TRExp

Spitfire & GT6 Forum

rockers, OEM - Spitbits change

Moss Motors
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor

colodad Avatar
colodad Silver Member Calvin Williams
Grand Junction, CO, USA   USA
Rocker's width is minor change, but moving the pivot point closer to the push rod would increase the rocker ratio.
Some added tappet pressure against the cam lobe?

. Hide banner ads & support this website by becoming a > Gold Supporting Member <

Attachments:
cwIMG_4289 Spitbits - OEM rockers.jpg    57.9 KB
cwIMG_4289 Spitbits - OEM rockers.jpg

cwIMG_5189 .750'' OEM.jpg    41.3 KB
Sign In or Register to view this photo
cwIMG_5190 .755'' Spitbits.jpg    38.7 KB
Sign In or Register to view this photo
Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, NV, USA   USA
Guess they figure it'll wear off,....like dirt.

clshore Carter Shore
Beverly Hills, FL, USA   USA
Appears to me that the pivot hole is misplaced, since the rocker pad looks farther away by same distance that the adjuster is closer.
But visual evaluation of the pivot centers of shiny spherical and cylindrical sections is always subject to error.

A measurement fixture could be fangled, but unless you are the manufacturer, a racer, or a QC inspector, a lot of work for little reward.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
Lizzard d id
san jose, CA, USA   USA
Its not uncommon for the ratio to be other than what is claimed , a 1.5 will be other that 1.5 and so on . The idea is that the flex in the system makes up the differance . Until you measure the lift the lift / ratio is unknown , the replacement rockers might be closer to the original spec .

Manana Avatar
Manana Steve Wten
Thornhill, ON, Canada   CAN
I'd say 5 thou on that measurement is insignificant, in fact, depending on how your calipers work, it could be a delta of only 1 thou with rounding accentuating the delta. I think it would only be an issue if you were using the old shaft, where the grooves in the shaft from the old rockers may mildly offset the geometry. Using a new shaft would alleviate that.

Looks to me like the pad is fine but Carter you may be right about the pivot hole being a bit off. If that pushrod seat/nub/whatever is off a bunch it may put a lateral force on the tappet, but I suspect it would need to be a huge difference before it actually affected it; and given how deep tappets are, again, I suspect your are golden.



Steve
http://stevew10.wix.com/spit16

Lizzard d id
san jose, CA, USA   USA
In reply to # 1518018 by Manana If that pushrod seat/nub/whatever is off a bunch it may put a lateral force on the tappet, but I suspect it would need to be a huge difference before it actually affected it; and given how deep tappets are, again, I suspect your are golden.
Lateral ? I think the concern is about tappet to cam and not so much tappet to block .

colodad Avatar
colodad Silver Member Calvin Williams
Grand Junction, CO, USA   USA
rocker pad contact on valve stem.
Spitbits off center and forward, forward enough to show shaft hole was bored off center.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <

Attachments:
cwIMG_5197 Spitbits left, OEM right.JPG    48.1 KB
cwIMG_5197 Spitbits left, OEM right.JPG

cwIMG_5205 Spitbits contact valve stem off center.JPG    68.7 KB
Sign In or Register to view this photo
clshore Carter Shore
Beverly Hills, FL, USA   USA
Unless you know where the contact line between the pad and valvestem tip is, staring at the backside really tells nothing.
Use some dykem blue to or similar to see where the contact line on the tip is.
The contact pad 'face' is just a portion of a virtual cylinder whose axis is parallel to the rocker arm shaft.
The whole cylinder is not required, nor is it present, only the portion that bears upon the valvestem tip.
What's important is the distance between the rocker arm shaft axis and the virtual cylinder axis.
That said, I'd reject the parts based on the adjuster screw distance alone.

Lizzard d id
san jose, CA, USA   USA
Can you do a valve lift off seat test with a new and an old rocker ? Same cylinder , same lobe ?

