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Rocker arm strength? 

 

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 Post subject: Rocker arm strength?
Posted: Mon Apr 13, 2009 2:09 pm 
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After all my drama of getting my noisy lifters sorted once and for all, I had the motor idling 10mins whilst adjusting the timing and then heard a very unusual noise in which made the motor stall. I decided to remove the rocker cover to have a look and discovered that no:6 exhaust rocker arm had broken at the lifter, upon further inspection no:6 exhaust valve is now bent and holding about half open, and you can guess the reaction.
Does anyone know how strong these rocker arms actually are? and why would it break if only at idle, cause we heard about "Green Machine's" rocker arm drama from high revs. or could my problem be too of hard valve springs?
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 Post subject: Re: Rocker arm strength?
Posted: Mon Apr 13, 2009 2:29 pm 
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I have seen the rockers break before, but it was caused by the cam bolt snapping off, or a cam chain breaking.
Have you checked your cam timing????, maybe a piston has given the valve a whack???

 

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 Post subject: Re: Rocker arm strength?
Posted: Mon Apr 13, 2009 3:15 pm 
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the other reason it could break around the rocker tip is if the HLA wasnt fitted back in the tip correctly... they can jam slightly which would apply uneven pressure to the rocker tip causing breakage. i wouldnt have expected this to bend a valve tho..



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 Post subject: Re: Rocker arm strength?
Posted: Mon Apr 13, 2009 3:56 pm 
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or not enough hla lash clearence/too much pre load...
hp is this your ported head with the stg 3 cam?
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 Post subject: Re: Rocker arm strength?
Posted: Tue Apr 14, 2009 10:53 am 
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Troyman, yeah it was the ported head with stg 3 cam
can I re-use the head bolts after they have only be under running conditions for 10mins?, and I hope theres no piston or bore damage, won't find time till weekend to remove head. will post pics up of damage somehow.
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 Post subject: Re: Rocker arm strength?
Posted: Tue Apr 14, 2009 4:08 pm 
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hmm bugger..
maybe the rocker clearence was to tight??
as for the head bolts? i would say that you possably could use them again.
if it was only running for a few mins and the engine didnt really get then ok.
others might have different opinions on it though..
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 Post subject: Re: Rocker arm strength?
Posted: Tue Apr 14, 2009 10:20 pm 
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Mate i would not reccomend useing the head bolts again they are designed to be torqued once. It is not an issue of the engine heat gettiong to them, they stretch when they are torqued, that is how the torgue is measured, so when you try to retorque them the torque is not accurate. I had the exact same thing happen to me :) I put the lash in wrong WOOPS, I reused the head bolts and it kept lifting the head. After an hour dyno session i had a very small pool of coolent under the car. I replaced the bolts the next weekend and problem solved. If you cheap out now and reuse them you will be ripping the head off again in 6 months and doing a head gasket. Be safe and replace them!!!!!!!!!!!!!!!!!!!!! I guarentee you will regret it if you don't!!!!!!!!!!!!!!!!!!!!!!!!!

 

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 Post subject: Re: Rocker arm strength?
Posted: Tue Apr 14, 2009 10:30 pm 
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Yeah but as for the strength, if everything is set up properly they are fine, I have adjustable solid lashes tapped into mine and they have not broken yet. Speedway engines with cams with around the 550 thou of lift and rev limiters at 8000rpm don't brake them. One mate of mine has mentioned that he ran EA - ED rockers in his speedway engines, he says they are stronger????????? But if you are Really worried Billet rockers are available i just can't remember the name of the machine shop that makes them. They are for adjustable solid lashes only (VW lashes) and are $2600 for just the rockers. I guess that is why you never see them in anyones cars :)

 

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 Post subject: Re: Rocker arm strength?
Posted: Wed Apr 15, 2009 2:03 pm 
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yeah $30 for new bolts is better than having to replace them all again later.
I'll get another set of rocker gear from wreckers that havn't had any abuse :| and use them.

The clearance was ok, I used 2 standard shims as recomended from joe.
Hopefully I get back on the road for next weekend.
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 Post subject: Re: Rocker arm strength?
Posted: Wed Apr 15, 2009 2:41 pm 
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Id be just a bit sus that it didnt break because the valve/piston collided?

Slightly bigger timing issues perhaps - are you playing with a vernier cam gear?
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 Post subject: Re: Rocker arm strength?
Posted: Wed Apr 15, 2009 6:40 pm 
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I would be cranking it around a few times using the ballencer bolt to check what Nigel mentioned too! Better safe than sorry again!

 

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 Post subject: Re: Rocker arm strength?
Posted: Sat Apr 18, 2009 11:33 am 
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I do have a vernier gear but its set to zero, joe has yet to dyno run and degree the cam.
Didn't have a problem with clearance before, and I spun the motor over by hand several times and it was all good, and nothing clashed when I was cranking motor with out the plugs in. must have just been a weak rocker arm.
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 Post subject: Re: Rocker arm strength?
Posted: Sat Apr 18, 2009 1:48 pm 
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xr6eat 50 wrote:
I have adjustable solid lashes tapped into mine and they have not broken yet. One mate of mine has mentioned that he ran EA - ED rockers in his speedway engines, he says they are stronger????????? But if you are Really worried Billet rockers are available i just can't remember the name of the machine shop that makes them. They are for adjustable solid lashes only (VW lashes) and are $2600 for just the rockers. I guess that is why you never see them in anyones cars :)


interested in how u went about the solid setup...

would u have any pics of it?

 

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 Post subject: Re: Rocker arm strength?
Posted: Sat Apr 18, 2009 2:00 pm 
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got pics, got to post them up soon
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 Post subject: Re: Rocker arm strength?
Posted: Sat Apr 18, 2009 7:38 pm 
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sorry no pics, but i can tell you how to do it. You need to use VW ball foot lash adjusters out of the Beetle motor. I used Skat ones. BUT you do need to run a solid cam solid lash setup will chew up a hydraulic cam..

Basicly all you need to do is drill and tap the old oil hole in the top of the rocker arm with the 8mm thread and also make a threaded bushing to go into the rocker arm where the lash used to fit, due to the old hydraulic lash being 12mm and the solid being 8mm. The only difficult part of it is the arms are tool steel so you wonlt be doing this with a drill at home it will need to be done by a machine shop. Thanks Tighe! Solid lashes do need to be set and reset alot with feeler gauges though. I only went that way because the cam i have coming is custom and has some crazy numbers associated with it, i got sick of replacing ticking lashes and it is a more posative valve train using solid items.No lash slop.

 

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