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10-07-2020, 12:08 PM | #1 |
Senior Member
Join Date: May 2010
Location: Eastern Tennessee
Posts: 11,519
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I think I have found another controversial topic like 'Which Oil to Use'
...and it goes something like this. What is the proper length a replacement one-piece valve guide is supposed to be exposed (protrude) from the valve guide bore?
This should be an easy topic to determine. The replacements one-piece guides are roughly 2-¼ (2.2500") inches in overall length. The original guides have an overall length of 2-⁹⁄₆₄ inches (2.1400"). The original guide has a shelf located approximately 1.3000" from the top of the guide that locates each guide to a uniform height. So where does the ⁷⁄₆₄" difference between the guide lengths go? Should the replacement one-piece guide; ..... ◆ -protrude upward into the port area by the 0.110" potentially impeding airflow yet adding more stability to the valve stem. ..... ◆ -protrude downward into the spring area, ..... ◆ -split the difference making it protrude 0.055" higher than stock, and 0.055" lower than stock. Bonus round question, how much valve seat spring pressure is lost when the 0.1250" thick guide shelf is no longer used? (I think you will be surprised.) . . |
10-07-2020, 12:42 PM | #2 |
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Join Date: Jun 2014
Location: Land of Lincoln
Posts: 3,131
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Re: I think I have found another controversial topic like 'Which Oil to Use'
Or machine the new to look and fit like the old :-)
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10-07-2020, 02:07 PM | #3 | |
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Join Date: May 2010
Location: Fresno, Ca.
Posts: 3,636
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Re: I think I have found another controversial topic like 'Which Oil to Use'
Quote:
Best guess,...it could be as high as 20 pounds..PLUS the spring doesn't seat well ! Also,..I think that the one piece guides should have "liners" installed,...that makes them bomb proof.. djm |
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10-07-2020, 02:22 PM | #4 |
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Join Date: Apr 2018
Location: Mebane NC
Posts: 2,355
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Re: I think I have found another controversial topic like 'Which Oil to Use'
Do we know the measurements on the modern-guide-with-shoulder that some vendors sell?
Ever since Jim Brierley recommended that type I've been anticipating using it for any valve work. Last edited by alexiskai; 10-07-2020 at 02:38 PM. |
10-07-2020, 03:08 PM | #5 | |
Senior Member
Join Date: May 2010
Location: Eastern Tennessee
Posts: 11,519
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Re: I think I have found another controversial topic like 'Which Oil to Use'
Quote:
Hey Dudley, you are in the ballpark for sure. I am not sure about the K-liner approach due to substantial costs and extra labor without much reward. The biggest gain in that area would be if I had a machining center where the hole could be correctly located in reference to tappet bore and seat opening. As a side-note, I do know that the concentricity of many of the new valves are off requiring at least half of the faces to be re-ground before use. I generally see from 0.0020 - 0.0080 in variance straight out of the box. My older SVS2 can generally get around 0.0005 - 0.0007 on them after grinding, so while not perfect, it is a far cry better. As I know you know all too well, it seems a good concentricity seat gauge is about a must to get a good seat seal, and most engine rebuilders likely do not own either gauge nor do they check them. Most people never realize that a portion of the performance in their newly-rebuilt Model-A engine is escaping past poorly bored cylinders and leaky new valves. I would be interested in your opinion but I would guess a 10% loss in performance is likely. Thoughts??? |
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10-08-2020, 09:55 AM | #6 |
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Join Date: May 2010
Location: Fresno, Ca.
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Re: I think I have found another controversial topic like 'Which Oil to Use'
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You know this is a can of worms ! First off is the valves...best first.. 1. One piece valve with hard Chrome stem.. 2. Two piece valve with hard Chrome stem.. 3. Junk valves with NO hard Chrome stems.. That's why I said "liners",...the guide is a "dry" material and the Chrome keeps them from sticking too the guide..."the valve is stuck in the guide"...AND with liners it last forever. All this is for "straight stem" valves and guides.. djm |
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