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BUSY BOLTERS Are you one?  The Shop Area
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Jul 21st, 2025 | | | | Joined: Dec 2011 Posts: 241 'Bolter | | 'Bolter Joined: Dec 2011 Posts: 241 | I'm looking for a set of new exhaust valves for my 52 9430 GMC. The valves in it have a depression on the bottom where the set I see on Ebay are flat bottom. They are Thompson S1867. Does anyone know if the depression matters? Possible compression difference?
Mark
Last edited by 52_Ton; 08/28/2014 12:51 AM.
| | | | | Joined: Feb 2014 Posts: 215 Shop Shark | | Shop Shark Joined: Feb 2014 Posts: 215 | The cupped head designs used the combustion pressure to assist in the sealing of the valve at the seat face by flexing to fit the seat angle. They also weighed less. Most valves today are flat head. Either design will work fine when installed properly. | | | | | Joined: Dec 2011 Posts: 241 'Bolter | | 'Bolter Joined: Dec 2011 Posts: 241 | Would you recommend trying to find the cupped face then if possible? | | | | | Joined: Feb 2014 Posts: 215 Shop Shark | | Shop Shark Joined: Feb 2014 Posts: 215 | I guess I personally would look. If they aren't readily available, don't worry about it. | | | | | Joined: Jun 2010 Posts: 1,001 Shop Shark | | Shop Shark Joined: Jun 2010 Posts: 1,001 | ...and, anything that increases compression, if only a little, is a good thing. But, I fear the depression in the valve (either there or not) will make such a small impact that it would not be noticed. | | | | | Joined: Mar 2002 Posts: 9,112 'Bolter | | 'Bolter Joined: Mar 2002 Posts: 9,112 | I don't know where you are but the people at Perry Automotive can source those for you. | | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | Not sure about the 216, but the 235 exhaust valve is identical to a small block Chevy V8. Those things are about a nickel a dozen on Ebay.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Dec 2011 Posts: 241 'Bolter | | 'Bolter Joined: Dec 2011 Posts: 241 | Does the 235 valves have the depression in them? | | | | | Joined: Dec 2011 Posts: 241 'Bolter | | 'Bolter Joined: Dec 2011 Posts: 241 | I don't know where you are but the people at Perry Automotive can source those for you. Is that a local place to you? I'm close to London. | | | | | Joined: Mar 2002 Posts: 9,112 'Bolter | | 'Bolter Joined: Mar 2002 Posts: 9,112 | It is in Orillia. I think CarQuest has a big machine shop in London. I think London has a substantial number of automotive support industries. | | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | Looking for cupped-head valves is nitpicking to the max. They're completely interchangeable, and with the very low compression ratio these engines have, a tablespoon or two of carbon buildup difference between cylinders will have more influence on compression pressure than the valve shape.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Dec 2011 Posts: 241 'Bolter | | 'Bolter Joined: Dec 2011 Posts: 241 | There is lots of auto supply facilities its just hard to find anyone willing to pull the old reference material out to look when its not on their computer | | | | | Joined: Dec 2011 Posts: 241 'Bolter | | 'Bolter Joined: Dec 2011 Posts: 241 | Thanks Jerry, I didn't think it would matter much but wanted to be sure,
Mark | | |
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