Jackshaft pumping grooves

[oldchieft]

Hi all.
I noted in another post the Jackshaft has pumping grooves in it.

This is something I did not know, or I have forgotten about.

Can someone (Rohan?) give me the reason, and the how it works.

Jon the Chief.

[rgh0]

I presume you are referring to the cutouts in the front bearing journal that meter oil up to the cylinder head as the jack shaft rotates. The twin cam had extra cutouts compared to the orginal Ford shaft to increase the oil flow due to the extra lubrication needs of the twin cams versus the orginal rocker system.

cheers
Rohan

[oldchieft]

OK
That's worth knowing, I was going to use my old cam shaft.

However as it is a Piper 270/2 I guess I will trade it rather then butcher it.

Anyone got a shaft they don't need?

Also the Jackshaft spacer would be a good thing to have if someone has a spare.

Jon the Chief

[john.p.clegg]

Is it my age or can I remember talk of the head receiving too much oil??

John

[alan]

there certainly is a lot of oil Under the cam cover and it doesn't always want to stay under the cover

[john.p.clegg]

Well I was going to add the rumour about oil draining but as there is a big hole at the front of the head (timing chest) thought better about it...
John

[elanman999]

John,
No it's not your age. I have spoken to Twink racers who say that they use a restricter (small orifice) in the feed to the head.
Cheers
John

[rgh0]

Generally a restriction orifice in the feed to the head is there to hide a problem caused by a high pressure pump and worn cam bearings. Keep the cam bearing clearances in spec and even with a high pressure pump you don't end up with to much oil in the head IMHO.

cheers
Rohan

[SJ Lambert]

A standard twink jack shaft has 4 flats milled into the front journal, I think Jamie Larner recommended putting a full groove all the way around for race motors.

Does that sound like a plan Rohan?

(I intend to keep cam bearings within spec.)

[rgh0]

Yes I have seen engines with a full groove for a constant feed it may be something that Larner do on their race motors. I have never used it and have stayed with the standard Lotus 4 flats arrangement, no restriction orifice and kept my cam bearings in spec clearances and never had any problems.

A groove of the right size would act like a metering orifice to some degree rather than metering via the flats so I assume it works but I would talk to Larner about all the details of what they do and why before doing it

cheers
Rohan

[SJ Lambert]

Spoke to Jamie, he uses a block restrictor & 360 groove.

I'm not keen on the restrictor, but do still like the idea of a full groove. I figure that I can control oil volume up top in my long bolt motor by altering oil drillings/grooves in the cam sprocket bolts and can do so without having to pull the motor down in the process. If I'm a bit too generous with the feed I can change to bolts with smaller oil feeds pretty easily.

Interestingly, when looking at the oil g?llery schematic once you blank the rear jackshaft bearing off for a short jackshaft application then the front main bearing /gallery up to the front jackshaft bearing feed is going almost all the work (after the 5 main bearings have all had a feed, it looks like number 3 gives oil to the middle jackshaft bearing) - the front one heads up top and feeds the timing chain too.

[elanman999]

If you use any sort of restrictor it needs to go in the block. If you put it in the head it overloads the gasket at the head/block interface on cold start up. I've got the very oily T shirt.
Cheers
John

[SJ Lambert]

The half length jackshafts that QED supply have a full circumferential groove.