C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Change valve springs, how to hold valves?

 
Old 07-19-2001, 05:13 PM
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65Z01
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Since my L98 has 110k miles, I decided to change valve springs, seals, etc before installing ProMagnum 1.6:1 rockers.

Since this is a "driveway job, I don't have access to an air compressor (no ac power). I believe that with a piston at TDC the valve will not drop too far when released.

I tested the end of a valve with a "magnetic wand" I found that the valve is strongly attracted so I can hold it in the up position.

Has anyone used this method to hold the valve in position while changing springs, etc? Or should I just spring for a tank, fill it with compressed air at the service station and use the conventional approach?



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Old 07-19-2001, 05:21 PM
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Nathan Plemons
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An air tank would leak down, expecially if your rings are starting to get worn. I don't THINK you could drop a valve with the cylinder at TDC, but it still wouldn't be easy. You'd be best to get an air compressor (borrow if you have to) and set it up somewhere you can plug it up, then just get enough air hose to reach the car. Springs are a fairly simple job that can turn into a much harder problem if you drop a valve.

Another trick I've heard but haven't tried. Get some thin rope, like the slick nylon stuff you can get at Lowes. Remove the plug and thread rope into the cylinder until it is full, this should prevent the valve from dropping. I've never tried this one, so I don't know how well it'll work, but it might be worth a shot.

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Old 07-19-2001, 05:31 PM
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Thanks Nathan. I'd foregotten about that "rope trick". Sounds like the best way in my case.

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Old 07-19-2001, 05:33 PM
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I this mod on my 96 Impala. I started with the rope trick, but soon found there was little reason to use it. I just located the piston at TDC (by using the rope to sense when the piston was at TDC). I attached a ratchet to the harmonic balancer and rotated the crank. When the piston was at TDC, the rope was trapped. The compressor trick works, but a lot of extra work, IMHO.

Eric

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Old 07-19-2001, 05:40 PM
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Sounds like the spark plug is located so the rope holds both valves closed. Hmm, sure wish I had a set of heads on the bench to check this out.

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Old 07-19-2001, 06:46 PM
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silver & red CE
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I have two sets of heads on my bench, they're LT1 heads but the chamber size isn't too different. When the piston is at TDC, there's no way for the valve to drop so far that you can't grab the stem. The total travel for the valve when the piston is at TDC is ~0.5". When I did this mod, I started trying to shove a bunch of rope into the cylinder, but this is a PIA. I ended up using the rope to sense when the piston was at TDC, I just pushed in enough rope to touch the rear of the chamber, then rotated the crank until the rope was trapped in the squish zone.



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Old 07-19-2001, 07:22 PM
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The way the rope trick works is to put the piston at the bottom of the cylinder, put in as much rope as you can through the spark plug hole, then rotate the crank until the piston squishes the rope in the chamber...thus preventing the valves from moving when the springs are removed.

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Old 07-19-2001, 09:02 PM
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I tried a compressor on my daughter's Nissan, worked great until I had to leave the garage for a few minutes and the cylinder leaked. Of course the air pressure rotated the crank so the piston was at the bottom (started at the top) and the rest, as they say, was history Ended up pulling the head. I used the rope trick from then on. I buy a soft braided nylon rope and with the piston part way down, feed it in and squash it by rotating the crank. Problem with using nothing is that you need the valve pretty much closed to compress the spring enough to get the keepers on. If the valve is down at all, it is hard to pull it up, hold it, put on the spring and then the keepers.

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Old 07-20-2001, 04:20 AM
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Well tomorrow I'm off to the hardware store to get some nylon rope. I'll start it in with the piston nearly at TDC and tighten it up.

I couldn't quickly find the press-down spring compressor so I got one at Sears that hooks under the bottom coils and screws down on the cap over the spring to compress it enough to release the keepers.

BTW, I've recently placed two orders with Comp Cams instead of Summit, to avoid an "out of stock" situation. Each was shipped the day of order and received the next day. So I'm duely impressed with their service.

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Old 07-20-2001, 09:56 AM
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ya- the press-down compressor won't work anyway, unless you pull the intake off. Rope method was a lot less of a hassle than the compressor
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