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nbristow01

Tight exhaust vale issue

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I have had this issue since I rebuilt the motor the first time. I have an IE 284 regrind, over sized eccentrics, stock valves and springs, new (when installed) rockers. About every 6 months my car starts to idle rough. I go to check the valves and sure enough 1 or 2 of the exhaust valves are so tight they are not closing all the way. So I adjust back to .006 or .007 cold. Car runs great until it happens again.

So what the heck is causing this issue? Was it an error buying a reground cam?

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The only ways the valve lash can tighten up is if the adjuster moves, the valve stem gets longer (ie you are streching the valve, and it will soon break) the valve seat is moving in the head because it was not properly installed or the most likely cause is the valve face is not hardened correctly and is distorting. There is the possibility you are running very lean and the exhaust temps are well above 1500 deg, have you looked at your plugs? If there was something wrong with the cam and/or rockers they would wear and the lash would be getting looser NOT tighter.

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The only ways the valve lash can tighten up is if the adjuster moves, the valve stem gets longer (ie you are streching the valve, and it will soon break) the valve seat is moving in the head because it was not properly installed or the most likely cause is the valve face is not hardened correctly and is distorting. There is the possibility you are running very lean and the exhaust temps are well above 1500 deg, have you looked at your plugs? If there was something wrong with the cam and/or rockers they would wear and the lash would be getting looser NOT tighter.

My car runs a hair rich. I thought about it the valves may be stretching a bit. I also thought that if it was a bad cam etc they would get loose. Cams don't usually grow in size LOL.

At any rate I sourced a good e12 head. So just need a 292 cam and new SS valves, guides etc. I just think better safe than sorry with a valve head snapping and grenading the motor

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your valves are not stretching ! if they were prepare to

have one break and destroy the piston/head&cylinder bore!!!

a more likely condition is the valves have been ground too

thin as illustrated below. The edge of the valve is receeding

and your clearance tightens up

14264_96_1.jpg

history lesson:

ages ago the 1st Gen turbo saab 99 had exhaust valve breakage-

the exhaust valve head filled with sodium would snap off the stem

where the two were joined in production - a lot of warranty

head repairs back in 1978/9 period - over reving was a factor

and a bad valve design

M-Benz always had sodium filled exhaust valves but with the sodium

in the stems - never a broken valve because there was no weak link connection between the head and stem

Ate (yes your brake maker) made the mercedes valves = Quality = $$$

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CD. So what is then cure? Buy new valves? The stainless ones are pretty inexpensive. I appreciate your post. That seems to make the most sense yet

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..or there is something wonky with your adjuster ecentrics ?

unfortunately - removal and disassembly and

inspection of the parts might be needed to resolve it

keep driving it, keep checking the adjustments

every 200 mile or sooner if the idle "goes off"

untill it stops changing, or something breaks!

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Is it possible that someone installed soft valve seats? Unleaded fuel requires hard exhaust seats to prevent the valves from sinking into them. This was big problem right after leaded fuel was outlawed.

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I've had similar experiences with "reworked" heads for my 1600. In one case a valve just kept migrating into the valve seat until adjustment was impossible. I have the problem again woth another "reworked / rebuilt" head. I must adjust the valve in question every two weeks. I've had mostly bad results with valves and valve seats which have been reground. In one case the head was rebuilt by a so called "racing" shop. They even stamped their name on the head. In my opinion, the best thing to do with the exhaust valves is to replace them with new units. I've already purchased two NOS heads with valve seats installed by the factory. I've also purchased all new valves, and I will assemble the head myself. I've lost a lot of confidence in a lot of the machine shop work. I also have my doubts about the 3 angle valve jobs. A stock rebuilt engine will last you a "Loooooong" time compared to anything else.

Slavs

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I agree. I would rather be safe than sorry. No matter what it is it requires digging in. I have about 60k miles on this head. I have a spare E12 head so I plan to buy new valves, guides, seals and a 292 (non regrind)Cam, build another then swap them out. Just don't want to risk eating a valve and ruining an otherwise great running motor

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someone recut the seats with a 3 angle valve cutter and made the margins to narrow. There's not enough width between the seat and the valve to properly transfer heat out of it and the valve is just erroding away.

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One more item to the check list….

Check the valve guide ID and guide centerline location (if possible) they are critical for proper valve seating. If the valve is not seating properly the wear on the valve and seat will be increased. Then you combine bad seating with high temperatures (eg lower yield strength) and high RPM there will be all kinds of mechanical badness going on.

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