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Help! Oilway to No3 Main on 6 cyl Block


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Hi Folks

 

Anyone Know or have 6 cyl block open that they could look at.

 

Block just back from shop and I'm in process of deep clean, and yes folks even after a hot chemical wash those oilways are filthy!.

 

Anyway am cleaning the oilways and realise that I don't know how No 3 main journal gets its oil feed, or rather I thought I did in which case I have a real problem, so need a sanity check from someone.

 

The oil gallery is cast down the side of the block, at the position of each main there is a grubscrew/filler plug from which there is a crossways drilling that then intersects a drilling from the main journal and hence oil frows from the gallery to the main via this path, OK what about No 3, on the gallery at that point which is also where the casting for the oil pump/distributor drive is there is the hole that normally takes the oil pressure switch, this is in the exact same orientation as the plugs for 1,2,4 so I expected that there would be a drilling that went across from it through the column for the oil pump shaft and across to intersect with the drilling down from the main journal, I don't seem to have one! or if I shine a torch up there I can see what looks like a depression oposite the the oil switch drilling but I cant even poke a fine wire down it. The drilling from the journal heads in the correct direction to intersect with a drilled passage in that orientation.

 

OK what have I missed, is the No 3 fed differently, or do I have a real blockage problem.

 

Yes I have looked at the oil flow diagram in the manual but that is as clear as mud. I cant see anywhere else that a drilling could be made to intersect the passage from the journal, but I may just be panicking!

 

Alan

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Yes, the bush is in the way. If you want to clean things properly you need to withdraw it. This is best done with a bit of studding and suitable spacers.

 

You might find this interesting

http://sideways-technologies.co.uk/forums/index.php/topic/5712-competition-oiling-draft/

 

and this

http://sideways-technologies.co.uk/forums/index.php/topic/5783-2l-engine-build/(some gems amongst the gibberings)

 

Nick

Edited by Nick Jones
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"....they put a rotary union on the front of the crank and measured the oil pressure inside the crank during a dyno pull. They found the oil pressure dropping to zero during the high RPM’s essentially starving the front bearings."

 

Zero oil pressure in the crank centre does not necessarily indicate zero flow through there. The centrifugal force pulling oil out ot the bigend will power a flow away from the centre. So, if the gallery supply to the m/b is impaired, the pressure in the crank will drop as a result. Its chicken and egg, flow and pressure.

I see the culprits being the centre four bigends where centrifugal force results in greaty enhanced flows through them back to the sump. Leaving little oil flow for the front m/b.( which is itself being centrifugally scavenged!)

In short, my view is at high rpm there are six centrifugal pumps acting on the oil in the b/e drillings, which will distort flows. Flows were originally designed to be dependnent solely upon positive pressure from the oil pump when cenrifugal forces were relatively small. Balancing these high rpm enhanced centrifugal flows between bearings might be a way of tackling the problem. See GT6's current thread. But ultimately pump flow capacity will be exceeded by the 6 centrifugal scavengers, and even if flow are equalised between all six the psi will drop in the gallery.

 

Peter

Edited by Peter Cobbold
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Well Thanks Nick! Had been planning on an early night and just when I thought it was safe to rebuild the engine this weekend.

 

Good links thanks, and yes I think that I will have to pull the bushing and clean in there as it was No5 BE that failed and is fed from that journal and its the only way to clean it, and given the **** I found in the other oilways of a "cleaned" block ......

 

Although its more work than I planned (I want the engine fitted by end of long weekend) I think I'm going to check the oilway drillings just in case.

 

Also like the idea of an external feed from No 4 to No1 How did you and John D get on with yours?

 

Alan

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Alan,

 

Haven't installed the short engine I built yet. Partly due to time with a house move having given priorities a good stir and partly because the old Triumph-built bottom end is hanging on in there. It still has good oil pressure and doesn't knock even on cold start, just uses large quantities of oil (partly controlled with Wynns!), slobbers alot when thrashed and is starting to loose it's top-end sparkle due to loss of lift on the two end cam lobes. Still respectably nippy though. This engine has a bone stock bottom-end which has had plenty of hard use and has seen the wrong side of 7k once or twice (I've corrected the rev-limiter now!) so there isn't that much wrong with the factory system even for enthusiastic road use.

