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lub/oil pressure release

derek

Well Known and Active Website User
VOC Member
Having been a vincent owner for the past 50 years, I don't ever remember reading or hearing very much said about the lub/oil pressure relief valve. However, I recently had to remove two from separate timing cases, in both instances they were both seized requiring plenty of release oil and heat to remove.
This set me thinking, how many others may be seized either shut or partly open, could this account for cam and follower failures or big end problems. How can we check that all is OK. Looking at the return to the oil tank when starting up may show a return, but what when the oil heats up with a partially open valve!
Also, both valves although the same dimentions were made from different material. One was brass and the other hardend steel (why hardend?).

At what pressure should this valve relieve?
How and why was this pressure decided?
What damage would too high a pressure cause?
Are there any pressures given for various parts of the LO system?
 

Tnecniv Edipar

Well Known and Active Website User
Non-VOC Member
Too high a pressure could at the least cause oil leaks , at worst blown flexible oil lines , burst filters etc. However , with the standard oil pump I doubt that even with a non functioning pressure release valve that it could develop enough pressure to do the above ! Low pressure is more of an issue but the system runs at very low pressure anyway.
 

lindie

Well Known and Active Website User
Non-VOC Member
pardon my ignorance on this one but i thought the pressure relief valve was only controlling the pressure and not the suction/scavenge side of the pumps oil circuit. i can't think that checking the return in the tank will tell you of the positionining, stuck or otherwise of the valve as the suction pump picks up the dumped pressured oil whether it is recieved via the normal route of timing case-> bigend quill-> cam and cylinder jet spindles->sump, or trickled though the reliefvalve and through the timing case back into the sump.

is there another relief valve somewhere for the the other circuit? the feed out union looks too close to the pump for it to have one unless it's built on the inlet side of the pump which would kind of defeat it's own purpose. unless theres a blockage up the return line somewhere i can't see how it'd blow lines and the oil feed hose would be under suction not pressure. the filter has a relief valve of it's own so that would bypass by rights well before it got a chance to explode unless it's a spin on type of somesort or another via a conversion. in which case a dent or crease in the casing is a more likely weakspot.
 

timetraveller

Well Known and Active Website User
VOC Member
Lindie is correct. The pressure release valve is only on the feed to the big ends, cams etc. Roller bearing big ends as used on Vincents are not capable of holding a significant pressure and the Vincent type of oil pump will wear quickly if it tries to provide pressure. Various people have tried to measure the oil pressure obtained with a hot Vincent engine and it is about 1 lb/square inch. Negligible! Possibly about 5 lb/sq inch when cold and if using an old style single grade oil. I too have seen them jammed shut but with no sign of problems with the engine. :)
 

John Appleton

Well Known and Active Website User
VOC Member
Too high a pressure could at the least cause oil leaks , at worst blown flexible oil lines , burst filters etc.

On the Vincent engine the "high" pressure oil does not pass through any flexi pipes, all oil ways being internal. The function of the pressure relief valve is to reduce the "hammer" effect on the oil pump drive when cold 40 or50 weight oils are being forced through a filter, such as the standard felt items or the paper replacements , prior to working temperature being reached.
At this cold stage it is quite possible for a lot of the oil pump delivery to pass directly back into the timing chest, via the relief valve port, without oiling the bits it is supposed to ,so here is another reason why high revs on a cold engine is not a good idea.
This brings me onto another subject:- in the Vincent engine oil passes through the fiter from the outside to the inside and standard filters and good quality paper replacements have perforated steel liners to support the filter material when flow is impeded by thick oil or less than clean filter.I have recently seen some very cheap paper replacements that do not seem to have this support, but I was unable to investigate fully as it wasn't my filter. Has anybody else had a look?
As a summary, here is my take on matters for what it is worth:-
1 ) use 10/40 oil as it can get through the oil tank gauze and down the pipe easier when cold. It also has an easier passage through the filter and gets where it is needed that much sooner.
2) dont rev the engine from cold, and dont leave it lumping over at idle either. a slightly fast tickover is all that is required.
3) Only use better quality filters with support liners, and paper from preferance as its flow rate seems better than compressed felt.

