FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: PaulProe on May 27, 2022, 04:56:47 PM
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I have a Shelby alum block w/ TrickFlow heads in a cobra replica. Valve train uses PRW Stainless Rocker system. All has been well for 650 miles till one cylinder decided not to play
This seems to be a common occurrence with the PRW system. My builder said he'd had excellent results with them so I followed his advice. He, unfortunately, passed away during the pandemic so this fix is going to be on me.
Couple questions
1) any confidence that I could just replace the broken arm and all would be well? The car is not driven that hard, the spring pressure isn't that high, nor is the lift.
2) any guys who have experienced this, did you replace or repair? Anyone have a system their not using that I could by a few rockers?
Suggestions?
Paul
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You probably don't want to hear this, but I would just replace them all. I think it will happen again.
Back when I first started my business, this was one of the lines that I carried. I got a lot of complaints from rockers breaking. I dropped the line.
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I got a call from another forum member who is not usually online. He saw your post and mentioned that he'd had a PRW rocker that broke, and also an adjuster. He said a call to PRW got him a replacement part in just a few days, all he had to do was send them a picture of the broken part. In his experience they were really good to deal with, and he didn't mention any further problems. Might be worth a call to them to see if they would just send you a new one...
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Jay and Brent,
Thanks for your comments and ideas. I had already sent a post and pictures to PRW, explaining the issue and asking for their input and support.
I guess the two alternatives is to fix the broken one and hope (0-$100, depending on PRW), or replace the system which looks like $1000 rough. Makes for a very difficult decision. Wish the two options were a little closer, financially
Fortunately, the break was clean and it doesn't look like any loose pieces went into the engine. Just wish I had some confidence that there aren't 15 more waiting to do the same thing. I see multiple posts of similar failures and same results. Some replaced just the one and were fine, others replaced the system.
Thanks, going out to look for my crystal ball
Paul
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If it's a mild cam to begin with, as you stated, what confidence do you have that it won't happen again? I would replace them with something better, even if it's stock stuff, which never break. Next time it may hang open a valve, and that could ruin your day.
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Theoretical question for those with more experience than me… How often do rockers break this early on a tame cam without an underlying cause?
Probably want to look for a cause and verify there’s no further damage. Check for damaged pushrods, lifters etc. Definitely check both push rods and lifters in the affected cylinder but check rest of them as well. Make sure the affected valve is at the right height (I.e not bent and hanging open). Look for signs the push rods are rubbing the intake tunnels, I don’t think you have to run it hard to break stuff if things aren’t right.
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Seems to come up weekly across forums and Facebook. It'll break again. You have some money in that engine, I'd put a better set and press on. What if something bound up and popped a keeper or pieces when through an aftermarket oil pimp pickup? It will sting only once to do it right.
Hang them on the wall, or see if you can replace rockers only with a name brand. I haven't see a set up close to know rocker width and shaft size, but failures almost always are a split at the bottom of the rocker or an adjuster failing, so I'd likely gamble on reusing the shaft if it was a standard size
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There appears to be not much "beef" in the area that broke. Contact Doug at Precision Oil Pumps about a set of his roller rockers. Looks like your spacers etc are fine. With 16 new rockers and your existing hardware, it would really be a small price to pay for peace of mind. He is a vendor here and a stand up guy.
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Appears to be a nicengine with some good, top quality parts. Do yourself a favor, and get those Chinese bargain basement rockers off of there, before they cause serious damage. Those rockers are notorious for breaking, your engine deserves better rockers.
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I believe the PRW aluminum ones are better than the stainless. That being said I would not use PRW rockers on a lawnmower engine.
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I pulled the PRW rockers out before they gave trouble. Replaced the rockers & shafts with Harland Sharp parts and used the PRW stands and shims (they do have shaft end supports). You may need to re shim your rocker stands to acquire correct rocker geometry. This is cost effective.
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Thanks for the support, guys, I really appreciate it.
Can anyone tell me more about re-using my existing hardware with new "other brand" rockers? Any experience with re-using the shaft? Harland Sharp vs T&D vs Precision Oil Pumps - is one preferred over the others? Does only one work with existing PRW stands?
Hoping to learn from everyone's experience
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Can't go wrong with any of those three, including the one ones from lykins motor sports
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One last question for the experienced:
The shafts are .840" dia., the same as the HSharp bushed shafts.
So I can use the PRW stands if I choose to use new Harland Sharp rockers and shafts?
The shafts appear to be OK but there is some bushing wear indicated in just 600 miles/21 hrs run time. If I'm going this far, $300 for new shafts might be cheap insurance. I'd also feel a little more comfortable with the sizing between Sharp shafts and Sharp Rockers.
The geometry was pretty good on the last set - if I keep the stands and just change shafts and rockers, what is the probability of the geometry being off. I don't know if the profile of the two brands of rockers is significantly different or not.
Thoughts and Thanks. My local engine builder passed away last winter and I don't have anyone local to bounce these things off of.
Paul
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PRW stands will fit Harland Sharp rockers and shafts. I believe that I removed a small amount of shim under the stands because the rockers have slightly different architecture. Every setup is different so you must check. If you are able, install two ten lb. springs install two rockers and roll the engine through the valve event to check geometry. Something that I forgot to mention is you may need to change to a shorter pushrod length (as I did). Also you don't want the adjusters in the rockers to extend more than a few threads. Just go step by step.
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The shafts appear to be OK but there is some bushing wear indicated in just 600 miles/21 hrs run time. If I'm going this far, $300 for new shafts might be cheap insurance. I'd also feel a little more comfortable with the sizing between Sharp shafts and Sharp Rockers.
I can't comment on geometry because I've never used PRW, and never will, but bushing wear does not mean the shafts are bad. Check them out. Some light scuffing or signs of use on the shafts really won't matter, as long as there's no heavy scoring or "lip" where the rocker was riding. The bushing is the wear item here. But if they are PRW shafts, and there is signs of scoring, it could be cheap material used in the shafts, or too tight of a clearance, not allowing oil to flow between them.
Buying Harland Sharp shafts does not automatically mean the shafts are the perfect size for their rockers. In a perfect world, things go together perfectly. We don't live in that world though. The last 2 sets of HS shafts and rockers I used were too tight, and would have wiped out the bushings in short order by not allowing enough oil to lubricate. They must be checked for size. I ended up having to use a brake hone on the rocker bushings to open them up about .001. From the factory, they had to be twisted on the shafts and had resistance to turning. Way too tight! Never take anything for granted.
I know it sounds like a lot of work, and I suppose it is (more time than actual work), but they need to be right. Too loose and you'll lose oil pressure and flood the heads. Too tight and they won't lubricate well and will eat the bushings and shafts up, if not completely seize on the shafts and start bending pushrods.
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same here, I had to hone my H.S, rockers with a two stone brake hone quite a bit.
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As expected, PRW is blaming the builder - not their fault. How come I knew this was coming. Saying the pushrod was too long and hit the rocker and the spring pressure is probably too high.
- no witness marks on the pushrod or cup
- no witness marks on the body of the lifters
- spring pressure at full open is 365lbs, there spec says 375+ is OK
Can anyone comment on the travel path on the end of the valve stems. The rocker failed on the intake side (left in the picture). In my mind, the travel path/geometry looks pretty close but I defer to the experts.
Thanks
Paul
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The one on the left looks fine but the one on the right unless it’s just a weird picture it looks like the rocker need to move over to the right. But to answer your question the geometry seems right.
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"use a brake hone on the rocker bushings to open them up about .001."
Just a note: Best to limit the use of a common "brake-hone" to de-glazing and just general clean-up operations; though good results are possible with exceptional technique, generally if attempting to remove any significant sum of material (and .001" is significant :o ) it will prove challenging to keep the hole round and without taper or hourglassing in it's length. :-\
Preferably, take the rocker arms (with the shafts ;) ) to a machine shop, preferably one with availability of a 'pin-hone' machine to execute the job properly and should be holding the tolerance to within tenths of thousandths of an inch; and just specify the clearance value desired. 8)
I wish that these rocker clearances were always delivered "tight", that way the engine builder could have the option of setting the desired clearance, that rather than the all to often excessive sum as is often the case; so feel fortunate if yours show up out of the box tight and take advantage of the opportunity to make for something closer to ideal. :)
Scott.