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
colodad Avatar
colodad Silver Member Calvin Williams
Grand Junction, CO, USA   USA
In reply to # 1518058 by Lizzard Can you do a valve lift off seat test with a new and an old rocker ? Same cylinder , same lobe ?

Can't do same lobe, canley is still in the block. Head gasket push rod openings are only 0.747" Tappet 0.8"

Running valve lift measurements later, and oil flow changes before-after parts changes.

The 2018 Cam lift lobe degeneration measurements to compare with 2015 measurements.

V#1- 0.2305"
V#2- 0.2325"
V#3- 0.226"
V#4- 0.2295"
V#5- 0.2305"
V#6- 0.2315"
V#7- 0.2295"
V#8- 0.230"

spitfire50 Avatar
spitfire50 Paul Mugford
Rochester, N.H., USA   USA
Calvin,
By swapping rockers you can find out how much the lift is changed. First check the lift on a valve. Then swap to the old (or new) rocker. Now check the lift on the same valve. Yes it does involve talking the rocker shaft assembly at least partly apart, but you get a pretty good comparison. The only factor that wouldn't be accounted for is wear in the pivot hole in the old rocker.
All the best,
Paul

1964Spitfire Avatar
1964Spitfire Tim P
Santa Clara, CA, USA   USA
Couldn't this be done in-place. Assume 3/8-24 threads on the adjuster. One full turn should net a .0417 change on the ball end, and assuming 1.5 rocker ratio you'll see a .0625 change on the valve stem end. All ballpark numbers, use a pair of dial indicators if you want a bit more precise measurement. But should give you the ability to compare old versus new rockers.

Lizzard d id
san jose, CA, USA   USA
In reply to # 1518153 by 1964Spitfire Couldn't this be done in-place. Assume 3/8-24 threads on the adjuster. One full turn should net a .0417 change on the ball end, and assuming 1.5 rocker ratio you'll see a .0625 change on the valve stem end. All ballpark numbers, use a pair of dial indicators if you want a bit more precise measurement. But should give you the ability to compare old versus new rockers.
It should be done in place , a dial indicator is placed on top of the spring retainer , the engine crank is turned by hand and the total movement of the valve is watched via the dial indicator . If the dial indicator is zero'd for zero lift , then the dial is watched until it doesn't climb anymore . That would be the total valve lift , then check it against the spec sheet . Do the math and you will get the ratio .

Or do a dial indicator on the cam and see what its lift is and then check the valve lift at the valve spring retainer , then do the math to figure the rocker ratio .



Edited 1 time(s). Last edit at 2018-03-11 03:42 PM by Lizzard.

colodad Avatar
colodad Silver Member Calvin Williams
Grand Junction, CO, USA   USA
I'll get to the valve lift monday..out of time today, headed out to the farm.

colodad Avatar
colodad Silver Member Calvin Williams
Grand Junction, CO, USA   USA
Rocker...... cam lift....... if 1.5-1...... valve lift .....actual rocker
.....................................ratio..........(average)......ratio
#1 OEM.....2305".........34575"........3305"..........1.434
#2 SBits.....2325..........34875"........3515"..........1.512
#3 OEM.....226 "..........339"............328"............1.451
#4 SBits.....2295".........34425"........348"............1.516
#5 SBits.....2305".........34575"........352"............1.527
#6 OEM.....2315".........34725"........333"............1.438
#7 SBits.....230"...........345"............352"............1.530
#8 SBits.....230"...........345"............349"............1.517

OEM was less than 1.5 at 1.44, but the rocker pad set center of the valve stem.
SpitBits was improved at 1.52, but it has some other effects, the valve stem contacts the rocker pad at the side, and some pushrods are slightly leaning.
SB needs some side adjustment to align the pads to the VS, and should help with the PR's angle.

Spitbits asked for some photos, they don't know how the shaft bore could be off center.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <

To add your reply, or post your own questions




Registration is FREE and takes less than a minute!


Having trouble posting or changing forum settings?
Read the Forum Help (FAQ) or contact the webmaster