Kent - Cylinder Head - Valve Gear Oil Restrictor

[Vne165]

Hi all,
Curious as to whether anyone has ever installed a restrictor bushing in the oil feed gallery to the rocker gear.
I have built other engines that tend to over-supply oil there, and which benefit from an .080" to .100" orifice to maintain better overall oil pressure.

Might help with the post race low pressure scenario on a looser engine.

Thanks in advance
Vne

[pooch776]

I tap the oil supply gallery that feeds the rocker assembly at the top of the block with a 5/16-18 tap. Then I drill a 3/32 (.0937) hole through a 5/16-18 set screw and screw it into the hole.

Joe

[Vne165]

Hi Joe,
Thanks for the feedback.

I was contemplating doing similar in the rocker pedestal that has the oil feed.
Any issues with that approach do you think?

[Hawke]

Hi all,
Curious as to whether anyone has ever installed a restrictor bushing in the oil feed gallery to the rocker gear.
I have built other engines that tend to over-supply oil there, and which benefit from an .080" to .100" orifice to maintain better overall oil pressure.

Might help with the post race low pressure scenario on a looser engine.

Thanks in advance
Vne

I’ve had engines that have had restrictors, and some that have not. I’ve not seen any difference in pressure or wear.

[Vne165]

Thanks Hawke,
I have a bunch of spare rocker shaft pedestals, think I'll try a restriction there.
The low oil pressure after a race bothers me.

Rgds
Vne

[JHerscher]

It is normal to see the oil pressure warning light come on after a race as you are coming into the pit. Just blip the throttle occasionally on the way back to your paddock.

not normal at speed.

[Jon Jeffords]

The low oil pressure after a race bothers me.

For an engine like the Kent that has no components that require oil pressure to properly function (eg: hydraulic lifters or hydraulic chain tensioners) oil pressure is not as critical as oil flow (gallons per minute). Adequate oil film thickness between critical components (piston to cylinder wall, crank journal to bearing, cam lobe to tappet, etc) is achieved via oil flow and viscosity, not oil pressure.

Granted, oil pressure is proportional to flow and viscosity. But my point is you still have sufficient oil film thickness while motoring through the pits after the race at low rpm and low throttle angle, even if the oil pressure is low.

[Vne165]

All good feedback, thanks.

Despite understanding/doing all of the above and noting that the bearings and journals looked ok on the last refresh (no signs of starvation), it still bothers me that oil pressure drops so low.
Just long-standing paranoia I suppose.

Cheers
Vne

[stonebridge20]

Posted in wrong thread.

Carry on !

[Vne165]

Ok, so I have drilled and tapped the rocker pedestal oil feed gallery 1/8" NPT and drilled a socket head plug to 2.5mm (~.100").
Will report back any observations if anyone interested.

Rgds
Vne

[Vne165]

Hi all,
just some feedback for those contemplating a similar mod. A total of five hours of dyno testing over the last couple of weeks, oil pressure seemed more stable, but of course I won't know until after the next race meeting whether the low pressure following 10 laps still persists.

Plenty of oil on the valve gear, no worries about lack of lubrication, still tons flooding the rocker shaft and surrounds.
Here's a picture of the restrictor.

Rgds
Vne

[DaveW]

I always have low oil pressure after sessions (5-10 psi). That's totally normal and has never caused issues on any of my race engines

[Keith Robinson]

As a FF racer of 6 different cars in the last twenty years.
I've never had any problem with the low idle oil pressure and as has already been mentioned flow is more important. Have you considered that the oil flowing from the rocker shaft (as long as it's not causing any leaks) is actually helping with cooling the cylinder head?

Note; If Dave W has not had a problem, there isn't a problem !!

All good feedback, thanks.

Despite understanding/doing all of the above and noting that the bearings and journals looked ok on the last refresh (no signs of starvation), it still bothers me that oil pressure drops so low.
Just long-standing paranoia I suppose.

Cheers
Vne

[Vne165]

Hi Keith,
Thanks for your thoughts, whilst I saw improved operating oil pressure during the last race meeting weekend just gone, I still had the zero indication on pit entry after the cooldown lap. Investigation now shifting towards the sender unit (calibration), data logging dashboard (alarm set point) and perhaps the grade of oil (10W-30).

Failing that, it's possibly an issue with the primary oil pump, although visually it looks ok and clearances are in spec. I just get the heebie jeebies when I see no/low pressure, though many have said it's no issue.

As far as head cooling, I just don' think that's a concern on such a low powered engine.
Certainly no difference in jacket water temps noted anyway & plenty of oil around the valve gear.

Vne

[Keith Robinson]

I just run a 20psi sender and an oil gauge which regularly reads under 20psi when I leave the track but never ZERO, that's another problem altogether. Hope you find the problem before any damage is done, chances are that as long as you have over 20psi above 2,000rpm you'll be OK. My 'double check' is to raise the rpm to 4,000rpm just as I'm coasting off the track at which time I should have 40psi.
I run 10/30 weight fully synthetic oil.
Good luck.

Hi Keith,
Thanks for your thoughts, whilst I saw improved operating oil pressure during the last race meeting weekend just gone, I still had the zero indication on pit entry after the cooldown lap. Investigation now shifting towards the sender unit (calibration), data logging dashboard (alarm set point) and perhaps the grade of oil (10W-30).

Failing that, it's possibly an issue with the primary oil pump, although visually it looks ok and clearances are in spec. I just get the heebie jeebies when I see no/low pressure, though many have said it's no issue.

As far as head cooling, I just don' think that's a concern on such a low powered engine.
Certainly no difference in jacket water temps noted anyway & plenty of oil around the valve gear.

Vne

[BeerBudgetRacing]

FWIW, I had the no pressure problem in a Pinto engine. Talked to Doug Lerned (TDC pumps) and he had me measure the oil pump. Seems the pump I had was built for the pro series and they wanted to squeeze every fractional HP out of the engine so they ran a pump that built less pressure but rebuilt the engine every weekend!

He rebuilt my pump with a larger pressure section. Never had the low pressure problem again.

[Keith Robinson]

That makes a lot of sense; these engines are running over 4,000rpm for most of their 'lives' wasting hp with a pump that has lots of pressure at 1,000rpm isn't necessary.
Years ago a racer friend of mine was running in the old Cities Sports Racer series (Pinto engines). He phoned his engine builder (a very reputable shop in the North West) because he was concerned about oil pressure. "if it's over 20psi it'll be fine, it's the flow that counts" was his answer!

FWIW, I had the no pressure problem in a Pinto engine. Talked to Doug Lerned (TDC pumps) and he had me measure the oil pump. Seems the pump I had was built for the pro series and they wanted to squeeze every fractional HP out of the engine so they ran a pump that built less pressure but rebuilt the engine every weekend!

He rebuilt my pump with a larger pressure section. Never had the low pressure problem again.

[Roland V. Johnson]

Try a mechanical gage first to see what you really have. I have seen a lot of incorrect readings from gages. Coming off the track with 10 pounds or less, is common. With modern lightweight oil I have seen 30 pounds at 6800 RPM with a fresh top line engine.

That makes a lot of sense; these engines are running over 4,000rpm for most of their 'lives' wasting hp with a pump that has lots of pressure at 1,000rpm isn't necessary.
Years ago a racer friend of mine was running in the old Cities Sports Racer series (Pinto engines). He phoned his engine builder (a very reputable shop in the North West) because he was concerned about oil pressure. "if it's over 20psi it'll be fine, it's the flow that counts" was his answer!