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| Holy Valve Recession Batman...... https://www.slantsix.org/forum/viewtopic.php?t=17340 |
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| Author: | emsvitil [ Sun Apr 30, 2006 5:47 pm ] |
| Post subject: | Holy Valve Recession Batman...... |
Well I didn't want to believe that the rough idle I've been trying to solve was due to an valve adjustment because I adjusted the valves 1600 miles (1608 to be exact) ago..... BTW: there's only 17616 miles on the engine and car The intakes were fine, .001 tighter (one was .000) than the last adjustment which could just be I was on the tight side last time, and this time I was on the looser side of spec. The exhausts however have changed..... The best exhaust valve was .005 tighter, the average was .008 tighter, and the worst valve (#6) was .012 tighter than last time. #6 is incidentally the valve that was quite a bit tight last time too. The adjusters are nice and snug and I can't see how they would change adjustment, so it seems that my exhaust valves are actually receding (especially #6). 1. So how lose can I safely have the exhaust lash? (sort of let it wear thru, but I want to make sure I'm on the takeup-ramp of the cam lobe) 2. Found references to CD2 lead substitute, will it help or slow the recession down? BTW2: found a reference on the internet of a car having a valve recession rate of 1.5mm / 12000km (think it was a MG), which is equivalent to .0118"/1500miles which is right in line with my #6 valve. BTW3: idle is good again.. |
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| Author: | sandy in BC [ Sun Apr 30, 2006 7:37 pm ] |
| Post subject: | |
Sounds like you need to adjust valves fairly frequently and think about a big valve head.... Lead substitute= bad |
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| Author: | REDNECKMOBILE [ Mon May 01, 2006 7:57 am ] |
| Post subject: | |
The valves may be getting too much heat as in the motor is running lean, I'd check the plugs and if they are white I would jet up until I got a tan insulator. |
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| Author: | MitchB [ Mon May 01, 2006 8:44 am ] |
| Post subject: | |
Valve recession is basically terminal. I experienced recession with the same symptoms - diminishing exhaust valve lash. At this point, the seats on the affected valves have sunk into the head and in all likelihood will not provide a good seal for long. Have you done a compression check? #1 exhaust seat on my head showed a very small area of blowby. Yet, the this cylinder showed 110 compression. The telltale sign was the lash. The question is: what is the underlying cause for this? In my case, I ran the engine a little too lean with too much spark. Mitch |
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| Author: | emsvitil [ Mon May 01, 2006 1:44 pm ] |
| Post subject: | |
Not lean, if anything slightly rich. Haven't recently checked the compression, but when I did about 5000 miles ago all of them were within 5PSI. (don't remember the number though) |
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| Author: | Slant6Ram [ Tue May 02, 2006 5:57 am ] |
| Post subject: | Replace the burnt valve |
Take it apart and have the valves machined. I did this on my truck and have liked the improvement. If you have ever seen a burnt valve, it looks a lot like a rotary file. This rough surface grinds slowly at the valve seat. I bet on such a low mileage motor, that the #6 exhaust valve stayed open for a long time and got rust due to moisture, this will cause similiar decay as burnt valves. A vacuum leak or blown vacuum acessoryon attached to #6 vacuum tree will create a lean condition and cause burnt valves as well. I think I paid a couple bucks a valve to have them all refaced and then lapped them in with some compound. You may find that only a few of the valves need machined if you are doing just a spot fix. The valves that look really white are burnt. That should slow the progression down a good bit. This is a good bit of work, but low buck fix. |
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| Author: | emsvitil [ Tue May 02, 2006 2:23 pm ] |
| Post subject: | |
There's nothing on the #6 runner. Valve adjustment did the trick for smoothing the idle. When I got the car (was grandparents) it had 12200 miles on it, and had not moved for 11 years. So the #6 exhaust valve could have been open. I did find a reference that the more valve rotation there is, the more valve recession you can get, so #6 maybe rotating more too. It seemed fine until 16000 miles (the first time I noticed the #6 valve being tight). From that, I'd quess the valve recession started after 14000 miles as that's when I finally got rid of the old bias-ply tires, and started driving on the highway, rather than putting around locally. Any residual lead wore away, then it started receding. I'm not in a position to tear the head off at the moment, thus the lead substitute. Just want to slow it down until I can tear the head off. |
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| Author: | REDNECKMOBILE [ Wed May 03, 2006 1:29 pm ] |
| Post subject: | |
Quote: There's nothing on the #6 runner.
Drive the car just like it is and see how long it goes before another five thousandth grows in the lash. My bet is the motor will normalize to a pattern that you can live with hopefully until you can get a set of hard seats.
Valve adjustment did the trick for smoothing the idle. When I got the car (was grandparents) it had 12200 miles on it, and had not moved for 11 years. So the #6 exhaust valve could have been open. I did find a reference that the more valve rotation there is, the more valve recession you can get, so #6 maybe rotating more too. It seemed fine until 16000 miles (the first time I noticed the #6 valve being tight). From that, I'd quess the valve recession started after 14000 miles as that's when I finally got rid of the old bias-ply tires, and started driving on the highway, rather than putting around locally. Any residual lead wore away, then it started receding. I'm not in a position to tear the head off at the moment, thus the lead substitute. Just want to slow it down until I can tear the head off. |
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