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Valve lift and rocker ratios with an RE13 cam
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Author:  drmini in aust [ Sun Jul 29, 2007 8:12 am ]
Post subject:  Valve lift and rocker ratios with an RE13 cam
As I'm building the 1132 Moke engine with an RE13 cam and 1275LS head, I thought I'd plonk the finished head on and see how bad/good the various stock rockers are.
Note the ratios I obtained are less than usually advertised, this is because rockers lose their ratio a bit when measured with higher lift cams.
These tests were done on #1 inlet valve, with new Cooper S double valve springs fitted. Rocker shaft was a NEW thick wall one.

Cam lift at lobe, RE13 cam = 0.290"
Valve clearance set = 0.016"

rocker ratio = (valve lift + rocker clearance)/lift at cam lobe

Valve lifts achieved:
Cooper S forged rockers = 0.321"
late 998 sintered rockers = 0.327"
998 pressed steel rockers = 0.339"

Actual rocker ratios from calcs above:
Cooper S 1.16:1
Sintered 1.18:1
Pressed steel 1.22:1

I would like to get .350" lift or more lift at valve, so I'm going to offset bush a pressed steel rocker this week and test that.
Stay tuned..
:wink:
<edit> if anybody has a pressed steel 1275 (oval pad) rocker handy to me in Sydney, I'd like to test that too.
Author:  smac [ Sun Jul 29, 2007 9:25 am ]
Post subject: 
Interesting...isn't that the opposite of what we're told to expect from the stock types?? Was that an average or a single sample?
Author:  drmini in aust [ Sun Jul 29, 2007 9:40 am ]
Post subject: 
Cooper S originals are recognised as being all over the place as far as ratio goes. So are worn out sintered A+ style ones. :lol:
The rockers I used here all had good unworn bushes/bores and wear pads, and as said I used a new HD shaft to avoid flexing.

,edit> oval pad pressed steel type 1275/1300 ones are reputed to be nearer 1.3:1 ratio, we'll see when I find one. :wink:
Author:  9YaTaH [ Sun Jul 29, 2007 9:42 am ]
Post subject:  Try another...
drmini in aust wrote:
Cooper S originals are recognised as being all over the place as far as ratio goes. So are worn out sintered A+ style ones. :lol:
The rockers I used here all had good unworn bushes/bores and wear pads, and as said I used a new HD shaft to avoid flexing.


Corolla?? :D
Author:  drmini in aust [ Sun Jul 29, 2007 9:45 am ]
Post subject:  Re: Try another...
9YaTaH wrote:
drmini in aust wrote:
Cooper S originals are recognised as being all over the place as far as ratio goes. So are worn out sintered A+ style ones. :lol:
The rockers I used here all had good unworn bushes/bores and wear pads, and as said I used a new HD shaft to avoid flexing.


Corolla?? :D

I measured the Corollas before (see the 1.5 high lift rocker sticky thread above) with the same RE13 cam, I got 1.46:1 ratio. :wink:
At .016" clearance they gave .407" valve lift.
But a bit much for an 1132 Moke motor, IMO.
Author:  9YaTaH [ Sun Jul 29, 2007 12:08 pm ]
Post subject:  Re: Try another...
drmini in aust wrote:
9YaTaH wrote:
drmini in aust wrote:
Cooper S originals are recognised as being all over the place as far as ratio goes. So are worn out sintered A+ style ones. :lol:
The rockers I used here all had good unworn bushes/bores and wear pads, and as said I used a new HD shaft to avoid flexing.


Corolla?? :D

I measured the Corollas before (see the 1.5 high lift rocker sticky thread above) with the same RE13 cam, I got 1.46:1 ratio. :wink:
At .016" clearance they gave .407" valve lift.
But a bit much for an 1132 Moke motor, IMO.


