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MG MGB Technical - Question about reconditioned rockers

I have just put the head back on the engine and was setting the clearances when I noticed that the rocker face didn't look to be sitting squarely over the valve stem. Does this look ok to you? The overall length of the rocker is 76 to 77 mm nose to tail.


Steve Church

Did you have the head milled down and are you using a stock camshaft? It would appear that the rocker arm geometry has been thrown off. RAY
rjm RAY

It's a Peter Burgess fast road head so has been skimmed. It's a Piper HR270 cam also. I also sourced the followers and pushrods from Peter. The nose of the rocker looks a bit short, almost as if they they are not of the correct type (midget?). I don't have the originals as I exchanged them when I bought the new rockers. I would expect head/cam changes to affect the adjustment mechanism but not the pivot to nose distance of the rocker. I don't remember what the original geometry looked like so am asking forum members for their opinion. This may be normal for all I know!
Steve Church

Hi Steve

As long as you have adequate clearance you will be ok. You can check to see what lift you get but bear in mind Bs tend to lift a standard cam to around 320 thou instead of 365 thou. In theory, at half lift, rockers should be parallel(theory goes out the window with Bs!).

Peter
Peter Burgess Tuning

1)Talk to Peter.
2)You are out of adjustment. You either need a) shorter pushrods or b) shims under the rocker pillars. b) may rectify the geometry problem as well. When the valve is halfway open, there should be a straight line through the pushrod ball, rocker pivot, and rocker/valve contact point, and the rocker should be contacting at the center of the valve stem or a bit outboard.
3)Talk to Peter.

FRM
FR Millmore

Steve,
I'm hoping Peter was in a hurry for his tea as his answer seems a little short on detail ;o)
FRM has similar thinking to me and I would do some more checks and/or talk to Peter. I might well read his book first... The picture suggests you are going to be short of contact area at full lift and hence the possibility of rapid wear in use.
Check your cam lift is actually as per spec. and shim the rockers under the pedestals. By doing this you'll get more adjustment and the rocker should be nearer the geometry mentioned. Then check the contact point at full lift. If its right on the end of the rocker, get another set for comparison. If getting a spare set is a problem let me know and I'll take some pic's of one of my sets.
As Peter says B's do not always conform to the theory but as you've take such care on the rebuild thus far, a couple of extra hours getting as close to ideal will give you great satisfaction.

MGmike
M McAndrew

Thank you all for your comments. I just feel that the nose of the rocker is too short.

FRM.
I'll check the geometry when the rocker is horizontal but from what I am seeing there is no way the contact point will be in the centre of the stem, let alone aoutboard of it. All of the downward pressure on the valve stem is to one side of the centre line of the stem. I would expect lots of wear on the stem/guides.

Could someone measure the length of a standard rocker for me?

If I need to shim the pillars am I ok to slacken and then retorque the head as I shall have to remove the pillar nuts?

Can someone tell me the standard head thickness so I can work out how much has been taken off this head. I can then get appropriate shims.
Steve Church

Here's a picture of rockers 4,5 and 6. No. 5 is fully down. No. 4 has been adjusted for clearance. I noted that I had nearly run out of adjustment (max clearance I could get on the thread was 25 thou) which confirms the need for some shims perhaps.


Steve Church

from comp tune manual:
std head thickness is 3 11/64 +.015, -.000; or 80.6mm +.38, -.000
1/16" off should be 3 7/64 +.015, -.000; or 79mm +.38, -.000
1/16" off should raise CR about 1 full point, depending on other factors, and where you start.

Agree on guide wear.
I say start with about 1/16" shim plates from the eyeball of pics.

FRM
FR Millmore

Yes you should be OK to slacken/retorque, especially if you haven't put water in yet.
If you have, then leave the non pillar nuts about 10lbft, then tighten and retorque as usual.

One thing is that with the adjusters screwed out so far, you could well have less than requisite adjustment available after the head settles, after heat cycling.

FRM
FR Millmore

I'll hunt down some shim material after I measure the head thickness. Peter told me the head should produce a CR of just under 10:1 so you're spot on with the 1/16th" shim requirement.

Does anyone know where to get suppliesof shim stock in the UK?
Steve Church

It's just sheet metal, 16 gauge in old money, 1.5 mm in new. Pieces of bodywork will do. Or two thinner bits etc. Nothing critical here.

