using combined over and under cam bucket shims

[Sam_Q]

I have a head that I want some custom cams for but no billets are available, I have been quoted $990 for a weld and grind which just isnt an option. I am thinkinnking of keeping the current shim over bucket design but also fit an aditional shim under the bucket much like a 4age 20V. This would let me have the radius of the base circle reduced effectively increasing the lift and giving me some extra material for a change in duration.

I have seen this approch demonstrated in a euro engine in a book however I want to know if anyone has heard of it being done here and what might be wrong with the idea.

-sam

[Chrisso]

Just thoughts, but would an additional under bucket shim put the over bucket shim too high? That is, increase it's propoensity to fall out?

Also, if the cam grind is designed so a certain part of the lobe makes contact with the shim at a given angle, would lifting the shim higher change the angle of contact and put enough sideways pressure on it to push it out?

I'm just sitting at work speculating, but I would say that as long as you've considered it thoroughly, there's no reason it shouldn't work. adding meat to the shims should be the same as adding meat to the lobes. These would be my initial thoughts.

[Sam_Q]

yes this is what I have been thiking about also. The whole bucket would be higher however I believe that structually there would be heaps of support still to hold the bucket into place. increasing the shim thickness is a different story though and sopposedly any more than a 0.5mm increase will cause a fair force in a shim getting pushed out.

Here is a pic of the head in question:



By grinding off the base circle of the cam lobe the angle of contact between the bucket will still solely depend on the cam timing duration. There has to be a good reason why people arent doing this though as the old weld and grind job on cams is somewhat common

[oldeskewltoy]

my opinion.... get tall enough shims for the under bucket... even if you have to have them made....


OR.... you might look at "sinking" the valve further into the head(actually raising valve protrusion is more accurate description) and then go from there using an underbucket system......

[Sam_Q]

as in convert tottaly to a shim under bucket design? I could use shimless buckets and then use a normal valve end shim with that. Next up I need to measure my valves and see what shims are compatable

as for the second option; wouldnt recessing the valves 2mm into the head potentially open a big can of worms?

[oldeskewltoy]

How much do you intend to reduce the base circle by????

[Chrisso]

Sam. If your goal is to get more lift, could you use longer stemmed valves? So long as this doesn't affect their ability to close completely.

[gianttomato]

Biggest problem would be increasing valve train weight. Then you'd need stiffer springs to control valve travel. Ultimately, this saps power. Also, depending on profile, you may find shim over bucket arrangement may be prohibitive.

As suggested above, stay with shim under bucket and use thicker shims or use valves with longer stems to accomodate the reduction in base circle diameter. That said, by the time you price stuff out, I dare say your $990 weld and grind option will be looking very attractive.

[Rodger]

Sam Q

Not being able to see the pics at work does not help me with this question. Anyway.

Does the design of the spring cap allow for a shim to sit within it? As per 2T-G 18R-G etc shim under setups?
The kit I am using in a 3S-G has both the bucket and the cap.

Regards

Rodger

[oldcorollas]

close and rebore the cam tunnels on the head ie if came cap slit is flat with rest of head, deck head by the increase in lift you wnt, the refit caps and get lower half rebored...

might get a little pricey tho..

[gianttomato]

Does the design of the spring cap allow for a shim to sit within it? As per 2T-G 18R-G etc shim under setups?

Rodger

Looks like a 4AFE head so I doubt very much.

[jezza323]

would sideloads on the bucket in its bore become an issue if it is sitting up an extra shim width out of its normal spot?

[Sam_Q]

oldeskewltoy: I will reduce the base circle to whatever the new shims are, 2mm sounds good to me. From what I hear there is no hardened layer for cams that I have to worry about and I also cant see it weakening them to any point to worry about.

Chrisso: I am sure I could and it would have the same effect however I also think that custom valves means decent money.

gianttomato: I did consider this and the way I see it is if I just end up fitting an underbucket shim ontop of what I already have then its only an extra few grams. Regardless I have some 4age TRD valve springs that are going to go in. What I was really hoping for is to find a set of shims from some donor engine for a cheap price that I can just put in there, get the cam ground to suit and then use the stock shims on the top ajust the clearence. In theory if this is even possible it will mean that my valvetrain cost is no more than a set of second hand valve end shims.

Rodger: any chance you could explain how this system works or have a pic of it?

oldcorollas: in my desperation I did think of this one! it probably would be quite expensive though as you say. I might as well as a head place and see what they say.

gianttomato: well observed, its a 7afe which is the same as the later 4afe head bar some extra valve lift.

jezza323: considering just how big the diameter of the buckets are compared to any 4age engine I would assume that theres more inherit support and hence strength there to handle the extra load. I will need to see an expert about this.

There may be an option to push the cam gear off the intake and exhuast, swap them and then possibly use a intake cam in the exhuast. With its 8.6mm stock lift that gives me a fair bit of meat to grind to change the duration if I go back to the stock 7.8mm lift.

Well anyway thanks guys for all the tips so far. I will measure my valves soon to see whats theoreticly available

[oldeskewltoy]

Sam.... have you contacted Web Camshafts in the USA? They do quite a bit of hardwelded cams(pretty successfully I might ad....) If you supply the cores, I can't see them charging you more than $600

I like the idea of a longer valve stem.... From memory(4AG application) you can use the 3SG valves and gain some in the stem( 3SG valves usually require shortening on a 4AG) You might be able to call a valve company(Ferrea?) and get valves to your spec.......

[Sam_Q]

the postage cost and haslte wouldnt be worth it for me I think.

However I might as well call about the custom valves and find out what sort of cost I am looking at, thanks