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Location:
Brisbane
Registered:
October 2002
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a nice bit of info for u 18RG-o-philes
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Fri, 07 May 2004 12:15
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as alot of u know i have an 18RGU in my corona, i have been having problems with it of late backfiring thru the carbs. I thought to myself, hmmm, better check the valve clearances.
all should be between 0.24 and 0.34
I1: less than .03mm
I2: less than .03mm
I3: less than .03mm
I4: .10mm
all exhaust are fine still
Now, what does all that mean, that means i have very bad VSR {valve seat recession}, that means my valves are being driven back into the head. It has taken 17 months to get this bad.
"Traditionally" its the exhaust seat that gets VSR, because they run hotter.
The reason it happens on the intake side is they have a much larger valve {47 or 49mm}, and after a while with the single springs i have {88250 head} it valve floats and flogs the shit out of the head. And since i rev the hell out of it {8000 sometimes  } it happens alot.
I bought a new head a while back off Ben {people100}, it also had this problem, so i recently sent it to my dad to get work done. My father runs a speed shop in townsville {Melvins Automotive}, and he has had a lot of experience with 18RG's, he was working on them when they were only "fresh"  .
He has a mate who used to run one in a sprint car at the speedway, he would flog the other cars in all the qualifyers, but come the finals, the VSR on the intake side had gotten so bad that the car would not run, hence he'd lose.
He would then go home and re-set the clearance, go back a week later and the same thing would happen, he would try hard seats and it'd still do it.
The problem turned out to be the valves, so he got a hold of some Chev stainless steel valves, he'd machine the tops to be the correct length, and cut new collet grooves. NEVER had the problem again.
So i am gonna have this done to my head, and since u have to grind the tops off the valves, we thought we'd get some "base-circle grind" cams and not cut the valves as much so we dont have to make new shims. Money saved.
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Location:
Rocklea qld
Registered:
February 2003
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Re: a nice bit of info for u 18RG-o-philes
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Fri, 07 May 2004 12:20
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Hmmmm im sure ive heard of other people using holden valves in there heads some reason(never new what it was though until now, just though it was for bigger valves or something). Might be something to keep in mind if i decide to keep my motor.
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Location:
Northwestern Sydney
Registered:
August 2002
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Re: a nice bit of info for u 18RG-o-philes
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Sat, 08 May 2004 07:01
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Thank you Very Much... 
I'm going to hit you up on this a little further on. As my 18R has the same issues.
What valve springs are you going to be using?
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Location:
Brisbane
Registered:
October 2002
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Re: a nice bit of info for u 18RG-o-philes
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Sat, 08 May 2004 09:42
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not sure yet, my dad is in adelaide for the ANDRA meeting ATM, so when he gets back i'll ask
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Location:
Adelaide
Registered:
June 2003
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Re: a nice bit of info for u 18RG-o-philes
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Sat, 08 May 2004 13:57
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I find this quite interesting.
We've had some interesting things happen to vclearances in my brother's 18rg heads too, but not this problem.
When a head is rebuilt, it is common to expect the clearances to become smaller by by a couple of hundreths of a mm.
This happened with the 88253 head that we had on first.
After we replaced that head with an 88270 head, the clearances went the other way, they got bigger, and have continued to get bigger since.
These changes in clearance weren't restricted to one side as you found, but were almost uniform across all valves.
every mechanic I've asked about this problem has been stumped as to why the clearances grew on the second head.
We checked the uniformity of the grinding done on the shims and found that none of them were tapered.
About all we could come up with was, as this head appeared to be almost unused (could still see original machining marks where buckets go) that the machining ridges on both the buckets and the shims had receeded.
It is interesting that you've had this trouble using springs that have caused float.
We have "Performance Springs" heavy duty springs and have not had trouble like yours.
Wear and tear info is always good to know, thanks for posting it.
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