FRM
FR Millmore

Are the rear end (pushrod end) of the rocker arms all the same shape? The valve guides will take any side load and not wear. The maganese silicide load bearing needles will prevent wear.The amount skimmed off the head will vary with combustion chamber depth, which is dictated by seat depth required to get valve seats level from one chamber to the next. The original tuning manual does not seem to understand MGB chambers are not even one to another in terms of flat or seat depth. The shape of the combustion chamber will also dictate ccs and hence amount to be milled off. Contact area also depends if and how the rocker tips have been dressed. If you shim the rocker pedestals the rocker arm tips will be even closer to the spark plug edge of the valve. As I said, check rocker angle at half valve lift and see how far off level the arms are. There are about 4 different types of rocker arm fitted to Bs and the way they lift and sit does vary. Your arms look very early ones. Remember the curve of the rocker arm tip dictates where it sits on the valve tip.

Peter
Peter Burgess Tuning

Peter, all the rear ends of the rockers are the same. There is a small (3mm ish) diameter boss on the end. Maybe from where the casting was poured perhaps. I'm using reconditioned rockers from MGBHive. I didn't know there were different types. I also assume that the facings have been profiled correctly. I notice that the set could be split into ones with a left hand bias and ones with a right hand. Very slight difference but I could select the rocker to sit best over the valve stems. I'll do some more checking tonight.

I guess I can find some sheet metal laying about somewhere. I think I have the lid off an old tool box under the bench.
Steve Church

"The original tuning manual does not seem to understand MGB chambers are not even one to another in terms of flat or seat depth."
True, but they used to be pretty close before molestation, and MG were not about to tell people that factory stuff was all over the place! And it was a very sketchy book for amateurs, not real engine builders.

" The shape of the combustion chamber will also dictate ccs and hence amount to be milled off."
True, that's why it is approximate.

" Contact area also depends if and how the rocker tips have been dressed."
Yes, but this is more systemic, with the adjusters screwed way out and the rockers pointed uphill.

"If you shim the rocker pedestals the rocker arm tips will be even closer to the spark plug edge of the valve."
That's what he needs and wants.

FRM
FR Millmore

Hi Steve

I still think you will be ok but shimming would not hurt.

I forgot to do the pics of before and after for the oil pump for you so I post them now a little belatedly.

Peter


Peter Burgess Tuning

After

Peter


Peter Burgess Tuning

Hi FR

I thought Steve was worried about how close the tip of the rocker arm was to the plugside of the so making it closer would worry him more. But I think we write at cross purposes. I meant the valve will start lifting nearer the tip of the rocker arm therefore end up further across the valve tip at full lift.

Peter
Peter Burgess Tuning

Peter,
Thanks for the photo's. Oil pump is installed and sump on now. I did however find an article by Sean Brown about opening the oilways in after market pumps which will have improved the flow. I've not seen the mod you've done though.

As FRM says I'm concerned that the contact surface will be inboard of the centre of the valve stem. As I do not have the original rockers I have no reference to compare against. The second picture I posted was with the valve fully depressed and it is only at this point that the contact point is somewhere near the centre of the valve stem. I guess that shimming will bring this point further outboard (plugside) and therefore give a more even distribution across the stem. I was also expecting the contact point on the rocker tip to be more inboard (towards the rocker pivot), thus giving rise to my questioning whether the rocker was actually long enough. I had not considered the geometry of the situation with a skimmed head before posting. I'll shim the pedestals and re-evaluate.
Steve Church

Steve,

Can you indicate on a repost of your original photo the "nose to tail" measurement points you used. I have two unmounted rocker sets I could measure but would need to be in sync with your measurement system.

Regards
Roger
Roger T

Hi Peter -
I thought Steve was concerned about the rocker contacting the valve at the inside edge of the stem, First pic and the two closed valves in the other show this clearly. The open valve in pic 2 is about where it should be at midlift.

When I've taken heads apart that have been run like this, I found a chamfer worn on the shaft side of the stem, a pocket in the rocker face, galling/scoring on the transverse sides of stems, extreme side to side wear on guides, and eccentrically worn seats. Such heads had generally had one or more valve jobs, probably without guide replacement, but it shows the tendency. No point in subjecting your good work to such abuse, plus it costs power due to lost lift (and friction).

PS: hate to be picky, but I hate that oil pump mod. It lets the pump drain when not running, giving no/low oil pressure at startup. Sean's cleanup is just as effective without the drawback.

FRM
FR Millmore

Roger,
the measurement was made with a vernier caliper with the rocker set between the jaws, so its measuring between the extremes.

