Hydraulic cam followers

[jimk04]

tappet crown observations, no objective measurements, I wouldnt have the means, but you can SEE a slight difference.

BGA



INA (admittedly with 50k miles on) definitely 'flatter'. I dont think there is any discernable wear on here, as the mark from the valve is very central, doesnt contact wide enough to have flattened out a crown.

[Gelbster]

Tappet crown- thank you for sharing the observations.
What significance does this have for the jammed-up-in-the-bucket tappet problem?
Does the crown(offset slightly?) cause the tappet to rotate rotate ? And does a little rotation prevent jamming?
Or does jamming occur if there is almost total leak-down of oil from the tappet when the car sits for a long time ? Then when you eventually restart ,the tappet has no hydraulic 'cushion' ,so it gets hammered up into the bucket ?
All WAG but it would be good to understand this issue.

[JFP in PA]

Originally Posted by Gelbster

Tappet crown- thank you for sharing the observations.
What significance does this have for the jammed-up-in-the-bucket tappet problem?
Does the crown(offset slightly?) cause the tappet to rotate rotate ? And does a little rotation prevent jamming?
Or does jamming occur if there is almost total leak-down of oil from the tappet when the car sits for a long time ? Then when you eventually restart ,the tappet has no hydraulic 'cushion' ,so it gets hammered up into the bucket ?
All WAG but it would be good to understand this issue.

Go back and reread Jake's comments about the crown finish and hardness. If the face against the cam is not hardened, and with a crown to promote rotation, the crown will wear into a mushroom shape, making it impossible to remove, while also tearing up the cams.

Anyone that has ever wiped out a flat tappet cam will know exactly what he is referring to.

[jimk04]

I cant comment on the crown's 'job', I can only see that the BGA tappet has a more pronounced crown. It isnt offset Gelbster, just me struggling to capture the image in a phone!

The tappet would only leak down and then get hammered in if the relief valve element was gunged up. I have had these to pieces and when you put them back together they spring about all over, but you fill this tappet in these pictures up with oil by depressing the tiny ball/spring and then it allows oil in, and it becomes pretty solid....how you need it.

I assume the ball depressing happens with engine oil pressure in situ, but like I say if the tiny relief mechanism is blocked with old oil, it wont work effectively.

This is all my take on the whole thing, nothing certain here.

[Jake Raby]

Originally Posted by JFP in PA

Go back and reread Jake's comments about the crown finish and hardness. If the face against the cam is not hardened, and with a crown to promote rotation, the crown will wear into a mushroom shape, making it impossible to remove, while also tearing up the cams.

Anyone that has ever wiped out a flat tappet cam will know exactly what he is referring to.

Exactly.. I don't give a damn about the contact surface to the valve stem, as long as its the proper hardness.

The crown that follows the cam lobe is whats absolutely unforgiving and effects lifter surface speed and reset as the cam lobe wipes across it. This is a critical dimension and one thousandth of an inch may as well be a mile.

FYI- I have seen brand new lifters come with improper crown radius, and we have to check every single lifter that we install because of this. It sucks, but we save our asses every time that we do it.

Assume nothing, quantify everything.