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Old 07-24-2007, 12:26 AM
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Valve seals.

Just a question on valve seals. I built a friend of mine`s vortec 350 to drop in his 84 cutlass. we used a comp roller cam, and several other goodies.
The heads were camel humps. He drove it for a while and it smoked real lightly on one side. In time it developed a skip that I traced to the number 2 cylinder, I checked the valves and springs, they seemed to be fine. the plug looked okay other than slight oil buildup, but it wasn`t fouled, so I last did a compression check, 80 psi. Come to find out, the exhaust guide, which was bronze, was some how binded, and the valve wasn`t closing all the way. So we pulled the heads and checked all the guides, all were okay but that one, it too alot of effort to get the valve out, when it came out, what looked like stripped threads, pieces of the guide, came with it. So we sold the heads and got a set of RHS vortec heads. We installed them along with a edelbrock performer vortec intake. Since then, the car smokes bad. at idle it`ll be boiling smoke out of both pipes. Compression checks good. so I asked the machinist who assembled the heads what valve seals did he use, he said "I installed seals on the intake side, but none on the exhaust" is this the cause of the problem? we`ve check the intake, it`s not leaking, and the oil seems to be on the top side of the plug, indicating it`s coming from the heads. Is the lack of seals on the exhaust the root of the problem as I`m thinking?
Sorry for the long post, but I like to make sure I didn`t leave anything out.
Thanks.

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Old 07-24-2007, 03:42 AM
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Valve seals.

so I asked the machinist who assembled the heads what valve seals did he use, he said "I installed seals on the intake side, but none on the exhaust" is this the cause of the problem?


As far as I have learned a lot of cylinder head manufacturers do not put valve seals on the exhaust side,this is apparently to help the exhaust valve guides get lots of oil,but this will lead to excessive smoking,so if you want to stop the smoke you will need valve seals on the exhaust valves.Viton seals are the preferred seals to use.I have a set of Brodix Race Rites to go on my big block and they didnt have seals on the exhaust side,but they do now.
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Old 07-24-2007, 06:29 AM
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My long block was built by a long-established shop that only does race and street rod motors. It has seals on the exhaust valves.
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Old 07-24-2007, 09:04 AM
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Yes, I would say it's the root cause.
I always put seals on the exhaust side, on all heads I rebuild.
Use the good umbrella type, The guides may have to be machined to do so.
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Old 07-24-2007, 10:50 AM
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Quote:
Originally Posted by DoubleVision
Just a question on valve seals. I built a friend of mine`s vortec 350 to drop in his 84 cutlass. we used a comp roller cam, and several other goodies.
The heads were camel humps. He drove it for a while and it smoked real lightly on one side. In time it developed a skip that I traced to the number 2 cylinder, I checked the valves and springs, they seemed to be fine. the plug looked okay other than slight oil buildup, but it wasn`t fouled, so I last did a compression check, 80 psi. Come to find out, the exhaust guide, which was bronze, was some how binded, and the valve wasn`t closing all the way. So we pulled the heads and checked all the guides, all were okay but that one, it too alot of effort to get the valve out, when it came out, what looked like stripped threads, pieces of the guide, came with it. So we sold the heads and got a set of RHS vortec heads. We installed them along with a edelbrock performer vortec intake. Since then, the car smokes bad. at idle it`ll be boiling smoke out of both pipes. Compression checks good. so I asked the machinist who assembled the heads what valve seals did he use, he said "I installed seals on the intake side, but none on the exhaust" is this the cause of the problem? we`ve check the intake, it`s not leaking, and the oil seems to be on the top side of the plug, indicating it`s coming from the heads. Is the lack of seals on the exhaust the root of the problem as I`m thinking?
Sorry for the long post, but I like to make sure I didn`t leave anything out.
Thanks.
I wouldn't have thought so but I'm open to surprises. There is a school of thought that since the intake sees vacuum and the exhaust pressure that seals are only required on the intake stems. I always seal up both in and out but there's some that don't.

Since the only change is the heads, I'd look to what are the stem to guide clearances, how much clearance there is between the retainer to the seal and top of guide. How the rocker is riding on the stem tip, and how much clearance exists between it and its mounting stud, pushrod to its guide as well just to make sure you don't have any binding/bending moments hiding in there.

The original failure of the guide insert bothers me, while it could just be a random failure, it might also be the result of one or more of the afore-mentioned clearances being marginal. So while it's apart I'd check it out.

Bogie
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