TW200 Forum banner

1 - 4 of 4 Posts

·
Registered
Joined
·
2,516 Posts
Discussion Starter #1
Just a question for you mechanical savy folk. Bikes that have been engineered in the valve train to use shims instead of screw type valves,is this done for less cost in manufacturing?.This does not have to be a painful technical answer....make it so if you wish?.It just seems to me that a shimmed vale-train would be a pain for the consumer,unlike the screw type valve adjustments as our TW's have and the XT-250. I was loafing on the ADVrider site and read about the new Honda CRF250L....seems like quite a pain to go through just to adjust valves!.I know, it is probably just me,seeing things as a pain when they are probably not at all;just the fact that one has to rely on the company,shop or what-have-you to have the shims you need in stock....eeekkkk!.Thanks to all that reply.
 

·
Registered
Joined
·
188 Posts
As a soon-to-be mechanical engineering graduate (one year left! WOO!) and someone who recently lost a lock nut
I would say the advantage to a shim-and-bucket type design is the durability and design. I have a lot of experience working on Toyota engines (both SOHC and DOHC) and all the SOHC have the TW/XT-like design with the lock nut. BUT! The DOHC (like the CRF250L) all have shim-and-bucket. Which, my guess, is because DOHC and rocker arms would make the head a mile wide. I'm sure things like demographic come in to play as well, when looking at the big picture. Yamaha sells the XT and TW to much poorer countries that don't have the resources to be pulling a cam just to adjust valves, so a screw and nut greatly benefits them. The CRF250L isn't sold as much as other SOHC bikes in developing countries. Long story short, I think it really comes down to camshaft configuration. Someone chime in if you can say otherwise, but I think the majority of SOHC motors contain rocker arms and DOHC have the shim-and-bucket design. The reasoning for cam design/configuration is a whole 'nother can of worms! Hope I cleared some things up for you




Kyle
 

·
Registered
Joined
·
2,665 Posts
There are less moving parts with the shim design so they typically require adjustment less often, fewer wear points. Fewer parts mean less weight in the valve train and higher rpm capabilities over a rocker arm valve train.
 

·
Registered
Joined
·
2,516 Posts
Discussion Starter #4
Definetly demographic has a roll.The folks who decide to pay (or will tolerate the extra payment & hassel of replacement) more money for shim's the better for the company. Plus the seat height for the folks in the developing countries is probably a bit too high,another bummer.Oh well,I'm glad I have valve adjustments that are not as hassel prone as shim and bucket types!....hoooray for TW & XT!.
 
1 - 4 of 4 Posts
Top