am not sure that I would agree with what Richard has said. On my MK VI the oil pump pushes oil into the main relief valve which has a bleed to feed the relief valve for the rockers etc. If the main oil pressure is, say, 10 lb/sq.in at tickover the main relief valve will be closed but the rocker relief valve will still be getting oil via the bleed hole and will control the pressure in the rocker feed to about 4 lb/sq.in. The main relief valve does not have to open before oil starts getting to the rockers.
If some oil is coming from the rocker mount hole when the engine is being cranked by the starter then this must prove that the oil feed up to that point is OK.
The second engine in my B420EY (A Jack Barclay rebuild, probably with standard valve stem seals) has done 109,000 miles without the head being removed and still only uses 1 gall of oil for every 200 galls of petrol and the compression is still perfect. I am quite happy with the standard valve stem seals and don't seem to have the troubles that other people have.
Post Number: 21
|Posted on Wednesday, 12 March, 2008 - 07:31: |
Dear Richard and Laurie
Thank you both for your quick replies, very much appreciated. Both give me comfort that things look reasonably normal. I considered looking at the LP valve again to make sure it was doing what it should (the manual says not to fit thinner washers but I certainly considered that).
I'll try a road test and report back.
Thank you again.
Post Number: 22
|Posted on Tuesday, 01 July, 2008 - 09:14: |
Having done now some 300 miles (400 km)the engine runs quiet and smooth, very little oil consumption, however looking through the oil filler - oil is visible but still not sloshing about.
Post Number: 78
|Posted on Tuesday, 01 July, 2008 - 19:28: |
How did you measure 28psi? Did you pull out the oil sender unit and screw in a gauge that was tested OK? 28psi is a bit low for a V8 isn't it?
Post Number: 1397
|Posted on Tuesday, 01 July, 2008 - 21:07: |
Ahem. It's a 6 cylinder car. 28psi is very healthy on idle for a cold rebuilt motor, albeit somewhat high. It should be much lower on idle when hot. In fact, 25 psi is the specification for a warm motor at about 1,500rpm and greater, but I prefer 28 psi. When hot, on idle 12psi is OK for a newly rebuilt motor albeit still a bit high. Even lower than 5 psi is fine on idle when hot. 5psi is stated as normal in the specifications for a hot motor on idle.
Post Number: 1398
|Posted on Thursday, 03 July, 2008 - 08:45: |
The S/SC 6-cylinder oil pressure figures are about the same as for the MkVI/R-Type, just a little higher at 1500 RPM hot, 28psi. Follow the links to the S/SC workshop manual.
The pressure valve spring free lengths may help too.
Here is an extract from the workshop manual: