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Thread Like Summary
Allan G, gavin eisler, Hillbilly bike, MarksterTT, pushrod tom, Stuart Kirk
Total Likes: 12
Original Post (Thread Starter)
by Tridentman
Tridentman
It is widely stated that the rocker arm should be at right angles to the valve at a point where the valve is at half lift.
Why/
Liked Replies
by Tridentman
Tridentman
Bob--thank you for your input.
I fully recognize that you are talking conventional wisdom in your response.

However as is my wont --- I would like to challenge the conventional wisdom!
The conventional wisdom is correct if (and only if) the force exerted by the valve spring is the same along all of the travel of the valve.
But patently it is not.
The force exerted by the spring is small at the initial movement from the rocker arm and increases as the spring is compressed until it is at a maximum at maximum valve lift.
Assume the angle between the line of the rocker arm and the plane of the top of valve collar is x degrees.
Then the side force on the valve guide at any point of the valve travel is given by (spring force at that point) times sine x.
So the side force is zero when x =0 degree -- which is the conventional wisdom point corresponding to half valve travel.
However as the valve opens beyond the point of half valve travel the side force increases rapidly from the combined effect of the spring force increasing and the angle x increasing thus increasing the value of sine x.

This analysis suggests that the angle x should be zero at the point of maximum valve spring force.--that is---the rocker arm should be at right angles to the valve stem at maximum valve lift. This would arguably minimize valve guide wear.

Perhaps the conventional wisdom is why the valve guide wear on my triples is so great!
1 member likes this
by triton thrasher
triton thrasher
There are many labour-intensive tuning procedures that don’t make your bike go any faster.

Lightened Triumph rockers and replacing Thackeray washers with shims are obvious examples.

Oh let’s not forget drilled camwheels!
1 member likes this
by GeoffLLLL
GeoffLLLL
There is no right or wrong here until you get to the extreme ends of things.

The problem in all the equations and theories is that most tend to contemplate things is a very slow cranking speed, all well and good if that is the speed the engine is going to run at all of the time, run the engine at 7000 rpm and the whole thing turns around on you.

Inertia plays a big part in this issue and as the engine revs are constantly changing so too is the ideal rocker angle.

At higher revs the pressure exerted on the valve tip at full lift is very low compared to what it would be at idle.

I imagine that one might arrive at a very different ideal angle for road use to that used for a racer.

Just some thoughts to give you a bigger head ache.
1 member likes this
by Hillbilly bike
Hillbilly bike
In my opinion rocker weight on a street Triumph is of no importance...My LSR Triumph has untouched rockers with the thrust springs. I did check the stock rocker adjuster sweep on the valve stem, it was fine with the .390 lift cams. I sorta checked the the rocker position at half lift...
This bike has a number of records in it's class.....Using the same lazy tuning technique my street Triumph with all Triumph internal parts surprises Commandos..However carefull assembly anf keeping tolerances in check is important
Sometimes it not what you do, but want you don't do...
'
1 member likes this
by Tridentman
Tridentman
Hi Geoff--thanks for your thoughts and contribution.
However--thick as I am-- I cannot see how engine speed affects the ideal rocker/valve geometry as long as the valve movement is under control---that is-- there is no valve float.
1 member likes this
by Hillbilly bike
Hillbilly bike
All the builders of the fastest/powerful pushrod engines say the weight of the tappet, pushrod and that half of the rocker is not important so long as it's reasonable..What's on the spring side is where weight savings is more important. With this in mind my Triumphs all have steel pushrods that are heavier than aluminum..
1 member likes this
by Andy Higham
Andy Higham
Triumph engines have very short rockers. this makes the angle of swing greater than longer rockers
1 member likes this
by GeoffLLLL
GeoffLLLL
I made a set of guides for my T160 I made them longer at the valve seat end and closed the clearances to just under 0.001" on the inlet and just over 0.001" on the exhaust, I took the head of at 12300 miles and almost no perceptible wear.

I therefore agree with your thinking for longer and tighter.
1 member likes this
by Hillbilly bike
Hillbilly bike
Anything other than a roller tip rocker and shimmed lash cap requires a total head redesign.But is is a great idea, thanks .. Of course roller rockers are custom items with a custom price tag. If you have a well tooled mill and the experience to use it, Like Dave does, why not just carve up a new head with with raised intake ports and revised rockers.Maybe even a more shallow valve angle using smaller valves taking advantages of the latest high velocity port designs...Or use an 8 valve head..
The extra power may require a $2000 billet crank, 180 or 90 degree...It's only money ...
In my opinion what makes Triumphs interesting is their faults, valve wear is just part of the game..Despite it all, they can make reasonable power with reasonable changes and be reliable..
1 member likes this
by MarksterTT
MarksterTT
Dave, no your friend wasn't exaggerating about San Diego's weather, the bay area (San Francisco) isn't too bad either, we'll get some cold rainy days in the winter but no salt on our roads....TR7RVman lives across the bay from me and he seems to be riding most year around. I don't like to get wet anymore so avoid those days but commuters ride year around. 2 seasons in Southern California...warm and a bit warmer.

My first ride on a Triumph was on the back of friends '68 TR6C with R pipes. Met a group of Triumph riders at AMA tour, south rim of the Grand Canyon, I was on a Honda CL77 and the gang said to park the Honda and get on back with my friend. Life changer, beautiful sound and seemingly endless torque that you only really feel when you're a pillion with no handlebars to hang on to. That night I called home and told my folks when I get home I'm getting a Triumph. At $1.35 an hour (4 hours a night after school) it took a while but eventually a used '66 Bonnie was mine. Mark R.
1 member likes this
by triton thrasher
triton thrasher
Originally Posted by tridentt150v
Suffice to say the [more] cross sectional area you place into a flow the more you block that flow.
I don't make the rules.....I just live by them.

Unless there was more than enough cross-sectional area to start with.
1 member likes this
by MarksterTT
MarksterTT
Originally Posted by Hillbilly bike
The later 650 and 750 ports are large enough or any street bike, but they are poorly shaped.....

So true, as 650 valves and ports got bigger the bike got slower...better sized for 750cc. Just read KC's report on Hayabusa engine changes to meet Euro 5 emissions standards and still maintain performance...I think you might be interested in the take on squish (though effective for power) and why it was detrimental to emissions and what they're doing instead (hint; smaller higher velocity intakes for turbulence lost without squish), less cam overlap as Ducati etc,, side mounted injectors splashing squirt off metal plate parallel and midstream to port flow...interesting to see what engineering can do to solve problems.
1 member likes this
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