| Author | Message | ||
     2stang |
Im freshening my heads and wanted to add some titanium retainers. I know some of you guys who race, have DSB spec engines. Where did you get parts like to valves and retainers? | ||
| Stevel |
To my knowledge and I have done very much searching, no valve springs and retainers of any style are available anywhere other than original for the Buell. Further, changing from the original steel to a titanium retainer would save little or no weight using the stock springs. They are already very thin and light weight. Sadly, the same story is true for all Buell head parts. If you want them, you must design and custom make your own. | ||
| Battyone |
It's a shame, as a retainer that held the shim better would be a huge improvement. In 4 years of dragging 1125s plus 7 for LittleJoe, all of the breakages have been the result of spitting shims. I tig-ed the last set in. | ||
| Stevel |
The problem with spitting shims is valve float, not the retainer. It is unfortunately too common. Changing the steel retainer for a titanium one, does not reduce mass very much, as the steel retainer is already very light. The issue is the valve springs being way too light. The problem is further aggravated if you run a racing cam with a higher than the stock 10mm lift. In order to get adequate lift clearance, the spring seat is typically cut back about 2mm and the top of the valve guide is shortened, but this also reduces spring pressure significantly. Seat pressure will fall from 80 lbs. to 60 lbs. using the factory springs. I have been searching for new springs and guess what, I haven't found any yet. This is a big problem. First, there is no clearance in the stock head to accommodate high lift cams. The standard springs are 1" in diameter. There is insufficient space to accommodate either taller or larger in diameter springs. It is possible to open up the spring pocket by plunge milling to not more than 1.25" as well as deepening the spring seat head surface about 2mm, but not more without hitting water. Even with those mods, additional lift can only be facilitated by reducing the cam base circle. Any changes made there must be compensated by longer stem valves to maintain proper geometry. I'm looking for beehive springs in a diameter just under 1.250" wound with ovate wire tall enough to give me 90 lbs. at the seat. When I find them, I'll make my own valve string retainers in 6AL4V Titanium. | ||
| Battyone |
Drag racing, we spit the shims with a failed shift. Shifting at 10,500 ish if the shifter fails for any reason and unfortunately they do, then momentum pushes the motor thru any limiter, even the kill. I've logged 12,750 on a failure. But the shims are the loosest fit I have ever worked with, ffs you can move the rocker fingers over, shut your eyes and poke a magnetic pickup tool about and the shims will fly out lol. | ||
| Battyone |
I'm not an expert in valve trains, but I've just built a head for a turbo busa and the uprated springs supplied only give 65lb at the seat.With 2 bar boost that'll only be 35lb effective on the inlet. I assume valve diameter has an effect on required spring force??? It's a shame, I've got the EFR cams out of Joe's destroyed 1230 project. Be nice to try them some time. I posted a while ago about finding the rear exhaust cam being timed differently to the front. I put a motor together with matching timing and it really messed up the fueling on the rear cylinder. | ||
| Stevel |
Battyone, First, the design used for this engine is a common, well proven one. The shim must intercede between the cam lobe and valve stem, not the spring retainer. Second, the spring retainer only provides a cage for the shim. There must be some clearance between the OD of the shim and the ID of the depression of the spring retainer in order that the cam's effort is applied to the valve stem and not the retainer. Actual shim detention depends on the ability of the valve and spring assembly to remain in contact with the cam lobe at all times except when the valve resides on the valve seat. The ability of the valve assembly to follow the cam's profile depends on the inertia of the complete valve assembly and the spring's ability to overcome this inertia. There will also always be a speed limit for this ability. Please also note that the surface area of the contact pad of the finger follower is quite small and excessive spring pressure will be catastrophic. The avenue of choice to increase the maximum speed of the valve train is inertia reduction, not spring pressure. The steps to be taken to reduce inertia would be Titanium valves over steel and single coil beehive springs wound with ovate wire. Unfortunately, nobody offers these yet, but I will find a source shortly. The available clearance for larger diameter springs does not exist and the spring pocket must be opened up to accept them, but it is possible. I believe spring seat pressure above 70 lbs. is not advisable. Another area that can easily create valve float is the incorrect ramps of the cam profile for this geometry. Using cam profiles meant for other engines must be avoided. It would be very nice to know just what cams you are using, please tell us. You mentioned boost pressure as an influence on spring tension. Well, it is virtually inconsequential, forget it. Also, your last statement on different cam timing and fueling makes no sense to me. Please be more specific. What engine, what timing difference and what was the perceived fault? |