John
 

Len Matthews

Well Known and Active Website User
VOC Member
Oil Pressure Relief Valve

Think about it chaps, if the valve is seized "open" then the big end, camshafts and bores will be starved but if seized "closed" there will be pressure build up in the filter chamber and oilways in the timing cover. This in turn may lead to smokey exhaust due to more oil than usual being forced into the cyl.bore.Norman Peach, one time road tester at theWorks, once told me that a Comet he was testing actually burst it's filter chamber because the long banjo bolt had not been cross-drilled and this error had not been spotted by the engine builder. Result: wrecked crankcase!
 

John Appleton

Well Known and Active Website User
VOC Member
Think about it chaps, if the valve is seized "open" then the big end, camshafts and bores will be starved but if seized "closed" there will be pressure build up in the filter chamber
I once worked on a comet ,owned by a novice rider, who,s father told him that the best way to quieten his mechanical noise was to run the engine on gear oil!
The result was a stripped oil pump worm and the oil pump sleeve so expanded by hydraulic pressure that I had to bore it out.( Are you still out there Alan Turp?)
John
 

Tnecniv Edipar

Well Known and Active Website User
Non-VOC Member
I was thinking of the rocker feed lines but they are in the scavenge side so are virtually open ended. I shall no be so generalised with my comments in future.
Oil pressure could easily be checked with an adaptor screwed into the big end quill or anywhere there is access to the main feed gallery. would need a low reading guage though.
Regarding oil grades , SAE 50 or 20w50 would never be needed with a Vincent , the oil temp is never high enough. 10w40 or monograde 30 are probably ideal.
 

roy the mechanic

Well Known and Active Website User
VOC Member
oil pressure

Upto yet you're all talking oil pressure. This means most have missed the point! with a motor with all rolling element bearings oil pressure is impossible to acheive, they all leak worse than seives. the best that can be achieved would be FLOW. That's what said bearings need to survive inside your motors. The vin pump is the worst part ,for my money, in the whole set-up, whoever passed it fit for production should be castrated with a blunt phillips screwdriver. Roy.
 

Tnecniv Edipar

Well Known and Active Website User
Non-VOC Member
I've made the same observation of the oil pump but the reaction is always that plenty of Vincents go many mile's without a problem. However , it was an old fashioned pump to use even back then. Personally , I think that if a gear or trochoidal pump could be designed to install in the stock position it would be a very worthwhile mod.
 

Tnecniv Edipar

Well Known and Active Website User
Non-VOC Member
It would certainly make life for the valve gear easier. My view is that Ducati use a gear pump on the Bevel twins which is a very similar architecture to the Vin. Ball & roller bottom end , gear cam drive etc. Now that engine is very durable with correct maintenance and withstands tuning very well.
Flames are still anticipated though !!
 

lindie

Well Known and Active Website User
Non-VOC Member
did i read once somewhere mr grosset had a honda pump conversion in the cases somehow?


or is all murky in this little head of mine?
 

Tnecniv Edipar

Well Known and Active Website User
Non-VOC Member
Yes , he did a mod using a Honda 50 (I think) oil pump installed in the timing chest to feed the valve gear. Apart from delivery rate the main advantage was instant oil feed rather than the delayed feed to the top end on the original system. Details are in 40 Years on.
 

derek

Well Known and Active Website User
VOC Member
lo/flow

Yes of course the return is from the scavenge side:
However talking of low flow rates there can't be a lot of flow through the 170 jet restricting oil to the all important heavily loaded cams (with little pressure), I know that a littlle extra comes down from the rocker gear. So, if so little pressure to the cams, it seems a lot too expect the oil to lubricate cam shaft bushes then force its way through the holes in the cam to lubricate the followers, especially on a twin with twice as much.
 

clevtrev

Well Known and Active Website User
VOC Member
Yes , he did a mod using a Honda 50 (I think) oil pump installed in the timing chest to feed the valve gear. Apart from delivery rate the main advantage was instant oil feed rather than the delayed feed to the top end on the original system. Details are in 40 Years on.
Nearly right, Hervé Hamons is the one featured in FYO. His driven off the large idler. François version is driven off the end of the large idler spindle, this a modified spindle, fixed in the gear and using bearings at either end. The pump used, is one fitted to several Honda`s, very small and very efficient.
 

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