Higher ratio rocker arms

[poolboy]

My thoughts on what was happening due to the combination was that the cam immediately began working on the bottom of the lifters. The pictures don't show the concave surface that developed when the valves ran out of spring compression. As a result of the stress, one rocker eventually broke and one had a hairline.
Richard Good replaced the broken ones and machined the others to his more recent design that prevented the pushrod from being trapped awkwardly in the rocker arm's socket.
That was what we originally thought caused the rocker to break.
After replacing with the new version, I started hearing that unusual noise.
I drove around for several weeks trying to either figure it out or hope it would just go ahead and break..while I was close to home.
The noise it turned out was the disintegrating lifters.
Everything in the crankcase needed replacement except the pistons themselves.
I now have 1300+ miles on the new engine and so far so good.
I kept the RR's but with a new post 72 stock cam and it runs very well with lots of torque, as much as I need for passing and coming out of curves.

 

[SkinnedKnuckles]

The pictures don't show the concave surface that developed when the valves ran out of spring compression.

Thanks for sharing the details. Ugh - a mess. So the bottom line was spring bind? I had some wrong advise on springs upon my rebuild and had a couple of broken inner ones after a few days. Got all that squared away, but now I'm itching to measure the cam lift to be sure all the lobes are OK. We'll see.

 

[poolboy]

Yeah Brent, that seems to be the bottom line. I've been reluctant to post all this for fear of worrying some folks who have similar set ups. I was torn, but then I thought maybe they should give it some thought. I know TR6BILL thought he had everyhing right when he built that engine and I know he had consulted some knowledgeable TR people and use reputable suppliers.And afterall it ran just fine some 20k miles until the day I tore it down.
What else can you do ?

 

[Hap Waldrop]

Forgive me for the long post, but this is complicated subject.

I didn't read thru all this, so forgive me if any of this has already been mentioned. Alot of the time when you hear guys talk about just buying roller rocker arms, by themselves like from suppliers like Harland Sharp or less than knowledgable Ebay sellers alot is left to be done than one would think, HS is not a brand I think very highly of, and 90% of guys will apt for higher ratio rocker arms, not realizing much more has to be done than just intalling the higher ratio rocker arms by temseves. First off if the ratio changes, so should the pivot point in the pedestal, otherwise everthing is moved over center on the valve side, and pull the pushrod towards the center of the engine, needless to say this askews geomentry and kill the extra lift you bought the rocker arm for in the first place. IMHO, you should never buy a higher ratio rocker arm set up that does not come with the pedestal relfecting that ratio change, Titan is great company that supplies pedestal with it higher lift rocker arms, there are some guys out there offering HS roller rocker arms with custom pedestals. Sometimes a very samll increase in ratio, like a half point can be pulled off on stock pedestals, but you are still askewing the goemenrty and losing the lift you are aiming for.

Ok, with being said lets move on the the next issues with alternate and higher ratio raocker arms. Most aftermarket roller rocker set assemblies even the better ones like Titan are designed around stock shaft center line, but almost always this does not work out for the lift gains you are looking for because of the physcial demensions of the aluminum roller rocker arm to begin with, when folks take the time to check theoretcial valve lift, (cam lift x rocker ratio - valve lash = theoretical valve lift) they find they are way short of where they thought they would be valve lift wise, this invloves two different things, one being the shaft center line, the other being most of the time when a guy is using something like high ratio roller rocker arms, he also is uing a higher lift cam as well. OK, to correct the shaft center line issue is fairly easy, you need to shim the rocker arm pedestals, I wrote a post on this in the racing forum here with pictures, about a MG Midget 1275 (actually 1380cc) hot rod street engine I helped a buddy build, by adding 1/8" of shim under the pedestal we were able to gain .030" of our lost lift back and correct the rocker arm geomentry as for the angle of the rcoker arm at full closed position, we probably could hve even got more lift back with longer custom pushords, but my buddy was happy with the gains we made. The second issue is higher lift cams, as we use a higher lift cams we are asking the rocker arm to depress the valve more than normal and due to arcing motion of the design of pushrod rocker arm engine the further down the arc the rocker move, this lessen the rocker arm ratio, this cannot be overcome, it's a design shortcoming of our enignes, so one will never reach theoretcial lift with a given engine of this type, however gains can still be had.

Sean Brown at Flowtech wrote a great article on his website (www.flowspeed.com) about using pedestal shims to raise the shaft center line of roller rocker arm assemlby to get back lost valve lift, while his work was on MG engine, all this applies to Triumph engines as well.


Putting roller rocker arms on engine is alot more work than most would think, I can easily spend 8-10 hours on race or street performance engine setting up a rolle rocker arms assembly, and dong everything that is required to optimize them, and if one is not willing to do this, I would pass on them.

Hope this helps.

 

[Hap Waldrop]

Poolboy, after looking back at few threads, I saw your picture and yes one should always check for vlave spring coil bind, but I think I know what broke your rocker arm, and while coil bind may have contributed to this, the extra machining someone did to the rockewr arms left sharp 90 degree angles and created stress risers. I know this one too well myself, on the MG race engines we used to use larger diameter race valve spring and had to clearence the underside of the roller rocker arms to give clearnece betwen the larger diameter retainer and valve springs. The first set I did I left a sharp 90 degree angle on them like the ones you have pictured, and at Daytona while racing at about 8500 rpm that when the rocker arm decided to give up, broke right where I had the sharp angle, later I always modify the rocker arms to have a large radius in this area and never had the same failure again.

 

[poolboy]

Yes, Hap, the rockers are from Richard Good and were his initial design.
When I contacted Richard, he told me that he has since changed the design and increased the radius on all the rockers he now sells.
He replaced and/or modified my entire assembly; I also bought his pedestals at that time for replacement.
At first I thought that was the sole problem and once I replaced all the rockers with the latest design, my problems would be over.
Unfortunately that was not the case, instead of being the actual culprit, the rockers were just one of the victims

 

[TonyPanchot]

What is the conclusion on the GP RR set up and using his pedestals

 

[TonyPanchot]

What is the conclusion on the GP RR set up and using his pedestals

 

[poolboy]

If that was directed to me, Tony, I'm going to refrrain from making any recommendations based solely on the fact that I don't know nearly enough to do so.
I'm using them, but the whole combination of cam, valve springs, rocker ratio, pushrod length, and the head thickness are factors determining what works and what doesn't.

 

[TonyPanchot]

Thanks PB, I went with the Sharp set and hardened shaft with solid spacers
unitizing stock peds, after all of the links I have read I am rethinking
the stock ped and wondering if I should order GP's ped