E: Engine How critical are the rear cylinder oil feeds!

Marcus Bowden

VOC Hon. Overseas Representative
VOC Member
Same cams for over 300k miles fitted 1970 Mk2's originals with holes in leading face of cam (thanks to Pete Green) first 100k wear was evedent 0.006" to 0.012" most wear noted on exhaust cams (opening against greater pressure) first pump fitted by the originator Herve" Hamon in 1990 whilst sleeving main bearing housings .Since p/p fitted less than a 0.001" on roughly the same time period.
When fitting the Honda P/P the first thing was to fit a wear to the suction of main P/P. this allows the oil level in the cavity behind flywheels to build up BUT not so high that it is higher than the cavity wall.
The tube can be seen with a hole very near the top and suction line secured to outside wall of c/case and set back into into the aluminum of the c/case as flywheel very close, set suction end to 1/4 of diameter of bore to the bottom of C/case for optimum flow.

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BETTER OVER VIEW

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INTO TIMING CHEST THEN A BLACK PLASTIC PIPE IS USED AND THREADED THROUGH THE TO LEFT HAND SIDE OF THE IDLER BOSS BRACKET PIPE HOLDER.
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vibrac

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Well then it would seem to me that lacking an actual hole in the cylinders the best course would be to just leave all as is. Some oil would get down to the crankcase but I guess the supply to the cams would be better
certainly with the changes on this big bore twin the hole could never be in the right place
 

greg brillus

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Big bore engines say with the TP top end kits, I extend the oiling groove around the rear of each crankcase mouth with a dremel and small rotary burr to the center as per original, then double check the piston ring to bore/liner heights and drill the feed holes through each liner, then run a small vertical channel up to meet the groove in the case mouth. Lets not forget that the biggest restriction in feed to the cams and cylinder feeds is the 170 jet in the timing chest. There is nothing stopping you opening that up larger or remove it completely. With the racer that's what I did, but kept the jet holder in there, this in itself is enough of a restriction via the two holes on either side which allow plenty of oil flow. There are mods you can do to allow better feed to the cam lobes and follower surfaces without going to too much trouble.
 

Oldhaven

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My Rapide has undrilled/blank restrictor disks in the cylinder feeds. It is a '48 with 2 piece cylinder studs so oil taking the usual route to the liner hole is injected into an area where the ET158's in early machines are seated. The installation/removal castellations in them below the outers can allow oil to get into the space between the inner and outer stud and travel up the stud to the top of the head. Not a problem with later one piece studs fitted with sealant. This means more oil to the cams I guess.

I had not known that it was an option to not use the .170 jet in the jet holder, or to use a bigger one, and I remember some discussion years ago about how that might decrease the oil going to the big end, and maybe the top end and rockers. I imagine for a twin that might be the case, but for a single with half the bleed off and demand it might make some sense. I'd like to hear more on this.

My big bore Comet project will also have a blank disk in the cylinder feed and no liner drilling, partly due to the bad location of the incoming gallery, (which, as Greg mentions, can be remedied), but mostly because I can't see sending oil off into unused areas for no reason.
 
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greg brillus

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Hi there Ron, Not so much that it is an option to either use or not use the Jet or its holder, more so for a racing engine. The jet or "Restrictor assembly" is there obviously to keep some oil flow/pressure to the crankshaft. It is well known that a roller bearing crank does not need much lubrication to work well, and high pressure to a roller crank will cause it to fail as the pressure will "Lock up" the rollers causing them to skid across the tracks. Given most race Vincent engines run a two start pump, the oil delivery is better, so you can afford to open up the passage to supply the cams a bit more. A lot of racers run the standard pump and this too can work fine, it all comes down to what works for any individual engine. From my limited experience with racing Vincent engines, it is the cams/followers that are the weak link, but I strongly believe it is the choice of components and how well they have been made/hardened that affects this.
 
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vibrac

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VOC Member
Had a final check on the oil feed position at BDC the oil hole slot in the barrel will need a 12mm move towards the drive side and a drop of at least 5mm to exit below the oil ring and keep in the crankcase/bore coverage area (Excuse for foreign measurements its a stroke and bore area:oops:) however at TDC and for a considerable crank rotation it will be squirting into the abyss as the skirt wings its way upwards
I think I shall block the supply as suggested.
 

erik

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VOC Member
if someone is not shure to block or not to block the oilfeed to the cylinders ,i think only blocking the rear is an other idea .because the flywheels throw the most oil towards the rear cylinder not the front one. Erik
 
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