| Author | Topic |
|---|
Location:
Lost in the K hole
Registered:
May 2002
|
|
cam grind and bucket/shim assembly ...
|
Sun, 23 February 2003 09:45
|
 |
ok, time for ed's dodgy box of cheap ass ideas to be re-opened...
i would really like to get new cams to support all the headwork ive recently done, but alas, getting the cam faces welded and reground is a *tad* expensive.
so, ive been thinking how i could get away with simply regrinding my existing cams, and figuring out some way of dealing with the reduced lobe base circle dia...
so, im thinking, say i grind 2mm of the base of the cam lobe. to compensate, it seems possible that i could whack an *extra* valve shim UNDER the bucket, thus pushing the whole bucket assembly out of the hole some 2mm. as the etra shim would be about 3mm thick, i'd also have to grind the valve stem down some ~1mm to make all the clearances correct spec.
give the rest of the cam grinding id, be doing, i cant imagine id be increasing lift to over 8.8mm or so, and the profile wont be to steep, so hopefully i wont be facing shim spitting issues (for the top shim).
question is, can anyone see something terribly WRONG with this idea? is the 'under' shim going to be prone to dislodging (i cant see thats possible - its a tight fit for it inside the bucket). is it potentially BAD for the bucket to be protruding an extra 2mm? (theres still A LOT of bucket inside it bore)
heres an image of what i mean... 30k big
any thoughts at ALL as to why this wouldnt work would be appreciated. as too a pat on the back for this being a potentially UN-stupid idea
cheers
ed
|
|
|
I supported Toymods
Location:
I renounced punctuation
Registered:
May 2002
|
|
|
Location:
Lost in the K hole
Registered:
May 2002
|
|
Re: cam grind and bucket/shim assembly ...
|
Sun, 23 February 2003 10:35
|
|
**in the ghetto** (cartman voice)
it will add the weight of 24 shims, minus the weight of 24mm of valve stem 
hehehe, minus the rotational inertia of the cam meat removed!!
sriously, is this a completely barmy idea, or is it kinda do-able?? is there anything fundamentally wrong with grinding the base circle of the cam too btw??!!
anyway. i knew id net you in with this one!
cheers
ed
(ps - screw you and your 'colourism!')
|
|
|
I supported Toymods
Location:
I renounced punctuation
Registered:
May 2002
|
|
Re: cam grind and bucket/shim assembly ...
|
Sun, 23 February 2003 10:39
|
|
I choose to spell 'color' without the superfluous 'U'. I think I went into this at great length once......
See edited post above. Might just work, but I'd try it on something cheap, nasty and disposable like a 4AG first.........  (joke)
|
|
|
Location:
Lost in the K hole
Registered:
May 2002
|
|
Re: Ed's ghetto spec high lift cams
|
Sun, 23 February 2003 11:10
|
|
| gianttomato wrote on Sun, 23 February 2003 21:16 |
What is the under bucket shim resting/loaded against?
|
the underside of the bucket has a small flat 'nipple' who's machined face usually interfaces with the stem of the valve. the face of this nipple sits about .25mm proud in the roof of the bucket. the UNDER shim would sit between the machined face of said 'nipple' and the valve stem immediately beneath it.
thus, in a completely 'unloaded' situation, the shim could potentially rock ever so margianlly from side to side. i doubt this would happen thou, as the shim sits ever so snugly within the side walls of the bucket. nishad just raised this issue - re making sure the valve stem has somthing square and stable to interface with to prevent deflection of the stem during load cycles.
i could potentially use that loctie high temp, high strength epoxy to bond these UNDER shims into place (thats extreme, but an outside option none the less). i have to go see how possible it is for the UNDER shim to deflect.
| gianttomato wrote on Sun, 23 February 2003 21:16 |
Just wonder if having the bucket sitting out of its bore by 2 mm more might result in a slight increase in the bucket rocking, with greater wear/ increased propensity for the shim to spit? Just wondering...
|
thats a point. but hopefully ill be able to make a gentle, long dur, lower lift profile that can help avoid shim spitting issues.
even being 2mm extra out of the hole, there is still a LOT of bucket still in the bore. hopefullt this will resits rocking a bit. (and theyre in ex condtion atm - very little existing wear)
cheers
ed
|
|
|
I supported Toymods
Location:
I renounced punctuation
Registered:
May 2002
|
|
Re: Ed's ghetto spec high lift cams
|
Sun, 23 February 2003 12:05
|
|
Also just wondering, with lobe being just that bit smaller, even though the profile is the same, because it's smaller, acceleration is higher so therefore a bit nastier than you might expect so maybe top shim more likely to be spat out?
