13 replies to this topic

[stevemkeen]

Hi All,

 

In the process of completing my 1380 engine with SW5 cam, using the 12G940 head, the head didn't come with a rocker assembly, so using a rocker assembly from a 998 , I am using the original 1275 push rods which are 8.5 inch long .

 

Noticed the rocker tips doesn't sit centre on the valve tip (see pictures). I am aware that the spacing between cylinders is greater on a 1275 engine compared to a small bore which will account for the miss -alignment, also the rocker pillars don't sit flush with the head surface even with the adjustment completely out.

 

What rocker assemble would this head type come with originally ? . believe it to be the later type 12G 940 head.

 

So can this 998 engine rocker be used with this head , will having the rocker tip not sitting centre centre and seen in picture cause issues and undue stress on the components ?

 

Would it be possible or recommended to modify the spacing by using washers, would oil ways be out of alignment if this was done ?

 

 

Would pillar spacers be required to allow adjustment of the valve rocker to take place ?, I believe the engine block and head was slightly skimmed, would this result in

the rocker assembly not sitting flush. 

 

Any advice would be appreciated

 

Steve

Attached Files

•  rocker alighment.jpg   96.35K   17 downloads
•  rocker assembly 2.jpg   73.63K   10 downloads
•  rocker assembly 3.jpg   77.77K   14 downloads

Edited by stevemkeen, 17 August 2017 - 05:50 PM.

[Woolfie 640]

Hi Steve I have taken the head of a 1275 A+ to do the head gasket and found the same positioning of the rockers that you are having. When rebuilding the position did'nt improve and I am finding the idle is erratic and wondered if this alignment is causing the problem. Hope some good citizen will provide an answer.

[Avtovaz]

bore centers on a 1275 and a 998 are different so the rockers need shimming or replacing for 1275 ones

 

 

have a watch of this it may help you also

 

Edited by Avtovaz, 17 August 2017 - 08:37 PM.

[carbon]

I'm not so familiar with A+ sintered rockers, but think they are the same for 1275 and 998 A+ engines.

 

Difference with a 1275 is likely to be shimming of the rockers to get valve tips more central, but it will be almost impossible to get them all perfectly centred. As long as the valve tip is within the width of the rocker pad it should not make much difference.

 

But do check the face of the rockers where they touch the valve tip for any wear ridges.

[Northernpower]

I'm not so familiar with A+ sintered rockers, but think they are the same for 1275 and 998 A+ engines.
 
Difference with a 1275 is likely to be shimming of the rockers to get valve tips more central, but it will be almost impossible to get them all perfectly centred. As long as the valve tip is within the width of the rocker pad it should not make much difference.
 
But do check the face of the rockers where they touch the valve tip for any wear ridges.

When shimming rockers out it's important the push rods are still centred in the holes in the head.

[carbon]

Northernpower makes a very good point. With 1275 heads the valves don't exactly line up with the pushrod holes.

 

There can be over 3mm offset of pushrod holes from the valves, here are measurements taken from one 940 head:

- 1 & 8 = 3.4mm offset

- 2 & 7 = 2.3mm offset

- 3 & 6 = 0.7 mm offset

- 4 & 5 = 2.4 mm offset

 

If you use high lift rockers and shim them so they are central over the valve tips, then some of the pushrods can get very close to making contact with the head (at the upper face of the head) as the pushrod fulcrum point is closer to the rocker shaft.

 

Not usually so much of a problem with standard pushrods, but would imagine that anyone using larger diameter tubular pushrods may have found they can make metal-to-metal contact.

[stevemkeen]

Hi All,

 

Thanks for the comments, looks like the small bore A+ sintered rockers can't be used with a a larger bore engine with out the modifications mentioned, so did large bore engines and their head ever use sintered type rockers or did they just

use the pressed steel type, because the spacing would have to be different for a larger bore engine.

 

Can anyone answer what type of rockers would the later type 12G940 head used as standard.?.

There are pressed steel type out there second hand, would using roller rocker type be the best option for my engine/cam head setup , if so would i advised to used 1.3 or 1.5 ratio/lift type?

 

thanks again

 

Steve

[carbon]

All production A+ engines used the sintered rockers.

 

And as far as I know there is only one version, CAM289: http://www.minispare...ngs/CAM289.aspx

 

pre-A+ 1275 used pressed steel with wider rocker pad, to allow for alignment issues mentioned above.

[HUBBA.HUBBA]

They look fine to me

[Cooperman]

They always look like that.

[ACDodd]

They are fine, you will likely have problems further down the pushrod where it enters the block, mismatch here is usually quite large. Move the rockers will reduce one small issue and opftwn creates a much bigger one. One should concentrate ones efforts if correcting the geometry rather than bothering with the offsets.

Ac

[stevemkeen]

Thank Ac, I am more resumed that the degree of off set I have won't cause an issue, I can see now that because of the amount of metal removed from both the head and block will affect the geometry that isn't corrected when i used spacers under the posts to bring back valve into adjustment, I think I need to study a bit more, perhaps custom length pushrod could help if anyone does them.

 

Steve

[ACDodd]

I make 2 piece pushrods, ideal for longer Tha normal requirements. Not cheap though!

Ac

[ACDodd]

That assumes it was correct to start with. Maximising lift area usually means raising the rockers a little and a longer pushrod. But this again is all dependant on the original relationship of the rocker verses valve tip height and rocker ball falcrum point.

Ac