Finger Follower - Design Revisions 2000-2005
Discussion
Photographed 14th December 2005 - Noted the visual design changes. comments on this would be appreciated. I am off to measure these up and produce the engineering model for them.
The casting on the old item is a far better quality than the new, you can see how porus the material is in the machined 14mm dia bore finish, the supprise came from the oilway feed to the cam lobe being inconsistent. The holes do manage to penetrate, but are certainly "underdrilled" on some.
On measuring up the item, the oil feed has been drilled at a shallower angle to the 2000 model. This certainly would change the direction of the oil spray to the cam lobe.
>> Edited by justinbaker on Wednesday 14th December 15:33
The casting on the old item is a far better quality than the new, you can see how porus the material is in the machined 14mm dia bore finish, the supprise came from the oilway feed to the cam lobe being inconsistent. The holes do manage to penetrate, but are certainly "underdrilled" on some.
On measuring up the item, the oil feed has been drilled at a shallower angle to the 2000 model. This certainly would change the direction of the oil spray to the cam lobe.
>> Edited by justinbaker on Wednesday 14th December 15:33
As always, nice work Justin 
Interesting pics.
I could be wrong, but the square/rectangular raised part, which intersects the oil feed look like it is only the feed from which the lost wax casting was attached to, judging by the linishing marks very visable running accross the raised surface!
Interesting pics. I could be wrong, but the square/rectangular raised part, which intersects the oil feed look like it is only the feed from which the lost wax casting was attached to, judging by the linishing marks very visable running accross the raised surface!
justinbaker said:
The box and the followers were on the desk together - It had to be done!!!
Genius. Absolute genius Justin
Speaking as an engineer m8, bloody brilliant work you are doing. Patient, slow, piece by piece fact finding and quite a process orientated job. Exactly what needed to be done, very impressed.
This is fabulous work Justin-really positive stuff!
The as-cast finish on the old fingers looks a lot more coarse (I'm not referring to the porosity in the bore here), as if it's a sand casting (or shell moulding perhaps). The newer one looks more like an investment casting (aka lost wax as previous contributor said) due to the relatively fine as-cast finish.
If the earlier one is a sand casting, then that limits the type of material to various grades of iron, and I guess it's most likely to be ductile iron - my experience doesn't extend to processes for hardening iron castings. But investment castings can be made in high specification steels which can then be hardened to achieve very hard, tough, and high strength components.
Is it possible that the earlier castings were iron and the later ones steel?
The as-cast finish on the old fingers looks a lot more coarse (I'm not referring to the porosity in the bore here), as if it's a sand casting (or shell moulding perhaps). The newer one looks more like an investment casting (aka lost wax as previous contributor said) due to the relatively fine as-cast finish.
If the earlier one is a sand casting, then that limits the type of material to various grades of iron, and I guess it's most likely to be ductile iron - my experience doesn't extend to processes for hardening iron castings. But investment castings can be made in high specification steels which can then be hardened to achieve very hard, tough, and high strength components.
Is it possible that the earlier castings were iron and the later ones steel?
I've just had a thought on the oil feed hole size difference in the new followers - perhaps there is a technical explanation for this; if the oil feed for the followers is through the cam, then the oil pressure will reduce along the length of the cam, thus the last followers will get less delivery of oil. This could be compensated by smaller holes at the higher pressure end causing a restriction, and larger holes at the lower pressure end to increase the delivery. I might be way out here because I don't know how the oil is delivered to this area, but I bet some of you guys do!
K.K. said:
AT LAST!!! Now I know what a finger follower looks like. Problem is I haven't got a clue what they do! Can someone explain it to me (as if you are explaining it to a 10 year old please - don't worry I won't feel patronised!)
OK, you did say keep it simple. The large hole you see is where the follower slides on to a shaft(parallel to crank), the shaft is there for it to pivot on. Imagine the camshaft is above the follower(also parallel to crank) and the valve is below in a similar plane to the cylinders, the follower acts as a pivoting spacer between the cam and valve. When the highest point of the cam lobe is pushing down on to the follower the valve is at it's lowest position(open). When the highest point of the cam lobe is pointing away from the follower the valve comes back up(closed) because it has springs to close it and closes leaving a tiny gap(valve clearance). If no cams were on the engine all valves would be closed. The total number of valves, cam lobes and followers is the same(for this type of engine design).
In short it transfers movement from the cam lobes to the valves.
The camshaft makes the valves work. The camshaft is driven from the crankshaft and goes round, the valves are driven from the camshaft and go up and down. Making a roundy-roundy thing drive an up and down thing tends to push the top of the up and down thing from side to side, which it doesn't like. Putting something between the roundy roundy thing and the up and down thing avoids this, and the finger followers are this something.
I'm only dipping into this from time to time so apologies if Im going over old ground, but have you inspected any worn/broken finger followers to see where they are failing? Based on some years old MG experience, the wear between the followers (rockers) and shaft wasn't a big deal, but if the sliding surfaces lost their hardness then the part would fail quite quickly.
AdrianR
I'm only dipping into this from time to time so apologies if Im going over old ground, but have you inspected any worn/broken finger followers to see where they are failing? Based on some years old MG experience, the wear between the followers (rockers) and shaft wasn't a big deal, but if the sliding surfaces lost their hardness then the part would fail quite quickly.
AdrianR
adrianr said:
...Making a roundy-roundy thing drive an up and down thing tends to push the top of the up and down thing from side to side, which it doesn't like. Putting something between the roundy roundy thing and the up and down thing avoids this, and the finger followers are this something.
NOW THIS I GET!!! Thanks guys.
One more question, does my Tam (June 2004) have the new good "somethings" or the old bad "somethings"???
K.K. said:
...Making a roundy-roundy thing drive an up and down thing tends to push the top of the up and down thing from side to side, which it doesn't like. Putting something between the roundy roundy thing and the up and down thing avoids this, and the finger followers are this something.
NOW THIS I GET!!! Thanks guys.
One more question, does my Tam (June 2004) have the new good "somethings" or the old bad "somethings"???
Ditto for a June 2005 Tamora 3.6 Red Rose...
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