No idea.....speculative....hopelessly bored at work
|
|
|
Location:
MACKAY
Registered:
May 2002
|
|
Re: cam grind and bucket/shim assembly ...
|
Sun, 23 February 2003 12:42
|
|
ed
A couple of things to check out ,
(1) If you tip the valves by 1 mm make sure the valve tips still protrude above the valve retainers or the extra shim will hit on the retainers , sometimes after tipping valves the tip ends up lower than the retainer , This is normally not a problem as the underside of the bucket has that protrusion you mentioned as so the bucket and retainer still has clearance .
(2) Is there enough heel on the cams to remove 2 mm , If so would the base circle of the cam lobe still be larger than the cam bearing journal as the edge of the buckets on some heads actually sit slightly under the edge of cam bearing journal , If the cam lobe base circle is smaller the buckets will hit on the cam bearing journals .
Otherwise I can't see any problems with this setup .
Trevor
|
|
|
Location:
Lost in the K hole
Registered:
May 2002
|
|
Re: cam grind and bucket/shim assembly ...
|
Sun, 23 February 2003 12:43
|
|
i dont get why 'smaller radius, same profile' = higher acceleration. i just cant conceptualise it tabula rasa...
say ALL i did was grind the back of the lobe off, with NO mod ification to the rest of the profile. surely the ONLY bit of the lobe that produces ANY acceleration different to stock is the transition from the low base circle to the existing ramp of the active lobe. and the slope (= acceleration) of this transition section is going to be nothing compared to the acceleration and associated forces produced by the slope of the main part of the cam lobe.
acceleration is the rate of change of the velocity, ie the rate of change of the height change of the lobe profile. i cant see how a transition from the now reduced base circle compares to the rate of change in the profile of the rest of the lobe...
but bill seems ADDIMENT that its a bad idea... 
cheers
ed
|
|
|
Location:
Lost in the K hole
Registered:
May 2002
|
|
Re: cam grind and bucket/shim assembly ...
|
Sun, 23 February 2003 12:50
|
|
| TA22-3SGTE wrote on Sun, 23 February 2003 23:42 |
(1) If you tip the valves by 1 mm make sure the valve tips still protrude above the valve retainers or the extra shim will hit on the retainers
|
yeahm theres plenty of meat there to remove 1mm without fouling the collets
| TA22-3SGTE wrote on Sun, 23 February 2003 23:42 |
(2) Is there enough heel on the cams to remove 2 mm , If so would the base circle of the cam lobe still be larger than the cam bearing journal
|
yeah, 2mm is the max i can take off. ive got one of those heads where the bucket will foul the bearing journal if it comes up too much. 2mm grind take the lobe to within 0.3mm of the journal, and then theres 0.5mm from there to the edge of the bearing journal to the actual bucket (not the shim - shim clears, i think).
the actual specifics of the grind are to be fully figured out. but just sussing the general concept for now
cheers
ed
|
|
|
I supported Toymods
Location:
I renounced punctuation
Registered:
May 2002
|
|
Re: cam grind and bucket/shim assembly ...
|
Sun, 23 February 2003 14:01
|
|
| ed_ma61 wrote on Sun, 23 February 2003 23:43 |
but bill seems ADDIMENT that its a bad idea...
|
I have to agree with him. It might just work, but I have this gut feeling it would fail early. The more I think about it the more I don't like it.
I don't like the fact the bucket is sitting 2-3mm higher, I don't like what the bottom shim might be sitting on, I don't like the extra weight you have introduced into the system, you still have the outer shim anyway with that ability to flick out, it'll still cost you plenty to have the lobes ground anyway, the rest of the money getting a normal weld and grind will go towards getting the other machining done to take valvetips off and grinding down shims to fit inside buckets, and in the back of your head is the perpetual doubt that it will fail, BADLY, such that you have to build another head properly, outlaying a second wad of money.
That's a long sentence.
|
|
|
Ed's ghetto spec high lift cams