I have to break off from the engine for a few days now so will leave any further investigation until next week.
Steve Church

Hi FR

Drainback not as bad as with a paper element upside down filter :)

The pumps have been running ok for us on all our B engines since 1996. No bearing losses yet.

Peter
Peter Burgess Tuning

Steve,

Some measures. These from two complete sets of rockers as removed from heads. Both offset oil feed. Vernier arm parallel with the centre line of the rocker arm.

Set one: these as yours in appearance, ie slightly veed along the top of the arm. I'm confident these came off an earlyish MGB head. Pedestal posts steel. The 'nipple' (where the oil feed drill line ends) is slightly more pronounced on this set - and would contribute to the slightly higher average length.

High measure 77.68mm
Low 76.49mm
Difference 1.19mm
Average of 8 77.26mm

Set two: these have a flat line to the top edge. Off a BMC vehicle but may have been other than a B, possibly a 1500 or 1300 head - not certain. Pedestal posts alloy, stamped MOWOG but with a 'map' of OZ, so local production.

High measure 77.81mm
Low 76.46mm
Difference 0.35mm
Average of 8 76.99mm

Very much according with your measurements.

General observations:

All rocker faces have a wear 'shine', but no feel-able depression edges. Those patterns vary in width and length, not surprisingly. The centres of the wear patterns however, are either pretty well centred on the rocker face or are outward, variably toward the end of the arm.

There was no correlation between that positioning pattern and the individual arm lengths as measured.

Given the position of the wear patterns is a factor of the arm length between bush centre and the contact point with the valve stem, this is something I cannot measure accurately on a built rocker arm.

Hope this helps. I'll follow this thread with interest as you solve the issue.

Regards
Roger

Roger T

Hmm - not a problem I generally have with rocker gear - overall length of the rocker is immaterial, the shaft centre to pad is the determining factor and if the pad has been over ground or ground to the wrong profile then you will have issues. There is also a fair amount of slack in the mounting holes in the posts and in the head holes too.

My first move would be to slacken off the rocker assembly nuts and see if you can lever the shaft nearer to the plug side of the head.

Here are three shots of a (XRN) reconditioned late assy on a PB Econotune head.

Left - fully open, centre - half lift, right - fully closed.




Chris at Octarine Services

Sorry about the tiny pictures - I forgot how limited this forum is!

Better ones on my forum here - http://ultra.octarine-services.co.uk/view_topic.php?id=405&forum_id=38

Chris at Octarine Services

Back from my travels so can get on again.

Roger, thanks for posting the dimensions of your rockers. Sounds like I have the right ones!.

I have checked the thickness of my PB fast road head and I measure between 3.045 and 3.042 inches. I measured the old head at 3.108. That gives a difference of about 65 thou or just over 1.6 mm. Does this seem feasible Peter? So I'm going to get hold of some 16 gauge steel at about 1.5mm (as FRM states). Looks like the job for the weekend.
Steve Church

Head new would have been 3.172- 3.187, per the specs I quoted above.
But, .065 plus what Chris said about positioning the rocker pillars above, you should be OK.

Don't forget to drill the oil feed hole in the shims!

FRM
FR Millmore

Good luck Steve

Peter
Peter Burgess Tuning

This is what it looks like after fitting 2mm thick spacers under each pillar. I also pushed the pillars towards the valves when tightening.

Fully open


Steve Church

Half open.

Last posting should be fully closed, sorry.



Steve Church

And fully open.


Steve Church

Interesting pushing rockers across, how far do you think they can be moved across the head? Have you measured the achieved valve lift with and without the shims Steve?

Peter
Peter Burgess Tuning

Peter, there really isn't much movement at all butI thought every little helps. I havent done any comparative lift tests. I've torqued the head up again now so think I'll leave it at that. I reckon that looking at the adjusters I'm not far off. Certainly better than it was.
Steve Church

Much mo betta!
You are just about dead on (my pics load so slowly that I got a nice horizontal line across to judge by. Meets the rule I gave you in 2)b in my first post.

FRM
FR Millmore

Steve,

Much better, aren't they?

You did drill the rear shim for oil flow?

Thinking about the head thickness figures discussed by you and Fletcher, there was a fair bit of metal removed from the head.

Performance manual base figure 3.172"
Your max depth figure 3.045"

Removed depth 0.127"

Not surprising that some adjustment would be required to the geometry on fitting.

Well done.

Regards
Roger
Roger T

Steve, grrrrrreat stuff. Looks like it was worth the couple of weeks extra work. Now get it back in and go play.....

MGmike
M McAndrew

This thread was discussed between 19/03/2012 and 30/03/2012

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