Looks like it is time to replace the valve seals and maybe the guides on the 427/425. Anyone have recommendations on 1) a particular vendor 2) style/type/process etc for the valve gudes. I am getting smoke at startup out of both sides after the car has been sitting at temperature about 1.5 hours. No smoke on cold startup or between shifts or going down the road. I have had the car about 10 years. Motor has 4500 miles since rebuild. Had usual temp problems early on. It gets driven maybe 400 miles per year. Thanks in advance for the help.
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Re: C2 427/425 Valve Seals and Guides
Assuming you're doing a requisite annual oil change it's tough to get a handle on oil consumption with only 400 miles per year, but try to get and accurate figure.
A little smoke on startup could just be deposits in the exhaust system. I don't think it's worth going into the engine unless the consumption is less than 1500 miles per quart and even that is not "unacceptable" for a SHP engine.
Duke -
DO NOT replace the guides
instead sleeve them if needed because the orignal guides were bored after being installed in the heads and the bore sometimes is not concentric with the O.D. and will cause all kinds of problems with where the valve seat in the head will end upComment
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Re: C2 427/425 Valve Seals and Guides
Duke -- it is a lot of smoke out of both exhausts. Oil consumption is way more than it should be at times. It is not consistant. Sometimes it burns a qt in 100 miles. I always do an annual oil change. My theory is that I have had the car for 10 years and the seals have become brittle or cracked over time.Comment
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Re: DO NOT replace the guides
Clem -- sleeving sounds good. Do you recommend brass, spiral --- or what ???Comment
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Re: DO NOT replace the guides
The engine has stainless valvesComment
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Re: DO NOT replace the guides
i always used cast iron sleeves for steet engines as it absorbs the lube better for longer life.Comment
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PS pre lube the guides
i always used moly disufide,camshaft break in lube, as lube inside the guide and on the valve stem on fresh head work to make sure this area get good lubrication on startup till the oil gets flowing.Comment
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Re: C2 427/425 Valve Seals and Guides-John
john, I brlieve time well spent it you use a vacuum gun (Mity Vac) and devise some suction cup "thingy" about the diameter of the valve spring retainer. With your "made up tool" see if you can pull a vacuum on the valve spring retainer. If not (and I suspect Not) this will mean the little rubber ring on the valve stem is broken and allowing oil past to the valve head. Replace the little rubber rings and your oil mileage should improve vastly! Regards,Comment
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to replace the rubber "O" ring
you must collapse the spring and retainer below the "O" ring groove before installing the "O" ring and then let the retainer come up over the "O" ring while you install the keys. if you put on the "O" ring and then push down on the retainer you will ruin the "O" ringComment
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bronze....vs...iron
Clem...do you agree with the notion that thickwall bronze inserts which run at tighter stem/guide clearance help in valve heat transfer. If one is not going the hardened valve set route, wouldnt it be advisable to go bronze to minimize valve temps due to the higher heat transfer characteristics of the bronze guides to in effect lessen the chances of seat recession? This arguement is presented by David Vizard in his "Rebuild SBC" book. I realize cast and bronze each have there advantages, but given durability issues of BOTH the guides and valve seats on these vintage motors, is one choice or the other a clear choice?
Thanks....Comment
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Re: bronze....vs...iron
i do not think heat caused seat recession is a problem on a street driven car. race engines i use bronze wall but i never used them on a street engine because they require a positive type valve stem seal which i do not like on the street,JMHO. remember exhaust valve stems taper about .001 smaller at the head end,to allow for heat expansion, so when you check your clearance mic the top of the valve stem to set your clearance. remember loose valve stem clearance a little oil burning too tight a valve stem clearance,valve sticks in the guide and here comes engine damageComment
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Re: C2 427/425 Valve Seals and Guides
John, Big block exhaust guides go thru the water jackets, so make sure the holes the new guides are pressed into are clear and round without any pitting. Leaks of water into the exhaust is a very common problem with them old blocks. GM makes a special sealant if the problem is discovered.Comment
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this is another reason not to replace the guides
but to just sleeve themComment
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Re: this is another reason not to replace the guid
Clem,
How do you feel about new valves with slightly over size stems? I don't know the cost of new valves today but it can't be that much more than all of the machine work involved in replacing guides and it certainly isn't as scary. If I remember correctly, TRW serviced most valves in .003 and .013 oversize (?) so the additional mass isn't really an issue, especially for street applications. I would rather replace valves and ream the guides to the new size than chance replacing guides in a big block, although I've successfully replaced several sets in the past. Just curious....Comment
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