454 with Edelbrock top end kit, p/v clearance problems? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 08-17-2011, 04:43 PM
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454 with Edelbrock top end kit, p/v clearance problems?

Hello all,

Although I've been following hotrodders.com for years, this is actually my first post here. I'm from Turkey and we're currently rebuilding a 454 (Mark IV) for a friend of mine.

I've been into some SBC work before but I'm not experienced with Big Blocks at all. My friend ordered a BBC top end kit from Edelbrock (#2095) that has RPM oval port heads included and an RPM cam (#7162) that has .560" / .573" lift at valves.

The pistons we have are H426CP's from Sealed Power, kind of small dome around .100 and the block is not decked. With these pistons, standard deck height, .038 compressed gasket thickness and 110 cc combustion chambers, we would be around 9:1 compression and that sounded reasonable for a street engine running on crappy european gas. The octane figures are high over here, advertised as 95 and 97 octanes, but god knows what they would turn up when analyzed within US standards. And for any of you guys complaining about your gas prices being high, we are paying $2.50 per liter here, that makes $9.45 per gallon! Probably the highest price anywhere on the planet

Anyway, We had checked the piston to valve clearance before assembly and found approximately .080 clearance on the intake and .160 on the exhaust valves, without the head gasket. I can't remember for 100% sure because we're never doing our homework right and not taking any notes.

Well that's what brought us here. After adjusting the first set of valves with no.1 piston at TDC, per Edelbrock's instructions, we went on with turning the engine over one full revolution and we would adjust the next set of valves. (Although I prefer to adjust each cylinder individually, this method involves a lot less turning of the crankshaft and feels like it's better not to scrape off the prelube from the cam lobes too much).

Just as we approached the complete turn we felt a resistance and stopped immediately. I felt like it could be the valves getting into contact with the pistons because I've seen that once before and I know what it could do. But we thought we had enough clearance even without the gasket? what else could that be?

We were too scared to carry on and pass that resistance because all the parts are very expensive here, roughly about 2 times the cost in US. Then I went to thinking, are the pistons right for our setup to begin with? I know there are piston differences from open to closed chamber heads, and Edelbrock calls their RPM heads "semi-open" chambers. I don't have an idea if our pistons are for open or closed chambers. They're H426CP's, I'll try to attach a generic pic of these pistons.

I'll remove the heads and check for any contact marks on the piston tops tomorrow. I hope that wouldn't ruin the already compressed head gaskets. In the meantime any thoughts are most welcome. Thanks to anyone taking the time to read all of this, and a big hello from Turkey
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Old 08-17-2011, 05:17 PM
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On BBC's all builds that use non factory stock parts combos or juggled parts combos like oval port heads and TRW/speedpro domed pistons must check piston to chamber clearance. (the piston is hitting the head Valve to piston relief radial clearance should be verified too.

(Piston valve relief location and size)
All valve train motion clearances must be checked. Set the valve using the ICEO method for each cylinder.

Where on the degree wheel did the crank stop? near TDC is Valve to piston and or piston hitting the head. can be both.

near full lift is valvetrain or spring bind.
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Old 08-17-2011, 08:57 PM
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Piston dome is probably hitting the head. I have had problems with the these Edelbrock heads before. They are basic designed for a flat top piston. The chamber won't fit many of the available popular domed BBC pistons. Hits at edges and spark plug area..
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Old 08-18-2011, 08:28 AM
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Solved

Thanks for the replies. I removed one of the heads today. Fortunately the gasket was intact. I checked for any contact marks on the pistons and the heads, it was all clear. I removed all the pushrods and rockers from the other head and turn the engine over a couple of times with a single head on. Everything was smooth. So I went on without installing the other head and adjusted each cylinder's lifters one by one.

After adjusting only the first cylinder, I turned the engine over again. It didn't stop anywhere, it was free to turn but just a little bit resistance when the cam lobes came in. I checked the location of the piston and it was way down in the bore when the resistance appeared. So I had a relief it was not about the piston clearance.

Moved on to the next one, and a bit more resistance added when on the lobes. And it went that on that way, getting harder to turn but not stopping. I installed the other head and adjusted the valves on that one also, one by one.

So, finally it is all adjusted and the engine is hard to turn over but now I believe it's just the cam lobes are steep and I was a chicken to push it a little harder the first time Well, considering we have to pay $5000 for the top end kit in my country, can you blame me?

I'll start a new thread about this engine's specs and see what you guys think about it.
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