assembling the head...

[zaq123]

My first M20 head build...
Can someone share some knowledge on the following:
I'm using test springs at this point just to measure things and noticed that the bracket (pn 11331264677) has some minimal play and allows for some rocker shafts movement. Is it normal? This is not noticeable when the actual valve springs are used due to the pressure on the shaft but I'm not sure if it's something to be concerned about.

Also the above mentioned bracket has one side flat and one side slightly rounded. Is there a particular direction this rounded side should face (front or back)? Bentley says to make sure this bracket is properly oriented but doesn't go into details and I didn't pay much attention when first disassembling the head.

Thank you in advance

[digger]

it should have no axial play but rotational there will be some but make sure the lock sits all the way down. it wont matter if you are test fitting things

[zaq123]

it should have no axial play but rotational there will be some. it wont matter if you are test fitting things

Thank you sir. Lock is all the way down, its wings are touching shafts on both sides. Is this typical issue area with these heads? Any idea how to rectify this? The bracket(lock) has about 0.0015" difference between its thickness and the width of the slot in the head. that clearance translates to 0.012" axial play at the rocker shafts.

PS. Lock has some minor dings on it from rocker shafts hitting it but its center area (where it sits in the slot) is perfect and with 0.0015" clearance there is no way to avoid the axial play at the shaft. Is there an issue with the head? Lock slot looks perfect.

[digger]

I've always found them to be snug. What thickness is yours?

[zaq123]

I've always found them to be snug. What thickness is yours?

0.157" thick. Have you tried to install the lock when rocker shafts are in but no rockers? I can see how it will feel snug when there is a pressure on these shafts from rockers/valve springs.


I did try it with with 0.0015" shim in the lock slot...there is zero movement in the lock itself but there is still some minor axial movement in shafts that appears to be from the lock leg and the shaft's lock cut out. Am I taking it too far or I have an issue that needs to be addressed?

[digger]

Let me look at some spare heads when I get home, I'm only going from memory

[zaq123]

Let me look at some spare heads when I get home, I'm only going from memory

I appreciate it.

I actually did some research and had a hard time finding any info on this for M20.

Since M20 rocker design concept is somewhat similar to Porsche 911, could specs be somewhat similar?
911 rockers ride on the cam just like M20 but there is an individual rocker shaft for each rocker, pic below.


Anyway, spec for 911 rockers: axial play min is 0.1mm to 0.350 mm. Wear limit is 0.5mm.

My axial play is 0.3mm.

Thoughts?

[digger]

on the m20 the rockers on the shaft can move somewhat as the retaining clips are not fixed at both ends its just a spring

[zaq123]

on the m20 the rockers on the shaft can move somewhat as the retaining clips are not fixed at both ends its just a spring

Do you think that rocker shaft later at movement is acceptable by design?

[digger]

Doesn't seem to be an issue, there isn't much in the way of lateral forces if the parts are made properly

[digger]

i also got clearance between the locking piece and the slot in the head 0.0015" using a feeler gauge (0.0020" wouldn't go properly) the thickness of the locking plate is 4.00mm +0,-0.02mm so its a pretty close fit in the slot.

the thrust/axial play in the shaft is 0.25mm when the lock is installed using a dial indicator. these seem perfectly normal so i wouldnt worry mate.

the reason it moves as much as it does is because the lock is supported in the middle only so when you move the shaft the lock rotates in the slot magnifying the small clearances because of the distance ratios, if you hold the other shaft still by hand and then repeat the measurement the play reduces by almost a half. in service its probably not going to move because of friction

[zaq123]

thank you for the info.

[ForcedFirebird]

The rocker cover also has tabs that push down on the shaft retainer. Once everything is bolted up, it's only serving the purpose of holding the shafts from moving longitudinally, or rotating.

A local friend has his new spec e30 engine built by another local shop. Somehow they left the shaft retainer out, the shafts spun, spit all the retaining clips out and ate his head to pieces. The rocker shafts were walking out of the head too. o.0

[digger]

the cover does indeed stop the lock from coming out, the lock also can prevent the valve cover seating properly on the gasket so it should always be checked that there is a very slight gap between the cover and lock