 

Ideally I'd suggest feeding any external feed from the big drilling just above the oil filter (and slightly below the line of the main gallery). The gallery behind it is massive. It is blanked with an aluminium plug which tends to be fairly reluctant to come out but there is a 3/4" UNF thread in the block. Entirely up to you whether you use a hard line like mine (I had the makings to hand) or a flexi-line. My reasoning was to make the main gallery a ring main in effect and to bypass the heavily loaded area just behind the distributor bush. The pictures I've seen of Johns have him taking flow from that heavily loaded area, which I'd not recommend. Others have taken it from the rear-most main gallery drilling which is less loaded.

 

Peter,

 

I agree zero pressure doesn't necessarily indicate zero flow. I suggest it does indicate being on the verge of insufficient flow though. What should ultimately control the flow is the bearing gaps. Worn engines or engines built purposely loose for increased flow/cooling will flow more so greater capacity will be needed to maintain pressure.

 

I do not believe that low pressure anywhere in the system at high rpm can be blamed on the pump.

 

At 1000 rpm the pump will be doing 500rpm and at 6000 rpm it will be doing 3000 rpm (6:1 turndown). As it is a positive displacement pump (ignoring cavitation and entrained air), it's output at 6000 rpm will be 6 times it's output at 1000 rpm. There is no way you'll be getting 6 times the flow through the bearings, even with centrifuging effects. I suggest that anything over 2000rpm the relief valve will be open and by 4000 rpm more than half the pump output will be going through the relief valve. Therefore any low pressures measured at the front of the main oil gallery (say) are the result of the the rest of the delivery system (filter, various gallery drillings) being unable to support enough flow. As discussed in Steve Smith's competition oil draft on the Sideways forum, I believe the major bottleneck is the section of the main oil gallery between the filter outlet and the distributor bush.

 

Another interesting subject is what condition the oil is in on the suction side of the pump when the engine is working very hard. It will be hot and highly aerated. This increases the likelihood of cavitation and can cause the pumped volume of actual oil to drop as pump inlet volume is occupied by gases. Also, these gases will be compressed after the pump and occupy little space - until the pressure around them drops when they will expand again - which might be a good reason to want the whole oiling system to be under decent pressure all the way to the bearings........

 

I always thought it very revealing that Steve Smith commented that even with many mods of the stock wet sump system he was killing bearing shells in one race whereas after installing the dry-sump system he was changing them a couple of time s a season - and thenmostly from habit/guilt. The dry sump system allows time for the oil to de-aerate before being sent back out.

 

Nick

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Nick,

 

I am convinced that centrifugal effecst do become important. The very low crank centre pressure measured by Kastner leaves no positive pressure at all to feed the big end bearings. "No flow without a head". But its not the b/ends that suffer. So I think at high rpm they are fed almost entirely by centrifugal flow... theres no other mechanism. So the centrifugal pumping effects will influence the m'b pressures too. Centrifugal forces will rise with a square law with rpm. In effect the c'f forces pull flow out to the b'e leaving little pressure to supply the m/b journal. To me, Kastner's measure of zero psi at the crank centre doesnt means that the gallery pressure has all been dropped by oil flow out across the m/b journal. It means the flwo out to the b'e has been accelerated by centrifugal forces there and that starves the main/b journal of oil flow across it. Its as if at high rpm another pump has turned on to scavenge oil from rhe mains. Six of them actually, and that why the main pump cant keep pressure up in the m/b.

 

The problem is, m/bs 2 and 3 should suffer the most form centrifugal flows as they each feed two b/ends. So there must be some impairment of flow to m/b 1 that #2 and 3 do not encounter. It needs a fluid dynamicist.

 

Peter

 

( But what a great advert these threads are for supercharging and keeping within normal Triumph-designed rpm limits :D )

Edited by Peter Cobbold
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