Sounds like a search is required for a suitable standard rocker from yet another BMC product :idea: or maybe someone could alter the geometry (of say a pressed steel rocker - easier to cut and weld) :D
Author:  drmini in aust [ Sun Jul 29, 2007 1:04 pm ]
Post subject: 
Both the pressed steel rockers and S forged ones can have offset bushes fitted. I'll bore 1.0mm out of the rocker body first, then I can get a bit more offset than the old offset bushes gave without making the bush too flimsy..

Offset bushes used to be popular, but have been NLA for years.
Author:  drmini in aust [ Sun Jul 29, 2007 5:26 pm ]
Post subject: 
OK... I just couldn't wait, so I've already offset bushed a pressed steel 998 rocker this arvo and tried it.
I bored the rocker to 0.710" dia, pressed a bronze plug in and then bored it 0.563" dia in the mill. Offset from original bore is 1.0mm.

Valve lift at .016" clearance with this rocker is 0.359".

Rocker ratio is 1.293:1, I'll call `em 1.3s then. 8)
I'm a happy camper. Just need to do 7 more now... :lol:

I drilled the cast iron rocker post holes out to 11.5mm and 10.0mm and pushed them back on the studs, as Vizard suggests.
Image

<edit> typo, thanks DOZ!! :lol:
Author:  DOZ [ Sun Jul 29, 2007 5:51 pm ]
Post subject: 
drmini in aust wrote:
I drilled the cast iron rocker post holes out to 11.5m and 10.0mm and pushed them back on the studs, as Vizard suggests.


Big Drill Bit!!

DOZ
Author:  drmini in aust [ Sun Jul 29, 2007 5:53 pm ]
Post subject: 
DOZ wrote:
drmini in aust wrote:
I drilled the cast iron rocker post holes out to 11.5m and 10.0mm and pushed them back on the studs, as Vizard suggests.


Big Drill Bit!!

DOZ

D'oh.... 8) :lol:
Author:  DOZ [ Sun Jul 29, 2007 6:18 pm ]
Post subject: 
Is that adjustment to the rocker post holes to allow for pushrod clearance or to centre the pad better on the valve (for those without Vizard)?

Daniel
Author:  drmini in aust [ Sun Jul 29, 2007 6:39 pm ]
Post subject: 
The rockers are now 1.0mm further forward. This makes the underside of the pressed steel rocker foul on the spring cap and spring, as well as the pad being 1 mm too far forward on the valve stem.
Easiest way to get the shaft back 1mm is to oversize the holes. The posts are really too thick to mill the front side of the hole forward.
Once pushed back and bolted down, they won't move anyway. :wink:
You don't really need to go 1mm on radius- ie 2mm bigger, as the holes are already a bit oversize. The sizes above are about 1.5mm bigger than stock.
Author:  kiwiinwgtn [ Tue Jul 31, 2007 7:52 pm ]
Post subject: 
Hi Kev

Have you thought about altering the rocker pad

My engine builder has a machine to reface the rocker pad area which also changes the lift.

I got an even 0.351" of lift from my RE13 in my 1360, Avg Ratio also 1.22

I am still running it in so have not given it to much curry yet.

You can still by of off set rocker bushes (search ebay UK)

Cheers

Kiwiinwgtn
Author:  kiwiinwgtn [ Tue Jul 31, 2007 7:55 pm ]
Post subject: 
Kev try this link for your off set bushes

http://cgi.ebay.co.uk/1-5-degree-Offset ... dZViewItem
Author:  drmini in aust [ Tue Jul 31, 2007 10:12 pm ]
Post subject: 
Yep I saw that link, but it's easier for me to make `em....
1st rocker I did had 1.0mm offset, the bush is still pretty thick on the thin side so the set of 8 I'm doing now will have a little more.
Rocker pads on all these pressed steel rockers were still original and barely marked- I'm aware you can gain a bit by moving the pad face but you get more ratio change by moving the pivot point (da shaft).:wink:

<edit> no way those offset bushes in the link can give you a 1.5:1 ratio, if that's what's implied in their hazy description. The bushes are too small in diameter to be bored with enough offset. I had some years ago.
Near 1.3:1 ratio, if you are lucky. :)
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